Union Alpha: The Stealth Model Nobody Has Claimed
It appeared on OpenRouter on September 16, 2026 with no lab attached, burned through 2.4 billion tokens in 48 hours, and matches models costing 50 times more. Here is what is actually known.
What Is Union Alpha?
Union Alpha is a stealth model — an AI model published without a named developer. It appeared in OpenRouter's catalog on September 16, 2026, 14:42 UTC as stealth/union-alpha, listed under a provider called simply "Stealth", priced at zero dollars. There was no announcement, no model card, and no lab taking credit.
What it does have is numbers. The model scores 74.2% on SWE-bench Verified and 74.0% on DeepSWE — level with GPT and Opus-class models that charge roughly fifty times more per task. It carries a 262,144-token context window, accepts images alongside text, and supports tool calling. Within 48 hours of appearing, developers had pushed 2.4 billion tokens through it.
This site is an independent reference for the model: what is documented, what is merely rumoured, how to actually use it, and how it compares to models that do have names. Every figure here is sourced and dated, because with a stealth model the line between fact and speculation is the whole story.
Six Things Worth Knowing
The honest picture — including the parts that are not flattering.
It arrived with no name attached
At 14:42 UTC on September 16, 2026 a new entry simply appeared in OpenRouter's catalog: id stealth/union-alpha, provider 'Stealth', price $0. No blog post, no model card, no lab taking credit.
Frontier coding scores, budget pricing
74.2% on SWE-bench Verified and 74.0% on DeepSWE put it level with GPT and Opus-class models — which charge roughly $6.50 to $11.80 per task against an estimated $0.65.
Developers adopted it within hours
Around 2.4 billion tokens ran through the model in its first 48 hours as people wired it into Cursor, Cline, Roo Code and terminal agent loops while the preview stayed free.
262K context with image input
A 262,144-token window handles repository-scale context, and the model accepts images alongside text — enough for screenshot debugging and diagram-driven work.
It is genuinely slow
Independent measurement places it in the 6th percentile for speed. The benchmark wins are real, but so is the wait. This is a throughput tradeoff, not a free lunch.
The free window will close
Preview pricing is $0, with anticipated rates of $0.50 input and $1.50 output per million tokens. Plan for the model to cost money — just far less than its peers.
The First 48 Hours
Most model launches arrive with a blog post, a benchmark chart and a press embargo. This one arrived as a new row in a database.
Two days of adoption on that scale is normally the result of a marketing budget. Here it came from a free tier and a benchmark screenshot.
The Question Everyone Is Asking
Nobody knows who built Union Alpha. OpenRouter's listing says only that it is "developed and operated by a third-party provider" — and as of September 17, 2026, no lab has stepped forward.
There is precedent for how this ends. The previous stealth listing on OpenRouter, Ox Alpha, was eventually identified as Z.ai's GLM-5.3-Flash. That has pushed much of the community toward guessing the GLM family again — but the published specifications of the two models do not line up, which makes the easy answer the wrong one.
Explore the Reference
Who Made It →
Every documented clue, the Ox Alpha precedent, and why the obvious GLM theory does not survive the spec sheet.
Benchmarks →
SWE-bench 74.2%, DeepSWE 74.0%, Terminal-Bench v4 around 52% — with the speed caveat the leaderboards hide.
How to Use →
OpenRouter and OpenCode paths, plus setup for Cursor, Cline, Roo Code and terminal agents.
API Guide →
Model IDs, working curl and Python examples, image input, and the 262K context window in practice.
Compare Models →
Against GPT-class, Claude Opus 5 and GLM-5.3-Flash on score, cost, speed and availability.
Pricing →
Free today, roughly $0.65 per task at the anticipated rate, versus $6.50 to $11.80 for comparable models.
Common questions
What is Union Alpha?
Who made Union Alpha?
Is Union Alpha free?
How good is Union Alpha at coding?
What is the context window?
Does Union Alpha train on my data?
Is Union Alpha fast?
Can Union Alpha see images?
Try It While It Is Free
Preview access costs nothing and the model string is one line of config. The free window has no published end date — which is another way of saying it could close any day.