How the Codex Plugin Supports Different Reasoning Effort Levels

The Codex plugin controls model reasoning intensity through six validated effort levels (none, minimal, low, medium, high, xhigh) that are normalized from command-line input and forwarded to the Codex app-server via the --effort flag.

The openai/codex-plugin-cc repository provides a command-line interface for interacting with OpenAI's Codex model, including granular control over how much computational "thinking" the model applies to each task. Understanding how the Codex plugin handles different reasoning effort levels helps developers optimize the trade-off between response quality and latency for various coding workflows.

Valid Reasoning Effort Levels in the Source Code

In plugins/codex/scripts/codex-companion.mjs at line 71, the plugin defines a whitelist of valid reasoning effort values. These levels range from none (no reasoning effort) to xhigh (maximum reasoning effort), allowing precise tuning of model behavior.

The complete set of supported values includes:

• none
• minimal
• low
• medium
• high
• xhigh

Input Validation and Normalization

The normalizeReasoningEffort function (lines 114-127 in codex-companion.mjs) handles input sanitization by trimming whitespace, converting to lowercase, and validating against the whitelist. If an unsupported value is provided, the function throws a descriptive error message listing all valid options.

Command-Line Interface for Reasoning Effort Control

Users specify their desired reasoning level using the --effort flag on task-related subcommands such as task, rescue, or adversarial-review. The argument parser captures this value before the request is constructed.

Example commands:

# Run a task with minimal reasoning effort

codex task --effort minimal "refactor the authentication module"

# Run a rescue operation with high effort

codex rescue --model gpt-5.4-mini --effort high "investigate flaky integration test"

Building and Forwarding the Task Request

Inside buildTaskRequest (lines 604-609 in codex-companion.mjs), the normalized effort value is included in the request object sent to the Codex app-server. The function signature accepts an effort parameter alongside other task metadata like cwd, model, and prompt.

function buildTaskRequest({ cwd, model, effort, prompt, write, resumeLast, jobId }) {
  return { cwd, model, effort, prompt, write, resumeLast, jobId };
}

The effort field is then forwarded to the app-server's turn/start endpoint, as verified in tests/runtime.test.mjs (lines 766-785). The test suite confirms that fakeState.lastTurnStart.effort correctly receives the user-specified value, ensuring the backend actually processes the reasoning level.

Default Behavior and Configuration File Overrides

When the --effort flag is omitted, the plugin leaves the field unset, allowing the Codex model to apply its own default reasoning effort level. This behavior is documented in the README at line 161.

Projects can establish persistent defaults by setting model_reasoning_effort in a .codex/config.toml file:

[model]
model_reasoning_effort = "high"

As documented in lines 273-278 of the README, this configuration value is automatically applied when no explicit --effort flag is provided on the command line.

Summary

• The Codex plugin supports six validated reasoning effort levels: none, minimal, low, medium, high, and xhigh.
• Input validation occurs in normalizeReasoningEffort within plugins/codex/scripts/codex-companion.mjs, which normalizes case and validates against a whitelist.
• Users control effort via the --effort flag on task subcommands.
• The buildTaskRequest function incorporates the effort value into the payload sent to the Codex app-server.
• Default behavior allows the model to choose its own effort level when unspecified, with optional overrides available through .codex/config.toml.

Frequently Asked Questions

What reasoning effort levels does the Codex plugin support?

The plugin supports six distinct levels: none, minimal, low, medium, high, and xhigh. These values are defined in a whitelist at line 71 of plugins/codex/scripts/codex-companion.mjs and represent a spectrum from no reasoning effort to maximum computational investment.

How do I set a default reasoning effort for all tasks in a project?

Create a .codex/config.toml file in your project root and set the model_reasoning_effort key under the [model] section. For example: model_reasoning_effort = "high". According to the README at lines 273-278, this configuration applies automatically when you run commands without the --effort flag.

What happens if I provide an invalid reasoning effort value?

The normalizeReasoningEffort function throws an error with a clear message listing all valid options. Located at lines 114-127 in codex-companion.mjs, this validation ensures only supported values reach the Codex backend, preventing malformed requests.

Does the reasoning effort setting affect all Codex plugin commands?

The --effort flag is available on task-oriented subcommands including task, rescue, and adversarial-review. The value is normalized and forwarded to the app-server for any command that builds a task request via buildTaskRequest, as confirmed by the runtime tests at lines 766-785 in tests/runtime.test.mjs.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}