Charge each model call's cost to the customer who caused it

How to do it

Price every call and cap the spend computes each call's cost. This rule links that cost to a bill. Pass the customer ID and the usage event key down to the model gateway, and write both on the cost row. Count retries, failed calls and background work too, since you pay for them. Work that serves no single customer, such as a nightly index, goes to a shared cost line. Then cost per customer is one query, as in Track cost per request.

Examples

TypeScript example

export async function callModel(input: ModelInput, ctx: { customerId: string; usageEventKey: string }) {
  const response = await gateway.generate(input)
  await costs.insert({
    customerId: ctx.customerId,
    usageEventKey: ctx.usageEventKey,
    model: response.model,
    costMicroUsd: callCostMicroUsd(response.model, response.usage),
  })
  return response
}

Python example

def call_model(model_input, customer_id: str, usage_event_key: str):
    response = gateway.generate(model_input)
    costs.insert(
        customer_id=customer_id,
        usage_event_key=usage_event_key,
        model=response.model,
        cost_micro_usd=call_cost_micro_usd(response.model, response.usage),
    )
    return response

How to check

A query over last month's cost rows finds none without a customer ID or a shared cost label. A test makes a call that fails and is retried once, and both attempts appear under the same usage event key.

Related rules

• AIF-42 Price every call and cap the spend in AI features
• SCL-33 Track cost per request in Scaling
• USG-12 Keep every metered price above its cost in Usage-based billing