Rough estimate from the times I've counted is 85% CA's and 15% FO retirements.
I'm working on the end of 2018 seniority bid statuses (with DOH this time) per a request. Looking at the announced vacancies and they're in bid statuses that are more senior and/or have been stagnated recently. The big exception is LGA 777 FO. It's currently 11,748 at the bottom and the bottom G4 FO slot in the company. The six vacancies would have to drop 752 numbers to reach 12,500. If we were betting I'd be betting against 12,500 at the bottom in the June bid. I think there will be some more senior guys back filling.
We'll be smarter come Jan 15-18th!