AI Billing

Quick Start

Wrap any Vercel AI SDK model with tracked() to automatically bill for token usage:

import { Commet } from "@commet/node";
import { tracked } from "@commet/ai-sdk";
import { anthropic } from "@ai-sdk/anthropic";
import { generateText } from "ai";

const commet = new Commet({ apiKey: process.env.COMMET_API_KEY! });

const result = await generateText({
  model: tracked(anthropic("claude-sonnet-4-20250514"), {
    commet,
    feature: "ai_generation",
    customerId: "user_123",
  }),
  prompt: "Explain quantum computing",
});
// Tokens tracked, cost calculated, balance deducted. Done.

That's it. tracked() intercepts the model response, reports inputTokens, outputTokens, cacheReadTokens, and cacheWriteTokens to Commet, which calculates cost from the AI model catalog and deducts from the customer's balance.

How It Works

Your app                    Commet                         AI Provider
   |                          |                                |
   |-- tracked(model) ------->|                                |
   |                          |                                |
   |-- generateText() --------|-------- API call ------------->|
   |                          |                                |
   |<-- tokens + response ----|<------- response --------------|
   |                          |                                |
   |                          |-- resolve model price          |
   |                          |-- apply margin                 |
   |                          |-- deduct from balance          |
   |                          |-- record ledger entry          |
   |                          |                                |
   |<-- result (unchanged) ---|                                |

Balance Model Overview

AI billing uses the balance consumption model. Customers get a dollar balance (e.g., $10.00/month) that depletes as they use AI features. When the balance reaches zero, behavior depends on configuration:

blockOnExhaustion = true: API returns 402, customer must top up or wait for renewal
blockOnExhaustion = false: Usage continues, overage charged at period end

Balance resets to includedBalance at each billing period renewal.

Cost Formula

All values use rate scale (10000 = $1.00) for sub-cent precision:

inputCost    = ceil(inputTokens    x inputPricePerMillionTokens    / 1,000,000)
outputCost   = ceil(outputTokens   x outputPricePerMillionTokens   / 1,000,000)
subtotal     = inputCost + outputCost + cacheReadCost + cacheWriteCost
marginAmount = ceil(subtotal x margin / 10000)
total        = subtotal + marginAmount

Margin is configured per feature per plan in basis points (2000 = 20% markup). All costs use Math.ceil() to prevent underbilling.

Key Gotchas

#	Gotcha	Detail
1	Feature must be `pricingMode: "ai_model"`	Configure this in the Commet dashboard before tracking works
2	Model must exist in the catalog	Commet syncs models from AI Gateway automatically, but verify your model is listed
3	Tracking is non-blocking	If token reporting fails, the AI response still returns. Use `onTrackingError` to catch failures
4	Balance deduction is real-time	Cost is deducted immediately, not at period end
5	Rate scale, not cents	Token prices and costs use rate scale (10000 = $1.00), not settlement scale (100 = $1.00)
6	Margin is per feature per plan	Different plans can have different markups on the same AI feature

What Do You Need?

Task	Reference
Set up tracked() middleware	tracked-middleware.md -- installation, streaming, multiple models, error handling
Understand cost calculation	cost-calculation.md -- AI model catalog, pricing, margins, multi-currency
Configure balance model	balance-model.md -- how balance works, exhaustion, top-ups, choosing the right model

Prerequisites

Feature configured with pricingMode: "ai_model" in the Commet dashboard
Plan using the balance consumption model
Margin configured on the plan feature (0 basis points = pass-through cost)
Customer with an active subscription to that plan

Common Setup

API Key

Store in environment variable:

export COMMET_API_KEY=ck_xxxxxxxxx

Install

npm install @commet/node @commet/ai-sdk

Error Handling Quick Reference

Code	Condition	Action
402	Insufficient balance	Customer needs to top up or upgrade plan
403	Feature not in plan	Check customer's subscription includes the AI feature
404	Model not in catalog	Verify the model ID matches the catalog (e.g., `claude-sonnet-4-20250514`)
422	Missing required fields	`inputTokens` is required when `model` is provided

ai-billing