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Codex is OpenAI’s official AI coding agent for the desktop.

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Install Codex

Download and install the Codex desktop app from the OpenAI Codex page.

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Configure MiniMax API

1

Edit the config file

Open ~/.codex/config.toml and add the following, replacing <MINIMAX_API_KEY> with your key from the MiniMax Developer Platform:
model = "MiniMax-M3"
model_provider = "minimax"
model_context_window = 512000

[model_providers.minimax]
name = "MiniMax"
base_url = "https://api.minimax.io/v1"
experimental_bearer_token = "<MINIMAX_API_KEY>"
wire_api = "responses"
2

Restart Codex and start using MiniMax-M3

Restart Codex — MiniMax-M3 is now ready to use.

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Configure Model Capabilities (Optional)

Codex can use a custom model catalog to recognize MiniMax-M3 capabilities such as multimodal input, reasoning effort as the thinking switch, system prompt instructions, tool type, and other detailed model parameters. After this is configured, type /model in Codex CLI to see MiniMax-M3 and its available reasoning levels in the model list. Add the following line to ~/.codex/config.toml: 
model_catalog_json = "~/.codex/model-catalogs/custom-catalog.json"
Then create ~/.codex/model-catalogs/custom-catalog.json with the detailed model configuration: 
{
  "models": [
    {
      "slug": "MiniMax-M3",
      "display_name": "MiniMax-M3",
      "description": "MiniMax",
      "default_reasoning_level": "high",
      "supported_reasoning_levels": [
        { "effort": "none", "description": "Think-Off" },
        { "effort": "high", "description": "Deep" }
      ],
      "shell_type": "shell_command",
      "visibility": "list",
      "supported_in_api": true,
      "priority": 0,
      "base_instructions": "You are Codex, a coding agent based on MiniMax-M3. You and the user share the same workspace and collaborate to achieve the user's goals.",
      "supports_reasoning_summaries": true,
      "default_reasoning_summary": "none",
      "support_verbosity": false,
      "truncation_policy": { "mode": "bytes", "limit": 10000 },
      "supports_parallel_tool_calls": true,
      "experimental_supported_tools": [],
      "input_modalities": ["text", "image"]
    }
  ]
}
Common fields in this configuration:
  • slug / display_name: The model identifier and display name used in Codex config and the /model list. Keep this aligned with the model name used by the API.
  • default_reasoning_level: The default reasoning effort. For MiniMax-M3, any non-none value enables Adaptive Thinking; the value does not tune reasoning depth.
  • supported_reasoning_levels: Reasoning options users can switch between in /model. none turns thinking off; high enables Adaptive Thinking.
  • base_instructions: Base system prompt Codex adds when using this model. Use it to describe the model identity and collaboration style.
  • supports_reasoning_summaries: Enables Codex’s Responses API reasoning path for this model. Set this to true so Codex sends reasoning.effort; otherwise Codex omits the reasoning field even when default_reasoning_level is configured. In this example, default_reasoning_summary is set to none so Codex does not request a separate reasoning summary.
  • shell_type: Declares the shell tool-call type supported by the model. This example uses shell_command.
  • visibility / supported_in_api / priority: Control whether the model appears in the list, whether it is available through the API, and its ordering priority in the model list.
  • supports_parallel_tool_calls: Indicates that the model supports parallel tool calls, allowing Codex to handle multiple tool requests.
  • experimental_supported_tools: Reserved list for experimental tool capabilities. Leave it as an empty array when no extra tools are needed.
  • input_modalities: Supported input modalities. ["text", "image"] means text and image input are supported.
  • truncation_policy: Controls truncation behavior for retained context or tool output. This example limits retained content by bytes.
Restart Codex after changing the model catalog.