Thanks, Alex. We cannot measure the exact intersection, but existing
UseCounters provide an upper bound. Access to WebTransport.datagrams
peaked at 0.0126% of page loads over the last 30 days. For the common
getReader({mode: "byob"}) pattern, the upper bound is 0.00232%, fewer than
1 in 43,000 page loads.
The actual intersection may be lower because the BYOB counter covers all
APIs. Affected applications can preserve the current behavior with
datagramsReadableType: "bytes", and the change remains Finch-controlled
for rollback.
On Wednesday, October 28, 2026 at 8:32:01 AM UTC-7 Alex Russell wrote:
> Is there an upper bound for potential breakage? Do we have metrics for
> total use of datagram readable streams w/ BYOB behaviours?
>
> On Wednesday, October 28, 2026 at 7:35:15 AM UTC-7 Monica Chintala wrote:
>
>> We don’t have a metric for this exact usage pattern. The affected case is
>> limited to applications requesting a BYOB reader without opting into
>> "bytes".
>>
>> Default readers continue to work unchanged. Applications using BYOB can
>> preserve the existing Chromium behavior by adding: {datagramsReadableType:
>> "bytes"}
>>
>> This option can be added before rollout and works with both the old and
>> new behavior. Firefox and Safari stable already use the new default. The
>> rollout is Finch-controlled, so we can restore the previous default without
>> a new release if compatibility problems are reported.
>>
>> On Tuesday, October 27, 2026 at 12:02:26 PM UTC-7 Alex Russell wrote:
>>
>>> What's the potential for breakage, given that we're changing default
>>> behavior? Do our histograms tell us the fraction of pageloads that would be
>>> affected?
>>>
>>> Best,
>>>
>>> Alex
>>>
>>> On Wednesday, October 21, 2026 at 1:52:53 PM UTC-7 Chromestatus wrote:
>>>
>> *Contact emails*
>>>> [email protected], [email protected]
>>>
>>>
>>>>
>>>> *Explainer*
>>>> https://github.com/w3c/webtransport/blob/main/explainer.md
>>>>
>>>> *Specification*
>>>>
>>>> https://www.w3.org/TR/webtransport/#dom-webtransportoptions-datagramsreadabletype
>>>>
>>>>
>>>> *Summary*
>>>> Adds the WebTransportOptions.datagramsReadableType constructor
>>>> option. By default, incoming WebTransport Datagrams are exposed through a
>>>> default ReadableStream . Applications that require BYOB reading can
>>>> request a readable byte stream by setting datagramsReadableType: "bytes"
>>>> .
>>>>
>>>> *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*
>>>> WebTransport Datagrams are discrete messages rather than an
>>>> undifferentiated byte sequence. A readable byte stream can lose empty
>>>> Datagrams and can lose message boundaries when BYOB reads use a minimum
>>>> byte count spanning multiple Datagrams. Making a default ReadableStream
>>>> the default preserves Datagram boundaries and empty Datagrams.
>>>> Applications
>>>> that benefit from BYOB allocation control can explicitly opt into the
>>>> byte-stream behavior.
>>>>
>>>> *Initial public proposal*
>>>> *No information provided*
>>>>
>>>> *TAG review*
>>>> Not applicable — this is a small incremental addition within the
>>>> existing WebTransport specification.
>>>>
>>>> *TAG review status*
>>>> Not applicable
>>>>
>>>> *Goals for experimentation*
>>>> None
>>>>
>>>> *Risks*
>>>>
>>>>
>>>> *Interoperability and Compatibility*
>>>> Interoperability risk is low to medium. The API and default-stream
>>>> behavior are defined in the WebTransport specification and covered by WPT.
>>>> Firefox already uses a default non-byte stream when the option is omitted,
>>>> but does not yet support the explicit "bytes" mode in current public
>>>> test
>>>> runs. Compatibility risk is mitigated by runtime gating. Chromium
>>>> historically exposed the Datagram readable as a byte stream, so enabling
>>>> the feature changes the default behavior: existing applications using a
>>>> BYOB reader without specifying datagramsReadableType: "bytes" would fail.
