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Chat mode is the lighter of the two session modes. You open it from the Quick Changes card on the new-session page. The card’s own subtitle says it best: “Chat with an agent that has full codebase understanding to get it done.” There’s no phase breadcrumb, no ticket tree, no spec to write. You type, and p0 acts. Use chat mode for fixes, tweaks, refactors, code review, and anything else that doesn’t need a product spec. If you find yourself wanting tickets and a PR pipeline, switch to Plan & Build instead.

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Plan vs Agent

You pick one of two submodes when you start the session, and the session stays in that submode for its lifetime.
SubmodeWhat p0 does
AgentApplies changes directly. This is the default.
PlanWrites a plan of what it would change, without touching files.
The descriptions come straight from the slash-command registry. /agent is “Switch to Agent mode (applies changes directly)”. /plan is “Switch to Plan mode (creates plan before making changes)”. Use Plan when you want a written game plan before any code lands. Use Agent for direct edits.

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How chat mode differs from Plan & Build

Both modes use the same chat surface, the same slash commands, the same model picker, and (when configured) the same worktree. The differences:
AspectChat modePlan & Build
Sidebar badge.CHAT.SPEC.
Phases.None. You drive every turn.Five phases: Import → Improve → Watch → Done → Post-PR.
Spec document.None.Required. A product spec lives in the editor on the left.
Engineer team.None. One agent, one conversation.An orchestrated team of engineers and QA runs the build.
Slash entry point.Direct typing, or /refine for a recently built one.The Plan & Build card, or /build-from-spec.
If you started in chat mode and realize the task is bigger than a fix, open a fresh session from the new-session page and pick Plan & Build. There is no in-place upgrade from a CHAT session to a SPEC session.