100 + a few now (since age ~15). I briefly knew 400, but didn't put in the practice to keep it (some sections of those later 100s are still there, but I can't access them as I'm missing some digits in between). It takes about 40min. to get 100 new digits into my head (just straight repetition, paying attention to the sounds and patterns in rhythmic groups). Keeping them long-term requires a lot of time spent on spaced repetition. I run through the first 100 digits just a few times a year now, and it's all still easily there.
