Mixed
It hasn't had a break through, but it's certainly recreated everything anyone's tried before
wholinator2 on Hacker News
an entire PhD's worth of work time in a single month
In the thread “Claude Fable 5.2 and Mythos 5.2”, replying to this comment
Helped: Gathering data on every possible approach for impossible problems.
Got in the way: No breakthrough achieved; user cannot understand the process.
… There's zero chance i go through and understand what the hell it's doing, but for tackling problems which are accepted as "impossible" it's extremely useful for gathering data on every possible approach. It hasn't had a break through, but it's certainly recreated everything anyone's tried before.