>>>> Applications using ordinary readers continue to receive Uint8Array
>>>> chunks
>>>>
>>>> *Gecko*: Positive (https://bugzilla.mozilla.org/show_bug.cgi?id=2007755)
>>>> Firefox
>>>> is implementing datagramsReadableType: "bytes" and BYOB Datagram reads
>>>>
>>>> *WebKit*: In development (
>>>> https://bugs.webkit.org/show_bug.cgi?id=319830) WebKit main implements
>>>> the standardized datagramsReadableType option
>>>>
>>>> *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 default stream better matches Datagram message semantics.
>>>> Applications needing BYOB allocation control must explicitly opt into
>>>> "bytes" , making the semantic tradeoff visible in application code.
>>>>
>>>> *Activation*
>>>> The main activation risk is existing Chromium-specific code assuming
>>>> that transport.datagrams.readable always supports BYOB readers. Such
>>>> applications must explicitly request datagramsReadableType: "bytes" . The
>>>> feature remains experimentally gated while compatibility and
>>>> interoperability are evaluated.
>>>>
>>>> *Security*
>>>> Low. The option changes only the JavaScript stream adapter used to
>>>> expose already-received Datagrams. It does not provide additional network
>>>> access, expose new information, or alter WebTransport’s secure-context and
>>>> connection security requirements.
>>>>
>>>> *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 implementation is cross-platform Blink code and requires no
>>>> WebView-specific integration. The primary compatibility consideration is
>>>> the same as Chrome: applications using a BYOB reader must explicitly
>>>> request datagramsReadableType: "bytes" .
>>>>
>>>>
>>>> *Debuggability*
>>>> No feature-specific DevTools UI is required. Applications can inspect
>>>> whether datagrams.readable supports BYOB by attempting to acquire a BYOB
>>>> reader. Existing WebTransport logging, NetLog, and DevTools network
>>>> diagnostics remain available for connection and Datagram issues.
>>>>
>>>> *Will this feature be supported on all six Blink platforms (Windows,
>>>> Mac, Linux, ChromeOS, Android, and Android WebView)?*
>>>> Yes
>>>> Yes. Implemented in cross-platform Blink code without platform-specific
>>>> dependencies.
>>>>
>>>> *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/datagrams.https.any.html?label=experimental&label=master&aligned
>>>>
>>>> *Flag name on about://flags*
>>>> chrome://flags/#enable-experimental-web-platform-features
>>>>
>>>> *Finch feature name*
>>>> WebTransportDatagramsReadableType
>>>>
>>>> *Rollout plan*
>>>> Will ship enabled for all users
>>>>
>>>> *Requires code in //chrome?*
>>>> False
>>>>
>>>> *Tracking bug*
>>>> https://issues.chromium.org/issues/547572475
>>>>
>>>> *Availability expectation*
>>>> WebKit has implemented the option and corresponding default-stream
>>>> behavior in its main branch. Firefox implements the default non-byte
>>>> stream
>>>> behavior, although explicit "bytes" /BYOB mode does not yet pass current
>>>> public WPT runs. Broad availability is expected as implementations
>>>> converge
>>>> on the WebTransport specification.
>>>>
>>>> *Adoption expectation*
>>>> Adoption is expected mainly among WebTransport applications that use
>>>> BYOB readers or need reliable preservation of Datagram message boundaries.
>>>> Most applications using ordinary readers require no code changes.
>>>>
>>>> *Adoption plan*
>>>> Adoption is expected through WebTransport documentation and Interop
>>>> 2026 visibility. Existing Chromium applications using BYOB readers will
>>>> need to explicitly set datagramsReadableType: "bytes" when the feature
>>>> is
>>>> enabled.
>>>>
>>>> *Estimated milestones*
>>>> Shipping on desktop 159
>>>> DevTrial on desktop 155
>>>> Shipping on Android 159
>>>> DevTrial on Android 155
>>>> Shipping on WebView 159
>>>>
>>>> *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 currently anticipated. The option and default-stream behavior are
>>>> already defined in the WebTransport specification.
>>>>
>>>> *Link to entry on the Chrome Platform Status*
>>>> https://chromestatus.com/feature/5148774971342848?gate=5517621058469888
>>>>
>>>> *Links to previous Intent discussions*
>>>> Intent to Prototype:
>>>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/6aa86417.edf999b6.71d4e.0a07.GAE%40google.com
>>>>
>>>>
>>>> This intent message was generated by Chrome Platform Status
>>>> <https://chromestatus.com>.
>>>>
>>>
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