Apple owns the copyright for CUPS.

Apple employs the original developer of CUPS, which is Michael Sweet.

Apple employees (Michael Sweet) made 150 commits in the last year and a half. The next contributor has 7. He has 50k+ additions/deletions. The next contributor has 8k.

It's safe to say that Apple develops CUPS.

edit:

Michael Sweet himself in this announcement also uses the terms "Apple is excited to announce" and "we"[0]

[0] - https://lists.cups.org/pipermail/cups-devel/2017-November/01...