The regular 9 (not the Pro's) doesn't reserve the 3GB for AI (presumably because the Pros come with a year of Gemini Advanced, so they need to try and force it to work as well as it can by any means necessary).
On the Pixel 8 Pro and Pixel 9, we note just 0.26GB (275,336KiB) of locked RAM [...], a very small amount most likely used for some background tasks in the OS. However, on the Pixel 9 Pro XL, this leaps to 2.91GB (3,051,936KiB) of Unevictable and Mlocked RAM. Subtract out the Unevictable RAM from the Pixel 9, and there’s an extra 2.64GB (2,776,603KiB) reserved on the Pro models.