The GenAI Field Guide · Trending
An OpenID Connect sign-in that can also let a ChatGPT subscriber spend their plan's included usage inside a third-party app instead of an API key.
Sign in with ChatGPT started in July 2026 as an identity button and became, at DevDay on 29 September 2026, a way for Plus and Pro subscribers to point the usage already included in their plan at partner apps such as Devin, Amp, Warp, Kilo Code, Notion and Vercel. Under the name it is two separate OAuth grants: identity, and a scoped right to call the Responses API against the user's plan. Anyone building a developer tool or AI feature should understand it, because it moves who pays for inference from the app to the user's existing subscription.
There are two capabilities behind one button, and OpenAI's developer docs keep them apart. The first is ordinary federated login: an app adds Continue with ChatGPT, the user authenticates at OpenAI, and the app receives a verified identity with name, email and profile picture. OpenAI's docs state that identity scopes do not grant access to ChatGPT conversations or OpenAI API resources. The second is plan usage, which coverage calls token sharing: with a separate consent, the app can send model requests that are billed against the user's ChatGPT plan rather than a developer API key or the app's own credits.
The identity half launched in beta in July 2026 with partners such as Airtable, GitLab, HubSpot, Notion, Supabase and Vercel, as reported by Trending Topics. The DevDay announcement added plan usage, with 16 launch partners. Press lists differ, but the names that recur are Cognition's Devin, Amp, Warp, Kilo Code, OpenCode, OpenClaw, T3, Conductor, Dactyl, Notion and Vercel, with Lovable described as coming soon. One report separates sign-in-only partners (Airtable, Canva, GitLab, HubSpot, Supabase) from those that also accept plan usage.
Under the marketing, this is OpenAI turning a consumer subscription into a portable inference budget. Unofficial tools had already been reusing Codex logins to reach subscription usage; The New Stack describes the new feature as the officially supported replacement, with per-app tracking and limits managed in ChatGPT settings. For app makers it removes the API key setup step and the cost of serving the user's model calls. For users it means one subscription can fund several tools, within one shared weekly allowance.
Sign-in is OAuth 2.0 Authorization Code with PKCE plus OpenID Connect, against an issuer at auth.openai.com with a published discovery document and JWKS. A web app gets a client ID beginning oaiapp_, registers exact callback URLs, verifies the ID token signature, issuer, audience, expiry and nonce, keys the account on the sub claim rather than the email, and then issues its own first-party session cookie. The docs allow public clients with no secret and confidential clients using HTTP Basic client authentication.
Plan usage adds scopes on top of identity. For open-source and locally run apps the docs describe dynamic registration: the first sign-in uses a placeholder client ID with an app name hint, the user approves in the browser, and OpenAI issues a permanent oaiapp_ client ID for that install. The flow uses a loopback callback on 127.0.0.1, requests openid profile email offline_access resource.invoke chatgpt.tokens.use.direct, and names the OpenAI API as the token's resource. The app must check that chatgpt.tokens.use.direct was actually granted before offering plan usage, and store credentials with owner-only file permissions.
With that access token the app calls the public Responses API. Kilo's docs note that Chat Completions is not supported this way and that not every OpenAI model qualifies. Usage draws on the same weekly allowance as ChatGPT Work and Codex. In ChatGPT settings the user sees each connected app and can set a per-app cap, which Kilo's docs say defaults to 100 percent of the allowance. Most coverage says requests simply stop with an error at the cap; BigGo reports that credits beyond the plan can be spent only if the user has opted in and left the app at 100 percent, with that option off by default.
Disconnecting is separate from signing out. BigGo reports that signing out of a partner app does not remove its connection; you remove it in ChatGPT settings, and removing it neither restores used allowance nor deletes data the app already holds, which you must request from the app itself.
As a user you need a ChatGPT Plus or Pro plan and a partner app that supports plan usage. As a builder, open-source and locally run apps can use plan usage now through dynamic registration, while commercial apps join a limited trial through their OpenAI representative, per OpenAI's developer docs as read on 2 October 2026.