Is it still free?
The preview window, the reported price after it, and how to check the number yourself.
Stealth line · live tracker
What is Union Alpha? The Stealth Model That Turned Out to Be Unbiased Pareto
Union Alpha appeared on OpenRouter on 16 September 2026 with no announcement and no model card — 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). Two days later it was revealed as Unbiased Pareto and the stealth route disappeared. Facts and speculation are kept on separate surfaces on purpose: everything below is either re-checkable against the public catalogue or labelled as a claim.
Checking OpenRouter… Reading the public catalogue.
The short version
Maker
Unbiased
Revealed 2026-09-18
Revealed as
Unbiased Pareto
unbiased/pareto
Listed
16 Sep 2026
14:42 UTC
Delisted
18 Sep 2026
stealth route removed
Context
256K
262,144 tokens
Max output
128K
131,072 tokens
Price then
Free
$0 in / $0 out, 16–18 Sep
Price now
$2.50 / $7.50
per million tokens, in / out
Tools
Supported
tool_choice: auto
Verified specs
Read straight from the public model catalogue and re-checkable by anyone. Rows marked as third-party are things other people published, not things we confirmed.
| Field | Value |
|---|---|
| OpenRouter ID | stealth/union-alpha The stealth route — no longer served; the catalog answers 404 for it. |
| Maker | Unbiased Revealed 2026-09-18: OpenRouter's stealth page says the model was "developed and operated by Unbiased". |
| Revealed as | Unbiased Pareto (unbiased/pareto) Same 262,144-token window; now billed rather than free. |
| 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. |
| Price during the window | Free — $0 in / $0 out True from 2026-09-16 to 2026-09-18 only. The stealth route is gone; the revealed listing is billed. |
| 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. |
| Also served through | OpenCode free tier Third-party reports (including a Japanese write-up and the model's own landing page) say the same anonymous model is reachable from OpenCode's free tier as well as OpenRouter. Same weights, different front door — verify before relying on it. |
| Reported early usage | ~2B tokens in the first day A third-party news digest cited roughly 2 billion tokens consumed within 24 hours of launch. Directional evidence that the free window is genuinely popular, not a precise figure. |
| Added to OpenRouter | 2026-09-16 14:42 UTC Unix timestamp 1789569723. |
| Architecture claim (third-party) | Model orchestrator, not a single model A public landing page for the model describes it as running multiple LLMs in parallel and synthesising one answer. Matches the router theory testers raised on day one. Not confirmed by OpenRouter or the maker. |
| Reported pricing (third-party, did not hold) | $0.50 in / $1.50 out per million tokens A public landing page listed this as anticipated pricing after the free preview. The listing that actually appeared is $2.50 in / $7.50 out per million — the claim was wrong by roughly 5x, which is why claims stay in this column. |
Source
openrouter.ai/api/v1/models Verified 2026-09-18 Live status /api/union-alpha/status What the community claims
None of this is confirmed by OpenRouter or the maker. It is included because it is what testers are arguing about, with the evidence attached so you can weigh it yourself.
Union Alpha may be a router over several models rather than one model. Medium confidence
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. Low confidence
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. Low confidence
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. Low confidence
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
- 2026-09-16 14:42 UTCFirst listed on OpenRouterstealth/union-alpha appears in the public catalog under the anonymous stealth namespace.
- 2026-09-16 15:24 UTCCommunity picks it upA Hacker News submission about the new stealth model starts collecting test reports within the hour.
- 2026-09-16Identity guessing startsTesters report inconsistent behaviour, fuelling a router/ensemble theory and a possible GLM link; others suspect a Gemini-family model.
- 2026-09-17Specs re-verified against the catalog256K context, 128K max output, free pricing, text+image input and tool support confirmed by a direct catalog read.
- 2026-09-18Revealed: it is Unbiased ParetoOpenRouter's stealth page now states the model was developed and operated by Unbiased, revealed to be Unbiased Pareto. The catalog lists unbiased/pareto with the same 262,144-token window, priced $2.50 in / $7.50 out per 1M tokens.
- 2026-09-18The stealth route disappearsstealth/union-alpha is removed from the catalog — the single-model endpoint answers 404 and no stealth namespace is listed any more. The free window is over for good; the product continues under its real name.
How to use Union Alpha
- Create an OpenRouter account. Chat works in the browser; the API needs an OpenRouter key, not a key from the mystery maker.
- Select the model by ID. Use
stealth/union-alpha— the display name in the picker is just Union Alpha. - Use tool calling if you are building. The endpoint declares tools, tool_choice (auto), response_format, temperature, top_p and max_tokens.
- Call it by its real name now. stealth/union-alpha no longer resolves; unbiased/pareto is the same model, billed.
Via OpenCode: third-party reports said the same anonymous model was reachable from OpenCode’s free tier. We never confirmed that independently, and it is moot now — the anonymous model was delisted alongside the reveal. The OpenCode page keeps the record of the claim.
