Comprehensive side-by-side LLM comparison
GPT-5.1 Thinking leads with 1.9% higher average benchmark score. GPT-5.1 Thinking supports multimodal inputs. Both models have their strengths depending on your specific coding needs.
OpenAI
GPT-5.1 Thinking, released by OpenAI in November 2025, is an extended reasoning variant from the GPT-5.1 family that applies chain-of-thought processing to improve accuracy on complex reasoning, mathematics, and coding tasks. It targets analytical workflows where deliberate reasoning over a problem significantly improves output quality.
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.
3 months newer

GPT-5.1 Thinking
OpenAI
2025-11
Step-3.5-Flash
StepFun
2026-02-02
Average performance across 1 common benchmarks
GPT-5.1 Thinking
Step-3.5-Flash
Performance comparison across key benchmark categories
GPT-5.1 Thinking
Step-3.5-Flash
Available providers and their performance metrics
GPT-5.1 Thinking
Step-3.5-Flash
GPT-5.1 Thinking
Step-3.5-Flash