Forking

Start a new stream from another stream's history and take it in a different direction.

A fork is a new stream that starts with another stream’s history, then goes its own way. Use it to retry an agent from partway through a conversation, or to try two answers side by side.

Fork a stream

Create the new stream with Stream-Forked-From set to the source stream’s path:

curl -X PUT \
  -H 'Stream-Forked-From: /durable-streams/v1/stream/chat/session-1' \
  http://127.0.0.1:8642/durable-streams/v1/stream/chat/session-1-retry

The TypeScript client does not create forks yet. Once the fork exists, read and write it like any other stream.

Fork from an earlier point

By default a fork copies the whole history. Add Stream-Fork-Offset with an offset from a previous read to branch from that point instead, for example right before the agent’s last reply.

What a fork shares

• The fork keeps the source’s content type and history up to the fork point.
• History is shared, not copied, so forking a long stream is cheap.
• Writes to the fork never touch the source, and later writes to the source do not appear in the fork.

Next steps

• HTTP API: every request and header.
• Streams: create, expire, and delete streams.