diff --git a/crates/pf-capture/src/lib.rs b/crates/pf-capture/src/lib.rs
index ea3af07d..938bdd6f 100644
--- a/crates/pf-capture/src/lib.rs
+++ b/crates/pf-capture/src/lib.rs
@@ -254,6 +254,54 @@ pub struct ZeroCopyPolicy {
 pub fn capturer_supports_444(_encoder_ingests_rgb_444: bool) -> bool {
     true
 }
+
+/// Whether the **native-plane** capturer (a compositor virtual output) can deliver an HDR (10-bit
+/// PQ/BT.2020) source on this platform — the capture-side gate the punktfunk/1 handshake consults
+/// before negotiating 10-bit (mirroring [`capturer_supports_444`]).
+///
+/// Linux: `false`. GNOME 50 added HDR **screen sharing** for *monitor* streams only — Mutter's
+/// `RecordVirtual` virtual-monitor streams advertise 8-bit BGRx/BGRA exclusively (still true on
+/// the GNOME 51 dev branch), and virtual outputs report no BT2020/PQ colour capabilities, so they
+/// can't be flipped into HDR mode via DisplayConfig either. The Linux HDR path that DOES exist —
+/// the GNOME 50+ portal **monitor mirror** (`open_portal_monitor` with `want_hdr`) — is gated
+/// separately by the GameStream plane (`host_hdr_capable` + the live monitor colour-mode probe).
+#[cfg(target_os = "linux")]
+pub fn capturer_supports_hdr() -> bool {
+    false
+}
+/// Windows: the IDD-push capturer proactively enables advanced colour and delivers P010/Rgb10a2.
+#[cfg(target_os = "windows")]
+pub fn capturer_supports_hdr() -> bool {
+    true
+}
+#[cfg(not(any(target_os = "linux", target_os = "windows")))]
+pub fn capturer_supports_hdr() -> bool {
+    false
+}
+
+/// Process-wide latch: a `want_hdr` portal capture failed to negotiate the HDR (10-bit PQ) offer —
+/// the compositor never accepted it (monitor left HDR mode between the probe and the negotiation,
+/// NVIDIA EGL not listing LINEAR for XR30, a pre-50 Mutter…). Later sessions consult
+/// [`hdr_capture_failed`] and fall back to the SDR offer instead of re-running the same doomed
+/// 10-second negotiation timeout on every reconnect. Sticky until host restart (matching the
+/// zero-copy downgrade latches); the log line at latch time says so.
+#[cfg(target_os = "linux")]
+static HDR_CAPTURE_FAILED: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
+
+#[cfg(target_os = "linux")]
+pub fn hdr_capture_failed() -> bool {
+    HDR_CAPTURE_FAILED.load(std::sync::atomic::Ordering::Relaxed)
+}
+
+#[cfg(target_os = "linux")]
+pub(crate) fn note_hdr_capture_failed() {
+    if !HDR_CAPTURE_FAILED.swap(true, std::sync::atomic::Ordering::Relaxed) {
+        tracing::warn!(
+            "HDR capture negotiation failed — this host will offer SDR capture for the rest of \
+             the process lifetime (restart the host after fixing the monitor's HDR mode to retry)"
+        );
+    }
+}
 #[cfg(target_os = "windows")]
 pub fn capturer_supports_444(encoder_ingests_rgb_444: bool) -> bool {
     // IDD-push delivers full-chroma BGRA for an SDR 4:4:4 session (skipping the NV12 VideoConverter),
@@ -316,16 +364,28 @@ pub use idd_push::verify_is_wudfhost;
 #[cfg(target_os = "linux")]
 #[path = "linux/mod.rs"]
 mod linux;
+// The GNOME BT.2100 colour-mode probe — the host's capture-side gate for offering HDR on the
+// portal monitor path (see `open_portal_monitor`'s `want_hdr`).
+#[cfg(target_os = "linux")]
+pub use linux::gnome_hdr_monitor_active;
 #[cfg(target_os = "windows")]
 #[path = "windows/synthetic_nv12.rs"]
 pub mod synthetic_nv12;
 
 /// Open the Linux xdg-ScreenCast portal capturer for a client-sized monitor. `anchored` drives
-/// ScreenCast off a RemoteDesktop session (KWin/GNOME) so it inherits that grant headlessly. The
-/// [`ZeroCopyPolicy`] carries the pre-resolved encode-backend facts (the one-way edge).
+/// ScreenCast off a RemoteDesktop session (KWin/GNOME) so it inherits that grant headlessly.
+/// `want_hdr` offers the GNOME 50+ HDR formats (10-bit PQ/BT.2020 dmabufs) instead of the SDR
+/// set — pass it only when the mirrored monitor is actually in HDR mode (the host probes
+/// DisplayConfig) or the negotiation runs into its 10 s timeout and latches the SDR downgrade.
+/// The [`ZeroCopyPolicy`] carries the pre-resolved encode-backend facts (the one-way edge).
 #[cfg(target_os = "linux")]
-pub fn open_portal_monitor(anchored: bool, policy: ZeroCopyPolicy) -> Result<Box<dyn Capturer>> {
-    linux::PortalCapturer::open(anchored, policy).map(|c| Box::new(c) as Box<dyn Capturer>)
+pub fn open_portal_monitor(
+    anchored: bool,
+    want_hdr: bool,
+    policy: ZeroCopyPolicy,
+) -> Result<Box<dyn Capturer>> {
+    linux::PortalCapturer::open(anchored, want_hdr && !hdr_capture_failed(), policy)
+        .map(|c| Box::new(c) as Box<dyn Capturer>)
 }
 
 /// Open the Linux portal capturer bound to an already-created virtual output's PipeWire node. The
diff --git a/crates/pf-capture/src/linux/mod.rs b/crates/pf-capture/src/linux/mod.rs
index 5eae5cac..e019c9a9 100644
--- a/crates/pf-capture/src/linux/mod.rs
+++ b/crates/pf-capture/src/linux/mod.rs
@@ -62,6 +62,13 @@ pub struct PortalCapturer {
     /// the process-wide downgrade ([`pf_zerocopy::note_vaapi_dmabuf_failed`]) so the pipeline
     /// rebuild retries on the CPU offer instead of failing identically forever.
     vaapi_dmabuf: bool,
+    /// This capture ran the HDR (10-bit PQ/BT.2020 dmabuf) offer — see [`Self::open`]'s
+    /// `want_hdr`. Read by the negotiation-timeout diagnosis (a failed HDR offer latches the
+    /// process-wide SDR downgrade) and by [`hdr_meta`](Capturer::hdr_meta).
+    hdr_offer: bool,
+    /// Set once the stream negotiated one of the 10-bit PQ formats (`param_changed`), i.e. frames
+    /// really are PQ/BT.2020 — drives [`hdr_meta`](Capturer::hdr_meta).
+    hdr_negotiated: Arc<AtomicBool>,
     /// The PipeWire node this capturer consumes — surfaced in error messages for diagnosis.
     node_id: u32,
     /// Stops the PipeWire loop on teardown (sent in `Drop`). Without it a dropped or failed
@@ -80,8 +87,9 @@ pub struct PortalCapturer {
 impl PortalCapturer {
     /// `anchored` drives ScreenCast off a RemoteDesktop session (KWin/GNOME) so it inherits the
     /// RemoteDesktop grant and never raises a separate ScreenCast dialog; `false` uses a plain
-    /// ScreenCast session (wlroots, which has no RemoteDesktop portal).
-    pub fn open(anchored: bool, policy: ZeroCopyPolicy) -> Result<PortalCapturer> {
+    /// ScreenCast session (wlroots, which has no RemoteDesktop portal). `want_hdr` offers the
+    /// GNOME 50+ HDR formats (10-bit PQ/BT.2020, dmabuf-only) instead of the SDR set.
+    pub fn open(anchored: bool, want_hdr: bool, policy: ZeroCopyPolicy) -> Result<PortalCapturer> {
         // Portal handshake (async) on its own thread; hands back the PW fd + node id.
         let (setup_tx, setup_rx) = std::sync::mpsc::channel::<Result<(OwnedFd, u32), String>>();
         thread::Builder::new()
@@ -102,11 +110,12 @@ impl PortalCapturer {
         };
         tracing::info!(
             node_id,
+            want_hdr,
             "ScreenCast portal session started; connecting PipeWire"
         );
         // This portal path (GameStream / monitor capture) is always 4:2:0, so allow zero-copy as before.
         Ok(
-            spawn_pipewire(Some(fd), node_id, None, true, false, policy)?
+            spawn_pipewire(Some(fd), node_id, None, true, false, want_hdr, policy)?
                 .into_capturer(node_id, None),
         )
     }
@@ -135,12 +144,15 @@ impl PortalCapturer {
             want_444,
             "connecting PipeWire to virtual output"
         );
+        // Virtual outputs are SDR-only upstream (Mutter's RecordVirtual streams advertise 8-bit
+        // BGRx/BGRA exclusively, GNOME 50 and 51-dev alike) — never run the HDR offer here.
         Ok(spawn_pipewire(
             remote_fd,
             node_id,
             preferred_mode,
             allow_zerocopy,
             want_444,
+            false,
             policy,
         )?
         .into_capturer(node_id, Some(keepalive)))
@@ -160,6 +172,10 @@ struct PwHandles {
     /// This capture will offer LINEAR-dmabuf-only for the VAAPI passthrough (see
     /// [`PortalCapturer::vaapi_dmabuf`]).
     vaapi_dmabuf: bool,
+    /// This capture ran the HDR offer (see [`PortalCapturer::hdr_offer`]).
+    hdr_offer: bool,
+    /// See [`PortalCapturer::hdr_negotiated`].
+    hdr_negotiated: Arc<AtomicBool>,
     quit: ::pipewire::channel::Sender<()>,
     join: thread::JoinHandle<()>,
 }
@@ -177,6 +193,8 @@ impl PwHandles {
             broken: self.broken,
             stall_since: None,
             vaapi_dmabuf: self.vaapi_dmabuf,
+            hdr_offer: self.hdr_offer,
+            hdr_negotiated: self.hdr_negotiated,
             node_id,
             quit: Some(self.quit),
             join: Some(self.join),
@@ -199,6 +217,10 @@ fn spawn_pipewire(
     // 4:4:4 session: tiled dmabufs convert to planar YUV444 on the GPU (`ImportKind::Tiled444`)
     // instead of NV12/RGB, so the session stays zero-copy at full chroma.
     want_444: bool,
+    // HDR session (GNOME 50+ monitor mirror): offer ONLY the 10-bit PQ/BT.2020 formats as
+    // LINEAR dmabufs (SHM can't carry them — Mutter's SHM record path paints 8-bit ARGB32
+    // regardless of the negotiated format, and the tiled EGL de-tile blit is 8-bit).
+    want_hdr: bool,
     // Encode-backend facts resolved by the facade (never re-derived here) — the one-way
     // capture→encode edge (plan §W6).
     policy: ZeroCopyPolicy,
@@ -213,17 +235,29 @@ fn spawn_pipewire(
     let streaming_cb = streaming.clone();
     let broken = Arc::new(AtomicBool::new(false));
     let broken_cb = broken.clone();
+    let hdr_negotiated = Arc::new(AtomicBool::new(false));
+    let hdr_negotiated_cb = hdr_negotiated.clone();
     // pipewire's own cross-thread channel: the receiver attaches to the loop and quits it; the
     // sender lives on the capturer and fires in its `Drop`. Absolute `::pipewire` path — the
     // inner `mod pipewire` shadows the crate name at this scope.
     let (quit_tx, quit_rx) = ::pipewire::channel::channel::<()>();
     let zerocopy = allow_zerocopy && pf_zerocopy::enabled();
+    // HDR cannot ride the SHM path (see `want_hdr` above): under PUNKTFUNK_FORCE_SHM the HDR
+    // offer is dropped — SDR capture, loudly.
+    let force_shm = std::env::var("PUNKTFUNK_FORCE_SHM").as_deref() == Ok("1");
+    let want_hdr = if want_hdr && force_shm {
+        tracing::warn!(
+            "HDR capture requested but PUNKTFUNK_FORCE_SHM=1 — the SHM path is 8-bit only; \
+             offering SDR"
+        );
+        false
+    } else {
+        want_hdr
+    };
     // Mirror of the thread's `vaapi_passthrough` decision (deterministic from here: on a VAAPI
     // backend the EGL→CUDA importer is never built) — kept on the capturer so `next_frame`'s
     // negotiation-timeout branch knows a failed negotiation was the LINEAR-dmabuf offer.
-    let vaapi_dmabuf = zerocopy
-        && std::env::var("PUNKTFUNK_FORCE_SHM").as_deref() != Ok("1")
-        && policy.backend_is_vaapi;
+    let vaapi_dmabuf = zerocopy && !force_shm && policy.backend_is_vaapi;
     let join = thread::Builder::new()
         .name("punktfunk-pipewire".into())
         .spawn(move || {
@@ -235,8 +269,10 @@ fn spawn_pipewire(
                 negotiated_cb,
                 streaming_cb,
                 broken_cb,
+                hdr_negotiated_cb,
                 zerocopy,
                 want_444,
+                want_hdr,
                 preferred,
                 quit_rx,
                 policy,
@@ -252,6 +288,8 @@ fn spawn_pipewire(
         streaming,
         broken,
         vaapi_dmabuf,
+        hdr_offer: want_hdr,
+        hdr_negotiated,
         quit: quit_tx,
         join,
     })
@@ -354,6 +392,26 @@ impl Capturer for PortalCapturer {
     fn set_active(&self, active: bool) {
         self.active.store(active, Ordering::Relaxed);
     }
+
+    /// Generic HDR10 mastering metadata once the stream negotiated a 10-bit PQ format. Mutter
+    /// exposes no per-monitor mastering volume through the screencast, so this is the standard
+    /// HDR10 default block (BT.2020 primaries, D65 white, 1000 / 0.005 cd/m², CLL unknown) — the
+    /// same fallback Windows uses when a display reports nothing. The native stream loop prefers
+    /// the client display's own volume when the client sent one (`Hello::display_hdr`).
+    fn hdr_meta(&self) -> Option<punktfunk_core::quic::HdrMeta> {
+        if !self.hdr_negotiated.load(Ordering::Relaxed) {
+            return None;
+        }
+        Some(punktfunk_core::quic::HdrMeta {
+            // ST.2086 order G, B, R; (x, y) chromaticity in 1/50000 units.
+            display_primaries: [[8500, 39850], [6550, 2300], [35400, 14600]],
+            white_point: [15635, 16450], // D65
+            max_display_mastering_luminance: 10_000_000, // 1000 cd/m² (0.0001 units)
+            min_display_mastering_luminance: 50,         // 0.005 cd/m²
+            max_cll: 0,
+            max_fall: 0,
+        })
+    }
 }
 
 impl PortalCapturer {
@@ -372,6 +430,20 @@ impl PortalCapturer {
                          or capture never started)",
                         self.node_id
                     ))
+                } else if self.hdr_offer {
+                    // The HDR (10-bit PQ dmabuf) offer was never accepted — the monitor left HDR
+                    // mode between the probe and the negotiation, the compositor pre-dates the
+                    // GNOME 50 HDR formats, or its allocator can't do LINEAR for XR30/XB30.
+                    // Latch the process-wide SDR downgrade so the next session (Moonlight
+                    // auto-reconnects) negotiates SDR instead of re-running this same timeout.
+                    super::note_hdr_capture_failed();
+                    Err(anyhow!(
+                        "no PipeWire frame within 10s (node {}): the compositor never accepted \
+                         the HDR (10-bit PQ/BT.2020 dmabuf) offer — is the mirrored monitor in \
+                         HDR mode on GNOME 50+? Downgrading this host to SDR capture; reconnect \
+                         to stream SDR",
+                        self.node_id
+                    ))
                 } else if self.vaapi_dmabuf && !pf_zerocopy::vaapi_dmabuf_forced() {
                     // The LINEAR-dmabuf-only offer (VAAPI passthrough default) was never accepted.
                     // Latch the process-wide downgrade so the encode loop's pipeline rebuild
@@ -416,6 +488,85 @@ impl Drop for PortalCapturer {
     }
 }
 
