Grok 4.1 Fast (Reasoning) is one of two configurations in the Grok 4.1 Fast family released by xAI in November 2025, sitting alongside a non-reasoning sibling. It is positioned as a speed- and cost-oriented model that still supports explicit chain-of-thought reasoning, with Artificial Analysis reporting text-and-image inputs, text output, and a two-million-token context window. Within the family, Artificial Analysis's Intelligence Index v4.3.2 ranks the reasoning variant meaningfully above its non-reasoning counterpart, reflecting the boost that the reasoning mode brings to tasks requiring multi-step planning or tool use.
On independent benchmarks, the reasoning variant reaches an Artificial Analysis Intelligence Index of 20, ahead of the non-reasoning sibling's 11, and tracks competitively on coding-oriented work: third-party catalog BenchLM gives it a capability score of 54.82 out of 100, a 92-of-230 overall rank, and a coding sub-rank of 89, suggesting a practical fit for software engineering and agentic coding workloads where it can trade extra tokens for more reliable problem solving. The model's combination of a very large context window and image input also makes it usable for long-document analysis and visually grounded tasks, while the reasoning mode adds latency and token usage that callers need to plan for in production.
