What Gemini 2.5 Pro actually is (and what makes it unique)
Gemini 2.5 Pro is Google DeepMind's flagship model in the Gemini 2.x family, released in March 2025. It succeeded Gemini 2.0 Pro (which itself replaced Gemini 1.5 Pro in late 2024) and brought three step-changes: native thinking mode (configurable reasoning budget per call), tier-2-quality vision matching GPT-5's vision benchmarks, and stable 1M-token context behavior with recall that holds across the full window.
What makes Gemini 2.5 Pro structurally different from GPT-5 or Claude Opus: it is natively multimodal across more modalities than either. Text, image, audio, video, and PDF inputs all flow through the same `contents` array. Pass an MP4 video file, an audio recording, a stack of PDFs and a free-form text question — Gemini accepts all of it in one call and reasons across them. GPT-5 supports text + image. Claude supports text + image. Only Gemini 2.5 Pro (and its Flash sibling) support video and audio natively in production.
Thinking mode (Google's name for configurable reasoning) is enabled by default on Gemini 2.5 Pro with a model-decided budget. Force a specific budget with `thinking_config: {thinking_budget: 5000}`; disable thinking entirely with `thinking_budget: 0` for fastest possible response. Thinking tokens bill at the output rate like reasoning tokens on GPT-5 and thinking tokens on Claude.