+/// Whether any monitor of the live GNOME session is currently in BT.2100 (HDR) colour mode — the
+/// precondition for Mutter's monitor screencast advertising the 10-bit PQ formats (GNOME 50+;
+/// Mutter only appends the HDR formats while the mirrored monitor's colour state is BT.2020+PQ).
+/// Queried over the session bus: `DisplayConfig.GetCurrentState`, monitor property
+/// `"color-mode" == 1` (`META_COLOR_MODE_BT2100`). `false` on any error — not GNOME, a pre-48
+/// Mutter without colour modes, no monitors — so callers fall back to the honest SDR offer.
+/// Blocking (one D-Bus round-trip on a fresh connection); call from control-plane threads only.
+pub fn gnome_hdr_monitor_active() -> bool {
+    use ashpd::zbus;
+    // GetCurrentState reply: (serial, monitors, logical_monitors, properties); each monitor is
+    // (spec(ssss), modes a(siiddada{sv}), properties a{sv}) — "color-mode" lives in the monitor
+    // properties.
+    type Mode = (
+        String,
+        i32,
+        i32,
+        f64,
+        f64,
+        Vec<f64>,
+        std::collections::HashMap<String, zbus::zvariant::OwnedValue>,
+    );
+    type Monitor = (
+        (String, String, String, String),
+        Vec<Mode>,
+        std::collections::HashMap<String, zbus::zvariant::OwnedValue>,
+    );
+    type LogicalMonitor = (
+        i32,
+        i32,
+        f64,
+        u32,
+        bool,
+        Vec<(String, String, String, String)>,
+        std::collections::HashMap<String, zbus::zvariant::OwnedValue>,
+    );
+    type State = (
+        u32,
+        Vec<Monitor>,
+        Vec<LogicalMonitor>,
+        std::collections::HashMap<String, zbus::zvariant::OwnedValue>,
+    );
+    let probe = || -> Result<bool> {
+        // zbus is built async-only here (ashpd's tokio integration) — run the one round-trip on
+        // a throwaway current-thread runtime; this is a control-plane call, never per-frame.
+        let rt = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .context("build tokio runtime")?;
+        rt.block_on(async {
+            let conn = zbus::Connection::session().await.context("session bus")?;
+            let reply = conn
+                .call_method(
+                    Some("org.gnome.Mutter.DisplayConfig"),
+                    "/org/gnome/Mutter/DisplayConfig",
+                    Some("org.gnome.Mutter.DisplayConfig"),
+                    "GetCurrentState",
+                    &(),
+                )
+                .await
+                .context("DisplayConfig.GetCurrentState")?;
+            let (_serial, monitors, _logical, _props): State =
+                reply.body().deserialize().context("parse GetCurrentState")?;
+            Ok(monitors.iter().any(|(_spec, _modes, props)| {
+                props
+                    .get("color-mode")
+                    .and_then(|v| u32::try_from(v).ok())
+                    .is_some_and(|mode| mode == 1) // META_COLOR_MODE_BT2100
+            }))
+        })
+    };
+    match probe() {
+        Ok(hdr) => hdr,
+        Err(e) => {
+            tracing::debug!(error = %format!("{e:#}"), "GNOME HDR colour-mode probe failed — SDR");
+            false
+        }
+    }
+}
+
 /// Pick the ScreenCast cursor mode from what the backend advertises (`AvailableCursorModes`),
 /// preferring **cursor-as-metadata**: the compositor keeps its cheap hardware cursor plane and
 /// ships the pointer as PipeWire `SPA_META_Cursor` metadata (position + an occasional bitmap),
@@ -669,6 +820,10 @@ mod pipewire {
             VideoFormat::RGBA => PixelFormat::Rgba,
             VideoFormat::RGB => PixelFormat::Rgb,
             VideoFormat::BGR => PixelFormat::Bgr,
+            // The GNOME 50+ HDR screencast formats (packed 2:10:10:10; only ever negotiated by
+            // the `want_hdr` offer, whose MANDATORY colorimetry props pin them to PQ/BT.2020).
+            VideoFormat::xRGB_210LE => PixelFormat::X2Rgb10,
+            VideoFormat::xBGR_210LE => PixelFormat::X2Bgr10,
             _ => return None,
         })
     }
@@ -732,6 +887,9 @@ mod pipewire {
         /// irrecoverably gone for this stream — the import worker died, or tiled imports failed
         /// [`IMPORT_FAIL_POISON`] times in a row.
         broken: Arc<AtomicBool>,
+        /// Set when the negotiated format is one of the 10-bit PQ formats (`param_changed`) —
+        /// read by [`PortalCapturer::hdr_meta`](super::PortalCapturer).
+        hdr_negotiated: Arc<AtomicBool>,
         /// Consecutive tiled-import failures (reset on success); see [`IMPORT_FAIL_POISON`].
         import_fail_streak: u32,
         /// Present when zero-copy is enabled on NVIDIA: imports a dmabuf → CUDA device buffer,
@@ -886,6 +1044,80 @@ mod pipewire {
         serialize_pod(obj)
     }
 
+    /// Build one GNOME 50+ HDR format pod: `format` (xRGB_210LE / xBGR_210LE) as a LINEAR-only
+    /// dmabuf with **MANDATORY** BT.2020 primaries + SMPTE ST.2084 (PQ) transfer-function props —
+    /// the exact colorimetry Mutter's monitor stream advertises while the mirrored monitor is in
+    /// HDR mode (its HDR pods carry the same props MANDATORY, so both sides must speak them for
+    /// the intersection to exist; an SDR or pre-50 producer can never match this pod).
+    ///
+    /// LINEAR-only because every 10-bit consumer we have reads the buffer without a de-tile pass:
+    /// the CPU path mmaps it, and the VAAPI passthrough imports it into a VA surface. The tiled
+    /// EGL de-tile blit renders into an 8-bit `GL_RGBA8` texture — it would silently crush the
+    /// depth — so tiled modifiers are deliberately NOT advertised (a zero-copy 10-bit de-tile is
+    /// the follow-up). SHM is excluded entirely: Mutter's SHM record path paints 8-bit ARGB32
+    /// regardless of the negotiated format.
+    fn build_hdr_dmabuf_format(
+        format: VideoFormat,
+        preferred: Option<(u32, u32, u32)>,
+    ) -> Result<Vec<u8>> {
+        let (dw, dh, dhz) = preferred.unwrap_or((1920, 1080, 60));
+        use pw::spa::param::format::{FormatProperties, MediaSubtype, MediaType};
+        let mut obj = pw::spa::pod::object!(
+            pw::spa::utils::SpaTypes::ObjectParamFormat,
+            pw::spa::param::ParamType::EnumFormat,
+            pw::spa::pod::property!(FormatProperties::MediaType, Id, MediaType::Video),
+            pw::spa::pod::property!(FormatProperties::MediaSubtype, Id, MediaSubtype::Raw),
+            pw::spa::pod::property!(FormatProperties::VideoFormat, Id, format),
+            pw::spa::pod::property!(
+                FormatProperties::VideoSize,
+                Choice,
+                Range,
+                Rectangle,
+                pw::spa::utils::Rectangle {
+                    width: dw,
+                    height: dh
+                },
+                pw::spa::utils::Rectangle {
+                    width: 1,
+                    height: 1
+                },
+                pw::spa::utils::Rectangle {
+                    width: 8192,
+                    height: 8192
+                }
+            ),
+            pw::spa::pod::property!(
+                FormatProperties::VideoFramerate,
+                Choice,
+                Range,
+                Fraction,
+                pw::spa::utils::Fraction { num: dhz, denom: 1 },
+                pw::spa::utils::Fraction { num: 0, denom: 1 },
+                pw::spa::utils::Fraction { num: 240, denom: 1 }
+            ),
+        );
+        obj.properties.push(pw::spa::pod::Property {
+            key: pw::spa::sys::SPA_FORMAT_VIDEO_modifier,
+            flags: pw::spa::pod::PropertyFlags::MANDATORY,
+            value: pw::spa::pod::Value::Long(0), // DRM_FORMAT_MOD_LINEAR
+        });
+        obj.properties.push(pw::spa::pod::Property {
+            key: pw::spa::sys::SPA_FORMAT_VIDEO_transferFunction,
+            flags: pw::spa::pod::PropertyFlags::MANDATORY,
+            value: pw::spa::pod::Value::Id(pw::spa::utils::Id(
+                pw::spa::sys::SPA_VIDEO_TRANSFER_SMPTE2084,
+            )),
+        });
+        obj.properties.push(pw::spa::pod::Property {
+            key: pw::spa::sys::SPA_FORMAT_VIDEO_colorPrimaries,
+            flags: pw::spa::pod::PropertyFlags::MANDATORY,
+            value: pw::spa::pod::Value::Id(pw::spa::utils::Id(
+                pw::spa::sys::SPA_VIDEO_COLOR_PRIMARIES_BT2020,
+            )),
+        });
+        serialize_pod(obj)
+    }
+
     /// The default (shm/CPU-path) format offer: raw video in any encoder-mappable layout, any
     /// size, any framerate (0/1 = variable allowed — gamescope fixates exactly that).
     fn build_default_format_obj(preferred: Option<(u32, u32, u32)>) -> pw::spa::pod::Object {
@@ -1157,6 +1389,54 @@ mod pipewire {
         })
     }
 
+    /// Alpha-blend the cached cursor bitmap into a packed 10-bit (`X2Rgb10`/`X2Bgr10`) CPU frame:
+    /// unpack each u32, blend the 8-bit cursor channels scaled to 10 bits (`v<<2 | v>>6`), repack.
+    /// The frame samples are PQ-encoded, so like the 8-bit gamma-space blend this is a display-
+    /// referred approximation — fine for a cursor. `r_shift` is the R channel's bit offset (20 for
+    /// x:R:G:B, 0 for x:B:G:R); G is always at 10 and B mirrors R.
+    fn composite_cursor_rgb10(
+        tight: &mut [u8],
+        w: usize,
+        h: usize,
+        r_shift: u32,
+        cursor: &CursorState,
+    ) {
+        let b_shift = 20 - r_shift; // 0 or 20 — the opposite end from R
+        let (bw, bh) = (cursor.bw as i32, cursor.bh as i32);
+        for cy in 0..bh {
+            let dy = cursor.y + cy;
+            if dy < 0 || dy as usize >= h {
+                continue;
+            }
+            for cx in 0..bw {
+                let dx = cursor.x + cx;
+                if dx < 0 || dx as usize >= w {
+                    continue;
+                }
+                let s = ((cy * bw + cx) as usize) * 4;
+                let a = cursor.rgba[s + 3] as u32;
+                if a == 0 {
+                    continue;
+                }
+                // 8-bit cursor channel → 10-bit (replicate the top bits into the bottom).
+                let up10 = |v: u8| ((v as u32) << 2) | ((v as u32) >> 6);
+                let (sr, sg, sb) = (
+                    up10(cursor.rgba[s]),
+                    up10(cursor.rgba[s + 1]),
+                    up10(cursor.rgba[s + 2]),
+                );
+                let di = (dy as usize * w + dx as usize) * 4;
+                let px = u32::from_le_bytes(tight[di..di + 4].try_into().unwrap());
+                let blend = |dst: u32, src: u32| (src * a + dst * (255 - a)) / 255;
+                let dr = blend((px >> r_shift) & 0x3ff, sr);
+                let dg = blend((px >> 10) & 0x3ff, sg);
+                let db = blend((px >> b_shift) & 0x3ff, sb);
+                let out = (px & 0xc000_0000) | (dr << r_shift) | (dg << 10) | (db << b_shift);
+                tight[di..di + 4].copy_from_slice(&out.to_le_bytes());
+            }
+        }
+    }
+
     /// Alpha-blend the cached cursor bitmap into the tightly-packed CPU frame at its latched
     /// position. Cheap: a straight-alpha blit over at most ~256×256 pixels, clipped to the frame —
     /// the whole point of cursor-as-metadata (no forced full-frame composite on the producer).
@@ -1170,6 +1450,12 @@ mod pipewire {
         if !cursor.visible || cursor.rgba.is_empty() {
             return;
         }
+        // The packed 10-bit HDR layouts blend via bit unpack/repack, not byte offsets.
+        match fmt {
+            PixelFormat::X2Rgb10 => return composite_cursor_rgb10(tight, w, h, 20, cursor),
+            PixelFormat::X2Bgr10 => return composite_cursor_rgb10(tight, w, h, 0, cursor),
+            _ => {}
+        }
         let Some((ri, gi, bi, bpp)) = dst_offsets(fmt) else {
             return;
         };
@@ -1344,7 +1630,10 @@ mod pipewire {
         // through to the shm de-pad copy below.
         let mut gpu_import_broken = false;
         if let (Some(importer), Some(fmt)) = (ud.importer.as_mut(), ud.format) {
-            if datas[0].type_() == pw::spa::buffer::DataType::DmaBuf {
+            // Defense-in-depth: the 10-bit PQ formats must never enter the EGL→CUDA import (its
+            // de-tile blit is 8-bit RGBA8 — silent depth loss). An HDR offer never builds the
+            // importer, so this gate only matters if those invariants ever drift apart.
+            if datas[0].type_() == pw::spa::buffer::DataType::DmaBuf && !fmt.is_hdr_rgb10() {
                 let plane = pf_zerocopy::DmabufPlane {
                     fd: datas[0].fd(),
                     offset: datas[0].chunk().offset(),
@@ -1604,9 +1893,13 @@ mod pipewire {
         negotiated: Arc<AtomicBool>,
         streaming: Arc<AtomicBool>,
         broken: Arc<AtomicBool>,
+        hdr_negotiated: Arc<AtomicBool>,
         zerocopy: bool,
         // 4:4:4 session: tiled dmabufs take the worker's planar-YUV444 GPU convert.
         want_444: bool,
+        // HDR session: offer ONLY the 10-bit PQ/BT.2020 formats as LINEAR dmabufs (see
+        // `build_hdr_dmabuf_format`); the SDR offers are not built at all.
+        want_hdr: bool,
         preferred: Option<(u32, u32, u32)>,
         quit_rx: pw::channel::Receiver<()>,
         // Encode-backend facts resolved by the facade (never re-derived here) — the one-way
@@ -1645,7 +1938,10 @@ mod pipewire {
         // succeed and produce CUDA payloads the VAAPI encoder must reject. Also skipped once
         // repeated worker deaths latched the import off (a wedged GPU stack must not crash-loop).
         let backend_is_vaapi = policy.backend_is_vaapi;
-        let mut importer = if zerocopy && !backend_is_vaapi {
+        // HDR never builds the EGL→CUDA importer: its de-tile blit renders into 8-bit RGBA8,
+        // which would silently crush the 10-bit depth. The HDR consumers are the CPU mmap path
+        // (LINEAR de-pad → X2Rgb10 CPU frames) and the VAAPI raw-dmabuf passthrough.
+        let mut importer = if zerocopy && !backend_is_vaapi && !want_hdr {
             if pf_zerocopy::gpu_import_disabled() {
                 tracing::warn!(
                     "zero-copy GPU import disabled after repeated import-worker deaths — using CPU path"
@@ -1755,6 +2051,7 @@ mod pipewire {
             negotiated,
             streaming,
             broken,
+            hdr_negotiated,
             import_fail_streak: 0,
             importer,
             vaapi_passthrough,
@@ -1822,12 +2119,20 @@ mod pipewire {
                     let sz = ud.info.size();
                     ud.format = map_format(ud.info.format());
                     ud.modifier = ud.info.modifier();
+                    // HDR: the 10-bit PQ formats are only ever offered with MANDATORY BT.2020/PQ
+                    // colorimetry props, so a 10-bit negotiation IS an HDR negotiation — but log
+                    // what the producer actually fixated for diagnosis.
+                    let hdr = ud.format.is_some_and(|f| f.is_hdr_rgb10());
+                    ud.hdr_negotiated.store(hdr, Ordering::Relaxed);
                     tracing::info!(
                         width = sz.width,
                         height = sz.height,
                         spa_format = ?ud.info.format(),
                         mapped = ?ud.format,
                         modifier = ud.modifier,
+                        hdr,
+                        transfer_function = ud.info.transfer_function(),
+                        color_primaries = ud.info.color_primaries(),
                         "pipewire format negotiated"
                     );
                     if ud.format.is_none() {
@@ -2029,20 +2334,36 @@ mod pipewire {
         // (offering shm too makes the compositor pick shm). The modifier list is advertised with
         // DONT_FIXATE so the compositor's allocator chooses one; we re-emit the fixated format in
         // `param_changed` (the two-step DMA-BUF handshake). Otherwise offer the multi-format shm
-        // pod and let MAP_BUFFERS map it.
-        let shm_values = serialize_pod(obj)?;
-        let (dmabuf_values, buffers_values) = if want_dmabuf {
-            (
-                Some(build_dmabuf_format(&modifiers, preferred)?),
-                Some(build_dmabuf_buffers()?),
-            )
+        // pod and let MAP_BUFFERS map it. An HDR session replaces ALL of this with the two 10-bit
+        // PQ pods (LINEAR dmabuf, MANDATORY colorimetry — see `build_hdr_dmabuf_format`): offering
+        // SDR alongside would make the producer pick its earlier-listed SDR format, and the
+        // negotiation-timeout path latches the process-wide SDR downgrade if nothing matches.
+        let format_pods: Vec<Vec<u8>> = if want_hdr {
+            tracing::info!(
+                "HDR capture: offering xRGB_210LE/xBGR_210LE LINEAR dmabufs with MANDATORY \
+                 BT.2020 + SMPTE-2084 (PQ) colorimetry (GNOME 50+ monitor stream)"
+            );
+            vec![
+                build_hdr_dmabuf_format(VideoFormat::xRGB_210LE, preferred)?,
+                build_hdr_dmabuf_format(VideoFormat::xBGR_210LE, preferred)?,
+            ]
+        } else if want_dmabuf {
+            vec![build_dmabuf_format(&modifiers, preferred)?]
+        } else {
+            vec![serialize_pod(obj)?]
+        };
+        let buffers_values = if want_hdr || want_dmabuf {
+            // Dmabuf-only. For HDR this is load-bearing beyond zero-copy: Mutter's SHM record
+            // path paints 8-bit ARGB32 regardless of the negotiated format, so a MemFd buffer
+            // under a 10-bit format would carry mislabeled bytes.
+            Some(build_dmabuf_buffers()?)
         } else if force_shm {
             // True SHM: exclude DmaBuf so Mutter MUST download (glReadPixels orders against render).
-            (None, Some(build_shm_only_buffers()?))
+            Some(build_shm_only_buffers()?)
         } else {
             // CPU path still accepts mappable dmabufs (gamescope offers only those once its
             // modifier-bearing format pod wins the intersection).
-            (None, Some(build_mappable_buffers()?))
+            Some(build_mappable_buffers()?)
         };
 
