codex-model-router

Use models from different providers in the same OpenAI Codex setup — switch between GPT and third-party models (e.g. Meta Muse Spark) just by picking a model name, with no config.toml edits and no app patching.

A ~90-line, zero-dependency Node.js forwarder on 127.0.0.1. Codex talks to it as its normal OpenAI endpoint; the router reads the "model" field of each request and forwards it, unchanged, to the matching provider with that provider's API key. Responses stream straight through.

Codex ──► http://127.0.0.1:4141/v1 (router) ──┬─ "muse-*"  ─► api.meta.ai/v1      (META_API_KEY)
                                              └─ anything ─► api.openai.com/v1   (your Codex OpenAI key, passed through)

Context: openai/codex#46484 (native multi-provider model switching). Today model_provider is global, so a custom provider and GPT models can't coexist in one model picker. This router is a no-patch workaround.

One-click install (Windows)

Prerequisites: Node.js in PATH, and your provider keys as user environment variables, e.g.:

[Environment]::SetEnvironmentVariable('META_API_KEY', '<your-meta-key>', 'User')

Then double-click install.cmd (or run powershell -ExecutionPolicy Bypass -File install.ps1). It:

1. copies the router to %LOCALAPPDATA%\codex-model-router
2. adds a hidden launcher codex-model-router.vbs to your Startup folder (runs at login)
3. backs up ~/.codex/config.toml, then sets at the top:

   model_provider = "openai"
   openai_base_url = "http://127.0.0.1:4141/v1"   # codex-model-router
   

4. starts the router and checks http://127.0.0.1:4141/health

Restart the Codex app afterwards. Undo everything with uninstall.ps1.
Options: -Port 4141 -CodexHome <dir> -InstallDir <dir> -StartupDir <dir> -NoStart.

macOS/Linux: no installer yet — run node codex-router.js (e.g. via launchd/systemd) and add the two config lines above.

Adding a provider or model

1. Route — edit routes.json (in the install dir). First matching match prefix wins; "" is the catch-all.

[
  { "match": "muse-", "host": "api.meta.ai", "base": "/v1", "keyEnv": "META_API_KEY" },
  { "match": "",      "host": "api.openai.com", "base": "/v1", "keyEnv": "OPENAI_API_KEY", "passthroughAuth": true