Hi Alex, My understanding is that when WebTransport was initially shipped in Chromium, the core functionality of the W3C spec was considered fairly stable, and the decision was made to launch prior to Candidate Recommendation status. On the path to Candidate Recommendation, there have been some updates in response to implementation experience from other implementors and needs from use cases like MoQ. While we don't want to casually rename attributes for minor cosmetic reasons, this rename updates the attribute's name so that its meaning aligns with the reality of the functionality it provides.
The WebTransport API overall is used by 0.0025% of page loads <https://chromestatus.com/metrics/feature/timeline/popularity/3472>, and the highWaterMark attribute can only be a subset of that. However, we're starting to see some adoption in the ecosystem, especially with the specs nearing completion and other major browsers shipping WebTransport implementations, so we'd like to make these changes while there's still an opportunity to minimize developer and compatibility impact. WebTransport is also included in Interop 2026, so we're expecting to make additional updates to align our implementation with the current state of the spec as it enters Candidate Recommendation status. Best, Nidhi On Tue, May 12, 2026 at 3:45 AM Alex Russell <[email protected]> wrote: > Hey Nidhi, > > Thanks for all of this background. I'm sure naming alignment might be > nice, but it doesn't seem obvious to me that we should agree to a change > post-launch, particularly without usage data. In general, the I2S process > should be thought of as pouring concrete; everything's fluid until it has > set. As a result, we have a dislike of this sort of casual renaming > post-launch. The evidentiary bar to support a rename is high, although you > might be able to support strict aliasing with less pushback. > > Best, > > Alex > > On Friday, May 8, 2026 at 6:17:00 AM UTC-7 Nidhi Jaju wrote: > >> > Why was this renamed? Why would we agree to a cosmetic change after >> shipping? >> >> While we shipped our initial implementation of WebTransport in 2021, the >> specification has evolved since then as it progressed through the IETF and >> W3C, other browsers have also brought implementation experience, and other >> groups like Media over QUIC (MoQ) have highlighted the need for >> updates/additions to the spec. >> >> https://github.com/w3c/webtransport/issues/723 explains some of the >> reasoning behind this change. In the Streams API, a "high water mark" is a >> signal for backpressure and flow control, whereas in WebTransport, these >> attributes actually represent a hard cap on the number of datagrams >> retained in the queue. If this limit is exceeded, datagrams are dropped >> rather than just signaling backpressure, so the new names avoid developer >> confusion by more accurately describing the behavior. >> >> Best, >> Nidhi >> >> On Tuesday, April 14, 2026 at 3:36:22 AM UTC+9 Alex Russell wrote: >> >>> Why was this renamed? Why would we agree to a cosmetic change after >>> shipping? >>> >>> Best, >>> >>> Alex >>> >>> On Wednesday, April 8, 2026 at 7:58:36 AM UTC-7 Daniel Bratell wrote: >>> >>>> 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 >>>> On 2026-04-08 11:29, Chromestatus wrote: >>>> >>>> *Contact emails* >>>> [email protected] >>>> >>>> *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 >>>> <https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3ENetwork%3EWebTransport%22> >>>> >>>> *Web Feature ID* >>>> webtransport <https://webstatus.dev/features/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 >>>> <https://chromestatus.com>. >>>> >>>> -- >>>> 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/69d61ffa.050a0220.1c79a0.099e.GAE%40google.com >>>> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/69d61ffa.050a0220.1c79a0.099e.GAE%40google.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>>> -- You received this message because you are subscribed to the Google Groups "blink-dev" group. 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