         // Ask for cursor-as-metadata on every path (harmless if the producer can't supply it): the
@@ -2050,9 +2371,8 @@ mod pipewire {
         // compositor keeps its cheap hardware cursor plane (see `choose_cursor_mode`).
         let cursor_meta = build_cursor_meta_param()?;
         let mut byte_slices: Vec<&[u8]> = Vec::new();
-        match &dmabuf_values {
-            Some(d) => byte_slices.push(d),
-            None => byte_slices.push(&shm_values),
+        for pod in &format_pods {
+            byte_slices.push(pod);
         }
         if let Some(b) = &buffers_values {
             byte_slices.push(b);
diff --git a/crates/pf-encode/src/enc/linux/mod.rs b/crates/pf-encode/src/enc/linux/mod.rs
index 140e9296..7224c0ce 100644
--- a/crates/pf-encode/src/enc/linux/mod.rs
+++ b/crates/pf-encode/src/enc/linux/mod.rs
@@ -27,8 +27,8 @@ use super::libav::{
 use ffmpeg::ffi; // = ffmpeg_sys_next
 
 /// The swscale *source* pixel format for a captured packed RGB/BGR layout (the real byte order, not
-/// the NVENC-padded `*0` form). Used by the 4:4:4 RGB→YUV444P conversion path. Mirrors the VAAPI
-/// CPU-input mapping; YUV/10-bit inputs can't feed this path (the 4:4:4 session forces packed RGB).
+/// the NVENC-padded `*0` form). Used by the CPU conversion paths: 4:4:4 RGB→YUV444P, and HDR
+/// X2RGB10/X2BGR10→P010. Mirrors the VAAPI CPU-input mapping; YUV inputs can't feed this path.
 fn sws_src_pixel(format: PixelFormat) -> Result<Pixel> {
     Ok(match format {
         PixelFormat::Bgrx => Pixel::BGRZ, // bgr0
@@ -37,8 +37,12 @@ fn sws_src_pixel(format: PixelFormat) -> Result<Pixel> {
         PixelFormat::Rgba => Pixel::RGBA,
         PixelFormat::Rgb => Pixel::RGB24,
         PixelFormat::Bgr => Pixel::BGR24,
+        // The GNOME 50+ HDR capture formats (PQ/BT.2020 packed 2:10:10:10) — the HDR CPU path's
+        // swscale source for the X2RGB10→P010 conversion.
+        PixelFormat::X2Rgb10 => Pixel::X2RGB10LE,
+        PixelFormat::X2Bgr10 => Pixel::X2BGR10LE,
         PixelFormat::Nv12 | PixelFormat::P010 | PixelFormat::Rgb10a2 | PixelFormat::Yuv444 => {
-            bail!("NVENC 4:4:4 CPU-input path supports packed RGB/BGR only; got {format:?}")
+            bail!("NVENC CPU-input conversion supports packed RGB/BGR only; got {format:?}")
         }
     })
 }
@@ -136,6 +140,9 @@ fn nvenc_input(format: PixelFormat) -> (Pixel, bool) {
         // the Windows paths; the Linux capturer never emits them. Map to BGRA so the match is
         // exhaustive — unreachable here.
         PixelFormat::Rgb10a2 | PixelFormat::P010 => (Pixel::BGRA, false),
+        // The Linux HDR capture formats never take the RGB-passthrough input: `open` intercepts
+        // them onto the X2RGB10→P010 swscale path before consulting this mapping (like 4:4:4).
+        PixelFormat::X2Rgb10 | PixelFormat::X2Bgr10 => (Pixel::BGRA, false),
     }
 }
 
@@ -164,11 +171,12 @@ pub struct NvencEncoder {
     frame: Option<VideoFrame>,
     /// Zero-copy path: CUDA hwdevice/hwframes contexts (the encoder takes `AV_PIX_FMT_CUDA`).
     cuda: Option<CudaHw>,
-    /// 4:4:4 CPU path only: swscale context converting the captured packed RGB/BGR → planar
-    /// YUV444P into [`Self::frame`], because `hevc_nvenc` only emits 4:4:4 from a YUV444 *input*
-    /// (RGB-in is always 4:2:0). `None` on the 4:2:0 paths AND on the zero-copy 4:4:4 path (the
-    /// worker's GPU convert delivers YUV444 CUDA frames). Freed in `Drop`.
-    sws_444: Option<*mut ffi::SwsContext>,
+    /// CPU CSC paths only: swscale context converting the captured packed source into
+    /// [`Self::frame`] — RGB/BGR → planar YUV444P for a 4:4:4 session (`hevc_nvenc` only emits
+    /// 4:4:4 from a YUV444 *input*; RGB-in is always 4:2:0), or X2RGB10/X2BGR10 → P010 (BT.2020
+    /// limited) for an HDR session. `None` on the plain RGB paths AND on the zero-copy paths (the
+    /// worker's GPU convert delivers ready CUDA frames). Freed in `Drop`.
+    sws_csc: Option<*mut ffi::SwsContext>,
     /// This session opened as full-chroma 4:4:4 (FREXT) — via either input path.
     want_444: bool,
     src_format: PixelFormat,
@@ -191,7 +199,7 @@ pub struct NvencEncoder {
     args: OpenArgs,
 }
 
-// `CudaHw` holds raw `AVBufferRef`s and `sws_444` a raw `SwsContext`; the encoder lives on a single
+// `CudaHw` holds raw `AVBufferRef`s and `sws_csc` a raw `SwsContext`; the encoder lives on a single
 // thread. The CPU encoder is already `Send` via ffmpeg-next; assert it for the raw fields too.
 // SAFETY: `NvencEncoder` owns an ffmpeg-next `Encoder`/`VideoFrame` (already `Send`) plus a `CudaHw`
 // holding raw `AVBufferRef`s and an optional raw `SwsContext`, none of which are `Send` by default.
@@ -247,14 +255,27 @@ impl NvencEncoder {
         bit_depth: u8,
         chroma: ChromaFormat,
     ) -> Result<Self> {
-        // TODO(hdr): Linux 10-bit parity. Unlike the Windows raw-SDK path (which upconverts 8-bit
-        // ARGB → Main10 via pixelBitDepthMinus8), libavcodec hevc_nvenc needs a 10-bit input pixel
-        // format (p010) for Main10, so it's a bigger change; deferred until a Linux GPU box is
-        // available to validate. The Linux host stays 8-bit for now.
-        if bit_depth != 8 {
+        // HDR / 10-bit (GNOME 50+ HDR screencast): a 10-bit session whose capture negotiated a
+        // packed 2:10:10:10 PQ/BT.2020 format (`X2Rgb10`/`X2Bgr10`) encodes HEVC Main10 / 10-bit
+        // AV1 from a P010 input frame we produce by swscale (BT.2020 limited; the PQ transfer
+        // rides through per-channel — BT.2020 NCL Y'CbCr *is* derived from the PQ-encoded R'G'B').
+        // A 10-bit request whose capture stayed SDR (HDR offer downgraded) honestly encodes 8-bit.
+        let want_hdr10 = bit_depth == 10 && format.is_hdr_rgb10() && codec.supports_10bit();
+        if bit_depth == 10 && !want_hdr10 {
             tracing::warn!(
                 bit_depth,
-                "Linux NVENC 10-bit not yet wired — encoding 8-bit"
+                ?format,
+                codec = codec.nvenc_name(),
+                "10-bit requested but the capture format/codec has no 10-bit path — encoding 8-bit"
+            );
+        }
+        if format.is_hdr_rgb10() && !want_hdr10 {
+            // A 10-bit PQ capture on an 8-bit session would be encoded with a BT.709 VUI and
+            // garbage bit-packing — never silently; the session must renegotiate.
+            bail!(
+                "captured 10-bit HDR frames ({format:?}) on an 8-bit/{} session — refusing to \
+                 mislabel PQ content",
+                codec.nvenc_name()
             );
         }
         // Full-chroma 4:4:4 (HEVC Range Extensions). `hevc_nvenc` only emits 4:4:4 from a YUV444
@@ -263,6 +284,11 @@ impl NvencEncoder {
         // (planar-YUV444 CUDA frames — `cuda` true), or the CPU path's swscale RGB→YUV444P. Both
         // feed `profile=rext`; the range follows `PUNKTFUNK_444_FULLRANGE` in both.
         let want_444 = chroma.is_444() && codec == Codec::H265;
+        if want_444 && want_hdr10 {
+            // The handshake resolves 4:4:4∧10-bit down to 8-bit on Linux, so this can't happen —
+            // fail loudly if it ever does rather than picking one silently.
+            bail!("4:4:4 + 10-bit HDR is not a supported Linux NVENC combination");
+        }
         ffmpeg::init().context("ffmpeg init")?;
         if std::env::var_os("PUNKTFUNK_FFMPEG_DEBUG").is_some() {
             // SAFETY: `av_log_set_level` sets libav's global integer log level; `48` (= AV_LOG_DEBUG)
@@ -274,10 +300,13 @@ impl NvencEncoder {
         let av_codec = encoder::find_by_name(name)
             .ok_or_else(|| anyhow!("{name} not built into libavcodec"))?;
         let (rgb_pixel, rgb_expand) = nvenc_input(format);
-        // 4:4:4 feeds NVENC a planar YUV444P frame we produce by swscale; the ordinary path feeds the
-        // captured RGB straight in and lets NVENC's internal CSC subsample to 4:2:0.
+        // 4:4:4 feeds NVENC a planar YUV444P frame we produce by swscale; HDR feeds it a P010
+        // frame likewise; the ordinary path feeds the captured RGB straight in and lets NVENC's
+        // internal CSC subsample to 4:2:0.
         let (nvenc_pixel, expand) = if want_444 {
             (Pixel::YUV444P, false)
+        } else if want_hdr10 {
+            (Pixel::P010LE, false)
         } else {
             (rgb_pixel, rgb_expand)
         };
@@ -325,7 +354,21 @@ impl NvencEncoder {
         // visible win. Linux-only: the Windows path's NVENC-internal CSC range is unmeasured.
         let full_range_444 =
             want_444 && std::env::var("PUNKTFUNK_444_FULLRANGE").is_ok_and(|v| v.trim() == "1");
-        if matches!(format, PixelFormat::Nv12) || want_444 {
+        if want_hdr10 {
+            // HDR10: BT.2020 primaries + SMPTE-2084 (PQ) transfer, limited range — matches the
+            // swscale BT.2020 CSC below and the Windows paths' signalling. The client decoder
+            // auto-detects PQ from the VUI; static mastering metadata rides out-of-band.
+            // SAFETY: `raw = video.as_mut_ptr()` is the non-null, properly-aligned, sole-owned,
+            // not-yet-opened `AVCodecContext`; we set its four VUI colour enum fields to valid
+            // variants before `open_with`. Sole owner → no aliasing; synchronous writes.
+            unsafe {
+                let raw = video.as_mut_ptr();
+                (*raw).colorspace = ffi::AVColorSpace::AVCOL_SPC_BT2020_NCL;
+                (*raw).color_range = ffi::AVColorRange::AVCOL_RANGE_MPEG;
+                (*raw).color_primaries = ffi::AVColorPrimaries::AVCOL_PRI_BT2020;
+                (*raw).color_trc = ffi::AVColorTransferCharacteristic::AVCOL_TRC_SMPTE2084;
+            }
+        } else if matches!(format, PixelFormat::Nv12) || want_444 {
             // SAFETY: same `video` builder — `raw = video.as_mut_ptr()` is the non-null, properly-
             // aligned, sole-owned, not-yet-opened `AVCodecContext`. We set its four VUI colour enum
             // fields to valid `AVColorSpace`/`AVColorRange`/`AVColorPrimaries`/`AVColorTransfer-
@@ -370,17 +413,20 @@ impl NvencEncoder {
             None
         };
 
