Codex

Connect the Codex CLI to Fireworks with the Nexus CLI or manual setup, and see who pays for OpenAI model turns with Nexus Auto.

Codex keeps its own sign-in for OpenAI model turns. Codex cloud tasks aren’t supported.

Codex and the ChatGPT desktop app share ~/.codex/config.toml, so connecting one connects the other.

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Quick start

1. Install and sign in

   curl -fsSL https://nexus.fireworks.ai/install.sh | bash
   

   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.

   nexus login
   

   Sign in with your browser, or paste a Fireworks API key (fw_...).

   If the Nexus CLI is already installed and signed in, skip to step 2.

2. Connect Codex

   Close open Codex sessions and quit the ChatGPT desktop app, then run:

   nexus codex
   
3. Restart and pick Auto

   Start a new Codex session. Codex opens on Nexus Auto (Auto in /model).

To restore your original settings, run nexus codex off.

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Use Nexus Auto

• Fireworks model turns use your Fireworks key.
• OpenAI model turns use your Codex sign-in. When Codex asks, pick ChatGPT, a device code, or an API key, or run codex login.
• Anthropic model turns need an Anthropic Provider Key from your admin.

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Who pays for OpenAI model turns

Codex sign-in	Who pays for OpenAI model turns
ChatGPT	Your ChatGPT plan. Older models, such as gpt-5.6-terra, use an OpenAI Provider Key instead
OpenAI API key	That OpenAI key
Fireworks key only	An OpenAI Provider Key. Without one, an OpenAI model you pick fails with no usable openai credential

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MCP and tools

• MCP servers and ChatGPT connectors are unchanged.
• Native web search is supported. Fireworks runs the search server-side, so no search MCP server is required.

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Troubleshooting

• Nothing changed after --model: start a new or resumed session, because Codex loads a new model only at session start.
• Resuming an old session: select the provider explicitly with codex resume <id> -c model_provider="fireworks-ai".
• MiniMax models don’t work on Codex. Use a Chat Completions harness such as OpenCode for MiniMax.

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Manual setup (advanced)

Add a Fireworks provider to ~/.codex/config.toml, then run codex:

~/.codex/config.toml

model_provider = "fireworks-ai"
model = "glm-latest"

[model_providers.fireworks-ai]
name = "Fireworks"
base_url = "https://api.fireworks.ai/inference/v1"
wire_api = "responses"
env_key = "FIREWORKS_API_KEY"

Without the Nexus CLI, you take over the tasks it otherwise performs, such as undo and updates.

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What the Nexus CLI writes

Nexus CLI writes ~/.codex/config.toml and ~/.codex/fireworks-model-catalog.json.