WebTransport receive stream

Category: Network / Connectivity
Type: Chromium catches up
Status: Proposed (Chrome Proposed)
Intent stage: None

Breaking change: No
Enterprise impact: None
Chromium flag: enable-experimental-web-platform-features
Spec maturity: Published standard
Web Platform Tests: Yes

WPT details: https://wpt.fyi/results/webtransport/receive-stream-stats.https.any.html

Summary

Adds the standardized WebTransportReceiveStream interface, a ReadableStream subclass used for incoming unidirectional streams and the readable side of bidirectional streams. Its getStats() method returns per-stream byte counters: bytesReceived reports bytes received from the network, while bytesRead reports bytes delivered to the application.

Motivation

Incoming WebTransport streams have historically been exposed as generic ReadableStream objects in Chromium. The WebTransport specification defines a dedicated WebTransportReceiveStream subclass with stream-specific statistics. Applications that receive large or latency-sensitive streams need to distinguish bytes received by the browser from bytes actually consumed by JavaScript. This helps diagnose application backpressure, buffering, and slow-consumer behavior. Exposing the standardized subclass also aligns the runtime type of incoming streams with the WebTransport specification and other browser engines.

Standards & signals

Specification: https://w3c.github.io/webtransport/#webtransportreceivestream
Firefox: Under consideration — Partial implementation. Firefox ships WebTransportReceiveStream and exposes getStats(), but getStats() currently rejects with NotSupportedError, so receive stream statistics are not implemented. Implementation https://searchfox.org/mozilla-central/source/dom/webtransport/api/WebTransportReceiveStream.cpp
Safari: Shipped/Shipping — WebKit-7624.1.16 implements WebTransportReceiveStream and pipes real receive-stream statistics through WebCore and the network process. WebTransport shipped in Safari 26.4. Implementation - https://github.com/WebKit/WebKit/blob/WebKit-7624.1.16/Source/WebCore/Modules/webtransport/WebTransportReceiveStream.cpp#L54-L65
Web developers: Positive — The Interop 2026 WebTransport proposal received 28 positive reactions. Developers also reported active WebTransport use and significant cross-engine differences.
Tracking bug: https://issues.chromium.org/issues/568317222

Ecosystem

Web Platform Tests: https://wpt.fyi/results/?q=webtransport%2Freceive-stream-stats
Chrome Platform Showcase: https://chrome-platform-showcase.paulkinlan-ea.deno.net/features
GenDN reference: https://gendn.paulkinlan-ea.deno.net/features
chrome.dev demos search: https://www.google.com/search?q=site%3Achrome.dev+WebTransport%20receive%20stream
MDN Web Docs: https://developer.mozilla.org/en-US/search?q=WebTransport%20receive%20stream
Baseline status: https://webstatus.dev/?q=WebTransport%20receive%20stream

Explainers: https://github.com/w3c/webtransport/issues/372 https://github.com/w3c/webtransport/pull/395

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