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Installation

npm install @ai-billing/openai @ai-billing/core @ai-sdk/openai ai

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Overview

The @ai-billing/openai package provides middleware for tracking token usage and calculating costs when using OpenAI models with the Vercel AI SDK. It captures OpenAI-specific metrics, such as inputCacheReadTokens (for Prompt Caching) and webSearch (for search-enabled models), ensuring that all costs are accurately reflected.

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Usage

To use the middleware, wrap your OpenAI model using wrapLanguageModel from the ai package and pass the createOpenAIMiddleware.
1

Initialize the OpenAI provider

First, set up the OpenAI provider using your API key.
import { createOpenAI } from '@ai-sdk/openai';

const openai = createOpenAI({
  apiKey: process.env.OPENAI_API_KEY,
});
2

Define model pricing

Set up a price resolver to define the costs for the models you’ll be using. For OpenAI, you can specify costs for standard prompt/completion tokens, cached tokens (inputCacheReadTokens), and even webSearch usage.
import { createObjectPriceResolver } from '@ai-billing/core';

const priceResolver = createObjectPriceResolver({
  'gpt-5': {
    promptTokens: 1.25 / 1_000_000,
    completionTokens: 10.0 / 1_000_000,
    inputCacheReadTokens: 0.125 / 1_000_000,
  }
});
Using a Remote Pricing Provider (Narev):Instead of hardcoding prices, you can use a remote pricing provider like Narev to automatically fetch up-to-date pricing.
import { createNarevPriceResolver } from '@ai-billing/core';

const narevPriceResolver = createNarevPriceResolver({
  apiKey: process.env.NAREV_API_KEY ?? '',
});
3

Create the billing middleware

Initialize the OpenAI billing middleware. You need to provide a destination (such as consoleDestination) where billing events will be sent, along with your priceResolver.
import { createOpenAIMiddleware } from '@ai-billing/openai';
import { consoleDestination } from '@ai-billing/core';

const billingMiddleware = createOpenAIMiddleware({
  destinations: [consoleDestination()],
  priceResolver: priceResolver, // or narevPriceResolver
});
4

Wrap the model

Use wrapLanguageModel from the ai package to apply the billing middleware to your OpenAI model.
import { wrapLanguageModel } from 'ai';

const wrappedModel = wrapLanguageModel({
  model: openai('gpt-5'),
  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 and calculate costs.
import { generateText } from 'ai';

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

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Advanced Usage

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Web Search Models

When using models with web search capabilities like gpt-4o-search-preview, you can track the search costs by adding webSearch to your custom pricing map. 
import { createObjectPriceResolver, consoleDestination } from '@ai-billing/core';
import { createOpenAIMiddleware } from '@ai-billing/openai';
import { wrapLanguageModel, generateText } from 'ai';
import { createOpenAI } from '@ai-sdk/openai';

const openai = createOpenAI({ apiKey: process.env.OPENAI_API_KEY });

const customPricingMap = {
  'gpt-4o-search-preview': {
    promptTokens: 2.5 / 1_000_000,
    completionTokens: 10.0 / 1_000_000,
    webSearch: 0.03, // cost per search
  },
};

const billingMiddleware = createOpenAIMiddleware({
  destinations: [consoleDestination()],
  priceResolver: createObjectPriceResolver(customPricingMap),
});

const wrappedModel = wrapLanguageModel({
  // Use .chat() for search-enabled models
  model: openai.chat('gpt-4o-search-preview'),
  middleware: billingMiddleware,
});

const result = await generateText({
  model: wrappedModel,
  prompt: 'What are the latest AI news from this week?',
});