What it costs now, and how to call it
Read from GET /api/v1/models/unbiased/pareto/endpoints on
2026-09-18. One provider serves it, so there is one price and no
routing to reason about.
| Field | Value | Note |
|---|---|---|
| Input | $2.50 / 1M | prompt 0.0000025 per token |
| Cached input | $0.25 / 1M | input_cache_read 0.00000025 — a tenth of fresh input. If you
resend the same long prefix, this is the number that sets your bill, not
the $2.50.
|
| Output | $7.50 / 1M | completion 0.0000075 per token |
| Context window | 262,144 | unchanged from the stealth era |
| Max output | 131,072 | declared by the single endpoint |
| Accepts | text + image | text+image->text — the first Alpha-line model that took images |
| Parameters | 5 | max_tokens, temperature, top_p, tools, tool_choice |
Source
openrouter.ai/api/v1/models/unbiased/pareto/endpoints Verified 2026-09-18 Not quoted from a model card — read from the endpoint that serves it Calling it
The model id is unbiased/pareto — the stealth id
stealth/union-alpha no longer resolves. It is a normal
OpenRouter route, so the request shape is the same as for any other model on
the platform; only the id and the declared parameters above change.
curl https://openrouter.ai/api/v1/chat/completions \
-H "Authorization: Bearer $OPENROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "unbiased/pareto",
"messages": [
{ "role": "user", "content": "Summarise this error log." }
],
"temperature": 0.2,
"max_tokens": 2048
}'
Tool calling is declared on the endpoint, so agent harnesses that send
tools and tool_choice work without a wrapper. The
image modality is why the request above can carry an image part alongside
text — something Hunter Alpha and OX Alpha never accepted.
Parameters
read 2026-09-18 Request shape OpenRouter docs 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 | Unbiased Pareto |
Source
public catalogue reads, 2026-09-18 Background how the Alpha line works FAQ
What is Union Alpha?
Union Alpha was the anonymous codename for an OpenRouter stealth model listed on 2026-09-16. It was revealed on 2026-09-18 as Unbiased Pareto, made by Unbiased — the third Alpha-line codename to be disclosed, after Hunter Alpha (Xiaomi MiMo-V2.5) and OX Alpha (Z.ai GLM 5.3 Flash).
Is Union Alpha free?
It was, for the two days of the stealth window. The stealth route is gone, and the family now bills per token under dated ids — unbiased/pareto-26.9 is the current one — at $2.50 per 1M input tokens and $7.50 per 1M output tokens. If you are looking for the free endpoint, it no longer exists.
Who made Union Alpha?
Unbiased. OpenRouter's stealth page states the model was developed and operated by Unbiased and revealed as Unbiased Pareto. The published id has since moved to dated versions: unbiased/pareto-26.9 is the current row, read from the catalogue on 2026-10-16.
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?
You cannot — stealth/union-alpha is no longer served. Use unbiased/pareto-26.9 on OpenRouter instead (a ~unbiased/pareto-latest alias also exists and always points at the newest version); it is the same model with the same 262,144-token context window, now billed. The family moved from a single unbiased/pareto id to dated ids on 2026-10-13.
Will Union Alpha be revealed like Hunter Alpha and OX Alpha were?
It already was: on 2026-09-18, two days after it appeared. The pattern held a third time — Hunter Alpha → Xiaomi MiMo-V2.5, OX Alpha → Z.ai GLM 5.3 Flash, Union Alpha → Unbiased Pareto.
Should I trust Union Alpha with sensitive data?
The stealth endpoint is gone, so the question is now about Unbiased Pareto: the provider is named instead of anonymous, and the stealth terms noted that prompts and completions may have been retained by the provider but not used for training. Treat any preview model as unvetted for production secrets.
Is Union Alpha a single model or several models?
Evidence points to a single endpoint that orchestrates several models: testers reported inconsistent behaviour between sessions on day one, and a public landing page for the model describes it as running multiple LLMs in parallel and synthesising one answer. That would also explain why asking the model about its own identity gives unreliable answers. Neither OpenRouter nor the maker has confirmed it.
How much did Union Alpha cost after the free preview?
$2.50 per million input tokens and $7.50 per million output tokens, read from the catalogue on 2026-09-18 under the model's real name, unbiased/pareto — and unchanged on the dated ids that replaced it (unbiased/pareto-26.9, read 2026-10-16). The ≈$0.50 / $1.50 that a landing page listed during the preview did not hold — the real listing is roughly five times higher, which is the argument for quoting a catalogue read rather than an anticipated price.
What are Union Alpha's benchmarks?
There is no peer-reviewed benchmark set. The numbers circulating — including a Terminal-Bench v4 style cost-per-task figure on the model's own landing page — are self-reported or estimated, not independently reproduced. Treat benchmark claims for an anonymous model as marketing until someone publishes a reproducible run.
Get notified about the next codename
This reveal is over — Union Alpha ran for two days. Three reveals in, each codename has been free while anonymous and billed once revealed; a fourth, Space Bunny Alpha, ran thirteen days and delisted on 5 October 2026 without anyone claiming it — the first in this line to leave without a maker. Leave your email and we will tell you when the next reveal lands, and who it turns out to be.
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Union Alpha, in more detail
Using it in OpenCode
The free route through OpenCode’s tier, and what we can and cannot verify about it.
Errors and rate limits
Why the endpoint stopped on 18 September, and the other three failure modes that apply to every stealth release.
Open Union Alpha on OpenRouter → Other free models Full model directory