Claude Sonnet 5.5 vs Union Alpha (Stealth)
A direct, empirical evaluation of Claude Sonnet 5.5 (Anthropic) against Union Alpha (Stealth) (OpenRouter & OpenCode).
Claude Sonnet 5.5
Developed by Anthropic · Proprietary Frontier Dynamic Hybrid Reasoner parameters
Terminal-Bench 4.0 execution (70.6%), SWE-bench Verified coding (82.4%), GitHub Copilot multi-file edits, and low-latency autonomous agentic coding at $2/$10 pricing.
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 Sonnet 5.5 | Union Alpha (Stealth) |
|---|---|---|
| SWE-bench Verified | 82.4% | 74.2% |
| MMLU-Pro | 88.4% | 89.8% |
| MATH-500 | 95.2% | 95.4% |
| Context Window | 1,000,000 tokens | 256,000 tokens |
| Input Pricing (per 1M) | $2.00 | $0.00 |
| Output Pricing (per 1M) | $10.00 | $0.00 |