With Linux 6.17 was the decision by Linus Torvalds to mark Bcachefs as "externally maintained" and not accept any new Bcachefs code into the mainline kernel but keeping the existing code within the tree. That was useful for those relying on Bcachefs to still boot a mainline kernel at least. Now for Linux 6.18, the Bcachefs code was removed from the mainline kernel.

Linus Torvalds a short time ago stripped out the Bcachefs code from the mainline kernel. He commented in the removal :

"bcachefs was marked 'externally maintained' in 6.17 but the code remained to make the transition smoother.

It's now a DKMS module, making the in-kernel code stale, so remove it to avoid any version confusion."

With that 117k lines are removed from the kernel tree. Bcachefs users should now use the DKMS kernel modules out-of-tree but without any ability to boot the mainline kernel using the stale code found in v6.17.