Configuring a Third-Party API in Codex

Configuring a Third-Party API in Codex

If you want to use a third-party API in Codex, you need to complete two configurations:

  1. Configure config.toml

  2. Configure auth.json

After all configurations are complete, restart Codex for them to take effect.

How to find these two files:

MacOS / Linux:

Command+Shift+H (press all three keys together) (this step takes you to the user directory)

Then press Command+Shift+. (press all three keys together) (this step reveals all folders that start with a dot)

The .codex folder is here.

Windows:

Press Win+R, then enter %USERPROFILE% and find the .codex folder.

Alternatively, use the search next to Start to search for Run, open it, enter %USERPROFILE%, and find the .codex folder.

Step 1: Configure config.toml

First, find the Codex configuration file:

  • MacOS / Linux: ~/.codex/config.toml

  • Windows: %userprofile%/.codex/config.toml

If this file does not exist, create it first; if it already exists, edit its contents to:

model_provider = "OpenAI"
model = "gpt-5.4-mini"
review_model = "gpt-5.4-mini"
model_reasoning_effort = "medium"
disable_response_storage = true
network_access = "enabled"
windows_wsl_setup_acknowledged = true

[model_providers.OpenAI]
name = "OpenAI"
base_url = "https://rehdasu.cn"
wire_api = "responses"
requires_openai_auth = true

Configuration notes:

  • Copy it exactly as-is.

Step 2: Configure auth.json

Next, find the authentication file:

  • MacOS / Linux: ~/.codex/auth.json

  • Windows: ~/.codex/auth.json

If the file does not exist, create one; if it already exists, edit its contents to:

{
  "OPENAI_API_KEY": "sk-xxxxxxxxx"
}

Replace the value of OPENAI_API_KEY (sk-xxxxxxxxx) with the real key you obtained from the platform. (You can find this under API Keys in the left sidebar at https://rehdasu.cn.)

Important: auth.json has only 3 lines!!

Step 3: Restart Codex

After both files above have been configured, restart Codex.

If it still does not take effect after restarting, check these items first:

  • Whether the provider is OpenAI

  • Whether OPENAI_API_KEY is filled in correctly. Custom API keys are not currently supported; a randomly generated one is fine.