--- title: StepFun: Step 3.5 Flash API | Text Generation | ModelsLab description: Open-source MoE LLM with 196B total/11B active params excels in reasoning, coding & agentic tasks; 256K context, 350 t/s speed, $0.1/$0.3 per 1M. url: https://modelslab-frontend-v2-927501783998.us-east4.run.app/models/stepfun/stepfun-step-3.5-flash/api.md canonical: https://modelslab-frontend-v2-927501783998.us-east4.run.app/models/stepfun/stepfun-step-3.5-flash/api.md type: product component: Playground/LLM/Index generated_at: 2026-05-13T09:42:14.958821Z --- StepFun: Step 3.5 Flash --- [LLMs.txt](https://modelslab-frontend-v2-927501783998.us-east4.run.app/models/open_router/stepfun-step-3.5-flash/llms.txt) [.md](https://modelslab-frontend-v2-927501783998.us-east4.run.app/models/stepfun/stepfun-step-3.5-flash.md) stepfun-step-3.5-flash stepfun Closed Source Model $0.200000 / call StepFun: Step 3.5 Flash --- Choose a prompt below to get started or type your own message Explain quantum computing in simple terms Write a Python function to sort a list Create a marketing email for a SaaS product Compare REST vs GraphQL APIs Send ### StepFun: Step 3.5 Flash stepfun stepfun-step-3.5-flash Copy model ID PricingInput $0.10 / 1M tokens Output $0.30 / 1M tokens API EndpointsOpenAI Compatible `https://modelslab.com/api/v7/llm/chat/completions`Endpoint Anthropic Compatible `https://modelslab.com/api/v7/llm/v1/messages`Messages `https://modelslab.com/api/v7/llm/v1/messages/count_tokens`Count Tokens `https://modelslab.com/api/v7/llm/v1/models`Models Use with Claude Code cURL Example ParametersSystem MessageYou are a helpful AI assistant specialized in providing accurate and detailed responses. 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Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token.... ### Technical Specifications Model IDstepfun-step-3.5-flashCategoryLLM ModelsTaskText GenerationPrice$0.200000 per million tokensAddedFebruary 20, 2026 ### Key Features - Chat completion and multi-turn conversation API - Streaming response with token-by-token output - Function calling and tool use support - System prompts and role-based messaging - JSON mode and structured output ### Quick Start Integrate StepFun: Step 3.5 Flash into your application with a single API call. Get your API key from the [pricing page](https://modelslab-frontend-v2-927501783998.us-east4.run.app/pricing) to get started. PythonJavaScriptcURLPHP ``` import requests import json url = "https://modelslab.com/api/v7/llm/chat/completions" headers = { "Content-Type": "application/json" } data = { "model_id": "stepfun-step-3.5-flash", "messages": [ { "role": "user", "content": "Hello!" } ], "max_tokens": 1000, "key": "YOUR_API_KEY" } try: response = requests.post(url, headers=headers, json=data) response.raise_for_status() # Raises an HTTPError for bad responses (4XX or 5XX) result = response.json() print("API Response:") print(json.dumps(result, indent=2)) except requests.exceptions.HTTPError as http_err: print(f"HTTP error occurred: {http_err} - {response.text}") except Exception as err: print(f"Other error occurred: {err}") ``` View the [full API documentation](https://modelslab-frontend-v2-927501783998.us-east4.run.app/models/stepfun/stepfun-step-3.5-flash/api) for SDKs, code examples in Python, JavaScript, and more. ### Pricing StepFun: Step 3.5 Flash API costs $0.200000 per million tokens. Pay only for what you use with no minimum commitments. [View pricing plans](https://modelslab-frontend-v2-927501783998.us-east4.run.app/pricing) ### Use Cases - AI chatbots and virtual assistants - Code generation and developer tools - Content writing and copywriting automation - Data analysis, summarization, and extraction [Learn more about StepFun: Step 3.5 Flash](https://modelslab-frontend-v2-927501783998.us-east4.run.app/stepfun-step-35-flash) [Browse LLM Models](https://modelslab-frontend-v2-927501783998.us-east4.run.app/models?feature=llmaster) [More from Stepfun](https://modelslab-frontend-v2-927501783998.us-east4.run.app/models/open_router) [View Pricing](https://modelslab-frontend-v2-927501783998.us-east4.run.app/pricing) StepFun: Step 3.5 Flash FAQ --- ### What is StepFun: Step 3.5 Flash? Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token.... ### How do I use the StepFun: Step 3.5 Flash API? You can integrate StepFun: Step 3.5 Flash into your application with a single API call. Sign up on ModelsLab to get your API key, then use the model ID "stepfun-step-3.5-flash" in your API requests. We provide SDKs for Python, JavaScript, and cURL examples in the API documentation. ### How much does StepFun: Step 3.5 Flash cost? StepFun: Step 3.5 Flash costs $0.200000 per million tokens. ModelsLab uses pay-per-use pricing with no minimum commitments. A free tier is available to get started. ### What is the StepFun: Step 3.5 Flash model ID? The model ID for StepFun: Step 3.5 Flash is "stepfun-step-3.5-flash". Use this ID in your API requests to specify this model. ### Does StepFun: Step 3.5 Flash have a free tier? Yes, ModelsLab offers a free tier that lets you try StepFun: Step 3.5 Flash and other AI models. Sign up to get free API credits and start building immediately. --- *This markdown version is optimized for AI agents and LLMs.* **Links:** - [Website](https://modelslab.com) - [API Documentation](https://docs.modelslab.com) - [Blog](https://modelslab.com/blog) --- *Generated by ModelsLab - 2026-05-13*