WPT details: https://wpt.fyi/results/webtransport/idlharness.https.sub.any.html?label=experimental&label=master&aligned https://wpt.fyi/results/webtransport/datagrams.https.any.html?label=experimental&label=master&aligned https://wpt.fyi/results/webtransport/datagrams-writable.https.any.html?label=experimental&label=master&aligned https://wpt.fyi/results/webtransport/sendgroup.https.any.html?label=experimental&label=master&aligned
Adds the modern WebTransport Datagram sending API. WebTransportDatagramDuplexStream.createWritable() creates independent WebTransportDatagramsWritable streams. Each writable has mutable sendGroup and sendOrder attributes for expressing relative priority among queued WebTransport data in the same send group. Chromium currently applies this ordering among Datagram writables. The implementation also reports the negotiated maximum outgoing Datagram payload size and discards oversized writes as required by the WebTransport specification.
The original WebTransport Datagram API exposes only a single writable stream, preventing applications from independently scheduling different classes of latency-sensitive messages. The newer API allows applications such as games, remote-interaction systems, and real-time media applications to create multiple Datagram writables and prioritize urgent data over less time-sensitive data while preserving FIFO ordering within each writable. Implementing this API also resolves WebTransport Datagram interoperability failures included in Interop 2026.
Explainers: https://github.com/w3c/webtransport/blob/main/explainer.md#5-sending-and-receiving-datagrams