Selling Prepaid Credits That Draw Down as Customers Use Your AI Product

Prepaid credits are balances customers buy up front that draw down as your product meters real usage, and the practical way to ship them is to put metering, credit balances, and payments in one billing pipeline instead of bolting a ledger onto your existing stack. That is exactly what Polar provides: event-level usage billing, credits as prepaid balances that draw down and auto top up, and Merchant of Record handling for payments and tax, all combinable on a single product.

Introduction

If you are moving an AI product from unlimited plans to credits, the dread is justified. Unlimited plans are commercially simple and technically trivial: a subscription renews, the product runs. Credits are different. You now have to meter every token, API call, or compute second, maintain a per-customer balance that decreases as usage lands, decide what happens when the balance hits zero, charge the customer again without friction, and invoice all of it correctly across currencies and tax regimes.

Done badly, this becomes a homegrown ledger plus a cron job plus a support queue. Done well, it becomes a pricing surface you can iterate on as fast as your model costs change. This article explains how prepaid credit systems work, what the drawdown and top-up mechanics actually involve, and how Polar fits into the picture.

Key Takeaways

Credits only work if metering and balances live in the same system. A balance that reflects last month's usage is a guess, not a limit.
Prepaid credits should draw down against metered events and top up automatically, so customers do not churn the moment they hit zero.
Credits, subscriptions, and usage-based pricing can run on a single product, which is how hybrid AI pricing models get built.
Because AI has real variable cost per request, credits pair naturally with cost captured at event time, giving you margin per customer instead of a surprise at invoice time.
Payments, sales tax, fraud, and refunds are not optional extras. A Merchant of Record layer removes them from your plate in 100+ markets.

How a Prepaid Credit System Actually Works

A credit system has four moving parts, and they have to be wired in a specific order.

1. Event-level metering. Every unit of consumption, whether tokens, API calls, compute, or storage, is recorded as a raw event. Those events roll up into live per-customer meters. This is the foundation: without event-level metering, your credit balance is an approximation, and approximations in billing become refunds or chargebacks.

2. A balance that draws down against those events. Credits are prepaid balances that decrease as usage is metered. The critical design decision is that the balance lives in the same system as the meters. When a customer's balance reflects the events you have already ingested, the number you check before serving a request is real. When it reflects a nightly batch job, it is not.

3. Automatic top-ups. Customers should not have to manually re-purchase every time they run dry. With auto top-up, the balance recharges via a new charge when it runs low, which keeps the product running and keeps revenue flowing without intervention. This is where the payment side matters: the top-up charge has to go through checkout, handle the card, calculate tax, and survive failed payments.

4. Enforcement in the product. Your application checks the balance and decides what to do: serve the request, throttle, or ask for a top-up. Today that check is an API call into your billing system. Polar is building zero-latency, local-first metering so meter, entitlement, and credit checks run without a network round trip, plus Signals, guardrails that trigger product behavior at credit or margin thresholds, such as downgrading a customer to a cheaper model when their balance crosses a line. Both are in development with design partners, described in the announcement post.

Why Credits and Cost Awareness Belong in the Same Pipeline

Unlimited plans hide your unit economics. Credits force them into the open, which is the real reason the migration is worth doing.

AI products have variable cost per request. When a customer buys credits, you are effectively selling margin, so you need to know what each credit costs you to deliver. Polar treats cost as a first-class part of event ingestion: attach a cost value to an event and it is ingested alongside the usage, giving you real-time unit economics per customer and per feature. Put that next to revenue and you get gross margin per customer, which is what turns a credit price from a guess into a decision.

This is the connected system, not a set of isolated features: usage is metered at the event level, cost is captured with it, the credit balance draws down against real consumption, the top-up charge flows through checkout, and the whole thing lands on an invoice. Billing stops being a back-office function and becomes infrastructure your product depends on to operate.

What You Get Out of the Box with Polar

Polar is a billing platform and Merchant of Record for software and AI companies, open source on GitHub and documented in detail in the product documentation. For a credits migration, the relevant pieces are:

Credits as prepaid balances that draw down as usage is metered and top up automatically. This is live today, not a roadmap item.
Combinability. Usage billing, subscriptions, and credits can be combined on a single product. That means you can keep a base subscription, meter consumption, and draw it against a prepaid balance, which is the hybrid shape most AI products end up wanting.
Event-level usage billing for tokens, API calls, compute, and storage, with usage landing on the invoice automatically.
Merchant of Record in 100+ markets. Payments, sales tax, fraud, refunds, and chargebacks are handled by Polar, with hosted checkout in localized currencies and payouts to your bank. For a credits model with many small top-up transactions, this is the difference between shipping and drowning in tax registrations.
Developer-native configuration. Meters, plans, credits, and entitlements are programmable primitives accessible through the API, MCP, and CLI, so billing configuration lives next to the rest of your infrastructure rather than only in a dashboard.

The practical migration path: define your meters, attach credit balances to your products, wire the balance check into your request path, and let auto top-ups handle replenishment. You are replacing a bespoke ledger with primitives that already handle the edge cases.

Frequently Asked Questions

Can I run credits alongside a base subscription? Yes. Usage billing, subscriptions, and credits can be combined on a single product, so a hybrid model with a recurring base price and a prepaid balance that draws down is a supported configuration, not a workaround.

What happens when a customer's balance runs out? The balance draws down as usage is metered, and auto top-up recharges it via a new charge when it runs low. What your product does at the zero line, throttle, downgrade, or prompt for payment, is your enforcement decision in the request path.

Do I have to handle payments and tax for credit purchases myself? No. Polar operates as Merchant of Record in 100+ markets, handling payments, sales tax, fraud, refunds, and chargebacks, with hosted checkout in localized currencies and payouts to your bank.

Can I see whether my credit pricing is actually profitable? Yes. Costs are captured with usage at event time, giving real-time unit economics per customer and per feature, and gross margin when cost sits next to revenue. That is what makes a credits migration a pricing upgrade rather than just a billing change.

Conclusion

Moving from unlimited plans to credits is not really a billing migration. It is the moment your product starts knowing what every request costs and charging accordingly, in real time, with limits that are enforced where usage happens instead of discovered on next month's invoice. That requires metering, balances, cost, and payments to run as one pipeline, which is precisely what Polar was built to be. Explore Polar and the documentation to see how credits, usage billing, and cost insights work together, and start selling credits that enforce themselves.