Point Claude Code at GPT-5.6 via CLIProxyAPI (claudex)

The idea

Claude Code is two separable pieces: the harness — the TUI, the tools, the agent loop, the plugins — and the model endpoint it talks to. Point the harness at an Anthropic-compatible endpoint that forwards to GPT, and the same interface runs on a GPT model.

Tibo (@thsottiaux) described the approach:

Tibo@thsottiaux
If you aren't yet bold enough to install the Codex app, you can stay in the presence of your orange crab and point it at GPT 5.6 Sol. Takes 5 minutes. Kudos to Theo for explaining one of the ways to get this done. Step 1: Install CLIProxyAPI Step 2: Connect Step 3: Define
Theo - t3.gg@theo@thsottiaux tl;dr version: - set up CLIProxyAPI with Claude and Codex auth - Connect to Claude Code - Make "claudex" alias that sets some env vars Took like 2 prompts (I already had the proxy set up tbf)
Jul 12, 20267.4K likes524 replies

CLIProxyAPI is the local proxy that makes this work. It speaks the Anthropic Messages API and forwards to GPT — or Gemini, Grok, and others — using your existing ChatGPT/Codex subscription, with no OpenAI API key required. The result is a single command: claudex.

This is the setup I ran end to end, plus a copy‑paste prompt at the end if you’d rather have an AI wire it up.

What you’ll need

Homebrew (macOS)
A ChatGPT Plus/Pro or Codex subscription — the proxy authenticates against it over OAuth
Claude Code v2.1.129+ if you want proxy models to appear in the /model picker

Step 1 — Install CLIProxyAPI

brew install cliproxyapi
brew services start cliproxyapi

That starts a local server on port 8317, which restarts at login. Confirm it’s up:

curl -s -o /dev/null -w "%{http_code}\n" http://localhost:8317/   # expect 200

Step 2 — Authenticate with your ChatGPT account

cliproxyapi -codex-login

This opens a browser for OpenAI OAuth. Log in, pick the right workspace if you have Teams/Business, and approve. The credentials land in ~/.cli-proxy-api/ as a JSON file, and the proxy can now route GPT models on your behalf.

Step 3 — Set a client token

The proxy needs a token your client will present. In /opt/homebrew/etc/cliproxyapi.conf, replace the placeholder api-keys with one of your own:

api-keys:
  - "claudex-REPLACE_WITH_A_RANDOM_SECRET"

Generate a strong one with echo "claudex-$(openssl rand -hex 16)", then restart the service so it reloads:

brew services restart cliproxyapi

Verify the proxy answers an Anthropic-format request and serves the GPT models:

TOKEN="claudex-REPLACE_WITH_A_RANDOM_SECRET"
curl -s http://localhost:8317/v1/models -H "Authorization: Bearer $TOKEN" \
  | grep -oE '"gpt-5\.6-[a-z]+"' | sort -u
# "gpt-5.6-luna"  "gpt-5.6-sol"  "gpt-5.6-terra"

Step 4 — Point Claude Code at the proxy

Add an alias to ~/.zshrc that carries the proxy settings and launches Claude Code on a GPT model. It’s scoped to the alias, so plain claude is unaffected:

alias claudex='ANTHROPIC_BASE_URL=http://localhost:8317 \
ANTHROPIC_AUTH_TOKEN=claudex-REPLACE_WITH_A_RANDOM_SECRET \
CLAUDE_CODE_ENABLE_GATEWAY_MODEL_DISCOVERY=1 \
CLAUDE_CODE_SUBAGENT_MODEL=gpt-5.6-sol \
CLAUDE_CODE_ALWAYS_ENABLE_EFFORT=1 \
CLAUDE_CODE_MAX_TOOL_USE_CONCURRENCY=3 \
ENABLE_TOOL_SEARCH=false \
claude --model gpt-5.6-sol --dangerously-skip-permissions'

What each part does:

