bash
pip install --upgrade "openai>=1.0"

python
from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://api.stepfun.ai/v1", 
or "https://openrouter.ai/api/v1"
    
Optional: OpenRouter headers for app rankings
    default_headers={
        "HTTP-Referer": "", 
        "X-Title": "",
    }
)

completion = client.chat.completions.create(
    model="step-3.5-flash", 
Use "stepfun/step-3.5-flash" for OpenRouter
    messages=[
        {
            "role": "system",
            "content": "You are an AI chat assistant provided by StepFun. You are good at Chinese, English, and many other languages.",
        },
        {
            "role": "user",
            "content": "Introduce StepFun's artificial intelligence capabilities."
        },
    ],
)

print(completion.choices[0].message.content)

bash
via Docker
docker pull vllm/vllm-openai:nightly

or via pip (nightly wheels)
pip install -U vllm --pre \
  --index-url https://pypi.org/simple \
  --extra-index-url https://wheels.vllm.ai/nightly

bash  
vllm serve  \
  --served-model-name step3p5-flash \
  --tensor-parallel-size 8 \
  --enable-expert-parallel \
  --disable-cascade-attn \
  --reasoning-parser step3p5 \
  --enable-auto-tool-choice \
  --tool-call-parser step3p5 \
  --hf-overrides '{"num_nextn_predict_layers": 1}' \
  --speculative_config '{"method": "step3p5_mtp", "num_speculative_tokens": 1}' \
  --trust-remote-code \
  --quantization fp8

bash
vllm serve  \
  --served-model-name step3p5-flash \
  --tensor-parallel-size 8 \
  --enable-expert-parallel \
  --disable-cascade-attn \
  --reasoning-parser step3p5 \
  --enable-auto-tool-choice \
  --tool-call-parser step3p5 \
  --hf-overrides '{"num_nextn_predict_layers": 1}' \
  --speculative_config '{"method": "step3p5_mtp", "num_speculative_tokens": 1}' \
  --trust-remote-code    

bash
via Docker
docker pull lmsysorg/sglang:dev-pr-18084
or from source (pip)
pip install "sglang[all] @ git+https://github.com/sgl-project/sglang.git"

bash
sglang serve --model-path  \
  --served-model-name step3p5-flash \
  --tp-size 8 \
  --tool-call-parser step3p5 \
  --reasoning-parser step3p5 \
  --speculative-algorithm EAGLE \
  --speculative-num-steps 3 \
  --speculative-eagle-topk 1 \
  --speculative-num-draft-tokens 4 \
  --enable-multi-layer-eagle \
  --host 0.0.0.0 \
  --port 8000

bash
sglang serve --model-path  \
  --served-model-name step3p5-flash \
  --tp-size 8 \
  --ep-size 8 \
  --tool-call-parser step3p5 \
  --reasoning-parser step3p5 \
  --speculative-algorithm EAGLE \
  --speculative-num-steps 3 \
  --speculative-eagle-topk 1 \
  --speculative-num-draft-tokens 4 \
  --enable-multi-layer-eagle \
  --host 0.0.0.0 \
  --port 8000

python
from transformers import AutoModelForCausalLM, AutoTokenizer

MODEL_PATH = ""

1. Setup
tokenizer = AutoTokenizer.from_pretrained(MODEL_PATH)
model = AutoModelForCausalLM.from_pretrained(
    MODEL_PATH,
    trust_remote_code=True,
    torch_dtype="auto",
    device_map="auto",
)

2. Prepare Input
messages = [{"role": "user", "content": "Explain the significance of the number 42."}]
inputs = tokenizer.apply_chat_template(
    messages,
    tokenize=True,
    add_generation_prompt=True,
    return_dict=True,
    return_tensors="pt",
).to(model.device)

3. Generate
generated_ids = model.generate(**inputs, max_new_tokens=128, do_sample=False)
output_text = tokenizer.decode(generated_ids[0][inputs.input_ids.shape[1]:], skip_special_tokens=True)

print(output_text)

bash
git clone https://github.com/ggml-org/llama.cpp
cd llama.cpp

bash
cmake -S . -B build-macos \
  -DCMAKE_BUILD_TYPE=Release \
  -DGGML_METAL=ON \
  -DGGML_ACCELERATE=ON \
  -DLLAMA_BUILD_EXAMPLES=ON \
  -DLLAMA_BUILD_COMMON=ON \
  -DGGML_LTO=ON
cmake --build build-macos -j8

