BB(11)

The 11-state, 2-symbol Busy Beaver problem, BB(11,2), is unsolved and unexplored. The current BB(11) champion is 1LH1LA_1LI1RG_0RD1LC_0RF1RE_1LJ0RF_1RB1RF_0LC1LH_0LC0LA_1LK1LJ_1RZ0LI_0LD1LE (bbch), which takes over $f_{\omega }^2(2\uparrow \uparrow 12)$ steps to halt. It was dicovered by Racheline in 2024. Due to the discovery of Antihydra in BB(6), the existence of Collatz-like Cryptids in BB(11) is certain.

Based on a sample enumeration of BB(8), BB(11) is known to be very difficult to enumerate.