In the past year, both Codex and Sora have seen rapid adoption, with usage quickly pushing beyond what we originally expected. We’ve seen a consistent pattern: users dive in, find real value, and then run into rate limits.

Rate limits can help smooth demand and ensure fair access; however, when users are getting value, hitting a hard stop can be frustrating. We wanted a way for users to keep going, while protecting system performance and user trust in our approach.

To solve this, we built a real‑time access engine that counts usage. One of the layers in that engine is the ability to purchase credits. When users exceed their rate limits, credits let them keep using our products by spending down their credit balance.

Underneath this is a complex system that fuses limits, real‑time usage tracking, and credit balances in a single access model. This post covers why scaling Codex and Sora required rethinking access control, how a provably correct, real-time system blends rate limits and credits per request, and how that foundation now unlocks additional access for both products.

Rate limits can be helpful at first, but leave users with a bad experience when they run out: “come back later”

Usage‑based billing is flexible, but leaves users paying from the first token—not ideal for supporting early exploration

For Codex and Sora, neither was sufficient on its own. If we simply raised rate limits, we’d lose important demand-smoothing and fairness controls and run out of capacity to serve everyone. If we relied entirely on asynchronous usage billing, we’d introduce lag, overages, or reconciliation issues—exactly the kinds of problems users notice when they’re most engaged.

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