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Explainer https://github.com/w3c/webtransport/issues/544 https://github.com/w3c/webtransport/pull/574 Specification https://w3c.github.io/webtransport/#web-transport-configuration Summary Allows WebTransport applications to indicate how many incoming streams they expect to have open at once. Constructor hints configure the initial QUIC stream allowance, reducing the risk that a server that needs high stream concurrency is blocked by the initial stream limit. Blink component Blink>Network>WebTransport Web Feature ID webtransport Motivation Some WebTransport applications expect a server to open many streams at once. If the initial QUIC stream allowance is too low, the server must wait for more stream credit before opening additional streams, adding avoidable latency or limiting the number of open streams. Constructor hints let the application state its expected stream count when creating the connection, so the browser can advertise an appropriate initial allowance. Values above the required minimum are preserved; values below 100 do not reduce the effective allowance because the specification requires clients to initially permit at least 100 streams of each type. Initial public proposal No information provided TAG review This is a small incremental addition to an existing feature which is already standardized. TAG review status Not applicable Goals for experimentation None Risks Interoperability and Compatibility Compatibility risk is low because this is an additive API. Existing sites that do not use the new names are unaffected. Interoperability risk is low to moderate: WebKit implements these specific members, while Firefox supports WebTransport but does not currently expose them. Gecko: Positive (https://bugzilla.mozilla.org/show_bug.cgi?id=2007825) Firefox supports WebTransport, but not these two anticipated-incoming-stream members. Implementation work is in progress, no shipping milestone is announced. WebKit: Shipped/Shipping (https://commits.webkit.org/303419@main) Implemented in WebKit revision 303419@main and shipped in Safari 26.4, including Safari on iOS. Web developers: Positive (https://github.com/web-platform-tests/interop/issues/1121) The Interop 2026 WebTransport proposal received 28 positive reactions. Developers also reported active WebTransport use and significant cross-engine differences. Other signals: Ergonomics The constructor options are nullable unsigned-short hints and default to null. The corresponding attributes expose the currently stored values. [EnforceRange] rejects values outside the unsigned-short range. Values below 100 remain visible through the attributes but cannot reduce the effective initial stream allowance below the specification-required minimum. Activation No permission or user activation is required beyond the existing WebTransport requirements. A site opts in by supplying either constructor option. Security This does not grant a new capability or expose application data. It lets a site request a bounded initial stream allowance for its existing secure-context WebTransport connection. Stream credit does not eagerly allocate all streams. 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. The change is additive and does not modify behavior for applications that do not use the new options or attributes. The implementation uses the existing cross-platform WebTransport connection stack. Debuggability The hints can be inspected through the JavaScript attributes. Existing DevTools and NetLog support for WebTransport and QUIC remains applicable. 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? Yes https://wpt.fyi/results/webtransport/anticipated-concurrent-incoming-streams.https.any.html?label=experimental&label=master Flag name on about://flags enable-experimental-web-platform-features Finch feature name WebTransportAnticipatedConcurrentIncomingStreams Rollout plan Will ship enabled for all users Requires code in //chrome? False Tracking bug https://issues.chromium.org/issues/565837025 Availability expectation The API is part of the W3C WebTransport specification and is implemented by WebKit/Safari. Firefox supports WebTransport but does not yet expose these specific members. Cross-browser availability is expected to improve as implementations converge on the current WebTransport specification. Adoption expectation Adoption is expected among WebTransport applications whose servers need to create more than the minimum number of streams concurrently, including real-time communication, media, gaming, remote interaction, and multiplexed application protocols. Broader adoption will follow overall WebTransport usage. Adoption plan No dedicated outreach campaign is planned. Adoption is expected through WebTransport documentation, examples, and client/server library support. 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 151 Shipping on Android 158 DevTrial on Android 151 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 (eg links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (eg, changing to naming or structure of the API in a non-backward-compatible way). None known for these constructor options or attributes. The wider WebTransport specification continues to progress, but no known open issue requires a breaking change to these members before launch. Link to entry on the Chrome Platform Status https://chromestatus.com/feature/5089961022980096?gate=5533718100967424 This intent message was generated by Chrome Platform Status. -- 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/6ad7d82f.aaae3ce7.28552b.09c6.GAE%40google.com.
