3 month old with solid poop

My 3 month old has actual turds for over a week. They are still soft enough you can smush them. But he used to have liquidy poops. So I'm confused why he has actual turds. He poops once, sometimes 2 times daily. Hes always been on the same formula. Its the premixed Similac 360. He has a big appetite, drinks between 35 and 40 oz per day. But hes also 99th percentile. Just wondering if someone else has experienced this. I plan on asking at his appointment next week. Just looking to see if anyone else is in the same boat and how normal it is i guess?