I was trying puzzle number 68 before it got solved. With https://github.com/brichard19/BitCrack

But it makes no economic sense. I did the numbers for a RTX 3090 and the expected return was about 1/100 of the prize. So even if a pool could exist, it was not efficient.

And a pool can't exist, because anyone in the pool that finds the key could just claim the prize for themselves (unlike in mining).

The closest thing to a pool is https://btcpuzzle.info/ where explored areas are marked as “key not here”.