Union Alpha: the new stealth model on OpenRouter
Last verified 2026-09-17 · model ID stealth/union-alpha · added to OpenRouter 2026-09-16 14:42:03 UTC · open on OpenRouter
Union Alpha showed up on OpenRouter on 16 September 2026 with no announcement, no model card and no name anyone recognised — the third anonymous model in the Alpha line after Hunter Alpha (later Xiaomi MiMo-V2.5) and OX Alpha (later Z.ai GLM 5.3 Flash). This page keeps the two kinds of information apart on purpose: specs read from OpenRouter's public catalog above, and unverified community theories clearly labelled further down.
At a glance
Verified specs
Read from the OpenRouter public catalog on 2026-09-17. Stealth listings change without notice — the live badge at the top of this page is the current truth.
| Field | Value |
|---|---|
| OpenRouter ID | stealth/union-alpha Listed under the anonymous stealth namespace. |
| Maker | Undisclosed Provider shown as "Stealth". No lab has publicly claimed it. |
| Context window | 262,144 tokens (256K) A quarter of the 1M window of the earlier Alpha models. |
| Max output | 131,072 tokens (128K) Reported by the single serving endpoint. |
| Modality | Text + image in, text out First Alpha-line stealth model that accepts images; Hunter Alpha and OX Alpha were text-only. |
| Pricing | Free — $0 in / $0 out Free stealth previews have historically been repriced or delisted without notice. |
| Supported parameters | tools, tool_choice (auto), response_format, temperature, top_p, max_tokens Tool calling is enabled — the feature agent builders need. |
| Reported uptime | ~100% (last 5 min and 24 h) Single endpoint, provider tag stealth. |
| Added to OpenRouter | 2026-09-16 14:42 UTC Unix timestamp 1789569723. |
Community theories (unverified)
These are paraphrases of public discussion, not findings. Nothing in this section is confirmed by the maker or by OpenRouter, and models are unreliable witnesses about their own identity.
Union Alpha may be a router over several models rather than one model.
Testers in the launch discussion on Hacker News reported inconsistent behaviour between sessions and argued that the name points at an ensemble or routing layer. The model's own answers about its identity are not reliable evidence either way.
The routing layer may include a GLM-family model.
The same discussion claimed one underlying model comes from the GLM family (Z.ai), with no reproducible test published. Unverified.
Tool-use quirks that reminded testers of Gemini.
One tester reported the model looping on an interactive-editor command during a git rebase, a failure mode they associated with Gemini models. Single anecdote.
A system prompt may tell the model to stay anonymous.
A commenter described an alleged injected instruction telling the model to answer Union Alpha and call its maker anonymous when asked. The claim cannot be verified from outside and may itself be a hallucination.
Timeline
First listed on OpenRouter
stealth/union-alpha appears in the public catalog under the anonymous stealth namespace.
Community picks it up
A Hacker News submission about the new stealth model starts collecting test reports within the hour.
Identity guessing starts
Testers report inconsistent behaviour, fuelling a router/ensemble theory and a possible GLM link; others suspect a Gemini-family model.
Specs re-verified against the catalog
256K context, 128K max output, free pricing, text+image input and tool support confirmed by a direct catalog read.
How to use Union Alpha
- 1. Create an OpenRouter account. Chat works in the browser; the API needs an OpenRouter key, not a key from the mystery maker.
- 2. Select the model by ID. Use
stealth/union-alpha— the display name in the picker is just Union Alpha. - 3. Use tool calling if you are building. The endpoint declares tools, tool_choice (auto), response_format, temperature, top_p and max_tokens.
- 4. Keep it out of production. An anonymous provider with no published data policy, on a free preview that can be repriced or delisted overnight, is for evaluation only.
How it compares to the earlier Alpha models
| Model | Context | Vision | Revealed as |
|---|---|---|---|
| Hunter Alpha | 1M | No | Xiaomi MiMo-V2.5 |
| OX Alpha | 1M | No | Z.ai GLM 5.3 Flash |
| Union Alpha | 256K | Yes | Still anonymous |
FAQ
What is Union Alpha?
Union Alpha is an anonymous AI model that appeared on OpenRouter on 2026-09-16 under the stealth namespace. OpenRouter describes it as a multimodal model built for research, coding and agentic workflows. The maker has not been disclosed.
Is Union Alpha free?
Yes. It is currently listed at $0 per million input and output tokens. Free stealth previews are usually limited-time: earlier Alpha-line models were repriced or delisted after the maker was revealed, so do not build anything that depends on the free window.
Who made Union Alpha?
Unknown. No lab has claimed it. Community discussion suggests it may be a router over several models rather than a single one, and that a GLM-family model might be involved, but none of that is verified.
How much context does Union Alpha have?
262,144 tokens of context and up to 131,072 tokens of output — 256K in, 128K out. That is smaller than the 1M-token windows of Hunter Alpha and OX Alpha.
Does Union Alpha support images and tool calling?
Yes to both. OpenRouter lists the modality as text+image input, and the endpoint declares tools, tool_choice (auto), response_format, temperature, top_p and max_tokens as supported parameters.
How do I use Union Alpha?
Create an OpenRouter account, pick stealth/union-alpha in the model list, or call it through the OpenRouter API with that model ID. No separate key from the mystery maker is needed.
Will Union Alpha be revealed like Hunter Alpha and OX Alpha were?
Probably, but there is no schedule. Hunter Alpha turned out to be Xiaomi MiMo-V2.5 and OX Alpha turned out to be Z.ai GLM 5.3 Flash; both were revealed after their free windows ended. Union Alpha is the third model in that line.
Should I trust Union Alpha with sensitive data?
No. The provider is anonymous and there is no published privacy or data-retention policy. Treat it like any unvetted free endpoint: no production secrets, no customer data, no credentials in prompts.