> ## Documentation Index
> Fetch the complete documentation index at: https://www.narev.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Getting started

> First steps with Google middleware for tracking AI costs.

## Installation

```bash npm theme={null}
npm install @ai-billing/google @ai-billing/core @ai-sdk/google ai
```

```bash pnpm theme={null}
pnpm add @ai-billing/google @ai-billing/core @ai-sdk/google ai
```

```bash yarn theme={null}
yarn add @ai-billing/google @ai-billing/core @ai-sdk/google ai
```

## Overview

The `@ai-billing/google` package provides middleware for tracking token usage and calculating costs when using Google models with the Vercel AI SDK.

It captures Google-specific metrics, such as `internalReasoningTokens`, `inputCacheReadTokens`, and `inputCacheWriteTokens`, ensuring that Prompt Caching and reasoning costs are accurately reflected.

## Usage

To use the middleware, wrap your Google model using `wrapLanguageModel` from the `ai` package and pass the `createGoogleMiddleware`.

**1. Initialize the Google provider**

First, set up the Google provider using your API key.

```typescript theme={null}
import { createGoogleGenerativeAI } from '@ai-sdk/google';

const google = createGoogleGenerativeAI({
  apiKey: process.env.GOOGLE_AI_STUDIO_KEY,
});
```

**2. Define model pricing**

Set up a price resolver to define the costs for the models you'll be using. For Google, you can specify costs for standard prompt/completion tokens, cached tokens (`inputCacheReadTokens` and `inputCacheWriteTokens`), and `internalReasoningTokens`.

```typescript theme={null}
import { createObjectPriceResolver } from '@ai-billing/core';

const priceResolver = createObjectPriceResolver({
  'models/gemini-3.1-flash-lite-preview': {
    promptTokens: 0.00000025, // $0.25 per 1M tokens
    completionTokens: 0.0000015, // $1.50 per 1M tokens
    inputCacheReadTokens: 0.000000025, // $0.025 per 1M tokens
    inputCacheWriteTokens: 0.00000008333333, // ~$0.083 per 1M tokens
    internalReasoningTokens: 0.0000015, // $1.50 per 1M tokens
  },
});
```

**3. Create the billing middleware**

Initialize the Google billing middleware. You need to provide a destination (such as `consoleDestination`) where billing events will be sent, along with your `priceResolver`.

```typescript theme={null}
import { createGoogleMiddleware } from '@ai-billing/google';
import { consoleDestination } from '@ai-billing/core';

const billingMiddleware = createGoogleMiddleware({
  destinations: [consoleDestination()],
  priceResolver: priceResolver,
});
```

**4. Wrap the model**

Use `wrapLanguageModel` from the `ai` package to apply the billing middleware to your Google model.

```typescript theme={null}
import { wrapLanguageModel } from 'ai';

const wrappedModel = wrapLanguageModel({
  model: google('models/gemini-3.1-flash-lite-preview'),
  middleware: billingMiddleware,
});
```

**5. Use the wrapped model**

Finally, use the wrapped model with AI SDK functions like `generateText` or `streamText`. The billing middleware will automatically track tokens, handle caching and reasoning metrics, and calculate costs.

```typescript theme={null}
import { generateText } from 'ai';

const result = await generateText({
  model: wrappedModel,
  prompt: 'What is the capital of Sweden?',
});
```


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