# Step 5 Preview Step 5 Preview is StepFun's flagship model for agentic work, aimed at software engineering and professional knowledge work with particular strength in finance. It takes text and image input over a context of about one million tokens, reasons at a selectable effort level before answering, and supports tool calling and structured output. Its published context window is 1,024,000 tokens. The advertised input rate is $1.00 per million input tokens. The advertised output rate is $2.70 per million output tokens. - Model identifier: ` stepfun/step-5-preview ` - Creator: StepFun - Providers: StepFun - Model type: Text generation - Canonical model page: [Step 5 Preview]() - API availability: Listed as serving through Impossibl. - Creator release date: 2026-09-20 ## Providers StepFun hosts Step 5 Preview. Impossibl routes your request intelligently and handles failover automatically when a provider is down. | Provider | Endpoint location | Routes | Verified context window | Tool calling | | --- | --- | --- | --- | --- | | StepFun | Not specified | 1 | Not verified | Not verified | The model price applies whichever provider serves the request. Endpoint locations do not guarantee inference residency. ## Specs and Capabilities - Context window: 1,024,000 tokens - Maximum output tokens: Not published in the public catalog; this is separate from the context window. - Inputs: text, image - Outputs: text - Tool calling: Not published ## API access Use ` stepfun/step-5-preview ` as the model identifier through the Impossibl API. Published API endpoints: - ` /v1/chat/completions ` [API quickstart]() · [Models and billing documentation]() ## Published API prices All rates are in USD. An unpublished rate is unknown, not zero. Workspace-specific pricing, taxes, balance-purchase fees, billing adjustments, and tool charges can affect the amount paid. | Usage | Published base rate | Billing unit | | --- | --- | --- | | Input | $1.00 | per million input tokens | | Output | $2.70 | per million output tokens | | Cache read | $0.05 | per million cached input tokens | | Cache write (default retention) | Not published | per million tokens | | Cache write (one-hour retention) | Not published | per million tokens | | Audio input | Not published | per million audio input tokens | ## Benchmarks Last checked: 2026-10-14T17:57:48.915Z. Configurations are evaluated separately. API scores retain their original units. Unmeasured scores are omitted. ### Step 5 Preview Source: [Evaluation source]() | Benchmark | Score | | --- | --- | | Intelligence Index | 43.73 | | Omniscience Index | 16.38 | | Humanity’s Last Exam | 46.48% | | SciCode | 58.91% | | CritPt | 20.86% | | AA-LCR | 88.33% | | Multilingual LCR | 16.67% | | GDPval Elo | 1586.63 | | GDP.pdf All-pass | 14.80% | | AutomationBench Partial | 50.96% | | AnalystAgent | 35.00% | | MMMU-Pro | 76.36% | | APEX-Agents | 37.98% | | ITBench | 55.56% | Full benchmark data and breakdowns: [Complete benchmark snapshot](). ## Availability and retirement The model is listed as serving. No retirement is announced in the current public catalog. ## Frequently asked questions ### What is Step 5 Preview? Step 5 Preview is StepFun's flagship model for agentic work, aimed at software engineering and professional knowledge work with particular strength in finance. It takes text and image input over a context of about one million tokens, reasons at a selectable effort level before answering, and supports tool calling and structured output. Sources: [Step 5 Preview model page](); [StepFun reasoning model guide]() ### How much does Step 5 Preview cost? Step 5 Preview costs $1.00 per million input tokens and $2.70 per million output tokens through the Impossibl API. Cache reads cost $0.05 per million tokens. All rates are in USD. ### What is the context length of Step 5 Preview? Step 5 Preview has a 1,024,000-token context window through the Impossibl API. ### What inputs and outputs does Step 5 Preview support? Step 5 Preview accepts text and image as input. Step 5 Preview returns text. ### How do I use Step 5 Preview through an API? Step 5 Preview is available through the Impossibl API. Use stepfun/step-5-preview as the model identifier with /v1/chat/completions. The quickstart explains how to create an API key and send your first request. ### When was Step 5 Preview released? StepFun released Step 5 Preview on September 20, 2026. Sources: [Creator release announcement]() ## Sources and related links Prices, limits, capabilities, endpoints, and availability come from the public Impossibl catalog. Creator documentation supplies descriptions and release dates where available; it does not override the published API offering. - [Public Impossibl model catalog]() - [Full model directory as JSON]() - [Step 5 Preview: model details and pricing]() - [Model directory]() - [Step 5 Preview model page]() - [StepFun reasoning model guide]()