Google Gemini 3.1 Pro Review — Scientific Reasoning Leader, 5x Cheaper Than Opus

Google Gemini 3.1 Pro launched February 2026 with the highest GPQA Diamond score at frontier (94.3%), the largest single-generation ARC-AGI-2 jump ever recorded (31% → 77%), and pricing roughly 5x cheaper than Claude Opus 4.7. We review benchmarks, the hallucination picture, context window, pricing tiers, safety results, and where Gemini 3.1 Pro wins — and doesn't — against the 2026 frontier.