LGTM1; we've had intermittent feedback over the years about how WebTransport wasn't well suited to latency-sensitive work, and it's great to see these additions.
On Thursday, October 22, 2026 at 3:11:29 PM UTC-7 Monica Chintala wrote: > FYI, this feature depends on WebTransport send groups and stream > prioritization - Chrome Platform Status > <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fchromestatus.com%2Ffeature%2F5235261159112704&data=05%7C02%7Cmonicach%40microsoft.com%7C9e0b9f4149a541fafafe08df307d863d%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C639282987879917270%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=fMplyzw4jssGTpxdGq0wgG5zQ2s6HhhTQI6b1Zm6cps%3D&reserved=0>, > > which is currently in progress for I2S. I'm working on getting the > necessary approvals now so we're ready to proceed, while ensuring this > feature ships only after the dependent feature has shipped. > > On Thursday, October 22, 2026 at 2:24:42 PM UTC-7 Chromestatus wrote: > >> *Contact emails* >> [email protected], [email protected] > > >> >> *Explainer* >> >> https://github.com/w3c/webtransport/blob/main/explainer.md#5-sending-and-receiving-datagrams >> >> *Specification* >> https://www.w3.org/TR/webtransport/#datagram-writable >> >> *Summary* >> Adds the modern WebTransport Datagram sending API. >> WebTransportDatagramDuplexStream.createWritable() creates independent >> WebTransportDatagramsWritable streams. Each writable has mutable sendGroup >> and sendOrder attributes for expressing relative priority among queued >> WebTransport data in the same send group. Chromium currently applies this >> ordering among Datagram writables. The implementation also reports the >> negotiated maximum outgoing Datagram payload size and discards oversized >> writes as required by the WebTransport specification. >> >> *Blink component* >> Blink>Network>WebTransport >> <https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3ENetwork%3EWebTransport%22> >> >> *Web Feature ID* >> webtransport <https://webstatus.dev/features/webtransport> >> >> *Motivation* >> The original WebTransport Datagram API exposes only a single writable >> stream, preventing applications from independently scheduling different >> classes of latency-sensitive messages. The newer API allows applications >> such as games, remote-interaction systems, and real-time media applications >> to create multiple Datagram writables and prioritize urgent data over less >> time-sensitive data while preserving FIFO ordering within each writable. >> Implementing this API also resolves WebTransport Datagram interoperability >> failures included in Interop 2026. >> >> *Initial public proposal* >> https://github.com/w3c/webtransport/issues/451 >> >> *TAG review* >> This is an incremental API addition within the existing WebTransport >> specification and does not introduce a new architectural primitive. A >> separate feature-level TAG review is not planned. >> >> *TAG review status* >> Not applicable >> >> *Goals for experimentation* >> None >> >> *Risks* >> >> >> *Interoperability and Compatibility* >> Interoperability risk Medium. The API is defined in the WebTransport >> Candidate Recommendation and covered by WPT. Implementations may >> nevertheless differ in scheduling boundaries, particularly priority >> interaction between streams and Datagrams. Chromium currently implements >> ordering among Datagram writables; unified stream-and-Datagram arbitration >> may require additional implementation work and specification clarification. >> Compatibility risk Low. The API adds createWritable() and >> WebTransportDatagramsWritable without removing datagrams.writable. Existing >> applications continue to work. The negotiated maxDatagramSize and >> oversized-write behavior are intentional conformance improvements but could >> expose applications that assumed a fixed outgoing Datagram limit. >> >> *Gecko*: Shipped/Shipping ( >> https://bugzilla.mozilla.org/show_bug.cgi?id=2007174) Firefox >> implemented and related wpt tests are passing >> >> *WebKit*: Shipped/Shipping (https://github.com/WebKit/WebKit/pull/53733) >> WebKit >> implemented and related wpt tests are passing >> >> *Web developers*: Positive ( >> https://github.com/web-platform-tests/interop/issues/1121) The Interop >> 2026 WebTransport proposal received 28 👍 reactions and explicitly >> requested coverage of prioritization features and Datagram >> interoperability. Developers also reported active WebTransport use and >> significant cross-browser differences in Datagram behavior. >> >> *Other signals*: Consensus to add this feature was achieved at the W3C >> TPAC conference in November 2025: >> https://www.w3.org/wiki/WebTransport/Meetings2023#2025_W3C_TPAC_Meeting_-_Kobe,_Japan >> >> *Ergonomics* >> Low to medium. Multiple writable streams and mutable sendGroup and >> sendOrder attributes provide useful scheduling control but introduce >> concepts developers must understand. Higher sendOrder values take >> precedence within a send group, so badly chosen priorities can starve >> lower-priority data or produce unexpected ordering. FIFO behavior within >> each writable and standardized defaults preserve straightforward behavior >> for applications that do not