DeepSeek R1, released January 20, 2025, matched OpenAI's o1 on reasoning benchmarks with fully open weights under an MIT license — and, unlike o1, exposed its complete chain of thought. Its training recipe was the real breakthrough: reasoning learned primarily through reinforcement learning on the V3 base, with the R1-Zero experiment showing reasoning could emerge from RL alone.

The release caused the single largest one-day market reaction in AI history, wiping hundreds of billions from US tech valuations as investors reassessed what frontier capability costs. Its distilled variants brought reasoning to consumer hardware, and the updated R1-0528 followed in May 2025.