Gemini comes in three different "sizes" - Gemini Ultra, Gemini Pro, and Gemini Nano. Gemini Ultra is the largest and most capable model, designed for highly complex tasks. Gemini Pro is optimized for scaling across a wide range of tasks and is currently used in Bard, Google's chatbot. Gemini Nano is the most efficient model, suited for on-device tasks such as those in mobile devices like the Pixel 8.