OpenAI answers DeepSeek with o3-mini — and the first model rated Medium on autonomy
OpenAI released o3-mini in ChatGPT and the API, its cheapest reasoning model so far and the first small reasoning model with function calling, Structured Outputs and developer messages built in — the pieces agent builders actually wire together.
Three reasoning-effort levels let callers trade latency for depth. OpenAI says it produced math and factuality answers about 24% faster than o1-mini with 39% fewer major mistakes, tripled the Plus and Team limit from 50 to 150 messages per day, and put a reasoning model in front of free-plan users for the first time. There is no vision support. The accompanying system card rates CBRN, Persuasion and Model Autonomy Medium and Cybersecurity Low.

WHY IT MATTERS
The contrast is the story: six days after a free, openly downloadable Chinese reasoner broke the assumption that frontier quality requires frontier spend, OpenAI's counter was cheaper closed reasoning plus a safety scorecard that admits a real autonomy shift. For anyone building harnesses, the function calling, structured outputs and reasoning-effort surface matters more than the benchmark table — it makes a reasoning model usable as a tool-calling component rather than a chatbot.