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GPT-5.1 Codex vs Step-3.5-Flash
Comprehensive side-by-side LLM comparison
Both models show comparable benchmark performance. Both models have their strengths depending on your specific coding needs.
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OpenAI
GPT-5.1 Codex, released by OpenAI in November 2025, is a coding-specialized model from the GPT-5.1 family engineered for software engineering tasks including code generation, multi-file editing, and agentic development. It targets developers and automated coding pipelines requiring a GPT-5.1-generation model tuned for programming.
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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 Codex
OpenAI
2025-11
Step-3.5-Flash
StepFun
2026-02-02
Average performance across 1 common benchmarks
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GPT-5.1 Codex
Average Score:73.7%
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Step-3.5-Flash
Average Score:74.4%(+0.7%)
Performance comparison across key benchmark categories
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GPT-5.1 Codex
Coding73.7%
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Step-3.5-Flash
Coding74.4%(+0.7%)
Provider Availability & Performance
Available providers and their performance metrics
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GPT-5.1 Codex
0 providers
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Step-3.5-Flash
0 providers
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GPT-5.1 Codex
Avg Score:73.7%
Providers:0
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Step-3.5-Flash
Avg Score:74.4%(+0.7%)
Providers:0