OpenAI Ultrafast: Pay 6x Only When Latency Matters

OpenAI's DevDay on September 29 shipped a lot: Dots, the Agents API, GPT-6.1 Sol, a Decisions API in limited preview. The line item most developers will feel in their bill is smaller and easier to miss. Ultrafast is a new service tier, requested with service_tier="ultrafast", that OpenAI says generates up to 300 tokens per second, up to 6x faster than standard in the API. It costs 6x the standard rate.

That trade is only good in some places. A chat reply a user is staring at is worth it. A nightly summarization job is not. This guide builds a small Python router that picks the cheapest tier that still meets a latency budget, falls back gracefully when your account is not entitled to Ultrafast, learns your real tokens-per-second as it runs, and bills each call at the tier that actually served it.