How to track token usage

Prerequisites

This guide assumes familiarity with the following concepts:

• LLMs

This notebook goes over how to track your token usage for specific LLM calls. This is only implemented by some providers, including OpenAI.

Here's an example of tracking token usage for a single LLM call via a callback:

tip

See this section for general instructions on installing integration packages.

npm

npm install @langchain/openai @langchain/core

Yarn

yarn add @langchain/openai @langchain/core

pnpm

pnpm add @langchain/openai @langchain/core

import { OpenAI } from "@langchain/openai";

const llm = new OpenAI({
  model: "gpt-3.5-turbo-instruct",
  callbacks: [
    {
      handleLLMEnd(output) {
        console.log(JSON.stringify(output, null, 2));
      },
    },
  ],
});

await llm.invoke("Tell me a joke.");

/*
  {
    "generations": [
      [
        {
          "text": "\n\nWhy don't scientists trust atoms?\n\nBecause they make up everything.",
          "generationInfo": {
            "finishReason": "stop",
            "logprobs": null
          }
        }
      ]
    ],
    "llmOutput": {
      "tokenUsage": {
        "completionTokens": 14,
        "promptTokens": 5,
        "totalTokens": 19
      }
    }
  }
*/

API Reference:

• OpenAI from @langchain/openai

If this model is passed to a chain or agent that calls it multiple times, it will log an output each time.

Next steps

You've now seen how to get token usage for supported LLM providers.

Next, check out the other how-to guides in this section, like how to implement your own custom LLM.