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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