Kimi K2 Thinking vs Step-3.5-Flash

Moonshot AI

Kimi K2 Thinking, released by Moonshot AI on November 6, 2025, is a reasoning-focused variant of Kimi K2 with 1 trillion total parameters and 32 billion active parameters, featuring extended chain-of-thought processing for complex problem solving. It builds on K2's agentic coding strengths with additional capabilities for mathematical and scientific reasoning. Kimi K2 Thinking targets open-source deployments requiring deep, deliberate reasoning across coding and analytical domains.

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.