-        // 4:4:4 CPU path: build the RGB→YUV444P swscale (BT.709, range per the flag; no rescale).
-        // Mirrors the VAAPI CPU path's RGB→NV12 scaler, but the dst is full-chroma planar 4:4:4.
-        // Skipped on the zero-copy path (`cuda`): the worker's GPU convert already delivers
-        // planar YUV444 CUDA frames — no CPU pixels exist to scale.
-        let sws_444 = if want_444 && !cuda {
+        // CPU CSC paths: build the packed-RGB → planar swscale (no rescale) into the encoder's
+        // input frame. Two users: 4:4:4 (RGB→YUV444P, BT.709, range per the flag) and HDR
+        // (X2RGB10/X2BGR10→P010, BT.2020 limited — the PQ transfer is per-channel and rides
+        // through the matrix untouched). Skipped on the zero-copy path (`cuda`): the worker's GPU
+        // convert already delivers ready CUDA frames — no CPU pixels exist to scale.
+        let sws_csc = if (want_444 || want_hdr10) && !cuda {
             let src_av = pixel_to_av(sws_src_pixel(format)?);
+            let dst_av = pixel_to_av(nvenc_pixel);
             // SAFETY: `sws_getContext` allocates a swscale context for the given src/dst dims + pixel
             // formats. Both dims are the encoder's positive `width`/`height` as `c_int`; `src_av` is a
-            // valid `AVPixelFormat` (from the `sws_src_pixel`-validated, packed-RGB-only source), the
-            // dst is YUV444P. The trailing filter/param pointers are null = "use defaults" (documented
-            // as accepted). No Rust memory is borrowed; the returned pointer is null-checked below.
+            // valid `AVPixelFormat` (from the `sws_src_pixel`-validated packed-RGB source), the dst is
+            // YUV444P (4:4:4) or P010LE (HDR). The trailing filter/param pointers are null = "use
+            // defaults" (documented as accepted). No Rust memory is borrowed; the returned pointer is
+            // null-checked below.
             let sws = unsafe {
                 ffi::sws_getContext(
                     width as c_int,
@@ -388,7 +434,7 @@ impl NvencEncoder {
                     src_av,
                     width as c_int,
                     height as c_int,
-                    ffi::AVPixelFormat::AV_PIX_FMT_YUV444P,
+                    dst_av,
                     SWS_POINT,
                     ptr::null_mut(),
                     ptr::null_mut(),
@@ -396,17 +442,22 @@ impl NvencEncoder {
                 )
             };
             if sws.is_null() {
-                bail!("sws_getContext(RGB→YUV444P) failed");
+                bail!("sws_getContext(RGB→{nvenc_pixel:?}) failed");
             }
-            // SAFETY: `sws` is the non-null context from the call above (null-checked). The ITU-709
-            // coefficient table from `sws_getCoefficients` is a process-lifetime libswscale static,
-            // reused for src+dst matrices; `sws_setColorspaceDetails` only reads it and writes scalar
-            // CSC settings into `sws` (dstRange matches the VUI: 0 = limited, 1 = the
-            // PUNKTFUNK_444_FULLRANGE experiment). No Rust memory is passed.
+            // SAFETY: `sws` is the non-null context from the call above (null-checked). The
+            // coefficient tables from `sws_getCoefficients` (ITU-709 for 4:4:4, BT.2020 NCL for HDR
+            // — matching the VUI written above) are process-lifetime libswscale statics, reused for
+            // src+dst matrices; `sws_setColorspaceDetails` only reads them and writes scalar CSC
+            // settings into `sws` (dstRange matches the VUI: 0 = limited, 1 = the
+            // PUNKTFUNK_444_FULLRANGE experiment; HDR is always limited). No Rust memory is passed.
             unsafe {
-                let cs709 = ffi::sws_getCoefficients(SWS_CS_ITU709);
+                let cs = ffi::sws_getCoefficients(if want_hdr10 {
+                    super::libav::SWS_CS_BT2020
+                } else {
+                    SWS_CS_ITU709
+                });
                 let dst_range = i32::from(full_range_444);
-                ffi::sws_setColorspaceDetails(sws, cs709, 1, cs709, dst_range, 0, 1 << 16, 1 << 16);
+                ffi::sws_setColorspaceDetails(sws, cs, 1, cs, dst_range, 0, 1 << 16, 1 << 16);
             }
             Some(sws)
         } else {
@@ -432,6 +483,12 @@ impl NvencEncoder {
             // dropped on a future libavcodec.
             opts.set("profile", "rext");
         }
+        if want_hdr10 && codec == Codec::H265 {
+            // HEVC Main10. `hevc_nvenc` auto-selects it from the P010 input, but pin it explicitly
+            // so the depth is never silently dropped on a future libavcodec. (10-bit AV1 needs no
+            // profile — AV1 Main carries 10-bit, driven by the input format.)
+            opts.set("profile", "main10");
+        }
 
         // Split-frame encode across both NVENC engines (GB203 has 2) when the pixel rate exceeds
         // a single engine's HEVC capacity (~1 Gpix/s); e.g. 5120x1440@240 = 1.77 Gpix/s needs it,
@@ -501,7 +558,7 @@ impl NvencEncoder {
             enc,
             frame,
             cuda: cuda_hw,
-            sws_444,
+            sws_csc,
             want_444,
             src_format: format,
             expand,
@@ -640,7 +697,7 @@ impl NvencEncoder {
         );
         // 4:4:4: swscale the packed RGB straight into the planar YUV444P input frame (BT.709 limited),
         // then send it — no byte-expand. The 4:2:0 RGB path (below) feeds NVENC packed RGB directly.
-        if let Some(sws) = self.sws_444 {
+        if let Some(sws) = self.sws_csc {
             let frame = self
                 .frame
                 .as_mut()
@@ -810,7 +867,7 @@ impl NvencEncoder {
 
 impl Drop for NvencEncoder {
     fn drop(&mut self) {
-        if let Some(sws) = self.sws_444.take() {
+        if let Some(sws) = self.sws_csc.take() {
             // SAFETY: `sws` is the non-null `SwsContext` allocated by `sws_getContext` in `open` and
             // owned exclusively by this encoder (taken out of the field so it can't be freed twice).
             // `sws_freeContext` frees it; nothing else references it after this single-threaded drop.
@@ -855,3 +912,105 @@ pub fn probe_can_encode_444(codec: Codec) -> bool {
     unsafe { ffi::av_log_set_level(prev) };
     ok
 }
+
+#[cfg(test)]
+mod hdr_tests {
+    use super::*;
+
+    /// The Linux HDR (GNOME 50 portal) encode path end-to-end on a real NVIDIA GPU: a synthetic
+    /// PQ-ish X2RGB10 CPU frame → swscale BT.2020 → P010 → `hevc_nvenc` Main10, drained to a real
+    /// AU. `#[ignore]`d (needs NVENC):
+    /// `cargo test -p pf-encode nvenc_hdr10_smoke -- --ignored --nocapture`
+    #[test]
+    #[ignore]
+    fn nvenc_hdr10_smoke() {
+        let (w, h) = (640u32, 480u32);
+        let mut enc = NvencEncoder::open(
+            Codec::H265,
+            PixelFormat::X2Rgb10,
+            w,
+            h,
+            30,
+            2_000_000,
+            false,
+            10,
+            ChromaFormat::Yuv420,
+        )
+        .expect("open hevc_nvenc Main10 (P010 input)");
+        // Packed x:R:G:B 2:10:10:10 gradient (values are treated as PQ-encoded — fine for a smoke).
+        let mut bytes = vec![0u8; (w * h * 4) as usize];
+        for y in 0..h {
+            for x in 0..w {
+                let r = (x * 1023 / w.max(1)) & 0x3ff;
+                let g = (y * 1023 / h.max(1)) & 0x3ff;
+                let b = ((x + y) * 1023 / (w + h)) & 0x3ff;
+                let px: u32 = (r << 20) | (g << 10) | b;
+                let i = ((y * w + x) * 4) as usize;
+                bytes[i..i + 4].copy_from_slice(&px.to_le_bytes());
+            }
+        }
+        let frame = CapturedFrame {
+            width: w,
+            height: h,
+            pts_ns: 0,
+            format: PixelFormat::X2Rgb10,
+            payload: FramePayload::Cpu(bytes),
+            cursor: None,
+        };
+        let mut au = None;
+        for _ in 0..30 {
+            enc.submit(&frame).expect("submit X2Rgb10 frame");
+            if let Some(a) = enc.poll().expect("poll") {
+                au = Some(a);
+                break;
+            }
+        }
+        let au = au.expect("no AU produced within 30 frames");
+        assert!(!au.data.is_empty(), "empty AU");
+        assert!(au.keyframe, "first AU should be the IDR");
+        println!("HDR10 smoke: first AU {} bytes (IDR)", au.data.len());
+        // PF_HDR_SMOKE_DUMP=/path.h265: write the Annex-B AU for external inspection —
+        // `ffprobe -show_streams` should report Main 10, bt2020nc/smpte2084/bt2020 colours.
+        if let Ok(path) = std::env::var("PF_HDR_SMOKE_DUMP") {
+            std::fs::write(&path, &au.data).expect("dump AU");
+            println!("HDR10 smoke: AU written to {path}");
+        }
+    }
+}
+
+/// Probe whether this NVIDIA GPU + driver + libavcodec can actually encode 10-bit (HEVC Main10 /
+/// 10-bit AV1) from a P010 input — the exact path [`NvencEncoder::open`] takes for a live HDR
+/// stream (a tiny X2RGB10-sourced, P010-input open). The result is cached by the caller
+/// ([`crate::can_encode_10bit`]); a GPU/driver/ffmpeg without the 10-bit encode fails the open
+/// here, so the host resolves the session to 8-bit SDR before the Welcome (honest downgrade).
+pub fn probe_can_encode_10bit(codec: Codec) -> bool {
+    if !codec.supports_10bit() {
+        return false;
+    }
+    if ffmpeg::init().is_err() {
+        return false;
+    }
+    // Quiet ffmpeg's open error on a GPU that lacks 10-bit — the probe failing is an expected outcome.
+    // SAFETY: libav initialized above; `av_log_{get,set}_level` only read/write the global int level
+    // (no pointer args) and are always sound post-init.
+    let prev = unsafe {
+        let p = ffi::av_log_get_level();
+        ffi::av_log_set_level(ffi::AV_LOG_FATAL);
+        p
+    };
+    let ok = NvencEncoder::open(
+        codec,
+        PixelFormat::X2Rgb10,
+        640,
+        480,
+        30,
+        2_000_000,
+        false, // CPU input (the HDR swscale path)
+        10,
+        ChromaFormat::Yuv420,
+    )
+    .is_ok();
+    // SAFETY: restore the saved global log level (scalar arg, no pointers).
+    unsafe { ffi::av_log_set_level(prev) };
+    ok
+}
diff --git a/crates/pf-encode/src/enc/linux/nvenc_cuda.rs b/crates/pf-encode/src/enc/linux/nvenc_cuda.rs
index 418f9c88..dc8828fd 100644
--- a/crates/pf-encode/src/enc/linux/nvenc_cuda.rs
+++ b/crates/pf-encode/src/enc/linux/nvenc_cuda.rs
@@ -474,9 +474,13 @@ impl NvencCudaEncoder {
         // clear reason instead of an opaque session error on the first frame.
         try_api().map_err(|e| anyhow!("NVENC (Linux direct) unavailable: {e}"))?;
         if bit_depth >= 10 {
+            // An HDR (GNOME 50 portal) session never reaches this backend: its X2RGB10 frames ride
+            // the CPU/dmabuf paths (no CUDA import for the 10-bit formats yet), so the dispatcher
+            // opens the libav P010 path instead. Reaching here 10-bit means a CUDA capture payload
+            // on a 10-bit session — not wired; encode 8-bit rather than mislabel.
             tracing::warn!(
-                "Linux direct-NVENC: 10-bit requested but no P010 capture path exists yet \
-                 (Phase 5.1) — encoding 8-bit SDR"
+                "Linux direct-NVENC: 10-bit requested but the CUDA capture path has no 10-bit \
+                 import yet (HDR rides the libav P010 path) — encoding 8-bit SDR"
             );
         }
         Ok(Self {
diff --git a/crates/pf-encode/src/enc/linux/vaapi.rs b/crates/pf-encode/src/enc/linux/vaapi.rs
index 4634cdca..add1017d 100644
--- a/crates/pf-encode/src/enc/linux/vaapi.rs
+++ b/crates/pf-encode/src/enc/linux/vaapi.rs
@@ -61,6 +61,10 @@ fn vaapi_sws_src(format: PixelFormat) -> Result<Pixel> {
         PixelFormat::Rgba => Pixel::RGBA,
         PixelFormat::Rgb => Pixel::RGB24,
         PixelFormat::Bgr => Pixel::BGR24,
+        // The GNOME 50+ HDR capture formats (PQ/BT.2020 packed 2:10:10:10) — the HDR CPU path's
+        // swscale source for the X2RGB10→P010 conversion.
+        PixelFormat::X2Rgb10 => Pixel::X2RGB10LE,
+        PixelFormat::X2Bgr10 => Pixel::X2BGR10LE,
         PixelFormat::Nv12 | PixelFormat::P010 | PixelFormat::Rgb10a2 | PixelFormat::Yuv444 => {
             bail!("VAAPI CPU-input path supports packed RGB/BGR only; got {format:?}")
         }
@@ -101,6 +105,7 @@ fn low_power_override() -> Option<bool> {
 /// default on those kernels). AMD keeps its first-try full-feature open byte-for-byte unchanged.
 /// The resolved mode is cached per codec; `PUNKTFUNK_VAAPI_LOW_POWER` pins it.
 /// Safety contract is [`open_vaapi_encoder_mode`]'s (borrowed `device_ref`/`frames_ref`).
+#[allow(clippy::too_many_arguments)]
 unsafe fn open_vaapi_encoder(
     codec: Codec,
     width: u32,
@@ -109,6 +114,7 @@ unsafe fn open_vaapi_encoder(
     bitrate_bps: u64,
     device_ref: *mut ffi::AVBufferRef,
     frames_ref: *mut ffi::AVBufferRef,
+    ten_bit: bool,
 ) -> Result<encoder::video::Encoder> {
     let idx = lp_idx(codec);
     let modes: &[bool] = match low_power_override() {
@@ -130,6 +136,7 @@ unsafe fn open_vaapi_encoder(
             bitrate_bps,
             device_ref,
             frames_ref,
+            ten_bit,
             lp,
         ) {
             Ok(enc) => {
@@ -158,8 +165,9 @@ unsafe fn open_vaapi_encoder(
 }
 
