BB(4,4)

The 4-state 4-symbol Busy Beaver problem, BB(4,4), is unsolved and unexplored. With Cryptids like Bigfoot in the preceding domain BB(3,3), we know that we must solve a Collatz-like problem in order to solve BB(4,4). The current BB(4,4) champion is simply inherited from BB(3,4) as BB(4,4) has not been explored yet.

In September 2025, Terry Ligocki ran a test enumeration on one of 1 billion subtasks. The subtask ran for 1.5 hours and produced ~9000 holdouts. When corrected for the amount of subtasks involved, these values are 9000 times longer and 3500 times larger than the ones for BB(2,7).