How Redis Sliding Windows and Token Quotas Protect LLM API Spending

Rate limiting LLM APIs differs fundamentally from conventional APIs because a single model call carries real monetary cost, and agent loops can fire hundreds of requests autonomously. Developers must track both request counts and token usage separately, enforcing whichever limit binds first, since a one-line prompt and a 200-page document summarisation both count as one request but differ vastly in cost. Tenant identifiers used in rate-limit keys must be sourced from authenticated sessions, never from the request body, to prevent callers from manipulating or exhausting other tenants' quotas. Fixed time windows expose a known boundary exploit where a full quota can be consumed twice in rapid succession, making Redis sorted-set sliding windows a more reliable alternative when executed atomically via Lua scripts. Because actual token costs are only known after a model responds, the recommended approach is to reserve an estimated token count before the call and reconcile the difference once the response returns.