 /// Build the FFmpeg encoder context (shared by both inner paths): name, mode, low-latency RC,
-/// infinite GOP, BT.709-limited VUI, `pix_fmt=VAAPI`, and the given hw device + frames contexts.
-/// Returns the opened encoder. `device_ref`/`frames_ref` are borrowed (ref'd into the context).
+/// infinite GOP, the VUI (BT.709 limited SDR, or BT.2020 PQ limited for `ten_bit` HDR),
+/// `pix_fmt=VAAPI`, and the given hw device + frames contexts. Returns the opened encoder.
+/// `device_ref`/`frames_ref` are borrowed (ref'd into the context).
 #[allow(clippy::too_many_arguments)]
 unsafe fn open_vaapi_encoder_mode(
     codec: Codec,
@@ -169,6 +177,7 @@ unsafe fn open_vaapi_encoder_mode(
     bitrate_bps: u64,
     device_ref: *mut ffi::AVBufferRef,
     frames_ref: *mut ffi::AVBufferRef,
+    ten_bit: bool,
     low_power: bool,
 ) -> Result<encoder::video::Encoder> {
     let name = codec.vaapi_name();
@@ -181,23 +190,39 @@ unsafe fn open_vaapi_encoder_mode(
         .context("alloc video encoder")?;
     video.set_width(width);
     video.set_height(height);
-    video.set_format(Pixel::NV12); // sw view; pix_fmt overridden to VAAPI below
-                                   // Fixed rate, CBR, no B-frames, ~1-frame VBV — the shared low-latency RC contract.
+    // sw view (pix_fmt overridden to VAAPI below): NV12, or P010 for the 10-bit HDR session.
+    video.set_format(if ten_bit { Pixel::P010LE } else { Pixel::NV12 });
+    // Fixed rate, CBR, no B-frames, ~1-frame VBV — the shared low-latency RC contract.
     apply_low_latency_rc(&mut video, fps, bitrate_bps);
     let raw = video.as_mut_ptr();
     (*raw).gop_size = i32::MAX; // no periodic IDR (forced-IDR via pict_type=I on RFI)
-                                // We hand the encoder BT.709 *limited* NV12 (swscale CSC on the CPU path; scale_vaapi pinned
-                                // to `out_color_matrix=bt709:out_range=limited` on the zero-copy path, with the full-range
-                                // RGB input tagged), so signal that VUI — else the client decoder washes the picture out.
-    (*raw).colorspace = ffi::AVColorSpace::AVCOL_SPC_BT709;
-    (*raw).color_range = ffi::AVColorRange::AVCOL_RANGE_MPEG;
-    (*raw).color_primaries = ffi::AVColorPrimaries::AVCOL_PRI_BT709;
-    (*raw).color_trc = ffi::AVColorTransferCharacteristic::AVCOL_TRC_BT709;
+    if ten_bit {
+        // HDR10: BT.2020 primaries + SMPTE-2084 (PQ) transfer, limited range — matches the P010
+        // the CSC produces (swscale BT.2020 on the CPU path; scale_vaapi pinned to bt2020 on the
+        // zero-copy path). The client decoder auto-detects PQ from the VUI.
+        (*raw).colorspace = ffi::AVColorSpace::AVCOL_SPC_BT2020_NCL;
+        (*raw).color_range = ffi::AVColorRange::AVCOL_RANGE_MPEG;
+        (*raw).color_primaries = ffi::AVColorPrimaries::AVCOL_PRI_BT2020;
+        (*raw).color_trc = ffi::AVColorTransferCharacteristic::AVCOL_TRC_SMPTE2084;
+    } else {
+        // We hand the encoder BT.709 *limited* NV12 (swscale CSC on the CPU path; scale_vaapi pinned
+        // to `out_color_matrix=bt709:out_range=limited` on the zero-copy path, with the full-range
+        // RGB input tagged), so signal that VUI — else the client decoder washes the picture out.
+        (*raw).colorspace = ffi::AVColorSpace::AVCOL_SPC_BT709;
+        (*raw).color_range = ffi::AVColorRange::AVCOL_RANGE_MPEG;
+        (*raw).color_primaries = ffi::AVColorPrimaries::AVCOL_PRI_BT709;
+        (*raw).color_trc = ffi::AVColorTransferCharacteristic::AVCOL_TRC_BT709;
+    }
     (*raw).pix_fmt = ffi::AVPixelFormat::AV_PIX_FMT_VAAPI;
     (*raw).hw_device_ctx = ffi::av_buffer_ref(device_ref);
     (*raw).hw_frames_ctx = ffi::av_buffer_ref(frames_ref);
 
     let mut opts = Dictionary::new();
+    if ten_bit && codec == Codec::H265 {
+        // HEVC Main10. `hevc_vaapi` derives it from the P010 surfaces, but pin it explicitly so
+        // the depth is never silently dropped. (10-bit AV1 is input-driven — no profile knob.)
+        opts.set("profile", "main10");
+    }
     // async_depth=1: `send_frame` blocks until THIS frame's ASIC encode completes — the lowest
     // latency structure libavcodec's vaapi_encode offers. Measured on the 780M at 1440p60: depth 1
     // = 8.3 ms end-to-end p50 vs depth 2 = 18 ms, because with depth ≥ 2 frame N's packet only
@@ -242,10 +267,59 @@ pub fn probe_can_encode(codec: Codec) -> bool {
         let prev = ffi::av_log_get_level();
         ffi::av_log_set_level(ffi::AV_LOG_FATAL);
         let ok = match VaapiHw::new(ffi::AVPixelFormat::AV_PIX_FMT_NV12, 640, 480, 2) {
-            Ok(hw) => {
-                open_vaapi_encoder(codec, 640, 480, 30, 2_000_000, hw.device_ref, hw.frames_ref)
-                    .is_ok()
-            }
+            Ok(hw) => open_vaapi_encoder(
+                codec,
+                640,
+                480,
+                30,
+                2_000_000,
+                hw.device_ref,
+                hw.frames_ref,
+                false,
+            )
+            .is_ok(),
+            Err(_) => false,
+        };
+        ffi::av_log_set_level(prev);
+        ok
+    }
+}
+
+/// Probe whether the active VAAPI GPU can encode **10-bit** (HEVC Main10 / 10-bit AV1) from P010
+/// surfaces — the exact shape a live HDR session opens (P010 pool + Main10 profile + PQ VUI). The
+/// driver rejects what the video engine can't do; the result is cached by the caller
+/// ([`crate::can_encode_10bit`]), so a non-Main10 GPU resolves every session to 8-bit SDR before
+/// the Welcome (honest downgrade).
+pub fn probe_can_encode_10bit(codec: Codec) -> bool {
+    if !codec.supports_10bit() || codec == Codec::PyroWave {
+        return false;
+    }
+    if ffmpeg::init().is_err() {
+        return false;
+    }
+    // SAFETY: `ffmpeg::init()` returned Ok above, so libav is initialized. `av_log_{get,set}_level`
+    // only read/write libav's global integer log level (no pointer args). `VaapiHw::new` (an
+    // `unsafe fn`) builds a VAAPI device + P010 frames pool from the literal args and hands back a
+    // RAII handle; `open_vaapi_encoder` (an `unsafe fn`) borrows `hw.device_ref`/`hw.frames_ref` —
+    // the two non-null refs `VaapiHw::new` just created, live locals for the whole match arm — and
+    // `av_buffer_ref`s them into the probe encoder. Both `hw` and the encoder drop (RAII) at arm end.
+    unsafe {
+        // A missing VA device / no Main10 entrypoint is an expected probe outcome — quiet ffmpeg's
+        // error for the probe, then restore the level.
+        let prev = ffi::av_log_get_level();
+        ffi::av_log_set_level(ffi::AV_LOG_FATAL);
+        let ok = match VaapiHw::new(ffi::AVPixelFormat::AV_PIX_FMT_P010LE, 640, 480, 2) {
+            Ok(hw) => open_vaapi_encoder(
+                codec,
+                640,
+                480,
+                30,
+                2_000_000,
+                hw.device_ref,
+                hw.frames_ref,
+                true,
+            )
+            .is_ok(),
             Err(_) => false,
         };
         ffi::av_log_set_level(prev);
@@ -348,12 +422,21 @@ impl CpuInner {
         bitrate_bps: u64,
     ) -> Result<Self> {
         let src_pixel = vaapi_sws_src(format)?;
+        // A 10-bit HDR capture (X2RGB10/X2BGR10, PQ/BT.2020) uploads P010 and encodes Main10; the
+        // 8-bit paths keep NV12/BT.709 byte-for-byte unchanged.
+        let ten_bit = format.is_hdr_rgb10();
+        let staging_av = if ten_bit {
+            ffi::AVPixelFormat::AV_PIX_FMT_P010LE
+        } else {
+            ffi::AVPixelFormat::AV_PIX_FMT_NV12
+        };
         const POOL: c_int = 16;
         // SAFETY: `VaapiHw::new` (an `unsafe fn`) requires libav initialized — guaranteed because the
         // only path here is `VaapiEncoder::open` → `ensure_inner` → `CpuInner::open`, and `open` ran
-        // `ffmpeg::init()`. The args are valid: NV12 sw_format, the validated positive `width`/`height`,
-        // pool=16. It returns a RAII `VaapiHw` that unrefs its two `AVBufferRef`s on drop.
-        let hw = unsafe { VaapiHw::new(ffi::AVPixelFormat::AV_PIX_FMT_NV12, width, height, POOL)? };
+        // `ffmpeg::init()`. The args are valid: an NV12/P010 sw_format, the validated positive
+        // `width`/`height`, pool=16. It returns a RAII `VaapiHw` that unrefs its two `AVBufferRef`s
+        // on drop.
+        let hw = unsafe { VaapiHw::new(staging_av, width, height, POOL)? };
         // SAFETY: `open_vaapi_encoder` (an `unsafe fn`) borrows `hw.device_ref`/`hw.frames_ref` — both
         // non-null (`VaapiHw::new` guarantees it) and from the `hw` just built above, which is a live
         // local that outlives this synchronous call. The fn `av_buffer_ref`s them into the encoder, so
@@ -368,16 +451,19 @@ impl CpuInner {
                 bitrate_bps,
                 hw.device_ref,
                 hw.frames_ref,
+                ten_bit,
             )?
         };
-        // swscale RGB→NV12, BT.709 limited (matches the VUI), no rescale.
+        // swscale RGB→NV12 (BT.709 limited) or X2RGB10→P010 (BT.2020 limited, HDR) — matches the
+        // VUI; no rescale.
         let src_av = pixel_to_av(src_pixel);
         // SAFETY: `sws_getContext` allocates a swscale context for the given src/dst dimensions and
         // pixel formats. All four dims are the encoder's positive `width`/`height` cast to `c_int`;
         // `src_av` is a valid `AVPixelFormat` (from `pixel_to_av` of the `vaapi_sws_src`-validated
-        // `src_pixel`), the dst is NV12. The three trailing pointers (srcFilter, dstFilter, param) are
-        // explicitly null = "use defaults", which the API documents as accepted. No Rust memory is
-        // borrowed — only by-value ints/enums — and the returned pointer is null-checked just below.
+        // `src_pixel`), the dst is NV12/P010. The three trailing pointers (srcFilter, dstFilter,
+        // param) are explicitly null = "use defaults", which the API documents as accepted. No Rust
+        // memory is borrowed — only by-value ints/enums — and the returned pointer is null-checked
+        // just below.
         let sws = unsafe {
             ffi::sws_getContext(
                 width as c_int,
@@ -385,7 +471,7 @@ impl CpuInner {
                 src_av,
                 width as c_int,
                 height as c_int,
-                ffi::AVPixelFormat::AV_PIX_FMT_NV12,
+                staging_av,
                 SWS_POINT,
                 ptr::null_mut(),
                 ptr::null_mut(),
@@ -393,45 +479,51 @@ impl CpuInner {
             )
         };
         if sws.is_null() {
-            bail!("sws_getContext(RGB→NV12) failed");
+            bail!("sws_getContext(RGB→{})", if ten_bit { "P010" } else { "NV12" });
         }
         // SAFETY: `sws` is the non-null `SwsContext` from `sws_getContext` above (the `is_null()`
-        // check immediately preceding returned false). `sws_getCoefficients(SWS_CS_ITU709)` returns a
-        // pointer into a libswscale static const coefficient table valid for the whole process, reused
-        // here for both the inverse (src) and forward (dst) matrices. `sws_setColorspaceDetails` only
-        // reads those tables and writes scalar CSC settings into `sws`; the table pointer outlives the
-        // synchronous call and no Rust memory is passed.
+        // check immediately preceding returned false). The coefficient table from
+        // `sws_getCoefficients` (ITU-709, or BT.2020 NCL for the HDR path — matching the VUI) is a
+        // libswscale static const valid for the whole process, reused here for both the inverse
+        // (src) and forward (dst) matrices. `sws_setColorspaceDetails` only reads those tables and
+        // writes scalar CSC settings into `sws`; the table pointer outlives the synchronous call and
+        // no Rust memory is passed.
         unsafe {
-            let cs709 = ffi::sws_getCoefficients(SWS_CS_ITU709);
-            ffi::sws_setColorspaceDetails(sws, cs709, 1, cs709, 0, 0, 1 << 16, 1 << 16);
+            let cs = ffi::sws_getCoefficients(if ten_bit {
+                super::libav::SWS_CS_BT2020
+            } else {
+                SWS_CS_ITU709
+            });
+            ffi::sws_setColorspaceDetails(sws, cs, 1, cs, 0, 0, 1 << 16, 1 << 16);
         }
         // SAFETY: `av_frame_alloc` returns a fresh, uniquely-owned heap `AVFrame` (null-checked — on
         // null we free the already-built `sws` and bail). We then write the plain `format`/`width`/
         // `height` fields through the non-null, properly-aligned `f` (sole owner, not yet shared).
         // `av_frame_get_buffer(f, 0)` allocates backing storage for those dims/format; on failure we
         // free `f` and `sws` (unwinding the half-built state) and bail. On success `f` is a fully-owned
-        // NV12 frame stored in `CpuInner.nv12` and freed once in `CpuInner::drop`. `f` is a unique
-        // fresh pointer, so none of these writes alias anything.
+        // NV12/P010 frame stored in `CpuInner.nv12` and freed once in `CpuInner::drop`. `f` is a
+        // unique fresh pointer, so none of these writes alias anything.
         let nv12 = unsafe {
             let f = ffi::av_frame_alloc();
             if f.is_null() {
                 ffi::sws_freeContext(sws);
-                bail!("av_frame_alloc(NV12) failed");
+                bail!("av_frame_alloc(staging) failed");
             }
-            (*f).format = ffi::AVPixelFormat::AV_PIX_FMT_NV12 as c_int;
+            (*f).format = staging_av as c_int;
             (*f).width = width as c_int;
             (*f).height = height as c_int;
             if ffi::av_frame_get_buffer(f, 0) < 0 {
                 let mut f = f;
                 ffi::av_frame_free(&mut f);
                 ffi::sws_freeContext(sws);
-                bail!("av_frame_get_buffer(NV12) failed");
+                bail!("av_frame_get_buffer(staging) failed");
             }
             f
         };
         tracing::info!(
             encoder = codec.vaapi_name(),
-            "VAAPI encode active ({width}x{height}@{fps}, CPU→NV12 upload path)"
+            "VAAPI encode active ({width}x{height}@{fps}, CPU→{} upload path)",
+            if ten_bit { "P010 (HDR10)" } else { "NV12" }
         );
         Ok(CpuInner {
             enc,
@@ -563,6 +655,15 @@ impl DmabufInner {
     ) -> Result<Self> {
         let drm_fourcc = pf_frame::drm_fourcc(format)
             .ok_or_else(|| anyhow!("no DRM fourcc for {format:?} (VAAPI zero-copy)"))?;
+        // A 10-bit HDR capture (X2RGB10/X2BGR10 dmabufs, PQ/BT.2020) maps + CSCs to P010 and
+        // encodes Main10; the 8-bit paths keep the NV12/BT.709 graph byte-for-byte unchanged.
+        let ten_bit = format.is_hdr_rgb10();
+        let sw_format = match format {
+            PixelFormat::X2Rgb10 => ffi::AVPixelFormat::AV_PIX_FMT_X2RGB10LE,
+            PixelFormat::X2Bgr10 => ffi::AVPixelFormat::AV_PIX_FMT_X2BGR10LE,
+            // The 8-bit capture formats are all XR24-shaped packed RGB (the historical BGR0 view).
+            _ => ffi::AVPixelFormat::AV_PIX_FMT_BGR0,
+        };
         let node = render_node();
         // SAFETY: libav is initialized (`VaapiEncoder::open` ran `ffmpeg::init()` before
         // `ensure_inner` → `DmabufInner::open`). Every raw pointer dereferenced below is either freshly
@@ -628,7 +729,7 @@ impl DmabufInner {
             }
             let fc = (*drm_frames).data as *mut ffi::AVHWFramesContext;
             (*fc).format = ffi::AVPixelFormat::AV_PIX_FMT_DRM_PRIME;
-            (*fc).sw_format = ffi::AVPixelFormat::AV_PIX_FMT_BGR0; // packed XR24 RGB plane
+            (*fc).sw_format = sw_format; // packed XR24 RGB plane, or XR30/XB30 for HDR
             (*fc).width = width as c_int;
             (*fc).height = height as c_int;
             if ffi::av_hwframe_ctx_init(drm_frames) < 0 {
@@ -715,14 +816,24 @@ impl DmabufInner {
             }
             init!(src, ptr::null(), "buffer");
             init!(hwmap, c"mode=read".as_ptr(), "hwmap");
-            // Pin the VPP's output colour to what the encoder's VUI signals (BT.709 limited).
-            // Without the explicit options the conversion matrix is whatever the driver defaults
-            // to for an unspecified output (Mesa: BT.601) — a hue shift against the signaled VUI.
-            init!(
-                scale,
-                c"format=nv12:out_color_matrix=bt709:out_range=limited".as_ptr(),
-                "scale_vaapi"
-            );
+            // Pin the VPP's output colour to what the encoder's VUI signals (BT.709 limited SDR,
+            // or BT.2020 limited P010 for HDR — the PQ transfer is per-channel and rides through
+            // the matrix untouched). Without the explicit options the conversion matrix is
+            // whatever the driver defaults to for an unspecified output (Mesa: BT.601) — a hue
+            // shift against the signaled VUI.
+            if ten_bit {
+                init!(
+                    scale,
+                    c"format=p010:out_color_matrix=bt2020:out_range=limited".as_ptr(),
+                    "scale_vaapi"
+                );
+            } else {
+                init!(
+                    scale,
+                    c"format=nv12:out_color_matrix=bt709:out_range=limited".as_ptr(),
+                    "scale_vaapi"
+                );
+            }
             init!(sink, ptr::null(), "buffersink");
 
