Replay and fork

Experimental

Replay and fork work and are tested, but their shape may change within 1.x.

Fork a session

POST /v1/agents/{agent}/sessions/{key}/fork starts a new session with a copy of another’s history, up to a turn, under the same or another agent.

{ "into": "ana-try", "agent": "assistant-canary", "through_turn": "0198f2a4-..." }

The fork gets history and checkpoints up to the cut, and nothing else: no pending events, journal or live feed. The next event sent to it starts a turn on that history, with the target agent’s prompt, tools and model.

Replay a conversation

newt-replay assistant/ana assistant-canary/ana-replay

newt-replay sends each turn’s events from assistant/ana to the new session, one turn at a time, waits for the turn to finish, and prints what the turn did then and what it did now.

Flag	Effect
--from-turn N	Fork the first N turns in instead of replaying them
--turns N	Stop after N turns
--url	The newt server
--token-env	The variable holding the token (default NEWT_TOKEN)

Caution

A replay runs the target agent’s tools for real. Give the target agent an MCP server that is safe to call: a staging app, or newt-loadtest mock-app.

Point the target agent at the newt-loadtest fake-model route to replay for free, or at a real model to compare prompts or models.

Next

• Protocol 5.4 and 5.5.
• Load testing for the fake model and mock app.