TMBR: October 2026

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This Month in Beaver Research

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This edition of TMBR is in progress and has not yet been released. Please add any notes you think may be relevant (including in the form a of a TODO with a link to any relevant Discord discussion).

This Month in Beaver Research for October 2026.

BB Adjacent

• Register Machine
  • On October 1, sheep discovered a 12-state, 2-register Cryptid which halts iff 7 converges to 1 under the Collatz-like 5n+1 map, thus showing that MBB(12, 2) is hard.^[1]
  • On the same day, @-d enumerated MBB(8), which left 7,891 holdouts after reduction, or 404 holdouts if an ai-created decider is used.^[2]
  • On the same day, @mineralli discovered a family of champions for MBB(n, 1).^[3]
  • On October 2, @mineralli discovered a new champion for MBB(10, 2).^[4]
  • On the same day, sheep discovered 2 new tetrational champions for MBB(10).^[5][6]
  • On the same day, Shawn Ligocki released an MBB(8) holdout list consisting of 145 holdouts,^[7] using another ai-created decider similar to CTL.^[8]
  • On October 3, Shawn Ligocki released another MBB(8) holdout list consisting of 46 holdouts,^[9] later reduced to 6^[10] (from 7^[11]) holdouts.
  • On the same day, Shawn Ligocki discovered a cryptid similar to Space Needle amongst the 6 remaining holdouts, showing MBB(8) is hard.^[12]
  • On the same day, sheep analyzed the rest of the holdouts, discovering 4 equivalences and another Space Needle-like cryptid (Needle 1),^[13] meaning MBB(8) "probviously" = 3,394.
  • On the same day, Katelyn Doucette devised a method to show that a sizeable portion of powers of two could not be reached by Needle 1's path.^[14] She later concluded that this backwards reasoning-like method, though powerful, would not be enough to decide Needle 1.^[15]
  • On October 7, sheep rediscovered a 2003 dissertation by Rick Griffiths^[16] which investigated the (maximum register value) Busy Beaver function for register machines (Beaver(n)); Griffiths determines the values of Beaver(n) for sizes 1 to 4 (using the modern instruction counting convention), and provides lower bounds for sizes 5 to 8. It also provides a machine (constructed by Ortwin Gasper in 2003) which shows the bound MBB(11) > 10↑↑17.74.^[17]
  • On October 8, sheep marginally improved the bounds for MBB(10).^[18]
• SKI Calculus
  • On October 8, cppdecksucker shared a holdouts list for Ξ₀_SK(8) consisting of 17 terms, 2 of which have been decided to not have a normal form.^[19]
• Domain-Restricted Instruction-Limited Busy Beaver
  • On October 10, star, using Claude, discovered a new champion for BBi(10, 6, 2) (colloquially known as BB(5.5)).^[20]
  • On October 11, star, using Claude, reduced BBi(10, 6, 2) to 4 holdouts,^[21] all of which are present in the most recent holdouts equivalence list (BB6_holdouts_1581_eqv_740.txt).^[22] She believes that two of these holdouts (1RB1LA_1RC0RF_1RD---_0LE1RB_---0LA_1LD1RF (bbch) and another equivalent machine) are Cryptids.^[23]

Misc

• On October 1, dyuan shared a subset of BB(6) holdouts, consisting of 24 machines which are expected to be easily analyzable by longitudinal analysis.^[24]

Champions

• Jeff Ketchersid discovered a set of small Ackermann-level champions, created by modifying the current BB(7) champion, including:
• On October 4, a new BB(8) champion, 1RB0RA_1LC1LF_1RD0LB_1RA1LE_1RZ0LC_1RG1LD_1LC0RH_1RG1LF (bbch), which takes over $2{\uparrow }^{37}3$ steps to halt. Prior to this, the BB(7) champion, found by Pavel Kropitz, held the BB(8) championship by default.^[25]
• On October 7, a new BB(9) champion, 1RB0RA_1LC1LF_1RD0LB_1RA1LE_1LI0LC_1RG1LD_0RH0RF_0RG0RE_0LH1RZ (bbch), which takes over $f_{\omega }(2{\uparrow }^{13}3)$ steps to halt.^[26] Prior to this, the BB(9) champion, found by Jacobzheng, ran for just over $f_{\omega }(f_9(2))$ steps.
• On October 8, a new BB(10) champion, 1RB0RA_1LC1LF_1RD0LB_1RA1LE_1LI0LC_0RG1LD_1RH1LG_1LC0RG_0LJ0LI_1RZ0LC (bbch), which takes over $f_{\omega +1}(2{\uparrow }^{36}3)$ steps to halt.^[27] Prior to this, the BB(10) champion, found by racheline, ran for just over $f_{\omega }^2(25)$ steps. This is also the smallest 2-symbol machine (in states) known to run for longer than a Graham's number number number of steps; in other words, this machine shows that BB(10) > g₆₄, improving on 50_ft_lock's earlier result that BB(13) > g₆₄.

Holdouts

• BB(2,5)
  • On October 2, prurq, using Aristotle AI, claimed to have to proven one of the remaining holdouts halting, reducing the unofficial count to 38 out of initially 60 Rocq-proven.^[28]
  • On October 9, prurq simulated a machine to halting, reducing the unofficial count to 37.^[29]
  • On the same day, Andrew Ducharme released an unofficial holdout list of 37 machines.^[30]
• BB(2,7)
  • Terry Ligocki enumerated 20K more subtasks, increasing the number of holdouts to 3,125,433,611. All 1 million subtasks have been enumerated! This enumeration took from November 2025 to October 2026 using the resources [Ligocki] had available to work on this enumeration. Now we can start decreasing the number of holdouts!
• BB(6)
  • On October 1, Discord user oscar proved a machine non-halting, formalized in Rocq the next day.^[31]
  • On October 3, oscar proved a machine halting,^[32] formalized in Rocq the next day.^[33]
  • On October 6, Discord user Zuck proved a machine non-halting.^[34]
  • On October 7, mxdys released a holdout list of 778 machines up to equivalence.^[35]
  • On October 10, Discord user Dennis proved a machine non-halting.^[36]
  • On the same day, mxdys released a holdout list of 740 machines up to equivalence.^[37]
  • On October 11, Dennis proved another 4 machines non-halting.^[38]