             let link = |a: *mut ffi::AVFilterContext, b: *mut ffi::AVFilterContext| -> c_int {
@@ -766,6 +877,7 @@ impl DmabufInner {
                 bitrate_bps,
                 vaapi_device,
                 nv12_ctx,
+                ten_bit,
             ) {
                 Ok(enc) => enc,
                 Err(e) => {
@@ -779,7 +891,8 @@ impl DmabufInner {
 
             tracing::info!(
                 encoder = codec.vaapi_name(),
-                "VAAPI encode active ({width}x{height}@{fps}, zero-copy dmabuf → GPU NV12)"
+                "VAAPI encode active ({width}x{height}@{fps}, zero-copy dmabuf → GPU {})",
+                if ten_bit { "P010 (HDR10)" } else { "NV12" }
             );
             Ok(DmabufInner {
                 enc,
@@ -987,8 +1100,22 @@ impl VaapiEncoder {
         bit_depth: u8,
         chroma: super::ChromaFormat,
     ) -> Result<Self> {
-        if bit_depth != 8 {
-            tracing::warn!(bit_depth, "VAAPI 10-bit not yet wired — encoding 8-bit");
+        // 10-bit rides on the captured format: an HDR capture (X2RGB10/X2BGR10) opens the P010 /
+        // Main10 / PQ-VUI variant of whichever inner path the first frame selects. A 10-bit
+        // request whose capture stayed SDR honestly encodes 8-bit; the reverse (PQ frames on an
+        // 8-bit session) is refused so PQ content is never mislabeled BT.709.
+        if format.is_hdr_rgb10() && bit_depth != 10 {
+            bail!(
+                "captured 10-bit HDR frames ({format:?}) on an {bit_depth}-bit VAAPI session — \
+                 refusing to mislabel PQ content"
+            );
+        }
+        if bit_depth == 10 && !format.is_hdr_rgb10() {
+            tracing::warn!(
+                bit_depth,
+                ?format,
+                "10-bit requested but the capture stayed SDR — encoding 8-bit"
+            );
         }
         // VAAPI 4:4:4 is deferred (see `probe_can_encode_444`): no validated AMD/Intel hardware in the
         // lab exposes a HEVC 4:4:4 encode entrypoint, and the probe returns false so the host never
diff --git a/crates/pf-encode/src/enc/sw.rs b/crates/pf-encode/src/enc/sw.rs
index df056192..3a6b04e4 100644
--- a/crates/pf-encode/src/enc/sw.rs
+++ b/crates/pf-encode/src/enc/sw.rs
@@ -181,10 +181,10 @@ impl Encoder for OpenH264Encoder {
             PixelFormat::Bgr => (3, 2, 1, 0),
             PixelFormat::Rgba | PixelFormat::Rgbx => (4, 0, 1, 2),
             PixelFormat::Bgra | PixelFormat::Bgrx => (4, 2, 1, 0),
-            // 10-bit HDR comes only from the GPU NVENC path; the software 8-bit H.264 encoder
-            // can't represent it (and never receives it — the capturer pairs Rgb10a2 with NVENC).
-            PixelFormat::Rgb10a2 => {
-                anyhow::bail!("software H.264 encoder cannot encode 10-bit HDR (Rgb10a2)")
+            // 10-bit HDR comes only from the GPU paths; the software 8-bit H.264 encoder can't
+            // represent it (and never receives it — HDR is never negotiated on a software host).
+            PixelFormat::Rgb10a2 | PixelFormat::X2Rgb10 | PixelFormat::X2Bgr10 => {
+                anyhow::bail!("software H.264 encoder cannot encode 10-bit HDR ({:?})", self.src_format)
             }
             // NV12/P010 are GPU-resident video-processor outputs for the NVENC path; the software
             // encoder never receives them (it only gets CPU RGB frames).
diff --git a/crates/pf-encode/src/lib.rs b/crates/pf-encode/src/lib.rs
index 5ea0db64..6fde1365 100644
--- a/crates/pf-encode/src/lib.rs
+++ b/crates/pf-encode/src/lib.rs
@@ -288,8 +288,14 @@ fn open_video_backend(
         // stream never dies over the new path. `format`/`bit_depth`/`chroma` only matter to VAAPI —
         // the Vulkan backend imports the dmabuf and does its own 8-bit 4:2:0 CSC.
         let open_amd_intel = || -> Result<(Box<dyn Encoder>, &'static str)> {
+            // An HDR session (10-bit + a PQ/BT.2020 capture format) must skip the Vulkan Video
+            // backend — it hardcodes an 8-bit 4:2:0 BT.709 CSC — and take the libav VAAPI path,
+            // which has the P010/Main10/PQ wiring. SDR sessions keep the Vulkan default.
             #[cfg(feature = "vulkan-encode")]
-            if matches!(codec, Codec::H265 | Codec::Av1) && vulkan_encode_enabled() {
+            if matches!(codec, Codec::H265 | Codec::Av1)
+                && vulkan_encode_enabled()
+                && !(bit_depth == 10 && format.is_hdr_rgb10())
+            {
                 match vulkan_video::VulkanVideoEncoder::open(codec, width, height, fps, bitrate_bps)
                 {
                     Ok(e) => {
@@ -956,11 +962,10 @@ pub fn can_encode_444(_codec: Codec) -> bool {
 /// Backend truth: Windows **NVENC** queries the per-codec `NV_ENC_CAPS_SUPPORT_10BIT_ENCODE` cap;
 /// native **AMF** `Init`s a tiny P010 encoder with the 10-bit profile props (the driver rejects
 /// what the VCN can't do). **QSV** stays `false` until validated on Intel glass — the libavcodec
-/// Main10 incantation can silently encode 8-bit, the same stance as its 4:4:4 probe. Every
-/// **Linux** backend is `false` today: direct-NVENC/CUDA pins 8-bit until a P010 capture path
-/// exists (Phase 5.1), libav `hevc_nvenc` needs a 10-bit input format the capturer never feeds,
-/// VAAPI 10-bit isn't wired, and Vulkan-video hardcodes 8-bit — so Linux hosts honestly negotiate
-/// 8-bit SDR.
+/// Main10 incantation can silently encode 8-bit, the same stance as its 4:4:4 probe. **Linux**
+/// probes a tiny real Main10 open on the auto-resolved backend — libav NVENC (the HDR X2RGB10→
+/// P010 swscale path) or VAAPI (P010 pool + Main10) — for the GNOME 50+ HDR portal capture;
+/// the direct-SDK CUDA path and Vulkan-video stay 8-bit and a 10-bit session routes around them.
 #[cfg(any(target_os = "linux", target_os = "windows"))]
 pub fn can_encode_10bit(codec: Codec) -> bool {
     use std::collections::HashMap;
@@ -985,8 +990,18 @@ pub fn can_encode_10bit(codec: Codec) -> bool {
     let supported = {
         #[cfg(target_os = "linux")]
         {
-            // No Linux backend encodes 10-bit yet (see the fn doc) — never negotiate it.
-            false
+            // NVENC (libav, the HDR P010 swscale path) or VAAPI (P010 upload / dmabuf graph),
+            // probed by opening a tiny real Main10 encoder — the same honesty contract as
+            // `can_encode_444`. Vulkan-video and the direct-SDK CUDA path stay 8-bit; a 10-bit
+            // session routes around them (see `open_video_backend`). NOTE: encode capability is
+            // only half the Linux gate — the capture side (GNOME 50+ portal monitor in HDR mode)
+            // is resolved separately by the host (`capturer_supports_hdr` / the GameStream RTSP
+            // honor), since this probe can't know what the compositor will negotiate.
+            if linux_auto_is_vaapi() {
+                vaapi::probe_can_encode_10bit(codec)
+            } else {
+                linux::probe_can_encode_10bit(codec)
+            }
         }
         #[cfg(target_os = "windows")]
         {
diff --git a/crates/pf-frame/src/lib.rs b/crates/pf-frame/src/lib.rs
index 4e0274b4..1eda307b 100644
--- a/crates/pf-frame/src/lib.rs
+++ b/crates/pf-frame/src/lib.rs
@@ -56,6 +56,19 @@ pub enum PixelFormat {
     /// `DeviceBuffer::yuv444` — three full-res planes stacked in one allocation); NVENC encodes
     /// it natively under the Range-Extensions profile. Never a CPU payload.
     Yuv444,
+    /// 10-bit RGB packed `x:R:G:B 2:10:10:10` little-endian (SPA `xRGB_210LE`, DRM `XRGB2101010` /
+    /// `XR30`, ffmpeg `x2rgb10le`, NVENC `ARGB10`) — as an LE u32: B in bits 0-9, G 10-19, R 20-29.
+    /// The Linux GNOME 50+ HDR screencast source format: Mutter advertises it (with BT.2020
+    /// primaries + SMPTE ST.2084 PQ transfer) for a monitor in HDR mode, so the samples are
+    /// PQ-encoded BT.2020 RGB. Linux-only; the Windows HDR path stays `Rgb10a2`/`P010`.
+    X2Rgb10,
+    /// 10-bit RGB packed `x:B:G:R 2:10:10:10` little-endian (SPA `xBGR_210LE`, DRM `XBGR2101010` /
+    /// `XB30`, ffmpeg `x2bgr10le`, NVENC `ABGR10`) — as an LE u32: R in bits 0-9, G 10-19, B 20-29;
+    /// the same memory layout as the Windows [`Rgb10a2`](Self::Rgb10a2) (DXGI `R10G10B10A2`). The
+    /// second GNOME 50+ HDR screencast format (same PQ/BT.2020 colorimetry as
+    /// [`X2Rgb10`](Self::X2Rgb10)); kept separate from `Rgb10a2` so the Linux and Windows HDR
+    /// paths stay independently greppable.
+    X2Bgr10,
 }
 
 impl PixelFormat {
@@ -67,6 +80,12 @@ impl PixelFormat {
             _ => 4,
         }
     }
+
+    /// True for the packed 10-bit RGB layouts a Linux HDR (BT.2020 PQ) capture negotiates —
+    /// the formats that make a session's encode bit depth 10 (HEVC Main10 / 10-bit AV1).
+    pub fn is_hdr_rgb10(self) -> bool {
+        matches!(self, PixelFormat::X2Rgb10 | PixelFormat::X2Bgr10)
+    }
 }
 
 /// DRM FourCC for a packed 32-bit format name (little-endian, e.g. `b"XR24"`).
@@ -86,6 +105,9 @@ pub fn drm_fourcc(format: PixelFormat) -> Option<u32> {
         Bgra => drm_fourcc_code(b"AR24"), // DRM_FORMAT_ARGB8888
         Rgbx => drm_fourcc_code(b"XB24"), // DRM_FORMAT_XBGR8888
         Rgba => drm_fourcc_code(b"AB24"), // DRM_FORMAT_ABGR8888
+        // The GNOME 50+ HDR screencast formats (packed 2:10:10:10, PQ/BT.2020).
+        X2Rgb10 => drm_fourcc_code(b"XR30"), // DRM_FORMAT_XRGB2101010
+        X2Bgr10 => drm_fourcc_code(b"XB30"), // DRM_FORMAT_XBGR2101010
         // 24-bit packed RGB/BGR have no straightforward dmabuf import here; use the CPU path.
         // Rgb10a2/Nv12/P010 are the Windows HDR / video-processor formats — never produced on
         // Linux; Yuv444 is OUR convert's OUTPUT, never a capture source format.
diff --git a/crates/punktfunk-host/src/capture.rs b/crates/punktfunk-host/src/capture.rs
index af9e6d54..2a6ca074 100644
--- a/crates/punktfunk-host/src/capture.rs
+++ b/crates/punktfunk-host/src/capture.rs
@@ -12,7 +12,10 @@ use anyhow::Result;
 // `crate::capture::*` (the capture mechanics that used the rest moved into pf-capture).
 pub use pf_frame::{CapturedFrame, OutputFormat, PixelFormat};
 // The capturer types + trait + synthetics live in `pf-capture`; re-export them at the old paths.
-pub use pf_capture::{capturer_supports_444, Capturer, FastSyntheticCapturer, SyntheticCapturer};
+pub use pf_capture::{
+    capturer_supports_444, capturer_supports_hdr, Capturer, FastSyntheticCapturer,
+    SyntheticCapturer,
+};
 // `crate::capture::dxgi::{install_gpu_pref_hook, hdr_p010_selftest}` (main.rs subcommands) and
 // `crate::capture::synthetic_nv12` resolve through pf-capture's Windows modules.
 #[cfg(target_os = "windows")]
@@ -45,18 +48,20 @@ fn zero_copy_policy() -> pf_capture::ZeroCopyPolicy {
     }
 }
 
