# How to change reasoning effort in Codex CLI: model_reasoning_effort values and one-off overrides

> Source: <https://dev.to/aicoding-guide/how-to-change-reasoning-effort-in-codex-cli-modelreasoningeffort-values-and-one-off-overrides-2bf4>
> Published: 2026-09-13 15:25:00+00:00

*Originally published at [https://aicoding-guide.com](https://aicoding-guide.com/en/posts/codex-reasoning-effort/).*

Codex feels slow, or it overthinks a trivial fix. The knob for that is **reasoning effort**, the Codex counterpart of extended thinking in Claude Code, controlled by the `model_reasoning_effort` key.

In short: set `model_reasoning_effort = "high"` (or another value) in `~/.codex/config.toml` to change it permanently, use the `-c` flag for a single run, or `/model` during a session. The five levels are `minimal`, `low`, `medium`, `high`, and `xhigh`.

**Key point**

What you will learn

- The five values and when each fits
- Four ways to change effort: permanently, for one run, mid-session, and per profile
- The keys that change effort only for plan mode or subagents

The configuration reference defines `model_reasoning_effort` as a string with the values `minimal | low | medium | high | xhigh`. The reference does not state a default, and it may depend on the model, so none is given here.

| Value | Suited to | 
|---|---|
| `minimal` | one-line questions, formatting fixes, anything with little to reason about | 
| `low` | small bug fixes, simple refactors | 
| `medium` | everyday feature work and investigation | 
| `high` | multi-file design changes, bugs with no obvious cause | 
| `xhigh` | hard algorithms, reviews of large changes where mistakes are costly | 

Higher effort means slower responses and more tokens. Keeping everyday work around `medium` and raising it only for hard tasks is the easiest routine.

**Glossary**

**Reasoning effort**: how much the model reasons internally before answering. It is separate from how much of the reasoning summary is displayed; hiding the display is covered in [Hiding reasoning in Codex output](https://aicoding-guide.com/en/posts/codex-hide-agent-reasoning/).

One line in `~/.codex/config.toml`:

```
model = "gpt-5.5"
model_reasoning_effort = "high"
```

In a trusted project you can put it in the repository's `.codex/config.toml` to affect only that project; project settings outrank user settings.

To change effort for a single invocation without touching the file, use `-c` (`--config`). Values are **parsed as TOML**, so wrap the string in double quotes and wrap the whole thing in single quotes to keep the shell from eating them.

```
codex -c model_reasoning_effort='"high"' "Find out why this test fails and fix it"
```

The same form works with `codex exec` from scripts. According to the docs, a value that cannot be parsed as TOML is treated as a string, so a missing pair of quotes often still works, but quoting makes the intent explicit.

Run `/model` in a session to switch. The official command list describes it as choosing the active model "and reasoning effort, when available". Raise it before a hard investigation and drop it afterwards.

Rather than typing the override every time you review code, bundle the settings in a profile. Profiles live in `$CODEX_HOME` (default `~/.codex`) as `<name>.config.toml` and are selected with `--profile <name>`.

```
# ~/.codex/deep-review.config.toml
model_reasoning_effort = "xhigh"
approval_policy = "on-request"
codex --profile deep-review
```

Keep only the differences in the profile and shared settings in the base `config.toml`. Profiles as a whole are covered in the hub article [Configuring Codex with config.toml](https://aicoding-guide.com/en/posts/codex-config-toml/).

The configuration reference also lists keys that apply only in specific situations.

| Key | Applies to | 
|---|---|
| `plan_mode_reasoning_effort` | overrides effort in plan mode only | 
| `agents.default_subagent_reasoning_effort` | default effort for spawned subagents | 

If you want deep planning but ordinary implementation, add `plan_mode_reasoning_effort = "high"` and leave `model_reasoning_effort` alone.

**If nothing changes, check the model**

A value outside what the model supports may not take effect. If `/model` shows no reasoning effort choices for the current model, that model does not expose effort. When speed and quality do not change after editing the setting, confirm the model first.

`model_reasoning_effort`, with values `minimal`, `low`, `medium`, `high`, `xhigh`
`~/.codex/config.toml`; one run: `-c model_reasoning_effort='"high"'`; mid-session: `/model`
`<name>.config.toml` profile and select it with `--profile`
`plan_mode_reasoning_effort`; subagents have `agents.default_subagent_reasoning_effort`