What is FSRS, and how new is it?

FSRS (Free Spaced Repetition Scheduler) is an open-source algorithm developed since 2022 by Jarrett Ye and the open-spaced-repetition community — added to Anki in v23.10 (2023) and now its recommended scheduler.

Where SM-2 uses one mechanical multiplier, FSRS is built around an explicit model of memory and is fitted to real review data with machine learning. It's a direct successor: same job (decide when to show each card), but it actually predicts forgetting rather than just stretching an interval on success.

Because it's open source and trained on hundreds of millions of real reviews, it improved fast and displaced SM-2 as the modern default.