-/// Open a live capturer for a client-sized monitor via the xdg ScreenCast portal.
+/// Open a live capturer for a client-sized monitor via the xdg ScreenCast portal. `want_hdr`
+/// offers the GNOME 50+ 10-bit PQ/BT.2020 formats (pass it only when the session negotiated HDR
+/// AND the mirrored monitor is in HDR mode — see [`pf_capture::gnome_hdr_monitor_active`]).
 #[cfg(target_os = "linux")]
-pub fn open_portal_monitor() -> Result<Box<dyn Capturer>> {
+pub fn open_portal_monitor(want_hdr: bool) -> Result<Box<dyn Capturer>> {
     // On RemoteDesktop-capable desktops (KWin/GNOME) anchor ScreenCast to a RemoteDesktop
     // session so it inherits that grant headlessly; wlroots/Sway has no RemoteDesktop portal,
     // so use a plain ScreenCast session there.
     let anchored = crate::inject::default_backend() == crate::inject::Backend::Libei;
-    pf_capture::open_portal_monitor(anchored, zero_copy_policy())
+    pf_capture::open_portal_monitor(anchored, want_hdr, zero_copy_policy())
 }
 
 #[cfg(not(target_os = "linux"))]
-pub fn open_portal_monitor() -> Result<Box<dyn Capturer>> {
+pub fn open_portal_monitor(_want_hdr: bool) -> Result<Box<dyn Capturer>> {
     anyhow::bail!("portal capture requires Linux (xdg-desktop-portal + PipeWire)")
 }
 
@@ -69,11 +74,13 @@ pub fn capture_virtual_output(
     want: OutputFormat,
     _capture: crate::session_plan::CaptureBackend,
 ) -> Result<Box<dyn Capturer>> {
-    // The Linux host stays 8-bit (HDR is blocked upstream) and the portal negotiates its own pixel
-    // format, so `want.gpu` gates GPU zero-copy capture (the capture backend is always the portal —
-    // the `CaptureBackend` arg is a Windows-only dispatch) and `want.chroma_444` selects the
-    // worker's planar-YUV444 GPU convert. `gpu = false` (4:4:4 without zero-copy) forces the CPU
-    // mmap path so the encoder gets CPU-resident RGB to swscale into YUV444P.
+    // The Linux NATIVE plane stays 8-bit (Mutter's virtual-monitor streams are SDR-only upstream;
+    // the GNOME 50+ HDR path is monitor-mirror only — `open_portal_monitor`) and the portal
+    // negotiates its own pixel format, so `want.gpu` gates GPU zero-copy capture (the capture
+    // backend is always the portal — the `CaptureBackend` arg is a Windows-only dispatch) and
+    // `want.chroma_444` selects the worker's planar-YUV444 GPU convert. `gpu = false` (4:4:4
+    // without zero-copy) forces the CPU mmap path so the encoder gets CPU-resident RGB to swscale
+    // into YUV444P.
     pf_capture::open_virtual_output(
         vout.remote_fd,
         vout.node_id,
diff --git a/crates/punktfunk-host/src/gamestream/mod.rs b/crates/punktfunk-host/src/gamestream/mod.rs
index 1ba86747..87539d6b 100644
--- a/crates/punktfunk-host/src/gamestream/mod.rs
+++ b/crates/punktfunk-host/src/gamestream/mod.rs
@@ -50,21 +50,45 @@ pub const SCM_AV1_MAIN10: u32 = 0x0002_0000;
 /// The **SDR baseline** codec mask: H.264, HEVC Main, AV1 Main 8-bit (= 65793). HEVC Main10 (HDR) is
 /// layered on top of this at runtime by `serverinfo::codec_mode_support` when — and only when — the
 /// host can actually deliver it ([`host_hdr_capable`]); it is never a static claim, because a non-HDR
-/// host (Linux, or a Windows host without the `PUNKTFUNK_10BIT` opt-in) must not invite a client into
-/// an HDR mode it can't produce. (The previous placeholder 3843 = 0xF03 wrongly claimed HEVC Main10 +
+/// host (a host without the `PUNKTFUNK_10BIT` opt-in, or a Linux host whose video source / encoder
+/// can't do Main10) must not invite a client into an HDR mode it can't produce. (The previous placeholder 3843 = 0xF03 wrongly claimed HEVC Main10 +
 /// 4:4:4 and *no* AV1.) 4:4:4 stays off entirely on GameStream: stock Moonlight is 4:2:0 —
 /// full-chroma is a punktfunk/1-native negotiation only (`crate::capture::capturer_supports_444`).
 pub const SERVER_CODEC_MODE_SUPPORT: u32 = SCM_H264 | SCM_HEVC | SCM_AV1_MAIN8;
 
 /// Whether this host can deliver an **HDR** (HEVC Main10 / BT.2020 PQ) GameStream — the single gate
-/// for advertising [`SCM_HEVC_MAIN10`] in serverinfo and `IsHdrSupported` per app, and for honoring a
-/// client's `dynamicRangeMode` request. HDR capture+encode is **Windows-only** (the Linux host is
-/// 8-bit, blocked upstream) and behind the operator's `PUNKTFUNK_10BIT` opt-in — the same policy gate
-/// the native punktfunk/1 plane honors. When this is true the IDD-push capturer streams HEVC Main10 PQ
-/// whenever the desktop is HDR, and a client HDR request makes the GameStream video path proactively
-/// enable advanced color on the per-session virtual display so PQ flows even from an SDR desktop.
+/// for advertising [`SCM_HEVC_MAIN10`] in serverinfo and `IsHdrSupported` per app, and (together
+/// with the live capture-side check at RTSP time) for honoring a client's `dynamicRangeMode`
+/// request. Behind the operator's `PUNKTFUNK_10BIT` opt-in — the same policy gate the native
+/// punktfunk/1 plane honors — on both OSes.
+///
+/// **Windows**: the IDD-push capturer streams HEVC Main10 PQ whenever the desktop is HDR, and a
+/// client HDR request proactively enables advanced color on the per-session virtual display so PQ
+/// flows even from an SDR desktop.
+///
+/// **Linux**: the GNOME 50+ portal **monitor mirror** (`video_source=portal`) can negotiate the
+/// 10-bit PQ formats while the mirrored monitor is in HDR mode, and the NVENC/VAAPI encoders have
+/// a probed Main10 path ([`crate::encode::can_encode_10bit`]). The virtual-output source stays SDR
+/// (Mutter's RecordVirtual streams are 8-bit-only upstream), so this is `false` for it. Whether
+/// the monitor is ACTUALLY in HDR mode right now is checked live at RTSP honor time
+/// ([`pf_capture::gnome_hdr_monitor_active`]) — this fn is the static serverinfo capability.
 pub fn host_hdr_capable() -> bool {
-    cfg!(target_os = "windows") && pf_host_config::config().ten_bit
+    if !pf_host_config::config().ten_bit {
+        return false;
+    }
+    #[cfg(target_os = "windows")]
+    {
+        true
+    }
+    #[cfg(target_os = "linux")]
+    {
+        pf_host_config::config().video_source.as_deref() == Some("portal")
+            && crate::encode::can_encode_10bit(crate::encode::Codec::H265)
+    }
+    #[cfg(not(any(target_os = "windows", target_os = "linux")))]
+    {
+        false
+    }
 }
 
 /// Stable host identity + advertised capabilities, shared across control-plane handlers.
@@ -141,8 +165,11 @@ pub struct AppState {
     pub rfi_range: std::sync::Arc<std::sync::Mutex<Option<(i64, i64)>>>,
     /// Persistent screen capturer, reused across streams so reconnects don't spawn a second
     /// (conflicting) screencast session. The video thread borrows it for the stream's duration
-    /// and returns it; `set_active` gates its cost while idle.
-    pub video_cap: std::sync::Arc<std::sync::Mutex<Option<Box<dyn crate::capture::Capturer>>>>,
+    /// and returns it; `set_active` gates its cost while idle. The slot's `bool` records whether
+    /// it was opened with the HDR (10-bit PQ) offer — a stream whose negotiated `hdr` differs
+    /// drops the pooled capturer and opens a fresh screencast session at the right depth
+    /// (mirroring the audio capturer's channel-count reuse gate).
+    pub video_cap: stream::CapturerSlot,
     /// Persistent audio capturer, reused across streams when the channel count still matches
     /// (avoids a PipeWire stream setup per reconnect); drained on reuse so no stale audio is
     /// sent, dropped + reopened when a session negotiates a different channel count.
diff --git a/crates/punktfunk-host/src/gamestream/rtsp.rs b/crates/punktfunk-host/src/gamestream/rtsp.rs
index 766871dc..ad1b4cdf 100644
--- a/crates/punktfunk-host/src/gamestream/rtsp.rs
+++ b/crates/punktfunk-host/src/gamestream/rtsp.rs
@@ -396,18 +396,30 @@ fn stream_config(map: &HashMap<String, String>) -> Option<StreamConfig> {
         _ => Codec::H264,
     };
     // 10-bit/HDR request (Moonlight sets `dynamicRangeMode != 0` only when it both saw our Main10 SCM
-    // bit AND the user enabled HDR). Honor it only when the host can actually deliver Main10 (Windows +
-    // PUNKTFUNK_10BIT, `host_hdr_capable`); when honored, the video path proactively enables advanced
-    // color on the virtual display so a PQ stream flows even from an SDR desktop. A request we can't
-    // honor degrades to 8-bit SDR (and a desktop that is ALREADY HDR still streams PQ regardless, since
-    // the IDD-push capturer follows the display).
+    // bit AND the user enabled HDR). Honor it only when the host can actually deliver Main10
+    // (`host_hdr_capable` — Windows IDD-push, or the Linux GNOME 50+ portal mirror). On Windows,
+    // when honored, the video path proactively enables advanced color on the virtual display so a
+    // PQ stream flows even from an SDR desktop. On Linux the portal can only deliver PQ while the
+    // MIRRORED monitor is in HDR mode, so additionally probe the live colour mode here (one D-Bus
+    // round-trip, sync RTSP thread) — an SDR desktop honestly degrades to 8-bit SDR up front
+    // instead of running the capture negotiation into its timeout. A request we can't honor
+    // degrades to 8-bit SDR (and a Windows desktop that is ALREADY HDR still streams PQ
+    // regardless, since the IDD-push capturer follows the display).
     let hdr_requested = parse_u("x-nv-video[0].dynamicRangeMode").unwrap_or(0) != 0;
-    let hdr = hdr_requested && crate::gamestream::host_hdr_capable();
+    let mut hdr = hdr_requested && crate::gamestream::host_hdr_capable();
     if hdr_requested && !hdr {
         tracing::warn!(
             "client requested HDR (dynamicRangeMode != 0) but host is not HDR-capable — streaming 8-bit SDR"
         );
     }
+    #[cfg(target_os = "linux")]
+    if hdr && !pf_capture::gnome_hdr_monitor_active() {
+        tracing::warn!(
+            "client requested HDR but no monitor is in BT.2100 (HDR) colour mode — enable HDR in \
+             GNOME Settings → Displays (GNOME 50+) to stream it; streaming 8-bit SDR"
+        );
+        hdr = false;
+    }
     // The client's requested CSC (moonlight-common-c SdpGenerator.c: `encoderCscMode =
     // (colorspace << 1) | fullRange` — colorspace 0=Rec601, 1=Rec709, 2=Rec2020). Moonlight
     // renderers configure their YUV→RGB from this REQUESTED value (not the bitstream VUI), so a
diff --git a/crates/punktfunk-host/src/gamestream/stream.rs b/crates/punktfunk-host/src/gamestream/stream.rs
index 0a15b979..551b72c6 100644
--- a/crates/punktfunk-host/src/gamestream/stream.rs
+++ b/crates/punktfunk-host/src/gamestream/stream.rs
@@ -34,8 +34,9 @@ pub struct StreamConfig {
 }
 
 /// Slot for the persistent screen capturer, shared with the control plane and reused across
-/// streams so a reconnect doesn't open a second (conflicting) screencast session.
-pub type CapturerSlot = Arc<std::sync::Mutex<Option<Box<dyn Capturer>>>>;
+/// streams so a reconnect doesn't open a second (conflicting) screencast session. The `bool` is
+/// the pooled capturer's HDR-ness (see `AppState::video_cap`).
+pub type CapturerSlot = Arc<std::sync::Mutex<Option<(Box<dyn Capturer>, bool)>>>;
 
 /// A pending client reference-frame-invalidation range (lost `firstFrame..=lastFrame`), set by the
 /// control plane and drained by the video thread (see [`AppState::rfi_range`](super::AppState)).
@@ -120,7 +121,7 @@ fn run(
     running: &Arc<AtomicBool>,
     force_idr: &AtomicBool,
     rfi_range: &std::sync::Mutex<Option<(i64, i64)>>,
-    video_cap: &std::sync::Mutex<Option<Box<dyn Capturer>>>,
+    video_cap: &std::sync::Mutex<Option<(Box<dyn Capturer>, bool)>>,
     // Shared stats recorder for the web-console capture/graph. Threaded into `stream_body` (the
     // encode loop); per-frame sample emission is wired by a later pass.
     stats: &Arc<crate::stats_recorder::StatsRecorder>,
@@ -243,15 +244,31 @@ fn run(
     }
 
     // Reuse the persistent capturer (one screencast session → clean reconnect); create it on
-    // the first stream. Borrow it for this stream and return it on exit.
-    let mut capturer: Box<dyn Capturer> = match video_cap.lock().unwrap().take() {
+    // the first stream. Borrow it for this stream and return it on exit. Reuse is gated on the
+    // pooled capturer's HDR-ness matching this stream's negotiated `cfg.hdr` — the depth is a
+    // PipeWire-negotiation-time property of the screencast session, so an HDR↔SDR change needs a
+    // fresh session (same pattern as the audio capturer's channel-count gate).
+    let pooled = match video_cap.lock().unwrap().take() {
+        Some((c, was_hdr)) if was_hdr == cfg.hdr => Some(c),
+        Some((c, was_hdr)) => {
+            tracing::info!(
+                was_hdr,
+                want_hdr = cfg.hdr,
+                "video source: pooled capturer depth mismatch — opening a fresh screencast session"
+            );
+            drop(c);
+            None
+        }
+        None => None,
+    };
+    let mut capturer: Box<dyn Capturer> = match pooled {
         Some(c) => {
             tracing::info!("video source: reusing capturer");
             c
         }
         None if pf_host_config::config().video_source.as_deref() == Some("portal") => {
-            tracing::info!("video source: portal desktop capture");
-            capture::open_portal_monitor().context("open portal capturer")?
+            tracing::info!(hdr = cfg.hdr, "video source: portal desktop capture");
+            capture::open_portal_monitor(cfg.hdr).context("open portal capturer")?
         }
         None => {
             tracing::info!("video source: synthetic test pattern");
@@ -272,7 +289,7 @@ fn run(
         &client_label,
     );
     capturer.set_active(false);
-    *video_cap.lock().unwrap() = Some(capturer);
+    *video_cap.lock().unwrap() = Some((capturer, cfg.hdr));
     result
 }
 
