---
title: Caching
description: How to handle caching when working with the AI SDK
---

# Caching Responses

Depending on the type of application you're building, you may want to cache the responses you receive from your AI provider, at least temporarily.

## Using Language Model Middleware (Recommended)

The recommended approach to caching responses is using [language model middleware](/docs/ai-sdk-core/middleware)
and the [`simulateReadableStream`](/docs/reference/ai-sdk-core/simulate-readable-stream) function.

Language model middleware is a way to enhance the behavior of language models by intercepting and modifying the calls to the language model.
Let's see how you can use language model middleware to cache responses.

```ts filename="ai/middleware.ts"
import { Redis } from '@upstash/redis';
import {
  type LanguageModelV4,
  type LanguageModelV4Middleware,
  type LanguageModelV4StreamPart,
  simulateReadableStream,
} from 'ai';

const redis = new Redis({
  url: process.env.KV_URL,
  token: process.env.KV_TOKEN,
});

export const cacheMiddleware: LanguageModelV4Middleware = {
  wrapGenerate: async ({ doGenerate, params }) => {
    const cacheKey = JSON.stringify(params);

    const cached = (await redis.get(cacheKey)) as Awaited<
      ReturnType<LanguageModelV4['doGenerate']>
    > | null;

    if (cached !== null) {
      return {
        ...cached,
        response: {
          ...cached.response,
          timestamp: cached?.response?.timestamp
            ? new Date(cached?.response?.timestamp)
            : undefined,
        },
      };
    }

    const result = await doGenerate();

    redis.set(cacheKey, result);

    return result;
  },
  wrapStream: async ({ doStream, params }) => {
    const cacheKey = JSON.stringify(params);

    // Check if the result is in the cache
    const cached = await redis.get(cacheKey);

    // If cached, return a simulated ReadableStream that yields the cached result
    if (cached !== null) {
      // Format the timestamps in the cached response
      const formattedChunks = (cached as LanguageModelV4StreamPart[]).map(p => {
        if (p.type === 'response-metadata' && p.timestamp) {
          return { ...p, timestamp: new Date(p.timestamp) };
        } else return p;
      });
      return {
        stream: simulateReadableStream({
          initialDelayInMs: 0,
          chunkDelayInMs: 10,
          chunks: formattedChunks,
        }),
      };
    }

    // If not cached, proceed with streaming
    const { stream, ...rest } = await doStream();

    const fullResponse: LanguageModelV4StreamPart[] = [];

    const transformStream = new TransformStream<
      LanguageModelV4StreamPart,
      LanguageModelV4StreamPart
    >({
      transform(chunk, controller) {
        fullResponse.push(chunk);
        controller.enqueue(chunk);
      },
      flush() {
        // Store the full response in the cache after streaming is complete
        redis.set(cacheKey, fullResponse);
      },
    });

    return {
      stream: stream.pipeThrough(transformStream),
      ...rest,
    };
  },
};
```

<Note>
  This example uses `@upstash/redis` to store and retrieve the assistant's
  responses but you can use any KV storage provider you would like.
</Note>

`LanguageModelV4Middleware` has two methods: `wrapGenerate` and `wrapStream`. `wrapGenerate` is called when using [`generateText`](/docs/reference/ai-sdk-core/generate-text), while `wrapStream` is called when using [`streamText`](/docs/reference/ai-sdk-core/stream-text).

For `wrapGenerate`, you can cache the response directly. Instead, for `wrapStream`, you cache an array of the stream parts, which can then be used with [`simulateReadableStream`](/docs/ai-sdk-core/testing#simulate-ui-message-stream-responses) function to create a simulated `ReadableStream` that returns the cached response. In this way, the cached response is returned chunk-by-chunk as if it were being generated by the model. You can control the initial delay and delay between chunks by adjusting the `initialDelayInMs` and `chunkDelayInMs` parameters of `simulateReadableStream`.

You can see a full example of caching with Redis in a Next.js application in our [Caching Middleware Recipe](/cookbook/next/caching-middleware).

## Using Lifecycle Callbacks

Alternatively, each AI SDK Core function has special lifecycle callbacks you can use. The one of interest is likely `onEnd`, which is called when the generation is complete. This is where you can cache the full response.

Here's an example of how you can use [Upstash Redis](https://upstash.com/redis) and Next.js to cache the OpenAI response for 1 hour:

```tsx filename="app/api/chat/route.ts"
import {
  convertToModelMessages,
  createUIMessageStreamResponse,
  streamText,
  toUIMessageStream,
  UIMessage,
} from 'ai';
__PROVIDER_IMPORT__;
import { Redis } from '@upstash/redis';

// Allow streaming responses up to 30 seconds
export const maxDuration = 30;

const redis = new Redis({
  url: process.env.KV_URL,
  token: process.env.KV_TOKEN,
});

export async function POST(req: Request) {
  const { messages }: { messages: UIMessage[] } = await req.json();

  // come up with a key based on the request:
  const key = JSON.stringify(messages);

  // Check if we have a cached response
  const cached = (await redis.get(key)) as string | null;
  if (cached != null) {
    return new Response(cached, {
      status: 200,
      headers: { 'Content-Type': 'text/plain' },
    });
  }

  // Call the language model:
  const result = streamText({
    model: __MODEL__,
    messages: await convertToModelMessages(messages),
    async onEnd({ text }) {
      // Cache the response text:
      await redis.set(key, text);
      await redis.expire(key, 60 * 60);
    },
  });

  // Respond with the stream
  return createUIMessageStreamResponse({
    stream: toUIMessageStream({ stream: result.stream }),
  });
}
```