I had wondered if they run their inference at high batch sizes to get better throughput to keep their inference costs lower.

They do have a priority tier at double the cost, but haven't seen any benchmarks on how much faster that actually is.

The flex tier was an underrated feature in GPT5, batch pricing with a regular API call. GPT5.1 using flex priority is an amazing price/intelligence tradeoff for non-latency sensitive applications, without needing to extra plumbing of most batch APIs