Codex / ChatGPT

The ChatGPT app and the Codex CLI use the same setup. They pick their upstream by named provider in ~/.codex/config.toml, which takes two edits. Put the first part at the top of the file:

model_provider = "sleev"

Then put the second part at the bottom:

[model_providers.sleev]
name = "Sleev"
base_url = "http://127.0.0.1:17321/v1"
wire_api = "responses"
supports_websockets = true
requires_openai_auth = true

[model_providers.sleev.http_headers]
"sleev-provider" = "openai"
"sleev-harness" = "chatgpt"

Set sleev-provider to openai when you use an OpenAI API key, or codex when you sign in with your ChatGPT account.