Step 3.5 Flash
Step 3.5 Flash is worth evaluating for coding, agents, and long context when its provider route and context window match the workload.
Use it for
- Teams evaluating coding, agents, and long context
- Workloads that can use a 256k context window
- Buyers comparing 1 tracked provider route
Do not use it for
- Vision or document-understanding workloads
- Strict JSON or tool-calling flows
- Family
- Step
- Released
- 2026-01-29
- Context
- 256k
- Parameters
- 196B (11B active)
- Architecture
- Mixture of Experts
- Specialization
- general
- Openness
- Proprietary
- License
- ProprietaryCommercial use: conditional
- Weights
- Not released
- Code
- Unknown
- Training
- Pretrained
Cheapest of 1 route · OpenRouter
About
Step 3.5 Flash is StepFun's most capable open-source foundation model. Its sparse Mixture of Experts architecture activates only 11B of 196B total parameters per token, making it highly efficient at long contexts. Achieves 60.47% on SWE-Bench Verified and 56.2% on SWE-Pro, competing with frontier closed models on agentic coding benchmarks. Supports 256K token context.
Step 3.5 Flash is a proprietary model in the Step family. The structured metadata tracks a 256k-token context window and reasoning. This page tracks provider routes through OpenRouter, with the cheapest tracked route listed at $0.1 input and $0.3 output per 1M tokens. Headline tracked benchmarks include AIME 2025 97.3, LiveCodeBench 86.4, and SWE-bench Verified 74.4.
Top use-case fit: coding, agents, and build tasks
Coding
Q/$ B2 relevant benchmarks in the decision map.
Agents
Q/$ A1 relevant benchmark in the decision map.
Long context
Included by capability and metadata signals in the decision map.
Provider price ladder
Compare API pricing across 1 providers for input and output tokens, batch, and cached reads when available.
| Provider | Input / 1M | Output / 1M | Route |
|---|---|---|---|
| OpenRouter | $0.100 | $0.300 | Serverless |
Capabilities
Benchmark peer barsfor Coding
Benchmark scores(3)
| Benchmark | Score | Version | Evaluation | Source |
|---|---|---|---|---|
| AIME 2025 | 97.3 | From official StepFun blog post (accuracy%)Observed 2026-06-07 | — | Source |
| LiveCodeBench | 86.4 | LiveCodeBench-V6 (accuracy%)Observed 2026-06-07 | — | Source |
| SWE-bench Verified | 74.4 | From official StepFun blog post (resolved%)Observed 2026-06-07 | — | Source |
Migration checks
No linked migration route is available for this model yet.
Rankings & picks(1)
Compare Step 3.5 Flash with other models
Comparison and alternatives
Browse all comparisons →Show all 2 popular comparisonssorted by 7-day search impressions
Frequently asked questions
What is the context window of Step 3.5 Flash?
Step 3.5 Flash has a context window of 256k tokens.
How much does Step 3.5 Flash cost?
Step 3.5 Flash is available at $0.1/1M input tokens through OpenRouter.
When was Step 3.5 Flash released?
Step 3.5 Flash was released on 2026-01-29.
Which providers offer Step 3.5 Flash?
Step 3.5 Flash is available from 1 provider: OpenRouter.
What benchmarks has Step 3.5 Flash been tested on?
Step 3.5 Flash has been evaluated on 3 benchmarks, including AIME 2025, LiveCodeBench, SWE-bench Verified.
Cheapest of 1 route · OpenRouter