Setting	Effect
`ANTHROPIC_BASE_URL` / `ANTHROPIC_AUTH_TOKEN`	Route this session to the local proxy, scoped to the alias
`--model gpt-5.6-sol`	The GPT model that drives the session
`CLAUDE_CODE_SUBAGENT_MODEL`	Spawned subagents use the same model
`CLAUDE_CODE_ALWAYS_ENABLE_EFFORT`	Exposes the model’s effort controls
`CLAUDE_CODE_MAX_TOOL_USE_CONCURRENCY=3`	Caps concurrent tool calls
`ENABLE_TOOL_SEARCH=false`	Disables dynamic tool search
`CLAUDE_CODE_ENABLE_GATEWAY_MODEL_DISCOVERY`	Populates the `/model` picker from the proxy (see Step 5)
`--dangerously-skip-permissions`	Starts in bypass-permissions mode

Reload and run it:

source ~/.zshrc
claudex

You start on gpt-5.6-sol. To use terra, luna, or anything else the proxy serves, switch in-session with /model — no need to relaunch.

Step 5 — Enable model discovery

By default, /model shows only Claude Code’s built-in models. The CLAUDE_CODE_ENABLE_GATEWAY_MODEL_DISCOVERY=1 flag in the alias changes that. At startup Claude Code queries the proxy’s /v1/models and adds each one to the picker under a “From gateway” group. From there you can switch between sol, terra, luna, and the rest live. This is the documented gateway path and requires Claude Code v2.1.129+.

Optional — the management API

CLIProxyAPI also ships a management API and web control panel, disabled until you set secret-key under remote-management in the config (keep allow-remote: false for localhost-only). It’s tangential to claudex itself; if you want it, see CLIProxyAPI’s docs. Note that the management key is a separate secret from the api-keys token your client uses for model calls.

Let an AI set it up for you

If you’d rather not do this by hand, paste the following into a Claude Code (or any capable coding‑agent) session and let it drive. It pauses for the one interactive step and keeps the routing scoped to an alias:

Set up a "claudex" command on my Mac: the Claude Code interface running on
GPT-5.6 via CLIProxyAPI, using my existing ChatGPT/Codex subscription.

1. Install CLIProxyAPI with Homebrew and start it as a service. Confirm it
   listens on localhost:8317 (expect HTTP 200).
2. Generate a strong random client token, put it in the `api-keys` list of
   /opt/homebrew/etc/cliproxyapi.conf (back the file up first), and restart the service.
3. Authenticate the proxy to my ChatGPT account with `cliproxyapi -codex-login`.
   It opens a browser — pause, tell me to complete the login, then continue once
   credentials are saved to ~/.cli-proxy-api/.
4. Verify with an Anthropic-format call to http://localhost:8317/v1/messages for
   gpt-5.6-sol, and list the models from /v1/models.
5. Add a `claudex` ALIAS to ~/.zshrc (not a global settings change, so plain
   `claude` stays on Anthropic) that sets ANTHROPIC_BASE_URL, ANTHROPIC_AUTH_TOKEN,
   and CLAUDE_CODE_ENABLE_GATEWAY_MODEL_DISCOVERY=1, then runs
   `claude --model gpt-5.6-sol`. Verify it resolves, then summarize what changed
   and where the backups are.

Don't print my real tokens back in plaintext beyond what's needed. Ask me before
anything destructive.

Two deliberate omissions: I don’t ask the agent to add --dangerously-skip-permissions or to enable the management API. Add those yourself, on purpose, if you want them.

A few honest caveats

Bypass permissions is exactly that. --dangerously-skip-permissions removes every approval prompt, so the agent can run any command and edit any file unsupervised. Combined with a non‑Anthropic model, that’s an autonomous agent on your machine. Keep it for throwaway work, not in directories with secrets or important uncommitted changes.
Cloud stays on Anthropic. Remote agents, cloud code review, and the web/Slack surfaces run on Anthropic’s infrastructure and can’t reach a local proxy. They continue to use Claude, which is expected.
OAuth tokens expire. If claudex starts erroring, re-run cliproxyapi -codex-login to refresh.
It’s a personal, experimental setup. You’re using your own subscription through an unofficial proxy; treat model names and behavior as things to verify on your build, not contracts.

Bottom line

The Claude Code harness and its model are separable, and a small local proxy is all it takes to swap the model while keeping everything else. Scope the proxy settings to a claudex alias so your normal claude stays on Anthropic, and verify the proxy, the model list, and the selected model before you rely on it for regular work.