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Overview

Codex CLI is OpenAI’s terminal-based coding agent. It can be configured to use Znap AI through an OpenAI-compatible endpoint.

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Step 1: Install Codex CLI

Install globally using npm: 
npm install -g @openai/codex
Verify installation: 
codex --version

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Step 2: Log Out of Existing OpenAI Sessions

If you have previously logged into Codex using a ChatGPT account, clear the existing authentication first: 
codex logout
This ensures Codex uses your custom configuration instead of stored OpenAI credentials.

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Step 3: Configure Codex

Open the config file: 
C:\Users\<your-username>\.codex\config.toml
Add the following: 
openai_base_url = "https://api.znapai.com/v1"
model = "gpt-5.3-codex"
model_reasoning_effort = "high"
Save the file.

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Step 4: Start Codex

Launch the CLI: 
codex
Codex Terminal
When prompted, select: 
Provide your own API key
Paste your Znap AI API key.

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Step 5: Verify Setup

Run a simple prompt: 
What is 2 + 2?
If Codex responds successfully, the configuration is working.

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Changing Models

Update the model field in your configuration file: 
C:\Users\<your-username>\.codex\config.toml
Example: 
model = "gpt-5.3-codex"
Restart Codex after making changes.

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Notes

  • Codex uses the OpenAI Responses API internally.
  • Znap AI successfully routes Codex requests through its OpenAI-compatible endpoint.
  • At the time of writing, GPT-based models have been verified to work reliably with Codex.
  • If you encounter errors such as: 
    stream disconnected before completion
    try switching to a GPT-based model and restart Codex.

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Troubleshooting

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Requests Still Going to OpenAI

Run: 
codex logout
Then restart Codex and re-enter your Znap AI API key.

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Invalid API Key Error

Ensure you are using your Znap AI API key and not an OpenAI API key.

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Stream Disconnected Before Completion

This usually indicates a compatibility issue between the selected model and Codex’s Responses API requirements. Switch back to a GPT-based model: 
model = "gpt-5.3-codex"
and restart Codex.

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Current Recommendation

For Codex CLI, the most reliable configuration currently tested is: 
openai_base_url = "https://api.znapai.com/v1"
model = "gpt-5.3-codex"
model_reasoning_effort = "high"
This configuration has been verified to work successfully with Znap AI.