ADR 0011: Store money as integer micro-USD

• Status: Accepted
• Date: 2026-10-24
• Supersedes: none

Context

Floating-point numbers cannot show most decimal amounts exactly. Sums of many small costs drift. Budget checks must be exact and safe.

Decision

Store amounts as int64 micro-USD (1 USD = 1,000,000 micro-USD). Store prices as int64 micro-USD for each million tokens. Round the cost of each request up to the next micro-USD.

Alternatives

1. float64 USD. This drifts and gives different results in different orders.
2. A decimal library. This is exact, but it adds a dependency and is slower.

Consequences

• An int64 holds more than 9 trillion USD in micro-USD, which is sufficient.
• Rounding up can add at most 1 micro-USD to each request. This keeps budget checks on the safe side.