### What variant of Codex are you using? CLI ### What feature would you like to see? I may be missing something, but I could not find a documented way to start Codex in Plan mode by default. I checked the current docs/code and found: - `plan_mode_reasoning_effort`, which seems to control reasoning effort for Plan mode once Plan mode is already active - TUI startup logic that appears to initialize with the Default collaboration mode - core/session setup that still appears to default to `ModeK

Potential duplicates detected. Please review them and close your issue if it is a duplicate. - #12738 - #11988 *Powered by [Codex Action](https://github.com/openai/codex-action)*

Config option to start in Plan mode by default

Open 💬 5 comments Opened Mar 8, 2026 by azyu

💡 Likely answer: A maintainer (github-actions[bot], contributor) responded on this thread — see the highlighted reply below.

What variant of Codex are you using?

CLI

What feature would you like to see?

I may be missing something, but I could not find a documented way to start Codex in Plan mode by default.

I checked the current docs/code and found:

plan_mode_reasoning_effort, which seems to control reasoning effort for Plan mode once Plan mode is already active
TUI startup logic that appears to initialize with the Default collaboration mode
core/session setup that still appears to default to ModeKind::Default

Because of that, I am unsure whether:

this is already supported but undocumented,
this is intentionally not supported,
or this would be a useful feature request.

My use case:

I use Plan mode as my normal starting workflow
manually switching to Plan mode each session is repetitive
a config-based default would make that workflow much smoother

If this is already possible, could you point me to the correct config key or command-line option?

Thanks.

Additional information

_No response_

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5 Comments

github-actions[bot] contributor · 5 months ago

Potential duplicates detected. Please review them and close your issue if it is a duplicate.

#12738
#11988

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0xble · 5 months ago

Related to #13377.

This issue captures the config and default-startup side of the same problem, while #13377 captures the CLI, headless, and startup-parameter side.

If maintainers want one canonical tracker, I would suggest consolidating around #13377 and treating this as the config and default-start behavior under that umbrella.

Bdthomson · 4 months ago

Any movement on this? ClaudeCode has had this option for a while now, having it in Codex would be a nice quality-of-life improvement. Thanks!

bdcdo · 1 month ago

Looking forward to switching from claude code to codex to use GPT 5.6 and this would be a great quality of life improvement to make this switch have less friction

bdcdo · 1 month ago

I put together a reference implementation for this in my fork, in case it helps validate or accelerate the approach:

The proposed config is intentionally opt-in:

[tui]
default_mode = "plan"

When unset, the existing Default-mode startup path is preserved. The patch also keeps the existing root-level plan_mode_reasoning_effort behavior/schema unchanged, applies the configured mode to the first prompt, and lets an explicit resumed-session mode take precedence.

I added coverage for no opt-in, Plan startup, first-prompt contents, explicit Default and Plan session precedence, and a real ThreadResumeResponse through the first UserTurn. The affected config/core/TUI suites and snapshots pass locally.

I understand external code contributions are invitation-only, so I am sharing this as analysis/reference rather than opening an unsolicited PR. Happy to adjust the approach if maintainers think it fits the intended direction.