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Murmur resolves an agent’s model from the first source in this chain that sets one: For a running agent, murmur queue add --model overrides the model for all subsequent turns, with the same precedence as an explicit spawn model.

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When no model is set

On the Claude backend (the default), Murmur does not choose one:
  • Murmur does not set ANTHROPIC_MODEL on the agent’s VM.
  • Murmur never copies your local Claude Code settings — the VM runs its own pinned Claude Code installation.
  • That installation uses Claude Code’s own built-in default, which belongs to Claude Code, not Murmur, and can change when the pinned version is updated.
If your agent reports a model you never chose, it’s Claude Code’s default via this fall-through. Set model in .murmur/murmur.yaml to make the workspace default explicit.
On the Codex backend, the server fills in Murmur’s default Codex model at spawn time — a Codex agent never falls through to the coding agent’s own default.

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How the model reaches the agent

  • Claude backend: an explicit or workspace model is exported as ANTHROPIC_MODEL and set on the agent definition passed to Claude Code. A persona model travels only in the agent definition, so it can be active while ANTHROPIC_MODEL is absent.
  • Codex backend: the resolved model is passed to the Codex CLI as its model flag.