> ## Documentation Index
> Fetch the complete documentation index at: https://docs.murmur.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Model selection precedence for spawned agents

> How Murmur determines which model a spawned agent runs — the precedence chain from the --model flag down to Claude Code's built-in default.

Murmur resolves an agent's model from the first source in this chain that sets one:

| Priority | Source            | Set via                                                                                                                       |
| -------- | ----------------- | ----------------------------------------------------------------------------------------------------------------------------- |
| 1        | Explicit model    | [`murmur spawn --model`](/cli/spawn), the MCP [`spawn`](/mcp-server/spawn) `model` parameter, or the dashboard's model picker |
| 2        | Workspace default | [`model` in `.murmur/murmur.yaml`](/configuration/murmur-yaml#model)                                                          |
| 3        | Persona           | `model` in the [agent persona](/concepts/agent-personas) frontmatter                                                          |
| 4        | None set          | The backend's default (see below)                                                                                             |

For a running agent, [`murmur queue add --model`](/cli/queue-add) overrides the model for all subsequent turns, with the same precedence as an explicit spawn model.

## 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.

<Note>
  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.
</Note>

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.

## 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.

## Related

* [murmur.yaml Configuration](/configuration/murmur-yaml) — the workspace `model` field
* [Agent personas](/concepts/agent-personas) — the persona `model` field
* [`murmur spawn`](/cli/spawn) — the `--model` flag
* [`murmur queue add`](/cli/queue-add) — overriding the model on a running agent