Step 5 Preview

StepFun's flagship model for agentic work

600B total parameters  ·  27B active parameters  ·  Up to 1M context

Introduction  ·  Capabilities  ·  Specifications  ·  Performance  ·  Resources  ·  License

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Introduction

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.

Step 5 Preview is a sparse Mixture-of-Experts (MoE) model with 600B total parameters and 27B active parameters. It supports up to 1 million tokens of context and accepts text, images, and video, enabling sustained reasoning and tool use across complex tasks.

Key Capabilities

Software Engineering

Step 5 Preview supports repository-level software engineering, frontend and visual development, and programming for devices. It can navigate large codebases, coordinate changes across files, run and verify code, and iterate on the results.

Long-Horizon Agentic Execution

Step 5 Preview can carry out tasks that require repeated tool calls, execution, verification, and revision, drawing on long-context information throughout the workflow.

Professional Knowledge Work

The model combines research, multimodal understanding, and tool use to analyze long documents, charts, screenshots, images, and video, and produce structured reports and analyses.

A Focus on Finance

Step 5 Preview is particularly strong in financial tasks that combine quantitative reasoning with analysis of financial data and supporting documents.

Model Specifications

Specification	Step 5 Preview
Architecture	Sparse Mixture-of-Experts (MoE)
Total Parameters	600B
Active Parameters	27B
Context Window	Up to 1M tokens
Maximum Output	Up to 1M tokens
Input	Text, image
Output	Text

Performance

The following results summarize Step 5 Preview's performance across coding, agentic tasks, professional knowledge work, and finance.

Evaluation Notes

• Recommended inference settings: temperature=1.0, top_p=0.95, top_k=0.
• Step 5 Preview results shown above use the High reasoning setting.
• GDPval-AA v2.1 scores are based on results from Artificial Analysis as of September 20, 2026.
• DeepSWE v1.1 evaluations use the SWE-agent harness with temperature=1.0 and top_p=0.95.

For evaluation context, methodology, and detailed case studies, see the Step 5 Preview Model Page.

Resources

• Step 5 Preview Model Page — Model overview, evaluation context, and long-horizon case studies.
• Documentation — Official documentation and developer guides.
• API Platform — Model access and platform services.
• StepFun Website — Company information and model announcements.

License

This model, including its weights, parameters, configuration, tokenizer, model-specific code, and documentation, is licensed under the StepFun Model License 1.0. The full text of the License is available in the LICENSE.txt file in this repository. The StepFun Model License 1.0 is an Apache-2.0-Style license, with additional attribution and commercial-license conditions specific to model use, modification and distribution.

Where accompanying materials in this repository, including sample code, datasets, third-party components and other documentation, are separately marked as subject to a different license, such materials are licensed under that license.