API for pricing hypothetical usage using OpenMeter’s pricing engine

[vinh412]

We’re designing an AI platform using OpenMeter API v3, with a custom currency called credit. We want OpenMeter to be the source of truth for pricing, subscriptions, and credit accounting.

To enforce strict spending limits, our backend needs to:

1. Estimate usage before an AI request, including a maximum output token count.
2. Calculate its cost using the customer’s applicable pricing configuration.
3. Atomically reserve that amount in our quota service.
4. Settle the reservation against actual usage after completion.

The missing piece for us is a way to calculate the cost of hypothetical usage using OpenMeter’s existing pricing engine, without ingesting events or creating charges/invoices.

Conceptually, the API would accept:

• Estimated usage quantities for the relevant features.
• A reference to the applicable subscription item or an exact pricing revision.
• Any additional context required for tiered pricing or discounts.

It would return the calculated cost in the configured currency, ideally with a breakdown and the pricing revision used.

Is there an existing or planned v3 API for this? Alternatively, is there a supported way to reuse the pricing engine as a library?

We can handle reservation and concurrency ourselves. Our goal is to avoid duplicating OpenMeter’s rating logic in our backend and risking discrepancies between quota enforcement and billing.