It’s a customized Arch Linux. Basically manjaro, but with XFS BTRFS file system (as mentioned in the release note )
BTRFS is now the default selected file system instead of XFS. The XFS file system and all others can still be selected by the users and configured.
It used to default to XFS, according to ZDNet
CachyOS gets part of its speed by defaulting to the XFS file system. This is a curious choice for a desktop file system, I’d argue, mostly because XFS is a journaling file system designed to support very large files and ensure the file system’s integrity in the case of system crashes. XFS has been around since the early '90s and has been employed by large servers and storage arrays. - zdnet.com
if you’ve already been exposed to Linux and are looking to jump on board the Arch Linux train, CachyOS is a great option.