AI

Record Token Usage After Streaming Object

When you're streaming structured data with streamObject, you may want to record the token usage for billing purposes.

onFinish Callback

You can use the onFinish callback to record token usage. It is called when the stream is finished.

import { openai } from '@ai-sdk/openai';
import { streamObject } from 'ai';
import { z } from 'zod';


const result = streamObject({
  model: openai('gpt-4.1'),
  schema: z.object({
    recipe: z.object({
      name: z.string(),
      ingredients: z.array(z.string()),
      steps: z.array(z.string()),
    }),
  }),
  prompt: 'Generate a lasagna recipe.',
  onFinish({ usage }) {
    console.log('Token usage:', usage);
  },
});

usage Promise

The streamObject result contains a usage promise that resolves to the total token usage.

import { openai } from '@ai-sdk/openai';
import { streamObject, TokenUsage } from 'ai';
import { z } from 'zod';


const result = streamObject({
  model: openai('gpt-4.1'),
  schema: z.object({
    recipe: z.object({
      name: z.string(),
      ingredients: z.array(z.string()),
      steps: z.array(z.string()),
    }),
  }),
  prompt: 'Generate a lasagna recipe.',
});


// your custom function to record token usage:
function recordTokenUsage({
  inputTokens,
  outputTokens,
  totalTokens,
}: TokenUsage) {
  console.log('Prompt tokens:', inputTokens);
  console.log('Completion tokens:', outputTokens);
  console.log('Total tokens:', totalTokens);
}


// use as promise:
result.usage.then(recordTokenUsage);


// use with async/await:
recordTokenUsage(await result.usage);


// note: the stream needs to be consumed because of backpressure
for await (const partialObject of result.partialObjectStream) {
}