What is Union Alpha
Union Alpha is an anonymous "stealth" model available on OpenRouter, Cline, and OpenCode. The model supports text and image input, tool calling, has a 256K context and 131K maximum output, and is aimed at general tasks such as research, programming, and agentic workflows. The model's free period lasts about a week and promises zero data retention, making it suitable for whole-repository code analysis and long document processing.
Union Alpha's Main Features
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Ultra-long context: Supports a 262,144 token context window, capable of processing an entire repository's code or long documents in one pass.
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Ultra-long output: Maximum output reaches 131,072 tokens, suitable for generating long reports or complete code files.
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Multimodal input: Supports text and image input, output is plain text, video input is not supported.
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Tool calling: Fully supports interfaces such as tools, tool_choice, and response_format, adapted for Agent workflows.
How to Use Union Alpha
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Register an OpenRouter account: Visit OpenRouter to register and log in, and generate an API Key.
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Find the model: Search "union-alpha" in the model list, select
stealth/union-alpha。 -
Quick experience on the web: Chat directly on the OpenRouter chat page, and upload images to test multimodal capabilities.
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API call: Request through the OpenAI-compatible interface, fill the model field with
stealth/union-alpha, and you can pass in tools and system prompt. -
Cline integration: In the Cline plugin settings, select OpenRouter as the provider, and select Union Alpha from the model dropdown list.
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OpenCode integration: Connect directly through OpenCode's Zen/Go gateway, or configure a custom OpenRouter endpoint to use this model.
Union Alpha's Core Advantages
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Completely free for a limited time: During the preview period, both input and output are $0/M, allowing you to verify its performance on real tasks at zero cost.
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Zero data retention: Promises not to store or use user data for training, suitable for sensitive scenarios such as feeding in private code repositories.
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Agent-native support: Fully supports tool calling, structured output, and long-running tasks, officially optimized specifically for continuous agentic workflows.
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Multimodal input: Supports image input, and can directly process visual materials such as screenshots and architecture diagrams to assist programming and research.
Comparison of Union Alpha with Similar Competitors
| Comparison Item | Union Alpha | Ox Alpha（GLM-5.3-Flash） |
|---|---|---|
| Developer | Anonymous, unclaimed | Z.AI (Zhipu), confirmed to Bloomberg on August 26 |
| Context window | 262,144 tokens | 1,048,576 tokens（1M） |
| Maximum output | 131,072 tokens | 131,072 tokens |
| Input modality | Text + image | Text + image + video |
| Data terms | Zero data retention (ZDR), no storage and no training | Logs are retained by the provider, but not used for training |
| Price | Free (preview period about one week) | Converted to paid: $0.15/M input, $0.50/M output |
Union Alpha use cases
- Whole-repository code understanding and refactoring: The 256K context can load a medium-sized code repository in one go, enabling cross-file dependency analysis, architecture review, and batch refactoring suggestions.
- Agent coding workflows: Native tool calling + long output, suitable for driving agents such as Cline and OpenCode to complete multi-step development tasks.
- Long-document research and review: Feed in hundreds of pages of papers/financial reports/regulatory documents at once to generate a 100,000-token-level in-depth analysis report, with no need for chunking.
- Vision-assisted development: Combine image input to analyze UI screenshots, architecture diagrams, and error screenshots, and directly output fix code or a front-end implementation that recreates the design mockup.