Agent backends (Preview)

Agent backends let you choose which harness runs a new session. The selector is a Preview feature and remains behind Developer Mode.

1. Open Settings → Developer and turn on Developer Mode.
2. Open Developer → Agent Backend.
3. Review the capability card and installation status for the backend you want.
4. Select it, then start a new session.

The selector names any missing component and shows the matching installation command. A running session keeps the backend it started with.

Crew checks the permission path a backend exposes before the first prompt. The capability card in Developer → Agent Backend is the current source for model, reasoning, compaction, steering, MCP, and session-resume support.

Two constraints are especially important:

• Pi has no Crew MCP surface. Pi can run its own tools, but pi-acp does not forward the MCP server array. Choose another backend when the session needs Crew memory, scheduling, subagent, or other MCP tools. kirocrew doctor reports this condition.
• OpenCode applies server-level filtering. If any tool from one Crew MCP server is disabled, Crew withholds that whole server from the OpenCode session rather than presenting a partial tool set.

Compaction is supported on both Codex and OpenCode sessions. Monitor controls, project changes, follow-up cards, and conversation reset work across all backends, subject to what the capability card reports for the selected harness.

• A tool pre-approved in Claude Code's own settings can bypass Crew's approval flow, so Crew's deny and audit layers do not observe that call.
• Codex refuses to start while agent.sandbox is off.
• Crew verifies the required permission mode or gate for OpenCode, Pi, and goose before allowing the first prompt.

Review Security before changing backends when your workflow depends on a specific approval or audit boundary.