LGTM2
/Daniel
On 2026-10-21 17:31, Yoav Weiss (@Shopify) wrote:
LGTM1
On Tuesday, October 20, 2026 at 11:08:15 PM UTC+2 Chromestatus wrote:
*Contact emails*
[email protected]
*Explainer*
https://github.com/w3c/webtransport/issues/544
<https://github.com/w3c/webtransport/issues/544>
https://github.com/w3c/webtransport/pull/574
<https://github.com/w3c/webtransport/pull/574>
*Specification*
https://w3c.github.io/webtransport/#web-transport-configuration
<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
<https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3ENetwork%3EWebTransport%22>
*Web Feature ID*
webtransport <https://webstatus.dev/features/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
<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
<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
<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
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?*
Yes
https://wpt.fyi/results/webtransport/anticipated-concurrent-incoming-streams.https.any.html?label=experimental&label=master
<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
<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 (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 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
<https://chromestatus.com/feature/5089961022980096?gate=5533718100967424>
This intent message was generated by Chrome Platform Status
<https://chromestatus.com>.
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