> ## 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 Vertex AI middleware for tracking AI costs.

## Installation

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

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

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

## Overview

The `@ai-billing/google-vertex` package provides middleware for tracking token usage and calculating
costs when using Google Vertex AI's Gemini models with the Vercel AI SDK, via `@ai-sdk/google-vertex`'s
`createVertex`.

Vertex reports the same Gemini-native usage shape as `@ai-sdk/google`, but under
`providerMetadata.vertex.usageMetadata` instead of `providerMetadata.google.usageMetadata`. Reasoning
("thoughts") tokens are reported separately from the visible completion tokens
(`thoughtsTokenCount`), and this package adds them back into the billed completion count so reasoning
usage is never under-billed.

> [!NOTE]
>
> Vertex also reports `trafficType` (`'ON_DEMAND'` for pay-as-you-go calls vs `'PROVISIONED'` for
> committed-throughput calls). `ModelPricing` has no field for a provisioned-throughput rate, so this
> middleware bills every call at the same resolved rate regardless of `trafficType` — this is a known,
> intentional limitation, not a bug. The raw `trafficType` value is still surfaced on every emitted
> billing event's `usage.subProvider` field, so you can filter or re-rate provisioned traffic downstream
> if you need to.

## Usage

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

**1. Initialize the Google Vertex AI provider**

First, set up the provider using `createVertex` from `@ai-sdk/google-vertex`. Vertex authenticates via
Application Default Credentials, so make sure `GOOGLE_VERTEX_PROJECT`, `GOOGLE_VERTEX_LOCATION`, and
`GOOGLE_APPLICATION_CREDENTIALS` are set in your environment.

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

const vertex = createVertex({
  project: process.env.GOOGLE_VERTEX_PROJECT,
  location: process.env.GOOGLE_VERTEX_LOCATION,
});
```

**2. Define model pricing**

Set up a price resolver to define the costs for the models you'll be using. For Vertex's Gemini
models, you can specify costs for standard prompt/completion tokens, cache-read tokens, and reasoning
tokens (`internalReasoningTokens`).

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

const priceResolver = createObjectPriceResolver({
  'gemini-2.5-flash': {
    promptTokens: 0.3 / 1_000_000, // $0.30 per 1M tokens
    completionTokens: 2.5 / 1_000_000, // $2.50 per 1M tokens
    internalReasoningTokens: 2.5 / 1_000_000, // $2.50 per 1M tokens
  },
});
```

**3. Create the billing middleware**

Initialize the Google Vertex 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 { createGoogleVertexMiddleware } from '@ai-billing/google-vertex';
import { consoleDestination } from '@ai-billing/core';

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

**4. Wrap the model**

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

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

const wrappedModel = wrapLanguageModel({
  model: vertex('gemini-2.5-flash'),
  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 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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