Best LLM for Coding in 2026: Claude Opus 4.8 vs GPT-5.5 vs Gemini 3.1 Pro (With Enterprise Governance Guide)

GPT-5.5 and Claude Opus 4.8 tie on SWE-bench Verified (~88.7%), but Opus 4.8 leads on the contamination-resistant SWE-bench Pro (69.2% vs 58.6%). Gemi