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Installation

npm install @ai-billing/openmeter @ai-billing/core

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Overview

The @ai-billing/openmeter package provides a destination for sending calculated AI costs and token usage to OpenMeter. Unlike other destinations, OpenMeter ingests usage as CloudEvents. The destination automatically formats the AI SDK usage into CloudEvents, using the event type to identify the meter and the subject to identify the customer. Cost data is sent in nano-dollars (or your base currency) in the data payload, which is merged with other billing metadata.

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Usage

To use the OpenMeter destination, initialize it with your API key, then pass it to any billing middleware.
1

Initialize the OpenMeter destination

Set up the destination using your OpenMeter API key. You can optionally customize the eventType (defaults to llm_usage), apiUrl, and define a type for your billing tags for type safety.
import { createOpenMeterDestination } from '@ai-billing/openmeter';

type BillingTags = {
  userId?: string;
  org_name?: string;
};

const openMeterDestination = createOpenMeterDestination<BillingTags>({
  apiKey: process.env.OPENMETER_API_KEY,
  // Optional configurations:
  // eventType: 'llm_usage', // default
  // apiUrl: 'https://eu.api.konghq.com', // default
  // customerIdKey: 'userId', // custom key for identifying the user
});
2

Set up price resolution

In order for the OpenMeter destination to send costs, the cost property on the generated events must be populated.If you are using a provider that returns pricing natively (like OpenRouter or Anthropic), the cost is automatically calculated and you can skip this step.However, if you are using a provider that doesn’t return pricing natively (such as Groq or local models), you must supply a price resolver like Narev or a local object resolver. Without this, the cost will be undefined and the destination cannot send the meter event to OpenMeter.
import { createNarevPriceResolver } from '@ai-billing/core';

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

Create the billing middleware

Initialize the billing middleware for your preferred provider and include the openMeterDestination in the destinations array.
// Example using OpenRouter (pricing returned natively)
import { createOpenRouterV3Middleware } from '@ai-billing/openrouter';

const billingMiddleware = createOpenRouterV3Middleware<BillingTags>({
  destinations: [openMeterDestination],
});
4

Wrap the model

Use wrapLanguageModel from the ai package to apply the billing middleware to your model.
import { wrapLanguageModel } from 'ai';
import { createOpenRouter } from '@openrouter/ai-sdk-provider';

const openrouter = createOpenRouter({
  apiKey: process.env.OPENROUTER_API_KEY,
});

const wrappedModel = wrapLanguageModel({
  model: openrouter('openai/gpt-4o'),
  middleware: billingMiddleware,
});
5

Pass tags during generation

Finally, use the wrapped model with AI SDK functions like generateText or streamText.

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Understanding Billing Tags

The ai-billing-tags object has specific requirements for OpenMeter:
  • Customer Identity (Subject): By default, the destination looks for userId or openMeterCustomerId in your tags to populate the CloudEvents subject. If omitted, the event is skipped to avoid ingesting anonymous data. You can override this by providing customerIdKey in the destination options.
  • Data Payload: Metadata (like model_id, input_tokens, and your custom tags such as org_name) are merged along with cost_nanos and currency into the data field of the CloudEvent.
import { streamText } from 'ai';

const result = streamText({
  model: wrappedModel,
  prompt: 'What is the capital of Sweden?',
  providerOptions: {
    'ai-billing-tags': {
      userId: 'user_openmeter_test', // Used as the CloudEvents subject
      org_name: 'Acme Corp', // Sent as additional metadata in data payload
    } as BillingTags,
  },
});