What is the context length of Union Alpha?

Union Alpha has a 262,144 token context window.

What inputs and outputs does Union Alpha support?

Union Alpha accepts text and images as input and returns text.

When was Union Alpha released?

Union Alpha was released on September 16, 2026.

This stealth model was developed and operated by Unbiased, revealed to be Unbiased Pareto. Prompts and completions for this model may have been retained by the provider but are not used for training; all other use is governed by the Stealth Model Terms.

Union Alpha

stealth/union-alpha

Union Alpha is a multimodal model built for research, coding, and agentic workflows, while delivering frontier-level performance across a broad range of general-purpose tasks.

Union Alpha was a stealth model, revealed to be Pareto by Unbiased. OpenRouter routed requests to it and was not its developer, owner, or provider. Prompts and completions may be retained by the provider but are not used for training; all other use is governed by the Stealth Model Terms. The free stealth period has ended; use Pareto at https://openrouter.ai/unbiased/pareto.

Modalities

Context

262K

Released

Sep 16, 2026

Not currently available through EU in-region routing. In-region routing docs

Frequently asked questions

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Union Alpha

Activity

Frequently asked questions

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More models from Stealth

Union Alpha

Activity

Frequently asked questions

What is Union Alpha?

What is the context length of Union Alpha?

What inputs and outputs does Union Alpha support?

When was Union Alpha released?

Explore more models

More models from Stealth

More models from Stealth