How to Use Codex with Domestic AI Models: A Practical Guide for Everyone

In the realm of AI-assisted coding, Codex has emerged as a powerful tool, but its reliance on the ChatGPT model can be a barrier for many due to cost and access issues. This guide walks you through using Codex with domestic AI models like DeepSeek V4 and Mimo v2.5, making it accessible without a ChatGPT account, phone number verification, or special network configurations.

1. Understanding Codex and Its Ecosystem

Codex is an Agent product designed to assist with coding tasks. It's often used alongside tools like CC Switch, which lets you swap out its underlying model. By default, Codex uses the ChatGPT model, but you can replace this "brain" with domestic alternatives like DeepSeek V4 or Mimo v2.5 for better accessibility and cost-effectiveness.

Why Choose Domestic Models?

• DeepSeek V4: Highly recommended online, with excellent overall performance. However, it doesn't support multimodal inputs (e.g., image uploads).
• Mimo v2.5: Supports multimodal inputs and offers a great user experience.

2. Download and Install Codex

Visit the Codex official website and download the appropriate version for your operating system (Windows or macOS). The tool is free to download.

3. Install CC Switch

CC Switch is a tool that lets you swap Codex's underlying model.

1. Go to the CC Switch GitHub page.
2. Scroll down to find the installation package:
   • For macOS, download the file ending with .dmg.
   • For Windows, download the file ending with .msi.
3. If unsure which version to install, ask DeepSeek:

Which version of CC Switch should I install for my [your OS] system?

4. Obtain an API Key from DeepSeek

An API Key is like an access credential that allows Codex to communicate with the DeepSeek model.

1. Visit the DeepSeek Open Platform.
2. Click on "API Keys" in the left menu.
3. Create a new API Key, give it a name for easy recall, and copy the generated key. Keep it secure — it's your personal access credential.

5. Configure CC Switch

1. Open CC Switch and click on the third icon (OpenAI icon) at the top.
2. Click the "+" button on the right to add a model. Select "DeepSeek" (or your chosen domestic model).
3. Paste the DeepSeek API Key into the designated field. Ensure the toggle for model integration is enabled, then click "Add".

6. Test the Setup

1. Fully exit Codex and restart it.
2. In Codex, click on "Settings" in the bottom left corner. You should see that you're logged in via the API Key, and the model should show "DeepSeek".
3. Send a test message:

Hello, what can you help me with?

A normal response indicates success.

FAQ

Do I need a ChatGPT account to use Codex?

Not after this setup. By using CC Switch with a domestic model's API key, you bypass ChatGPT entirely. You only need a free DeepSeek account (or other domestic provider) to get an API key. This makes Codex accessible to anyone, regardless of OpenAI account restrictions or regional limitations.

Which domestic model should I choose — DeepSeek V4 or Mimo v2.5?

It depends on your needs. DeepSeek V4 offers better overall reasoning and coding performance, making it the top choice for pure code generation tasks. Mimo v2.5 supports multimodal inputs (you can upload images for the AI to analyze), which is useful for UI debugging or design-to-code workflows. If you mainly write and debug code, go with DeepSeek. If you need image understanding alongside coding, pick Mimo v2.5.

Is CC Switch free to use?

Yes, CC Switch is an open-source tool available for free on GitHub. You only pay for the API usage of the model you connect to — DeepSeek's API is extremely affordable at roughly one-twentieth of OpenAI's pricing.