Skip to main content
The Codex CLI and the ChatGPT desktop app both read ~/.codex/config.toml, so connecting one connects the other. Close open Codex sessions and quit the ChatGPT desktop app before connecting or running off. In a terminal, Nexus CLI waits for them to close. In a script, it exits with an error. --force writes anyway, which isn’t recommended. Generally available OpenAI Responses Nexus Auto Native web search

​
Quick start

Install and sign in

You need Node.js 22 or later, git, and bash. On Windows, run the installer from Git Bash. PowerShell breaks the script’s line endings.
Sign in with your browser, or paste a Fireworks API key (fw_...).Already set up? Skip to step 2.

Connect Codex

Restart and pick a model

Start a new Codex session. Codex opens on Nexus Auto (auto). Run nexus codex again at any time. It keeps the model you’re on.
/model lists Codex’s OpenAI models first, then an Auto row for Nexus Auto, then the other Fireworks models. Set effort in that picker.

​
Use Nexus Auto

Codex keeps its own sign-in. When Codex asks, pick ChatGPT, a device code, or an API key, or run codex login. Your Fireworks key pays for Fireworks models. Your Codex sign-in pays for OpenAI models. See Who pays for OpenAI model turns.
  • Nexus Auto (auto) is supported on the Responses API, and Codex defaults to it.
  • On Codex, auto picks a model for each turn from Fireworks open models and the closed models your Codex sign-in and keys allow. See which models auto can use.
  • With only a Fireworks key (no ChatGPT or OpenAI sign-in), auto can still use OpenAI models through an OpenAI Provider Key, and Anthropic models through an Anthropic key. Without either key, it uses open models.
  • Anthropic model turns: connect an Anthropic Provider Key, or save your own key with nexus auto --anthropic-api-key (it prompts for the key) and run nexus codex again. Nexus CLI adds the saved key to Codex’s http_headers.
  • Nexus CLI never sends an OpenAI key you saved with nexus auto to Codex. Your Codex sign-in covers OpenAI model turns.
  • With manual setup, Codex can send x-anthropic-api-key and x-openai-api-key headers.

​
Who pays for OpenAI model turns

With Nexus CLI, your Codex sign-in decides who pays for OpenAI model turns:
  • For OpenAI model turns, Nexus Auto uses an x-openai-api-key header first, then your Codex sign-in, then an OpenAI Provider Key.
  • Your ChatGPT plan doesn’t cover gpt-5.5, gpt-5.6-terra, or gpt-5.6-luna. Those turns need an OpenAI Provider Key.
  • Nexus CLI doesn’t hand a saved OpenAI key to Codex. To pay with it, sign Codex in with it: nexus key export --openai | codex login --with-api-key.
  • No browser on the machine? codex login --device-auth signs in with ChatGPT through a one-time code.

​
MCP and tools

Your servers stay in [mcp_servers] in ~/.codex/config.toml. MCP and app connector tools load through Codex’s tool search on every model.
Native web search is supported while connected through Nexus CLI. Fireworks runs the search server-side and returns the results. You don’t need an MCP server or a search service.

​
Troubleshooting

Nothing changed after --model? Start a new or resumed session. Codex loads a new model only then. Upgrading from an earlier version? See Upgrading from earlier versions. When you resume an old session, select the provider explicitly:
MiniMax models don’t work on Codex. Codex may insert assistant messages between tool_calls and tool_results, which MiniMax templates reject. Nexus CLI leaves MiniMax out of the Codex model list and rejects --model minimax-.... Use a Chat Completions harness such as OpenCode for MiniMax.

​
Manual setup (advanced)

Add a Fireworks provider

~/.codex/config.toml

Run Codex

Codex answers from glm-latest.
Without a model catalog, Codex warns that it has no metadata for Fireworks models and uses fallback limits. The catalog also turns on MCP tool search and runs auto-review on your chosen model. Nexus CLI writes that catalog for you. To pay for OpenAI model turns with your Codex sign-in, as Nexus CLI does, replace the env_key line with these two:
~/.codex/config.toml
Codex then sends its own sign-in, and reads your Fireworks key from the environment. See what changes without the Nexus CLI.

​
What the Nexus CLI writes

~/.codex
config.toml
fireworks-model-catalog.json
~/.codex/config.toml
  • requires_openai_auth = true makes Codex send its own sign-in. The Fireworks key travels in x-fireworks-api-key.
  • Nexus CLI writes the same provider table for every model. It never adds an OpenAI key. An Anthropic key saved with nexus auto --anthropic-api-key adds an x-anthropic-api-key entry to http_headers.
  • Nexus CLI keeps your other TOML settings, including [mcp_servers], and saves config.toml and the catalog with mode 0600.
  • fireworks-model-catalog.json tells Codex each model’s context window and capabilities. It also turns on MCP tool search for the Fireworks models, so MCP and app connector tools load on demand, and makes Codex auto-review run on the model you picked.