How to charge AI app users by token usage (with refunds and live balance)

1. Pick a unit: tokens, cents, or both

For pure token billing, use unit "tokens". For dollar-cost billing (where different models cost different amounts), use unit "cents" and convert at track time. Both work; cents is more flexible if you support multiple models with different costs.

2. Define a limit group with the right unit

In the dashboard, create a limit group on the user's plan. Unit: tokens or cents. Quota: how much they get this period. Period: usually monthly. Anchor: subscription_start (cleaner) or calendar (simpler).

3. Reserve an upper bound before the call

You do not know exact token count until the response. Reserve a safe upper bound - for chat, prompt token count + max_tokens.

import { encoding_for_model } from "tiktoken";

const enc = encoding_for_model("gpt-4o");
const promptTokens = enc.encode(JSON.stringify(messages)).length;
const maxOutTokens = 1500;
const upperBound = promptTokens + maxOutTokens;

const r = await vevee.reserve(userId, "llm.tokens", upperBound, { model: "gpt-4o" });
if (!r.allowed) throw new LimitError();

4. Call the AI provider, then commit and refund

After the response, you know the actual token count. Commit the reservation, then refund the difference between upper-bound and actual.

try {
  const res = await openai.chat.completions.create({
    model: "gpt-4o",
    messages,
    max_tokens: maxOutTokens,
  });
  const actual =
    (res.usage?.prompt_tokens ?? 0) +
    (res.usage?.completion_tokens ?? 0);

  await vevee.commit(r.reservationId!);

  if (actual < upperBound) {
    await vevee.track(userId, "llm.tokens.refund", upperBound - actual, {
      reservationId: r.reservationId!,
    });
  }
  return res;
} catch (err) {
  await vevee.release(r.reservationId!);
  throw err;
}

5. Show the live balance to the user

Use a pk_live_ public key in the browser. vevee.usage(userId) returns the user's counters with remaining quota.

// In a React component
const usage = await vevee.usage(userId);
const tokens = usage.counters.find(c => c.label === "Tokens")!;
return <div>{tokens.remaining.toLocaleString()} tokens left this month</div>;

6. For pre-paid credits: bump the quota on purchase

When the user buys 100k more tokens, bump their custom limit. Vevee counters keep ticking.

await vevee.upsertSubscription({
  userId,
  planId: "plan_paygo",
  customLimits: {
    tokens: { quota: currentQuota + addedTokens },
  },
});

Streaming chat: same pattern

For streaming responses, reserve up front, stream the result, count tokens at the end (most providers send a final usage chunk), then commit + refund. The reservation holds quota for the entire stream so a parallel request cannot race past.

Multiple model tiers

GPT-4o-mini at $0.15/M input is much cheaper than GPT-4o at $2.50/M. If you charge users $/token, you should adjust the cost-per-token by model. Easiest pattern: track in cents (not tokens) and compute cents-per-call at track time using a model price table.

Stripe meter sync

For post-paid billing, push the user's monthly token total to a Stripe meter at period close. Vevee tracks; Stripe bills. The /guides/usage-based-pricing-ai guide covers this in detail.

Refund accuracy matters

Users notice when their balance does not match what they actually consumed. Always issue refund events for unused reservations - the absolute worst feedback is "I sent one short prompt and you charged me 4000 tokens." Auto-refunding the unused portion makes balances match user intuition.