Step-3.5-Flash

Architectural Overview & Capability Profile

Step-3.5-Flash is developed by StepFun as an advanced foundation model engineered for production enterprise applications, reasoning workflows, and autonomous problem-solving. On the comprehensive RankLLMs composite evaluation index, Step-3.5-Flash registers an overall benchmark rating of 37.3 / 100.

Operating under a Open Weights license structure, Step-3.5-Flash is distributed as an open-weights architecture capable of local deployment, private VPC inference, and custom fine-tuning.

Benchmark Performance & Real-World Utility

In standardized laboratory and real-world evaluation suites, Step-3.5-Flash demonstrates calibrated proficiency across key performance vectors:

• SWE-bench Verified Software Engineering (20.8%): Measures multi-file GitHub issue resolution. The model demonstrates practical capability in localizing source code bugs, synthesizing functional patches, and passing rigorous integration test matrices. For evaluation methodology, consult our SWE-bench Pro guide.

• GPQA Diamond Scientific Reasoning (37.3%): Assesses graduate-level domain problem solving across physics, chemistry, and biology, minimizing hallucinations in multi-step deductive arguments. See our Humanity’s Last Exam benchmark analysis.

• MATH-500 Competition Mathematics (37.3%): Evaluates formal mathematical problem solving and symbolic derivation, providing foundational logic for algorithmic computing.

• Terminal-Bench Execution (20.8%): Reflects proficiency in interactive command-line environments, shell tool use, and automated DevOps scripting.

• Code Arena Preference Rating (762 Elo): Validates human developer satisfaction in blind side-by-side coding evaluations against contemporary alternatives.

Inference Latency & Cost Architecture

• Token Context Window: 256K tokens, allowing large documents, multi-file codebases, and long conversation memories to be processed in a single context window.
• Inference Speed: Reference throughput clocks at approximately 84 tokens/second, enabling responsive streaming in developer tools and interactive interfaces.
• Commercial Pricing: Zero per-token inference fee when self-hosted on owned GPU infrastructure (e.g. vLLM or Ollama), with marginal costs limited strictly to hardware compute.

Strengths, Limitations & Ideal Workflows

Primary Strengths

• High overall benchmark score of 37.3 on frontier evaluation suites
• Robust reasoning performance (37.3) and coding accuracy (20.8)
• Generation throughput of 218c/s with 66K token context

Known Considerations

• Subject to standard provider rate limits and API quota

Recommended Use Cases

Enterprise production applications, coding assistance, and advanced reasoning.

Related Comparisons & Leaderboard Context

• Compare with alternatives in the Model Comparison Engine
• Compare global rankings on the AI Model Leaderboard
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• Explore top coding models in our Best LLM for Coding Guide