DeepSeek-R1 vs Step-3.5-Flash

DeepSeek-R1

DeepSeek

DeepSeek-R1, released by DeepSeek on January 20, 2025, is a large reasoning model with 671 billion total parameters (37 billion active in its MoE architecture) designed for extended chain-of-thought reasoning. It features a 128K token context window and demonstrated strong performance on mathematics, coding, and scientific reasoning benchmarks at its release. DeepSeek-R1 targets complex analytical tasks, competitive programming, and applications requiring deep deliberative reasoning under an open MIT license.

StepFun

Step-3.5-Flash, released by StepFun on February 2, 2026, is a Mixture-of-Experts large language model with 197 billion total parameters and approximately 11 billion active parameters per inference. It features a 256K token context window using a 3:1 sliding-window-to-full-attention ratio, processing 100–350 tokens per second. Step-3.5-Flash targets agentic tasks, coding workflows, and open-source deployments requiring frontier reasoning capabilities with efficient inference, under an Apache 2.0 license.