LGTM1; thanks for closing this gap. On Wednesday, October 7, 2026 at 10:23:27 AM UTC-7 Chromestatus wrote:
> *Contact emails* > [email protected] > > *Explainer* > https://github.com/w3c/webtransport/blob/main/explainer.md#transport-modes > > *Specification* > https://www.w3.org/TR/webtransport/#dom-webtransport-reliability > > *Summary* > Adds the WebTransport.reliability instance attribute and static > WebTransport.supportsReliableOnly attribute. These APIs indicate whether > the user agent supports WebTransport over exclusively reliable connections > and whether an established session supports unreliable transport such as > datagrams. In Chromium, reliability initially returns "pending" and changes > to "supports-unreliable" after an HTTP/3 WebTransport connection is > established. Since Chromium does not currently support HTTP/2 fallback, > WebTransport.supportsReliableOnly returns false; any successfully > established session uses HTTP/3 and supports unreliable datagrams. > > *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* > WebTransport may operate over connections with different reliability > capabilities. Applications such as games, interactive media, and real-time > collaboration tools need to know whether unreliable datagrams are available > before selecting their transport strategy. > WebTransport.supportsReliableOnly reports whether the user agent supports > WebTransport over exclusively reliable connections. The per-session > reliability attribute is "pending" while connecting and becomes > "reliable-only" or "supports-unreliable" once the transport is known. > Chromium currently implements WebTransport over HTTP/3 with unreliable > datagram support, so established sessions report "supports-unreliable" and > supportsReliableOnly returns false. > > *Initial public proposal* > https://github.com/w3c/webtransport/pull/385 > > *TAG review* > This is a small incremental implementation of attributes already defined > in the existing W3C WebTransport specification. It does not introduce a new > API design or Chromium-specific extension > > *TAG review status* > Not applicable > > *Goals for experimentation* > None > > *Risks* > > > *Interoperability and Compatibility* > Compatibility risk is low because both attributes are additive and do not > change existing WebTransport behavior. Interoperability risk is low because > the attributes and their "pending" , "reliable-only" , and > "supports-unreliable" values are defined by the W3C WebTransport > specification. Equivalent APIs are implemented or partially implemented in > WebKit and Firefox, and WebTransport is an Interop 2026 focus area. > > *Gecko*: Shipped/Shipping ( > https://bugzilla.mozilla.org/show_bug.cgi?id=1709355) > > *WebKit*: Shipped/Shipping (https://github.com/WebKit/WebKit/pull/55124) > > *Web developers*: Positive ( > https://github.com/web-platform-tests/interop/issues/1121) The Interop > 2026 WebTransport proposal received 28 👍 reactions. Developers also > reported active WebTransport use and significant cross-engine differences. > > *Other signals*: > > *Ergonomics* > Ergonomics risk is low. reliability synchronously returns "pending" > while connecting, and applications can await WebTransport.ready before > reading its final value. The static supportsReliableOnly attribute > enables capability detection before creating a connection. > > *Activation* > Activation risk is low. This is an additive API that does not change > existing WebTransport behavior or require server changes. Developers can > use standard feature detection and retain existing fallbacks for older > browsers. > > *Security* > No new network capability or sensitive information is exposed. The > attributes report whether an implementation or session supports exclusively > reliable or unreliable WebTransport, which is already observable through > the available WebTransport APIs. They expose no server data, credentials, > addresses, or user-specific information. > > *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 API surface and does not modify the behavior of > existing WebTransport connections. WebView applications that do not use the > attributes are unaffected > > > *Debuggability* > The attributes can be inspected directly from JavaScript or the Chrome > DevTools Console. Developers can inspect transport.reliability before and > after transport.ready resolves and inspect > WebTransport.supportsReliableOnly without creating a connection. No > additional DevTools-specific support is required > > *Will this feature be supported on all six Blink platforms (Windows, Mac, > Linux, ChromeOS, Android, and Android WebView)?* > Yes > All Blink platforms on which WebTransport is supported. The implementation > is in cross-platform Blink code. > > *Is this feature fully tested by web-platform-tests > <https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?* > Yes > WPT coverage verifies that: • Initial "pending" state. • Transition > after ready . • Web IDL exposure. Static attribute and initial state: > https://wpt.fyi/results/webtransport/reliability.https.any.html?label=experimental&label=master&aligned > > State after connection establishment: > https://wpt.fyi/results/webtransport/reliability.https.window.html?label=experimental&label=master&aligned > > IDL harness: > https://wpt.fyi/results/webtransport/idlharness.https.sub.any.html?label=experimental&label=master&aligned > > *Flag name on about://flags* > chrome://flags/#enable-experimental-web-platform-features > > *Finch feature name* > WebTransportReliability > > *Rollout plan* > Will ship enabled for all users > > *Requires code in //chrome?* > False > > *Tracking bug* > https://issues.chromium.org/issues/545636884 > > *Measurement* > Measure through Web Platform Test results, Interop 2026 WebTransport > results, and developer feedback. No dedicated UMA metric is planned because > this is an additive capability-reporting API that does not change network > behavior. > > *Availability expectation* > Expected to become available across major browser engines as part of the > W3C WebTransport specification. WebKit implements both attributes, while > Firefox currently implements the per-session reliability attribute > > *Adoption expectation* > Expected to be adopted by WebTransport applications that use datagrams or > need to operate across transports with different reliability capabilities. > > *Adoption plan* > Adoption is expected to happen organically as WebTransport applications > use these attributes to select between reliable streams and unreliable > datagrams. > > *Non-OSS dependencies* > > Does the feature depend on any code or APIs outside the Chromium open > source repository and its open-source dependencies to function? > No > > *Estimated milestones* > Shipping on desktop 158 > DevTrial on desktop 155 > Shipping on Android 158 > DevTrial on Android 155 > Shipping on WebView 158 > > *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). > None. The attributes and WebTransportReliabilityMode values are already > defined in the W3C WebTransport specification. > > *Link to entry on the Chrome Platform Status* > https://chromestatus.com/feature/5094058497277952?gate=5518510552907776 > > *Links to previous Intent discussions* > Intent to Prototype: > https://groups.google.com/a/chromium.org/d/msgid/blink-dev/6a9705af.b5ef4c6f.265fb1.0007.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]. 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