hardOpenAI

Build a system to manage GPU credits across companies with wildly different usage patterns

A reported OpenAI build that looks like billing and is actually a data-structure question in disguise: credit grants that expire, usage that must burn the right grant first, and balance queries at arbitrary times. The earliest-expiry-first invariant carries the whole problem.

Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.

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