GPT-5.5 Pro vs GPT-5.4 Pro

Two premium models from consecutive generations that cost exactly the same at Standard on input and output — so the differences live where the price tag doesn't point.

Where they diverge

Knowledge cutoff is the clean one: GPT-5.5 Pro's training data is newer. Rate limits are the consequential one. On the Build, Launch and Grow ladder the two allow the same requests per minute at Build and Launch, and GPT-5.5 Pro allows more at Grow. GPT-5.5 Pro has the larger token ceilings at Build and Launch, the two match at Grow, and GPT-5.4 Pro keeps the larger batch queue at every tier. GPT-5.4 Pro also publishes a separate long-context table for prompts over 272,000 input tokens, with far fewer requests per minute; GPT-5.5 Pro's page has none. Compare the row for the tier your account is actually on.

Defaults differ, levels don't

Both accept medium, high and xhigh reasoning effort and nothing else. The default differs: high on GPT-5.5 Pro, medium on GPT-5.4 Pro. An unspecified request therefore reasons more, and costs more in reasoning tokens, on the newer model.

What stays the same

Neither offers Fast mode or a cached-input price. GPT-5.4 Pro states the long-context rule and publishes long bands for Standard, Batch and Flex; GPT-5.5 Pro's page doesn't state the rule, and its pricing row carries a long band for Standard only. Both can take minutes per request.

How to decide

With price tied and request rates identical at the two lower tiers, this comes down to recency against the rate-limit row for your tier and prompt size. Run your request shape through the tier planner against both. And for Pro-style extra model work on a current model, reasoning.mode: "pro" on GPT-5.6 and GPT-6 bills at that model's standard rates — usually far less per token than either of these.