Intent to Deprecate and Remove: Deprecate WebTransport incomingHighWaterMark/outgoingHighWaterMark

Chromestatus

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Apr 8, 2026, 5:29:47 AM Apr 8

to blin...@chromium.org, kpan...@microsoft.com, patil...@microsoft.com, sures...@microsoft.com

Contact emails

kpan...@microsoft.com

Explainer

No information provided

Specification

https://w3c.github.io/webtransport/#dom-webtransportdatagramduplexstream-incomingmaxbuffereddatagrams,https://github.com/web-platform-tests/wpt/pull/58612/changes

Summary

The incomingHighWaterMark and outgoingHighWaterMark attributes on WebTransportDatagramDuplexStream are deprecated in favor of incomingMaxBufferedDatagrams and outgoingMaxBufferedDatagrams, following a spec rename. The attribute type also changes from long to unsigned long. Developers should migrate to the new attribute names. The old names will show a console deprecation warning and will be removed in a future release.

Blink component

Blink>Network>WebTransport

Web Feature ID

webtransport

Motivation

The WebTransport specification renamed two attributes on WebTransportDatagramDuplexStream: - incomingHighWaterMark → incomingMaxBufferedDatagrams - outgoingHighWaterMark → outgoingMaxBufferedDatagrams The attribute type was also changed from long to unsigned long. The new names better describe the attributes' purpose (they control the maximum number of buffered datagrams, not a byte-based high water mark). The new attribute names are already exposed alongside the old ones. The old names should be deprecated and removed to align with the specification and avoid developer confusion from having two names for the same thing.

Initial public proposal

No information provided

Goals for experimentation

None

Debuggability

No information provided

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/issues/494380213

Estimated milestones

No milestones specified

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5143839699501056?gate=4911413786181632

This intent message was generated by Chrome Platform Status .

Daniel Bratell

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Apr 8, 2026, 10:58:36 AM Apr 8

to Chromestatus, blin...@chromium.org, kpan...@microsoft.com, patil...@microsoft.com, sures...@microsoft.com

Do you have a suggested "removal milestone"?

We have found that unless we name a specific milestone, many people ignore deprecation warnings and then they pile up and we get warning fatigue.

Also, do you have usage data? Use Counters or some other kind of upper limit on how many might be affected?

/Daniel

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Alex Russell

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Apr 13, 2026, 2:36:22 PM (9 days ago) Apr 13

to blink-dev, Daniel Bratell, kpan...@microsoft.com, patil...@microsoft.com, sures...@microsoft.com, Chromestatus

Why was this renamed? Why would we agree to a cosmetic change after shipping?

Best,

Alex

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