OpenAI o1 launched in late 2024 as OpenAI's first dedicated reasoning model — the one that popularized inference-time "thinking": spending extra compute to work through hard math, code, and logic before answering.
It worked, and it reshaped the whole field. By 2026 that idea is no longer a separate product line — reasoning is now built into every flagship model. The standalone "o-series" has effectively merged into the mainstream, so there is no current "o1" to sign up for, and no provider ships it as a standalone free API today.
If you came here for o1-style reasoning for free, use a current model instead. [GPT-5.5](/model/gpt-5-5) is OpenAI's latest flagship, with reasoning on by default — the best overall quality. [GPT-5.4](/model/gpt-5-4) is the prior flagship, still excellent and widely available on free tiers. For the same reasoning quality at a much lower price, [MiMo v2.5 Pro](/model/mimo-v2-5-pro) is a strong, cheaper alternative.
All three are listed here with their current free providers, quotas, and API keys — pick one and start building.