It doesn’t but can be added on easily. There are some good threads about adding on the clasp on this forum.
A very simple mod. I went the other way. I have an PO 8900 and went from adjustable clasp to one that does not adjust. The adjustable one is just a tad thicker. The OB installed it in 1-2 minutes.
This topic has been discussed previously at: https://omegaforums.net/threads/adjustable-clasp-for-the-8500-po-42mm.64910/#post-816282