LibreAI / Local LLM / Step-3.5-Flash
// local-llm · stepfun-ai/Step-3.5-Flash

Step-3.5-Flash

StepFun's open 196B MoE model that activates 11B parameters per token, built for fast agentic reasoning.

★ 2.1k stars⑂ 87 forksApache-2.0updated 2026-04
▦ visual — this project's README ships no embeddable screenshot,
so here's a placeholder. The guide below is complete regardless.
// project facts

Project facts

Step-3.5-Flash is an open-source local llm project by stepfun-ai (stepfun-ai/Step-3.5-Flash on GitHub). It has 2,083 GitHub stars and 87 forks, is released under the Apache-2.0 license, and was last updated on GitHub on 3 April 2026.

GitHub stars
2,083
Forks
87
License
Apache-2.0
Last updated on GitHub
3 April 2026
Category
Local LLM
Listing
Full install guide
Official site
Official site
// how it works

How it works

  1. Clarify your goal

    Decide how you will access the model: hosted API (OpenRouter or StepFun), or local deployment on high-end hardware.

  2. Get the project

    For local use, clone the repository to get its deployment patches, Dockerfiles, and guides.

  3. Install and configure

    Install a supported inference backend such as vLLM (nightly or the patched 0.15.1 build) or SGLang, and download the weights from Hugging Face or ModelScope.

  4. Run your first task

    Launch the server with the documented Step 3.5 parsers and expert-parallel settings, then call its OpenAI-compatible endpoint from your agent or app.

// features

Why people love it

Sparse MoE efficiency

288 routed experts per layer with top-8 selection give the knowledge of a 196B model at roughly 11B active parameters per token.

Multi-token prediction

The MTP-3 head predicts multiple tokens per forward pass, which the project credits for its high generation throughput in typical and coding workloads.

256K context with hybrid attention

A 3:1 mix of sliding-window and full-attention layers keeps long-context cost down across large codebases and datasets.

Agentic and coding focus

Tuned and evaluated for long-horizon agent tasks and software engineering, with published results on benchmarks such as SWE-bench Verified and Terminal-Bench 2.0 in the README.

Multiple deployment paths

Documented serving with vLLM, SGLang, Transformers for verification, and llama.cpp, plus fp8 and bf16 variants.

Hosted and agent-platform access

Available through OpenRouter (including a free tier model id) and StepFun's API, with integration guides for OpenClaw, Claude Code, and Roo Code.

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// run it

Run it yourself

  1. Clone the repository

    The repo holds deployment patches, Dockerfiles, and cookbooks; weights come from Hugging Face or ModelScope.

    git clone https://github.com/stepfun-ai/Step-3.5-Flash.git
    cd Step-3.5-Flash
  2. Install an inference backend

    The README recommends the vLLM nightly build, or the patched 0.15.1 image for full parser support.

    pip install -U vllm --pre --index-url https://pypi.org/simple --extra-index-url https://wheels.vllm.ai/nightly
  3. Serve the model

    Launch vLLM with the Step 3.5 reasoning and tool-call parsers and expert parallelism.

    vllm serve --served-model-name step3p5-flash --tensor-parallel-size 8 --enable-expert-parallel --reasoning-parser step3p5 --tool-call-parser step3p5 --trust-remote-code # add the model path/checkpoint per the README
// use cases

What you can build

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// faq

Questions, answered

Who maintains it?

It is developed and released by StepFun, the company behind the Step model series.

Is it free to use?

The model is Apache-2.0 licensed and the weights are openly downloadable. Hosted access has free and paid tiers via OpenRouter and StepFun; local serving costs your own hardware.

Does it need a paid API key?

Only for hosted access: OpenRouter or StepFun API keys are needed there. Local deployment with vLLM or SGLang needs no API key.

How does it compare to a well-known alternative?

Dense models activate every parameter per token; Step-3.5-Flash activates about 11B of 196B, trading total size for much lower decoding cost at comparable reported capability.

How do I get started?

For a quick trial, use the OpenRouter model id stepfun/step-3.5-flash:free with the openai Python SDK; for local use, follow the repo's vLLM deployment section.

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// alternatives

Alternatives in Local LLM

The most-starred other Local LLM projects in the LibreAI catalogue — the realistic shortlist if Step-3.5-Flash is not the right fit.

Get Step-3.5-Flash

Free and open — grab the source, star the repo, and start creating.