bash
cmake -S . -B build-cuda \
  -DCMAKE_BUILD_TYPE=Release \
  -DGGML_CUDA=ON \
  -DGGML_CUDA_GRAPHS=ON \
  -DLLAMA_CURL=OFF \
  -DLLAMA_BUILD_EXAMPLES=ON \
  -DLLAMA_BUILD_COMMON=ON
cmake --build build-cuda -j8

bash
cmake -S . -B build-vulkan \
  -DCMAKE_BUILD_TYPE=Release \
  -DLLAMA_CURL=OFF \
  -DGGML_OPENMP=ON \
  -DGGML_VULKAN=ON
cmake --build build-vulkan -j8

bash
./llama-cli -m step3.5_flash_Q4_K_S.gguf -c 16384 -b 2048 -ub 2048 -fa on --temp 1.0 -p "What's your name?"

bash
./llama-batched-bench -m step3.5_flash_Q4_K_S.gguf -c 32768 -b 2048 -ub 2048 -npp 0,2048,8192,16384,32768 -ntg 128 -npl 1

bash
Install nvm on Mac/Linux via curl：
Step 1
curl -o
https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.0/install.sh | bash


Copy the full command
export NVM_DIR="$HOME/.nvm"
[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"  
This loads nvm
[ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion"

Users in China can set up npm mirror
config set registry https://registry.npmmirror.com

Step 2
nvm install v22

Make sure Node.js is installed
node --version

npm --version

bash
install claude code via npm
npm install -g @anthropic-ai/claude-code

test if the installation is successful
claude --version 

json
  {
  "env": {
    "ANTHROPIC_API_KEY": "API_KEY_from_StepFun",
    "ANTHROPIC_BASE_URL": "https://api.stepfun.ai/"
  },
  "model": "step-3.5-flash"
  }
  

txt
  ❯ /status
  ─────────────────────────────────────────────────────────────────────────────────
  Settings:  Status   Config   Usage  (←/→ or tab to cycle)

  Version: 2.1.1
  Session name: /rename to add a name
  Session ID: 676dae61-259d-4eef-8c2f-0f1641600553
  cwd: /Users/step-test/
  Auth token: none
  API key: ANTHROPIC_API_KEY
  Anthropic base URL: https://api.stepfun.ai/

  Model: step-3.5-flash
  Setting sources: User settings
  

bash
  
install ccr via npm
  npm install -g @musistudio/claude-code-router

  
validate it is installed
  ccr -v
  

json
  {
  "PORT": 3456,
  "Providers": [
    {
      "name": "stepfun-api",
      "api_base_url": "https://api.stepfun.com/v1/chat/completions",
      "api_key": "StepFun_API_KEY",
      "models": ["step-3.5-flash"],
      "transformer":{
           "step-3.5-flash": { "use": ["OpenAI"]}
      }
    }
  ],
  "Router": {
    "default": "stepfun-api,step-3.5-flash",
    "background": "stepfun-api,step-3.5-flash",
    "think": "stepfun-api,step-3.5-flash",
    "longContext": "stepfun-api,step-3.5-flash",
    "webSearch": "stepfun-api,step-3.5-flash"
  }
  }
  

bash
  
Start Claude
  ccr code 

  
restart ccr if configs are changed
  ccr restart 
  

bash
Install codex via npm
npm install -g @openai/codex

Test if it is installed
codex --version

json
model="step-3.5-flash"
model_provider = "stepfun-chat"
preferred_auth_method = "apikey"

configure the provider
[model_providers.stepfun-chat]
name = "OpenAI using response"
base_url = "https://api.stepfun.com/v1"
env_key = "OPENAI_API_KEY"
wire_api = "chat"
query_params = {}

bash
/status
📂 Workspace
  • Path: /Users/step-test/
  • Approval Mode: on-request
  • Sandbox: workspace-write
  • AGENTS files: (none)