@@ -380,7 +397,9 @@ fn open_gs_virtual_source(
     // HDR: pass the negotiated `cfg.hdr` (client asked for HDR AND the host can deliver it). On the
     // Windows IDD-push path this proactively enables advanced color on the virtual display so a Main10
     // PQ stream flows even from an SDR desktop; an already-HDR desktop streams PQ regardless (the
-    // capturer follows the display). No-op on Linux (8-bit, and `cfg.hdr` is always false there).
+    // capturer follows the display). No-op on Linux: virtual-output capture is SDR-only upstream
+    // (Mutter RecordVirtual), and `host_hdr_capable` therefore keeps `cfg.hdr` false for this
+    // source — the Linux HDR path is the portal monitor mirror (`video_source=portal`).
     let capturer = capture::capture_virtual_output(
         vout,
         capture::OutputFormat::resolve(cfg.hdr, crate::encode::resolved_backend_is_gpu()),
@@ -399,7 +418,11 @@ fn open_gs_virtual_source(
 fn gs_bit_depth(format: crate::capture::PixelFormat) -> u8 {
     use crate::capture::PixelFormat;
     match format {
-        PixelFormat::P010 | PixelFormat::Rgb10a2 => 10,
+        // Windows IDD-push HDR formats, and the Linux GNOME 50+ portal HDR formats.
+        PixelFormat::P010
+        | PixelFormat::Rgb10a2
+        | PixelFormat::X2Rgb10
+        | PixelFormat::X2Bgr10 => 10,
         _ => 8,
     }
 }
diff --git a/crates/punktfunk-host/src/main.rs b/crates/punktfunk-host/src/main.rs
index 04cf568c..3956f5ea 100644
--- a/crates/punktfunk-host/src/main.rs
+++ b/crates/punktfunk-host/src/main.rs
@@ -283,6 +283,24 @@ fn real_main() -> Result<()> {
         // PASS/FAIL + max Y/Cb/Cr error.
         #[cfg(target_os = "windows")]
         Some("hdr-p010-selftest") => crate::capture::dxgi::hdr_p010_selftest(),
+        // Linux HDR readiness probe (GNOME 50+ portal path): prints whether a monitor is currently
+        // in BT.2100 (HDR) colour mode, whether the NVENC/VAAPI backend probes Main10 for
+        // HEVC/AV1, and the GameStream HDR capability the two combine into — the "why isn't my
+        // stream HDR?" diagnostic (no display/session needed for the encoder half).
+        #[cfg(target_os = "linux")]
+        Some("hdr-probe") => {
+            let monitor_hdr = pf_capture::gnome_hdr_monitor_active();
+            let hevc10 = encode::can_encode_10bit(encode::Codec::H265);
+            let av110 = encode::can_encode_10bit(encode::Codec::Av1);
+            println!("monitor in BT.2100 (HDR) colour mode: {monitor_hdr}");
+            println!("encoder Main10 (HEVC): {hevc10}");
+            println!("encoder 10-bit (AV1):  {av110}");
+            println!(
+                "GameStream HDR capable (PUNKTFUNK_10BIT + video_source=portal + encoder): {}",
+                gamestream::host_hdr_capable()
+            );
+            Ok(())
+        }
         // Compositor readiness probe: exit 0 iff the (detected or PUNKTFUNK_COMPOSITOR-forced)
         // compositor is up and able to create a virtual output *now*. A session-bringup
         // script polls this to gate on real readiness instead of a blind `sleep`.
diff --git a/crates/punktfunk-host/src/native/handshake.rs b/crates/punktfunk-host/src/native/handshake.rs
index 47e2543e..8f5779aa 100644
--- a/crates/punktfunk-host/src/native/handshake.rs
+++ b/crates/punktfunk-host/src/native/handshake.rs
@@ -212,10 +212,22 @@ pub(super) async fn negotiate(
     // label that matches the stream.
     let host_wants_10bit = pf_host_config::config().ten_bit;
     let client_supports_10bit = hello.video_caps & punktfunk_core::quic::VIDEO_CAP_10BIT != 0;
+    // The capture side must be able to deliver a 10-bit HDR source for the NATIVE plane's
+    // virtual-output capture — the honest-downgrade gate, mirroring `capturer_supports_444`.
+    // Windows IDD-push can (it proactively enables advanced colour); Linux cannot: Mutter's
+    // RecordVirtual virtual-monitor streams are 8-bit-only upstream (GNOME 50 added HDR for
+    // *monitor* streams only — the GameStream portal-mirror path uses that; see
+    // `gamestream::host_hdr_capable`), so a Linux native session honestly stays 8-bit SDR even
+    // though `can_encode_10bit` now probes true on a Main10-capable GPU.
+    let capture_supports_hdr = crate::capture::capturer_supports_hdr();
     // The GPU probe may open a tiny encoder on first use, so run it off the reactor like the
     // 4:4:4 probe below (blocking probes → spawn_blocking), short-circuited behind the cheap
     // gates. The result is cached process-wide per (GPU, codec).
-    let gpu_can_10bit = if host_wants_10bit && client_supports_10bit && codec.supports_10bit() {
+    let gpu_can_10bit = if host_wants_10bit
+        && client_supports_10bit
+        && codec.supports_10bit()
+        && capture_supports_hdr
+    {
         tokio::task::spawn_blocking(move || crate::encode::can_encode_10bit(codec))
             .await
             .context("10-bit capability probe task")?
@@ -227,6 +239,7 @@ pub(super) async fn negotiate(
         bit_depth,
         host_wants_10bit,
         client_supports_10bit,
+        capture_supports_hdr,
         codec = ?codec,
         gpu_can_10bit,
         client_video_caps = hello.video_caps,
diff --git a/crates/punktfunk-host/src/session_plan.rs b/crates/punktfunk-host/src/session_plan.rs
index 4bcd95e1..f34dafda 100644
--- a/crates/punktfunk-host/src/session_plan.rs
+++ b/crates/punktfunk-host/src/session_plan.rs
@@ -89,7 +89,9 @@ pub struct SessionPlan {
     /// Handshake-negotiated encode bit depth (8, or 10 = HEVC Main10).
     pub bit_depth: u8,
     /// The IDD-push HDR hint (`bit_depth >= 10`) — the want-HDR flag handed to the capturer so it
-    /// proactively enables advanced color on the virtual display. Linux is 8-bit (HDR blocked upstream).
+    /// proactively enables advanced color on the virtual display. The Linux NATIVE plane is 8-bit
+    /// (Mutter's virtual-monitor streams are SDR-only upstream — GNOME 50 HDR is monitor-mirror
+    /// only, which the GameStream portal path uses; see `capture::capturer_supports_hdr`).
     pub hdr: bool,
     /// Handshake-negotiated chroma subsampling (4:2:0, or full-chroma 4:4:4 when the client + host +
     /// GPU all support it). Resolved before the Welcome; `Yuv420` on every backend that declined it.
diff --git a/crates/punktfunk-host/src/spike.rs b/crates/punktfunk-host/src/spike.rs
index 0e22f8e5..4adc047d 100644
--- a/crates/punktfunk-host/src/spike.rs
+++ b/crates/punktfunk-host/src/spike.rs
@@ -87,8 +87,11 @@ pub fn run(opts: Options) -> Result<()> {
             }
         }
         Source::Portal => {
-            tracing::info!("spike source: xdg ScreenCast portal (live monitor)");
-            capture::open_portal_monitor().context("open portal capturer")?
+            // PUNKTFUNK_SPIKE_HDR=1: run the GNOME 50+ HDR offer (10-bit PQ dmabufs) — the dev
+            // validation lever for the Linux HDR capture path without a full GameStream client.
+            let want_hdr = std::env::var("PUNKTFUNK_SPIKE_HDR").as_deref() == Ok("1");
+            tracing::info!(want_hdr, "spike source: xdg ScreenCast portal (live monitor)");
+            capture::open_portal_monitor(want_hdr).context("open portal capturer")?
         }
         Source::KwinVirtual => {
             let compositor = crate::vdisplay::detect().unwrap_or(crate::vdisplay::Compositor::Kwin);
diff --git a/docs-site/content/docs/configuration.md b/docs-site/content/docs/configuration.md
index bc1d3e85..adcd5a43 100644
--- a/docs-site/content/docs/configuration.md
+++ b/docs-site/content/docs/configuration.md
@@ -88,7 +88,7 @@ See your desktop page ([KDE](/docs/kde), [GNOME](/docs/gnome)) for when to set t
 | Setting | Values | Meaning |
 |---|---|---|
 | `PUNKTFUNK_FEC_PCT` | `N` (percent) | Forward-error-correction redundancy for lossy links (the default is sensible for a normal LAN). Higher = more loss-resilient, more bandwidth. |
-| `PUNKTFUNK_10BIT` | `1` · `0` *(default on)* | HEVC Main10 / HDR. **On by default** — the host permits 10-bit; a session goes 10-bit only when the client advertises it (behind the client's HDR setting). Set `0` to force 8-bit. **Windows host only** (the Linux host stays 8-bit). |
+| `PUNKTFUNK_10BIT` | `1` · `0` *(default on)* | HEVC Main10 / HDR. **On by default** — the host permits 10-bit; a session goes 10-bit only when the client advertises it (behind the client's HDR setting). Set `0` to force 8-bit. Windows host, plus the Linux **GNOME 50+ GameStream desktop mirror** (`PUNKTFUNK_VIDEO_SOURCE=portal`, mirrored monitor in HDR mode — check with `punktfunk-host hdr-probe`). Linux **virtual displays** (native protocol, GameStream default) stay 8-bit: Mutter's virtual-monitor screencast is SDR-only upstream. |
 | `PUNKTFUNK_444` | `1` · `0` *(default on)* | Full-chroma HEVC 4:4:4 (Range Extensions) — sharper text/desktop, no chroma loss. **On by default** on the host; the client's own 4:4:4 setting (default off) is the real switch. Set `0` to force 4:2:0. **punktfunk/1 native only** (Moonlight stays 4:2:0), HEVC-only, honored only when the client advertises 4:4:4 **and** the GPU supports it (probed; NVENC is the validated path — VAAPI/AMF/QSV decline). Independent of 10-bit. |
 | `PUNKTFUNK_PYROWAVE_MAX_MBPS` | `N` (Mbps) | Cap the [PyroWave](/docs/pyrowave) Automatic bitrate pin, for a host on a link that the open-loop pin can outrun (e.g. 4:4:4 + HDR at 5120×1440@240 pins ~5.3 Gbps, over a 5GbE link). Unset = no cap. Only affects Automatic (bitrate `0`) PyroWave sessions; an explicit client bitrate bypasses it. |
 | `PUNKTFUNK_DSCP` | `1` | Opt-in DSCP / `SO_PRIORITY` QoS tagging on the media sockets. No-op on the wire on Windows without a qWAVE policy. |
diff --git a/docs-site/content/docs/roadmap.md b/docs-site/content/docs/roadmap.md
index 8e368c33..50bd68a9 100644
--- a/docs-site/content/docs/roadmap.md
+++ b/docs-site/content/docs/roadmap.md
@@ -24,7 +24,7 @@ see [Status & Progress](/docs/status).
 | Web console + pairing | ✅ |
 | Concurrent sessions (shared desktop) | ✅ |
 | Network speed test + bitrate | ✅ |
-| HDR / 10-bit streaming | ✅ Windows host · ⛔ Linux host |
+| HDR / 10-bit streaming | ✅ Windows host · 🚧 Linux host (GNOME 50+ desktop mirror; virtual displays blocked upstream) |
 | Surround audio (5.1 / 7.1) | ✅ |
 | Sub-frame pipelining (latency) | 🔭 |
 
@@ -100,10 +100,14 @@ see [Status & Progress](/docs/status).
 
 ## ⛔ Parked / blocked
 
-- **HDR / 10-bit on the *Linux* host.** HDR streaming already works from a
-  [Windows host](/docs/windows-host) to an HDR-capable client (Windows, Android). On Linux it's
-  blocked upstream — no shipping compositor emits a 10-bit/HDR capture stream yet — and ready the
-  moment one does.
+- **HDR / 10-bit on the *Linux* host — virtual displays.** GNOME 50 added HDR screencasting for
+  **monitor** streams, and the host now uses it: the GameStream desktop mirror
+  (`PUNKTFUNK_VIDEO_SOURCE=portal`) negotiates the 10-bit PQ formats and encodes HEVC Main10
+  BT.2020 PQ (`punktfunk-host hdr-probe` reports readiness; on-glass validation pending). What
+  stays blocked upstream is HDR on **virtual monitors** — Mutter's `RecordVirtual` streams are
+  still SDR-only (through the GNOME 51 dev branch), so the native protocol and GameStream's
+  default virtual-display source stream 8-bit until that lands; the host is ready the moment it
+  does.
 - **Advanced DualSense voice-coil haptics.** Scoped and shelved (it rides the controller's USB audio
   interface, with near-zero game support on Linux). Adaptive triggers, rumble, and the lightbar
   already ship.
diff --git a/docs-site/content/docs/status.md b/docs-site/content/docs/status.md
index 1c7b2534..3156e56e 100644
--- a/docs-site/content/docs/status.md
+++ b/docs-site/content/docs/status.md
@@ -35,9 +35,13 @@ host is newer than the Linux host.)
 - **Zero-copy GPU pipeline.** Captured frames stay on the GPU — dmabuf → CUDA → NVENC on NVIDIA, and
   VAAPI or Vulkan Video on AMD/Intel — with automatic split-encode at very high resolutions. Stable
   240 fps at 5120×1440 has been measured. A GPU-less software H.264 encoder exists as an explicit fallback.
-- **HDR (10-bit), on the Windows host.** An HDR Windows desktop is captured and encoded as HEVC
-  Main10 (BT.2020 PQ) to HDR-capable clients (Windows, Android). Linux hosts stream 8-bit for now —
-  HDR there is blocked upstream at the compositor.
+- **HDR (10-bit).** An HDR Windows desktop is captured and encoded as HEVC Main10 (BT.2020 PQ) to
+  HDR-capable clients (Windows, Android). On Linux, a **GNOME 50+** host can mirror an HDR monitor
+  over the GameStream desktop-capture source (`PUNKTFUNK_VIDEO_SOURCE=portal`): the portal
+  negotiates the 10-bit PQ screencast formats GNOME 50 added and encodes Main10 PQ (run
+  `punktfunk-host hdr-probe` to check readiness; pending on-glass validation). Linux **virtual
+  displays** — the native protocol and GameStream's default source — still stream 8-bit: Mutter's
+  virtual-monitor screencast is SDR-only upstream.
 - **Secure by default.** A **SPAKE2 PIN pairing** ceremony establishes trust (the host
   shows a 4-digit PIN; an attacker gets a single online guess, no offline dictionary
   attack). Trust-on-first-use (TOFU) remains an explicit opt-in for fully trusted LANs.