Union Alpha Model
A free multimodal model built for research, coding, and agentic workflows — with a 262K context window, text + image input, and frontier-level performance.
Specifications
| Model ID | stealth/union-alpha |
| Provider | Stealth (third-party, operated independently of OpenRouter) |
| Released | September 16, 2026 |
| Price | Free |
| Context window | 262,144 tokens |
| Max output | 131,072 tokens |
| Input → Output | Text + Image → Text |
| Tool calling | Supported (tools / tool_choice) |
| Structured output | Supported (response_format), JSON schema not enforced |
| P50 latency | ~17.6 seconds |
| P50 throughput | ~14 tokens / second |
| 3-day uptime | 98.08% |
| Data policy | Prompts and completions may be retained by the provider but are not used for training |
Quick Start
Union Alpha uses the OpenAI-compatible API via OpenRouter. Use the model ID
stealth/union-alpha in any client.
cURL
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": "Explain the transformer architecture in simple terms."}
]
}'Python
import openai
client = openai.OpenAI(
base_url="https://openrouter.ai/api/v1",
api_key="YOUR_OPENROUTER_API_KEY",
)
response = client.chat.completions.create(
model="stealth/union-alpha",
messages=[{"role": "user", "content": "Explain the transformer architecture."}],
)
print(response.choices[0].message.content)
Cline / OpenCode / Hermes Agent: just set the model ID to
stealth/union-alpha and point the API base to
https://openrouter.ai/api/v1.
Complete API Example
Real request and response from Union Alpha via Tokenra.io API proxy.
Request
POST https://tokenra.io/v1/chat/completions
Content-Type: application/json
{
"model": "union-alpha",
"messages": [
{
"role": "user",
"content": "what model"
}
],
"max_tokens": 1024,
"stream": false
}Response
{
"id": "gen-1789580899-b6F0U6o1wxcGXYak2Ahb",
"object": "chat.completion",
"created": 1789580899,
"model": "stealth/union-alpha",
"provider": "Stealth",
"choices": [
{
"index": 0,
"finish_reason": "stop",
"message": {
"role": "assistant",
"content": "I am Union Alpha. My maker is currently anonymous."
}
}
],
"usage": {
"prompt_tokens": 1,
"completion_tokens": 12,
"total_tokens": 13,
"cost": 0
}
}
Key points: Zero cost, OpenAI-compatible format, and clean responses.
Use union-alpha as model ID on Tokenra, or stealth/union-alpha on OpenRouter.
Who's Using Union Alpha
Token volume on OpenRouter since launch. Real production usage — not benchmarks.
What to Watch Out For
Free doesn't mean perfect. Here's what you should know before relying on Union Alpha in production.
- ⏳ High latency (~17.6s P50): Union Alpha is slow compared to most models on OpenRouter. Best suited for batch processing, long-form generation, and async workloads — not real-time chat or low-latency agents.
- 🐌 Low throughput (~14 tok/s): Token generation speed is modest. If your use case needs streaming responsiveness, consider faster alternatives.
- ⚠️ ~98% uptime: As a new free model from an anonymous provider, availability can dip. Don't build mission-critical pipelines on it without a fallback.
- 🕵️ Anonymous provider: The model is developed and operated by a third party ("Stealth"). OpenRouter routes the traffic but does not control the model. Prompts and outputs may be retained by the provider.
Frequently Asked Questions
Is Union Alpha free?
Yes. Union Alpha is currently free to use on OpenRouter with no per-token cost. It's a 262K-context multimodal model available at stealth/union-alpha.
What is Union Alpha?
Union Alpha is a free multimodal large language model on OpenRouter (stealth/union-alpha), built for research, coding, and agentic workflows. It supports text and image inputs with a 262K token context window.
What is the context length?
262,144 tokens. Maximum output is 131,072 tokens.
Does Union Alpha support tool calling?
Yes. It supports OpenAI-compatible function calling (tools / tool_choice) and structured outputs via response_format. JSON schema is supported but not enforced.
Who made Union Alpha?
Union Alpha is developed and operated by an anonymous third-party provider labeled "Stealth" on OpenRouter. No company name or research paper has been disclosed.
How is Union Alpha different from Ox Alpha?
Both are Stealth models on OpenRouter, but they differ in capabilities, pricing, and performance. See our detailed comparison for benchmark data.
Why is Union Alpha slow?
At ~17.6s P50 latency and ~14 tok/s throughput, Union Alpha prioritizes depth over speed. It is best suited for long-form generation and batch workloads rather than interactive chat.