Google announced Gemini 3.5 Pro at I/O on May 19, 2026 and put it into limited Vertex AI preview for select enterprise customers. As of June 23, general availability is expected within the week. The confirmed specifications include a 2 million token context window, which is double Gemini 3.5 Flash's 1 million token context and holds approximately 1,500 pages of dense technical documentation. Google has officially confirmed three capabilities before the GA release: the 2 million token context window, Deep Think reasoning mode, and multimodal input with text and image support at launch. Deep Think is gated behind the $250/month Gemini Ultra subscription tier and is not available on standard Pro API access or the $19.99/month Advanced plan. What is not confirmed includes official benchmarks, production pricing, and fine-tuning availability. Google has shared internal data suggesting 10-15 point SWE-bench Verified gains over the 3.1 generation, but those figures are unverified external estimates.