🧠 Model
  • Name: step-3.5-flash
  • Provider: Stepfun-chat

💻 Client
  • CLI Version: 0.40.0

tex
@misc{huang2026step35flashopen,
      title={Step 3.5 Flash: Open Frontier-Level Intelligence with 11B Active Parameters}, 
      author={Ailin Huang and Ang Li and Aobo Kong and Bin Wang and Binxing Jiao and Bo Dong and Bojun Wang and Boyu Chen and Brian Li and Buyun Ma and Chang Su and Changxin Miao and Changyi Wan and Chao Lou and Chen Hu and Chen Xu and Chenfeng Yu and Chengting Feng and Chengyuan Yao and Chunrui Han and Dan Ma and Dapeng Shi and Daxin Jiang and Dehua Ma and Deshan Sun and Di Qi and Enle Liu and Fajie Zhang and Fanqi Wan and Guanzhe Huang and Gulin Yan and Guoliang Cao and Guopeng Li and Han Cheng and Hangyu Guo and Hanshan Zhang and Hao Nie and Haonan Jia and Haoran Lv and Hebin Zhou and Hekun Lv and Heng Wang and Heung-Yeung Shum and Hongbo Huang and Hongbo Peng and Hongyu Zhou and Hongyuan Wang and Houyong Chen and Huangxi Zhu and Huimin Wu and Huiyong Guo and Jia Wang and Jian Zhou and Jianjian Sun and Jiaoren Wu and Jiaran Zhang and Jiashu Lv and Jiashuo Liu and Jiayi Fu and Jiayu Liu and Jie Cheng and Jie Luo and Jie Yang and Jie Zhou and Jieyi Hou and Jing Bai and Jingcheng Hu and Jingjing Xie and Jingwei Wu and Jingyang Zhang and Jishi Zhou and Junfeng Liu and Junzhe Lin and Ka Man Lo and Kai Liang and Kaibo Liu and Kaijun Tan and Kaiwen Yan and Kaixiang Li and Kang An and Kangheng Lin and Lei Yang and Liang Lv and Liang Zhao and Liangyu Chen and Lieyu Shi and Liguo Tan and Lin Lin and Lina Chen and Luck Ma and Mengqiang Ren and Michael Li and Ming Li and Mingliang Li and Mingming Zhang and Mingrui Chen and Mitt Huang and Na Wang and Peng Liu and Qi Han and Qian Zhao and Qinglin He and Qinxin Du and Qiuping Wu and Quan Sun and Rongqiu Yang and Ruihang Miao and Ruixin Han and Ruosi Wan and Ruyan Guo and Shan Wang and Shaoliang Pang and Shaowen Yang and Shengjie Fan and Shijie Shang and Shiliang Yang and Shiwei Li and Shuangshuang Tian and Siqi Liu and Siye Wu and Siyu Chen and Song Yuan and Tiancheng Cao and Tianchi Yue and Tianhao Cheng and Tianning Li and Tingdan Luo and Wang You and Wei Ji and Wei Yuan and Wei Zhang and Weibo Wu and Weihao Xie and Wen Sun and Wenjin Deng and Wenzhen Zheng and Wuxun Xie and Xiangfeng Wang and Xiangwen Kong and Xiangyu Liu and Xiangyu Zhang and Xiaobo Yang and Xiaojia Liu and Xiaolan Yuan and Xiaoran Jiao and Xiaoxiao Ren and Xiaoyun Zhang and Xin Li and Xin Liu and Xin Wu and Xing Chen and Xingping Yang and Xinran Wang and Xu Zhao and Xuan He and Xuanti Feng and Xuedan Cai and Xuqiang Zhou and Yanbo Yu and Yang Li and Yang Xu and Yanlin Lai and Yanming Xu and Yaoyu Wang and Yeqing Shen and Yibo Zhu and Yichen Lv and Yicheng Cao and Yifeng Gong and Yijing Yang and Yikun Yang and Yin Zhao and Yingxiu Zhao and Yinmin Zhang and Yitong Zhang and Yixuan Zhang and Yiyang Chen and Yongchi Zhao and Yongshen Long and Yongyao Wang and Yousong Guan and Yu Zhou and Yuang Peng and Yuanhao Ding and Yuantao Fan and Yuanzhen Yang and Yuchu Luo and Yudi Zhao and Yue Peng and Yueqiang Lin and Yufan Lu and Yuling Zhao and Yunzhou Ju and Yurong Zhang and Yusheng Li and Yuxiang Yang and Yuyang Chen and Yuzhu Cai and Zejia Weng and Zetao Hong and Zexi Li and Zhe Xie and Zheng Ge and Zheng Gong and Zheng Zeng and Zhenyi Lu and Zhewei Huang and Zhichao Chang and Zhiguo Huang and Zhiheng Hu and Zidong Yang and Zili Wang and Ziqi Ren and Zixin Zhang and Zixuan Wang},
      year={2026},
      eprint={2602.10604},
      archivePrefix={arXiv},
      primaryClass={cs.CL},
      url={https://arxiv.org/abs/2602.10604}, 
}