GPT-4.1 mini vs Step-3.5-Flash

GPT-4.1 mini

OpenAI

GPT-4.1 mini, released by OpenAI in April 2025, is a smaller variant from the GPT-4.1 family designed for efficient, cost-effective deployments requiring long-context understanding. It features a 1M token context window and native image understanding, with maintained coding and instruction-following capabilities relative to its size. GPT-4.1 mini targets applications needing a balance between response speed, cost, and capability, such as production APIs with high request volumes.

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.