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Every turn in Cortex Code runs in one of three interaction modes. Ask answers questions and reads the repository. Plan returns a plan you can review. Agent edits files, runs commands and opens a pull request. You pick the mode in the composer before you start a session, and again on every follow-up, so a single session can tighten to Ask to understand something and widen to Agent to carry it out. This page explains what each mode may reach, why the choice is worth trusting, when the change takes effect, and what none of the three modes can do. If you are looking for a first session end to end, start with the Code quickstart.

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What each mode may do

All three modes can read a file, list files by pattern, search the repository by regular expression, read the task list and read artifacts. Only Agent can write a file, edit a file, run a command, write the task list, or dispatch the background search worker.

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The lock is on the tools, not on the model

The three modes are worth trusting because of where the decision is made. In Ask and Plan the mutating tools, writing, editing, running a shell command, writing the task list and dispatching the background worker, are simply absent from the catalog the turn is built with. The model is not asked to behave: there is no instruction it could misread or talk itself out of, because the tool is not there to call. If one is called anyway, the call is refused a second time when it is dispatched. Plan gets one extra tool the others do not: the plan writer. That is the only thing that fills the Plan tab.
Because the catalog is chosen when the turn is built, a mode change takes effect on the next turn, not on the turn already running. Switching to Agent while a turn is in flight does not retroactively let that turn edit anything, and switching to Ask does not claw back an edit the running turn has already proposed. If you need a running turn to stop, press Stop in the composer’s send disc, then send the next turn in the mode you want.

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Choose a mode, and change it per turn

1

Pick the mode for the first turn

On Code Home, the controls row under the prompt carries Ask, Plan and Agent. The mode is stored on the session, and a new session defaults to Agent.
2

Send the task

Press Start session. The turn is built with the catalog that mode allows, and nothing widens it afterwards.
3

Change it on a follow-up

The follow-up composer inside the session carries the same mode menu, so the mode can change on every turn. Pick a mode and send the follow-up: the new mode applies to that turn. A follow-up that does not pick one keeps the session’s current mode.
A useful rhythm: Plan to agree on the approach, Agent to carry it out, Ask when something has gone sideways and you want to understand the repository before you let anything else change.

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What a Plan turn gives you

A Plan turn reads the repository and returns a structured proposal: titled steps, the files it expects to touch, the risks it sees, and a rendered diagram. The product’s own word for the diagram is mermaid, which is why the mode’s description mentions it. The Plan tab in the output pane appears only when the session has a plan. Nothing changes in the repository while you read it. Ask for adjustments as many times as you like, in Plan, and send an Agent turn when the approach is right. The cheap moment to redirect a change is before any file moves.

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Ask and Plan in the Changes pane

The Changes pane is where file writes wait for a human decision. In Ask or Plan there is nothing there to decide, and the pane says so outright:
Ask and Plan do not change files, so there is nothing to review here.
That is the mode reporting itself, not a failure. See Changes and diffs.

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Security is not a fourth mode

Under the three modes there is a fourth row labelled Security, with the hint Open Security mode for this repository. It is a link, not a mode: it leaves the composer for Cortex Security, which reads a pull request and posts a review instead of writing code. A session’s interaction stays Ask, Plan or Agent. See Pull-request review.

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What no mode can reach

The mode is chosen per session and per turn only. There is no workspace setting that pins a read-only default, and Code settings does not offer one. If you want a session to stay in Ask, keep choosing Ask on each turn.
A Code session does not receive the tools a Chat turn has: no web search, no web page extraction, no hosted snippet sandbox, no skills and no clock. When a task needs to run your repository’s own Python, an Agent turn runs it as a shell command inside the attached runtime, like any other command. A Code session is also built with no tool servers, connectors or plugins of its own, so widening the mode to Agent does not open a path to an external service. See Code integrations for what is configured at the workspace level and what a session reports.