Grok 4.1 Fast Reasoning

Grok 4.1 Fast Reasoning was released in November 2025 as xAI's high-throughput reasoning model, pairing extended chain-of-thought with the 2 million token context window and fast inference of the Grok 4.1 Fast line. It generates reasoning before responding, improving accuracy on math, code, and multi-step logic while keeping practical throughput. Compared to the non-reasoning variant, it trades some latency for higher accuracy on harder tasks, making it a fit for problem-solving applications that need both capability and long context. It supports vision, tool use, structured outputs, and function calling across multimodal inputs. Reasoning can be toggled through the API, so the same model line can serve fast direct replies or deeper deliberation depending on the request. It was trained with long-horizon reinforcement learning focused on multi-turn, tool-using scenarios.