How to use OpenAI Codex with Z.ai GLM-4.5 Coding Plan

Codex CLI is a coding agent similar to Claude Code from OpenAI.

When it was launched it had very basic features but lately they’re making it better.

How to get started?

You can install the package using npm

npm install -g @openai/codex

Or via brew

brew install codex

Configuration

Codex maintains configurations at ~/.codex/config.toml

Configuring z.ai model provider

First thing is that we need to create a new z.ai model provider. z.ai has OpenAI compatible API which is a hard dependency if you need to use Codex with custom models.

You’ll need to add these things in the config file.

[model_providers.z_ai]
# Name of the provider that will be displayed in the Codex UI.
name = "z.ai - GLM Coding Plan"
# The path `/chat/completions` will be amended to this URL to make the POST
# request for the chat completions.
base_url = "https://api.z.ai/api/coding/paas/v4"
env_key = "Z_AI_API_KEY"

Make sure to configure Z_AI_API_KEY env variable in your shell.

Creating GLM 4.5 LLM profile

Now in the config file, we need to create a new profile for the LLM that we want to use.

[profiles.glm_4_5]
model = "glm-4.5"
model_provider = "z_ai"

Basically, we’re creating a new profile that points to a particular model provider. And the model name will get passed through.

Testing

Once that is done, you should be able to run codex with a particular profile now.

codex --profile glm_4_5

And that will start the codex with the GLM 4.5 model from Z.ai

Reference

https://github.com/openai/codex/blob/main/docs/config.md

Happy AI-assisted coding!