Which apps can use your Claude or ChatGPT subscription?

You pay $20, $100, or $200 a month for Claude or ChatGPT. Then you try a new agent app, and it asks for an API key or sells you credits. The plan you already pay for does nothing there.

A plan login works in the vendor's own apps and agents. Another app can use your plan in two ways. It can run the vendor's agent for you, or it can use a sign-in the vendor has approved for that purpose.

Two ways an app can reach a model

An app can call the model's API from its own code. The API bills by the token, so the app charges you credits, sends a usage bill, or asks for your API key.

Or the app can start the vendor's own agent on your computer. Claude Code, Codex, Antigravity, and Grok Build are programs you install and sign in to with your plan. An app that runs one of them gets the model, the tools, and your plan's usage, and it never handles your login.

The second way is how a $100 plan can cover several hundred dollars of API-priced work. Subscription vs API has the measurements.

What each vendor allows

Anthropic

Anthropic tightened this in 2026. In January it blocked tools that reused Claude subscription logins outside Claude Code, and The Register reported the terms update that followed. OpenCode removed its Claude login.

The current policy has two parts. Developers may not "offer Claude.ai login into their own applications, or to route requests through Free, Pro, Max, or Ultra plan credentials on behalf of their users." The same page says this does not "prevent an end user from signing in to the unmodified Claude Code binary with their own Claude subscription, including where a platform hosts Claude Code."

An app may run Claude Code as Anthropic publishes it, and you sign in yourself. An app may not take your login and call Claude on its own.

Anthropic announced in May 2026 that this kind of usage would move to a separate credit, then paused the change. Its help article now says "Claude Agent SDK, claude -p, and third-party app usage still draw from your subscription limits." Anthropic can change this again.

OpenAI

OpenAI built a supported route called Sign in with ChatGPT. Its docs say "eligible ChatGPT Go, Plus, Pro, and Business subscribers can also choose to use their ChatGPT plan for AI requests" in other apps, and "App usage counts toward your existing plan limits."

The partner apps OpenAI lists include Conductor, Warp, Notion, Vercel, and Devin. It lists OpenCode and T3 as open-source integrations.

The Codex command-line tool signs in with a ChatGPT plan on Plus and above. OpenAI's app-server docs say local and open-source apps built on Codex's own sign-in can keep using it, and that commercial and hosted services should use Sign in with ChatGPT.

Google

Google replaced Gemini CLI with Antigravity for personal accounts in June 2026. Antigravity is free with weekly limits, and Google AI Pro and Ultra raise them.

Google's terms call "using third party software, tools, or services to access the Service" a breach. Google also documents a way for editors to run the Antigravity agent in their own chat panel with your sign-in.

xAI

Grok Build is xAI's agent. Its docs say it works "through the Agent Client Protocol (ACP) in other apps", and it signs in with your X subscription or an API key.

Apps that can use your subscription

The first five leave the sign-in to the vendor's agent. T3 Code's readme says to install each provider's tool and log in through it. Conductor's FAQ says it "uses the auth tokens already saved on your machine." Zed's docs say each external agent "owns its own authentication and billing."

OpenCode and OpenWork use OpenAI's Sign in with ChatGPT.

Mimzie is the only one on this list with its own editors for Word, Excel, and PowerPoint files. It runs each vendor's agent on your computer, and the agents edit your documents, spreadsheets, and slides. By default, you accept or reject every change.

Apps that bill by API key or credits

These call the model through the API, which bills by the token.

How to tell which kind an app is

• It asks you to paste an API key. It bills at API rates.
• It sells credits. It bills at API rates, with or without a fee.
• It asks you to install Claude Code or Codex, or installs one for you, and opens the vendor's sign-in page. It runs on your plan.
• It shows a "Sign in with ChatGPT" button that leads to OpenAI's site and offers your plan for its requests. It runs on your ChatGPT plan.

The rules can change

Anthropic changed its policy several times in 2026. Google replaced a whole product. A plan's limits are set by the vendor, and so are the rules about where you can use it.