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Explainer https://github.com/w3c/webtransport/blob/main/explainer.md Specification https://www.w3.org/TR/webtransport/#dom-webtransportoptions-congestioncontrol Summary Adds the congestionControl constructor option and read-only attribute to WebTransport. Applications can request "default", "throughput", or "low-latency" behavior, allowing the user agent to select suitable congestion-control behavior for each session. Blink component Blink>Network>WebTransport Web Feature ID webtransport Motivation WebTransport applications have different performance requirements. Interactive applications prioritize low latency, while bulk transfers prioritize throughput. This hint lets applications express that preference without selecting or controlling a specific congestion-control algorithm. Initial public proposal No information provided TAG review Not applicable as a separate review. This is an incremental implementation of an API already defined in the W3C WebTransport specification and covered by the broader WebTransport TAG review: https://github.com/w3ctag/design-reviews/issues/1212 TAG review status Not applicable Goals for experimentation None Risks Interoperability and Compatibility Low. The API is additive, standardized, and already implemented by Firefox and Safari. Implementations may choose different underlying algorithms while preserving the standardized hint and fallback behavior Gecko: Shipped/Shipping (https://github.com/mozilla/standards-positions/issues/167) WebKit: Shipped/Shipping (https://github.com/WebKit/standards-positions/issues/18) 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 Low. The three values are straightforward, but developers must understand that the option is a hint and may resolve to "default" when the requested behavior is unavailable. Activation Low. This is an additive constructor option and attribute. The value is a preference rather than a guarantee, and unsupported preferences may fall back to "default". Security Low. The API grants no new network access and does not expose congestion-window or network-state information. Applications provide only a high-level preference; the browser retains control of the selected algorithm. 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 option and attribute implemented in shared Blink and network-service code. Existing WebView applications are unaffected, and applications using the option must treat it as a preference that may fall back to "default". Debuggability The requested value is readable through transport.congestionControl . Existing DevTools networking, NetLog, and QUIC logging can diagnose connection 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? Yes https://wpt.fyi/results/webtransport/congestion-control.https.any.html?label=experimental&label=master&aligned Flag name on about://flags chrome://flags/#enable-experimental-web-platform-features Finch feature name WebTransportCongestionControl Rollout plan Will ship enabled for all users Requires code in //chrome? False Tracking bug https://issues.chromium.org/issues/501268547 Measurement Validate API exposure and connection behavior through WPT, Chromium tests, and developer feedback from latency-sensitive and high-throughput WebTransport applications. Availability expectation Already supported by Firefox and Safari as part of the W3C WebTransport specification. Chromium support is implemented behind an experimental runtime feature. Adoption expectation Expected to be adopted by games, interactive media, remote-interaction applications, and bulk-transfer services that need to express latency or throughput preferences. Adoption plan Adoption is expected to happen organically through existing WebTransport applications and documentation. Estimated milestones Shipping on desktop 158 DevTrial on desktop 150 Shipping on Android 158 DevTrial on Android 150 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. The option and attribute are already defined by the W3C WebTransport specification. Link to entry on the Chrome Platform Status https://chromestatus.com/feature/5180947573112832?gate=5529995941380096 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/6ad005f7.4ec1d848.c43ea.00a3.GAE%40google.com.
