---
title: Setup
description: Provide Ai.layer once at the edge of your app.
---

Every ai-effect function requires the `Ai` service. Provide `Ai.layer` once, next to your other layers:

```ts main.ts
import { Ai, generateText } from 'ai-effect';
import { Effect, Layer } from 'effect';

const program = generateText({
	model: 'openai/gpt-5',
	prompt: 'Hello!',
});

const AppLayer = Layer.mergeAll(Ai.layer /* , your other layers */);

program.pipe(Effect.provide(AppLayer), Effect.runPromise);
```

## Why a layer

Callbacks run after the call that registered them has returned: a stream's `onEnd` fires long after `streamText` hands you the stream. They need somewhere to run that outlives the call, and `Ai.layer` is that place. It owns:

- the fibers that run your callbacks and tool executions
- the `AbortSignal` passed to every `streamText` and `ToolLoopAgent.stream` call

Closing the layer, for example at app shutdown, aborts in-flight streams and interrupts the callbacks and tool executions still running.

Because the layer's lifetime is the app's, provide it once rather than per request. No ai-effect function requires `Scope`, so there is no `Effect.scoped` to place.

:::warning[Providing it per call]
Providing `Ai.layer` around a single call closes the layer when that call's effect finishes. For `streamText` that aborts the stream you just returned.
:::