GPT-4o vs Step-3.5-Flash

GPT-4o

OpenAI

GPT-4o, released by OpenAI in May 2024, is a multimodal large language model from the GPT-4 family that natively processes text, image, and audio inputs in a single end-to-end model. It features a 128K token context window and demonstrated competitive performance across coding, reasoning, and vision benchmarks at its release. GPT-4o targets general-purpose assistant applications, vision-enabled workflows, and use cases requiring low-latency multimodal understanding.

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.