01 / CONTEXT
Analyze long documents.
Use a 262,144-token context window to compare papers, examine project files, or work through a detailed brief in one conversation.
Research · synthesis · analysis
Stealth model Latest information about Union Alpha
UnionAlpha.
Intelligence, under cover.
Union Alpha is a stealth AI model for coding, research, and agentic workflows. It accepts text and images through OpenRouter, with a 262K context window and expected paid pricing of $0.50 input / $1.50 output per million tokens. Preview access is currently free.
~$1.50per task · Terminal-Bench v4OpenCode · anticipated pricing
stealth/union-alpha
262K context. Image input. Tool calling.262K
Context window · 262,144 tokens
131K
Max. output · 131,072 tokens
Text+ image
Multimodal input · text output
$0.50/ $1.50
1M Input / output · currently free
Model capabilitiesAvailability, pricing, and rate limits will change.
01 MODEL CAPABILITIES
What can
Union Alpha do?
Use Union Alpha for code reviews, document analysis, and visual questions, with support for tool calling and up to 131,072 output tokens.
02 / TOOLS
Connect your tools.
Use tools and tool_choice to let an agent call functions you provide. Set response_format when your app needs formatted replies.
Coding · agents · workflows
03 / VISION
Ask about images.
Send a screenshot, chart, or diagram with your prompt. Union Alpha accepts images alongside text and returns a text response.
Images · diagrams · visual context
02 TERMINAL-BENCH 4.0
Union Alpha
benchmarks.
Union Alpha sits at about 51% and an anticipated $1.50 per task, near Fable 5.1, below Astra (high), and much cheaper than either.
UNION ALPHA~51%
Terminal-Bench v4 task resolution
~$1.50anticipated average cost per task
EXPECTED TOKEN RATE$0.50 in · $1.50 outper 1M tokens · subject to change
Performance vs. cost
Selected OpenCode runs · logarithmic costMore benchmarksCoding, science, tools & vision +
Software engineering
SWE-bench Verified
Pending
About this evaluation
Measures whether model-written patches resolve issues in real software repositories. Benchmark source ↗
Scientific reasoning
GPQA Diamond
Pending
About this evaluation
Graduate-level questions in biology, chemistry, and physics. Benchmark source ↗
Agentic tool use
τ²-bench
Pending
About this evaluation
Tests whether an agent can complete tasks through conversation and tool use. Benchmark source ↗
Multimodal reasoning
MMMU-Pro
Pending
About this evaluation
Tests reasoning across images, diagrams, and expert-level questions. Benchmark source ↗
03 COMPARE THE MODELS
Union Alpha vs
Claude Opus 5.
Expected Union Alpha pricing is $0.50 input / $1.50 output per million tokens, versus Opus 5 at $5 / $25. Union Alpha remains temporarily free during preview.
Specifications & token costs
| Specification | Union Alpha | Claude Opus 5 |
|---|---|---|
| Context window | 262,144 tokens | 1,000,000 tokens |
| Maximum output | 131,072 tokens | 128,000 tokens |
| Input modalities | Text, images | Text, images, files / PDFs |
| Output modality | Text | Text |
| Input / 1M tokens | $0.50 Expected price · preview currently free | $5.00 Listed price |
| Output / 1M tokens | $1.50 Expected price · preview currently free | $25.00 Listed price |
| Tool calling | Listed | Listed |
| Response-format parameter | Listed | Listed |
| Structured-output metadata | Not listed | Listed · provider-dependentConfirm schema enforcement with your provider |
| Reasoning controls | Not listed | Listed |
What would your token volume cost?
Enter your total usage across all requests.
Union Alpha · expected
Claude Opus 5
Calculated with expected Union Alpha pricing of $0.50 input / $1.50 output per million and listed Opus 5 pricing of $5 / $25. Union Alpha's temporary free preview is excluded. Caching, tool charges, and routing fees are excluded.
Specifications and Opus 5 rates: OpenRouter public model catalog · 16 September 2026. Union Alpha pricing is the benchmark-derived expectation explained above; limits and rates may change.
04 TRY UNION ALPHA
Try Union Alpha.
Run a prompt here or copy the request in cURL, Python, or JavaScript. You can also chat directly on OpenRouter.
NO API KEY TO COPY
Try it in OpenRouter Chat
Sign in to OpenRouter and select Union Alpha from the model picker.
REQUEST / UNION ALPHATEXT PLAYGROUND
No API key to create or copy. Approve access on OpenRouter, then paste its one-time connection code here.
Connecting creates a revocable OpenRouter key for this tab. Your account’s limits and rates apply. How account connection works
Prompts go directly to OpenRouter. Credentials stay in this tab and are not saved to browser storage. Manage OpenRouter keys ↗
curl https://openrouter.ai/api/v1/chat/completions \
-H "Authorization: Bearer $OPENROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "stealth/union-alpha",
"messages": [{"role": "user", "content": "Hello, Union Alpha."}],
"max_tokens": 1024
}'MODEL RESPONSEReady
Enter a prompt and connect OpenRouter to start.
05 A FEW ANSWERS
Before your
first request.
What does “stealth” mean?
The developer’s identity is undisclosed. On OpenRouter, the model ID is stealth/union-alpha.
Is Union Alpha free to use?
Yes during the current preview. OpenRouter and OpenCode list $0 input and output pricing as of 16 September 2026. The benchmark implies a likely eventual rate near $0.50 input / $1.50 output per million tokens, but no paid price has been announced. Check the current pricing and availability before a large workload.
How does Union Alpha compare with Claude Opus 5?
Union Alpha has a 262,144-token context window and allows up to 131,072 output tokens. Opus 5 has a 1,000,000-token context window and a 128,000-token output limit. Both accept images and support tool calling. Union Alpha is currently free; its modeled paid rate is ~$0.50 input / ~$1.50 output per million, versus Opus 5 at $5 / $25. Use the comparison and cost calculator for your workload.
Does Union Alpha support images and tool calling?
Yes. The API accepts text and images, supports tools and tool_choice, and offers a response_format parameter. The playground on this page sends text only; use the API for image inputs and tool integrations.
How does Union Alpha perform on Terminal-Bench v4?
OpenCode's chart places Union Alpha at around 51%, near Fable 5.1 Max and Opus 5 Max and just below Astra (high), with an anticipated cost of roughly $1.50 per task.
Can I run Union Alpha locally?
Union Alpha is available through hosted inference on OpenRouter and OpenCode Zen. Downloadable model weights are not listed.
Can I try Union Alpha without an API key?
Yes. Sign in to OpenRouter Chat and select Union Alpha. To use the playground here, connect your OpenRouter account and enter its one-time authorization code. You do not need to create or copy an API key manually.
What happens to my prompt and credentials?
Prompts are sent directly to OpenRouter under its privacy policy. Credentials stay in this tab’s memory. Pasted keys are cleared after each request; connected keys are cleared when you disconnect or leave. Disconnecting here does not revoke the key on OpenRouter. You can revoke it in OpenRouter key settings.
Try Union Alpha.
Available through OpenRouter and OpenCode Zen.