> ## Documentation Index > Fetch the complete documentation index at: https://platform.stepfun.ai/docs/llms.txt > Use this file to discover all available pages before exploring further. # Step 5 Preview **Step 5 Preview is StepFun's flagship model for agentic work.** It delivers frontier-level performance across software engineering and professional knowledge work, with particular strength in finance. It natively supports text, image, and video input and provides a **1M-token context window**, making it suitable for tasks that require large amounts of information, tool calls, and continuous progress toward a deliverable. ## At a glance | Specification | Step 5 Preview | | :- | :- | | **Model ID** | `step-5-preview` | | **Context window** | **1M tokens** | | Input types | Text, images, and video | | Output type | Text | | Maximum input | **1M tokens** | | Maximum output | **64k tokens** | ## Core capabilities > [card] Long-context understanding and reasoning > > Analyze long documents, multiple source materials, and conversation history within a 1M-token context. > > **Typical tasks**: cross-document question answering and research material organization. > [card] Programming and software engineering > > Work across multiple programming languages and engineering tasks, with tools to advance development, modification, and verification. > > **Typical tasks**: troubleshooting, code changes, and test creation. > [card] Multi-step Agent tasks > > Use tools provided by an application to retrieve information, process documents, and continue through multi-step work. > > **Typical tasks**: deep research and analytical reporting. > [card] Multimodal understanding > > Combine images, video, and text to extract and analyze multimodal information. > > **Typical tasks**: chart analysis, screenshot question answering, and video summarization. ## Use cases * **Software development**: Combine code, dependency information, and error logs to locate problems, modify code, and recommend tests. * **Long-document processing**: Organize multiple sources in a long context, extract and summarize information, and cross-check details. * **Research and analysis**: Work with search, code execution, or document tools to break down tasks and produce structured results. * **Multimodal understanding**: Analyze screenshots, charts, and video, and output conclusions in a specified format. Tools, search, and code execution capabilities are provided by the application that integrates the model; the model does not itself access your local environment or external services. ## Input and output ### Image and video input | Item | Supported range | | :- | :- | | Image input method | URL or Base64 | | Image formats | JPG/JPEG, PNG, WebP, and static GIF | | Images per request | Up to 60 images | | Image detail level | `low`, `high` | | Video input method | URL, Base64, or a `stepfile://` reference from the Files API | | Video formats | MP4, QuickTime, and Matroska | | Video URL limit | Individual MP4 files under 128 MB; less than 5 minutes is recommended | See the [Quickstart](https://platform.stepfun.ai/docs/en/quickstart/overview.md) for image and video request examples. For complete limits, see [Image understanding best practices](https://platform.stepfun.ai/docs/en/guides/developer/image-chat.md) and [Video understanding best practices](https://platform.stepfun.ai/docs/en/guides/developer/video-chat.md). ## Features and configuration | Feature / configuration | Supported range / parameter | Guide | | :- | :- | :- | | Streaming output | Supported | [Streaming responses](https://platform.stepfun.ai/docs/en/guides/developer/stream.md) | | Tool calling | Supported | [Tool calling](https://platform.stepfun.ai/docs/en/api-reference/tool-call.md) | | Structured output | JSON Mode and JSON Schema supported | [JSON Mode](https://platform.stepfun.ai/docs/en/guides/developer/json-mode.md) | | Reasoning effort | Supports `low`, `medium`, and `high`; use `reasoning_effort` with the Chat Completions API and `output_config.effort` with the Messages API | [Reasoning models](https://platform.stepfun.ai/docs/en/guides/developer/reasoning.md) | | Prompt caching | Supported | [Prompt caching](https://platform.stepfun.ai/docs/en/guides/developer/prompt-cache.md) | | Output length | `max_tokens` defaults to `INF`; no limit is applied and the model determines it automatically | [Chat Completions API](https://platform.stepfun.ai/docs/en/api-reference/chat/chat-completion-create.md) | ## Integration 1. Create an API key on the StepFun Open Platform. 2. Open the [Quickstart](https://platform.stepfun.ai/docs/en/quickstart/overview.md), select Step 5 Preview, and switch between the text chat, image understanding, and video understanding examples. 3. Send a request with cURL or Python and read the result from `choices[0].message.content`. 4. Before going live, use the [API reference](https://platform.stepfun.ai/docs/en/api-reference/chat/chat-completion-create.md) to add timeout, retry, error-handling, and key-management logic. > [card] [Quickstart](https://platform.stepfun.ai/docs/en/quickstart/overview.md) > > See text, image, and video request examples. > [card] [Chat Completions API](https://platform.stepfun.ai/docs/en/api-reference/chat/chat-completion-create.md) > > See the complete request parameters, response fields, and usage information. > [card] [Step Code](https://platform.stepfun.ai/docs/en/step-code/quickstart.md) > > StepFun's terminal coding agent. Sign in with a Step Plan account to use this model. ## Pricing and rate limits Step 5 Preview is billed based on actual input and output token usage. For current prices, cache billing rules, and account rate limits, see [Pricing and Rate Limits](https://platform.stepfun.ai/docs/en/guides/pricing/details.md#pricing-for-multimodal-reasoning-models). ## More information [Quickstart](https://platform.stepfun.ai/docs/en/quickstart/overview.md) · [API reference](https://platform.stepfun.ai/docs/en/api-reference/chat/chat-completion-create.md) · [Step Code](https://platform.stepfun.ai/docs/en/step-code/quickstart.md) · [Pricing and Rate Limits](https://platform.stepfun.ai/docs/en/guides/pricing/details.md) This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.