need advanced prioritization. >> >> *Activation* >> Low. This is an additive API behind the WebTransportDatagramsWritable >> runtime feature. It does not remove or replace the existing >> datagrams.writable API. Enabling the feature also makes maxDatagramSize >> reflect the negotiated outgoing payload limit and discards writes that >> exceed that limit, as required by the specification. The main activation >> risk is inconsistent priority scheduling across browsers, particularly >> around the boundary between streams and Datagrams. Rollout should follow >> WPT and interoperability validation. >> >> *Security* >> Low. The API does not grant new network access, expose additional data, >> or weaken WebTransport's secure-context requirements. The primary >> implementation concern is renderer-driven resource exhaustion through >> excessive writable registrations or queued Datagram payloads. Chromium >> mitigates this through network-service validation and limits on writable >> registrations, queued Datagram counts, retained bytes, expiration, and >> scheduling batch sizes. Invalid renderer-provided identifiers and priority >> updates are rejected. >> >> *WebView application risks* >> >> Does this intent deprecate or change behavior of existing APIs, such that >> it has potentially high risk for Android WebView-based applications? >> Low. This is an additive WebTransport API implemented in cross-platform >> Blink and network-service code. It does not remove or change the >> availability of the existing datagrams.writable API and requires no >> WebView-specific integration. Behavior follows the existing availability of >> WebTransport in WebView. >> >> >> *Debuggability* >> Chrome DevTools does not currently provide feature-specific inspection >> for Datagram writable queues or priorities. Existing WebTransport >> diagnostics, NetLog, network-service logging, and QUIC logging can be used >> to diagnose connection and scheduling behavior >> >> *Will this feature be supported on all six Blink platforms (Windows, Mac, >> Linux, ChromeOS, Android, and Android WebView)?* >> Yes >> >> *Is this feature fully tested by web-platform-tests >> <https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?* >> Yes >> >> https://wpt.fyi/results/webtransport/idlharness.https.sub.any.html?label=experimental&label=master&aligned >> >> https://wpt.fyi/results/webtransport/datagrams.https.any.html?label=experimental&label=master&aligned >> >> https://wpt.fyi/results/webtransport/datagrams-writable.https.any.html?label=experimental&label=master&aligned >> >> https://wpt.fyi/results/webtransport/sendgroup.https.any.html?label=experimental&label=master&aligned >> >> *Flag name on about://flags* >> enable-experimental-web-platform-features >> >> *Finch feature name* >> WebTransportDatagramsWritable >> >> *Rollout plan* >> Will ship enabled for all users >> >> *Requires code in //chrome?* >> False >> >> *Tracking bug* >> https://issues.chromium.org/issues/547572475 >> >> *Availability expectation* >> The feature is expected to be available across major browsers as part of >> the W3C WebTransport specification. Firefox implements the Datagram >> writable and prioritization APIs, and WebKit has landed an implementation >> that is currently in development. >> >> *Adoption expectation* >> Adoption is expected primarily among latency-sensitive WebTransport >> applications, including games, remote-interaction systems, and real-time >> media. Applications that need multiple independently prioritized Datagram >> queues are expected to begin adopting the API within 12 months of broad >> browser availability. >> >> *Adoption plan* >> Adoption is expected to happen organically through WebTransport >> documentation, examples, and Interop 2026 visibility. Existing applications >> do not need to migrate because the existing datagrams.writable API remains >> available. >> >> *Estimated milestones* >> Shipping on desktop 159 >> DevTrial on desktop 155 >> Shipping on Android 159 >> DevTrial on Android 155 >> Shipping on WebView 159 >> >> *Anticipated spec changes* >> >> Open questions about a feature may be a source of future web compat or >> interop issues. Please list open issues (e.g. links to known github issues >> in the project for the feature specification) whose resolution may >> introduce web compat/interop risk (e.g., changing to naming or structure of >> the API in a non-backward-compatible way). >> No API-shape changes are currently anticipated. The WebTransport Working >> Group may further clarify scheduling boundaries and priority arbitration >> between streams and Datagrams in the same send group. Such clarification is >> expected to affect scheduling behavior only, not the exposed API. >> >> *Link to entry on the Chrome Platform Status* >> https://chromestatus.com/feature/5183354944225280?gate=6105683064913920 >> >> *Links to previous Intent discussions* >> Intent to Prototype: >> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/6a920d86.e8a51b51.6abb3.0299.GAE%40google.com >> >> >> This intent message was generated by Chrome Platform Status >> <https://chromestatus.com>. >> > -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/1b8eda2b-f976-4b29-9614-60378180f13cn%40chromium.org.
