AI

Add AI chat to your application with the AI SDK, through Vercel AI Gateway, OpenAI or Anthropic.

Syntax

$ vela enable ai [--provider <gateway|openai|anthropic>]

Without --provider you’re prompted to pick one. Outside a terminal (CI, scripts) the flag is required. You’re then asked for the provider’s API key, with the input hidden. A key already in your .env is kept without asking, and you can leave it blank to add it later.

AI has no dependencies and doesn’t need a backend: it works in any SvelteKit project with a server. A project that builds with @sveltejs/adapter-static is refused, because a static site has no server to keep the key private or stream the reply. vela enable backend moves a static project to @sveltejs/adapter-node.

What you get

src/lib/server/ai.ts, which exports languageModel(): the configured model, or undefined while the API key is blank. Import it from any server code.
A streaming chat endpoint at src/routes/api/chat/+server.ts. It validates the conversation, sends it to the model with streamText and streams the reply back.
A demo chat page at /ai, built on the Chat class from @ai-sdk/svelte, with streaming replies, a Stop button and errors shown inline.
A server test for the endpoint in src/routes/api/chat/server.test.ts, when the project has the vela test:server harness. Its requests never reach the model, so it passes without an API key.
The ai and @ai-sdk/svelte packages plus the provider’s own, and the button and textarea components.
The provider’s API key in .env.

The endpoint reads the key from $env/dynamic/private on every request. While it’s blank, the endpoint answers 503 with the name of the variable to set, and the demo page shows that message. Set the same key on each deploy target with vela env set.

In a project without shadcn-svelte, the demo page uses plain HTML elements instead. In a project without route groups, it lands directly in src/routes/ai.

Providers

Vercel AI Gateway

$ vela enable ai --provider gateway

Variable	Description
`AI_GATEWAY_API_KEY`	A Vercel AI Gateway API key.

One key reaches models from every major provider. Model IDs take the form creator/model, and the default is anthropic/claude-sonnet-5. The gateway provider ships inside the ai package, so nothing else is installed.

OpenAI

$ vela enable ai --provider openai

Variable	Description
`OPENAI_API_KEY`	An OpenAI API key, e.g. `sk-...`.

Installs @ai-sdk/openai. The default model is gpt-5.5.

Anthropic

$ vela enable ai --provider anthropic

Variable	Description
`ANTHROPIC_API_KEY`	An Anthropic API key, e.g. `sk-ant-...`.

Installs @ai-sdk/anthropic. The default model is claude-sonnet-5.

Who can chat

Every reply is billed to your API key. With auth enabled, the endpoint answers only signed-in users (401 otherwise) and the demo page sits behind sign-in in the (app) group. Without auth, both are public, so put the endpoint behind sign-in or a rate limit before you deploy.

Enabling auth later doesn’t change the endpoint. Run vela enable ai again to regenerate it with the sign-in check, then delete the old demo page in src/routes/(public)/ai.

Customising

Model: change the model ID in src/lib/server/ai.ts.
Instructions: INSTRUCTIONS at the top of the endpoint is sent ahead of every conversation, through the AI SDK’s instructions option. System messages sent by the browser are refused.
Tools and more: tools, structured output and the rest of the AI SDK work in the endpoint as usual. See the AI SDK docs.
Errors: in development, provider errors such as a bad key or an unknown model are shown in the chat. In production they stay in the server log and the chat shows a generic message.

The demo page is yours to change or delete. The endpoint and languageModel() don’t depend on it.

Switching providers

Run the command again with a different --provider. src/lib/server/ai.ts is replaced, the provider’s package is installed and its key is added to .env. The endpoint and demo page are written again too, so re-apply any changes you made to them. Remove the previous provider’s package and key yourself.

To remove AI entirely, run vela disable ai.