Claude Opus 5.5 vs Union Alpha (Stealth)
A direct, empirical evaluation of Claude Opus 5.5 (Anthropic) against Union Alpha (Stealth) (OpenRouter & OpenCode).
Claude Opus 5.5
Developed by Anthropic · Proprietary Frontier Reasoner parameters
Autonomous enterprise codebase migrations, GitHub Copilot multi-file edits, SWE-bench Pro issue resolution (89.9%), and CodeRabbit automated reviews.
Union Alpha (Stealth)
Developed by OpenRouter & OpenCode · Multi-Model Ensemble Mixture parameters
Terminal coding agents, pull-request synthesis, multi-model consensus verification, and zero-cost autonomous refactoring.
| Metric | Claude Opus 5.5 | Union Alpha (Stealth) |
|---|---|---|
| SWE-bench Verified | 89.9% | 74.2% |
| MMLU-Pro | 92.4% | 89.8% |
| MATH-500 | 97.2% | 95.4% |
| Context Window | 500,000 tokens | 256,000 tokens |
| Input Pricing (per 1M) | $4.00 | $0.00 |
| Output Pricing (per 1M) | $20.00 | $0.00 |