Now, a new message has been spotted in the Photos app on macOS 10.13.6 and states that final purchases for the built-in photo printing service will need to be placed by September 30, 2018. Afterwards, it appears that Mac users will have to opt for third-party companies like Shutterfly to craft physical books made from their digital photos.
Apple explains that users can integrate these third-party services into Photos with a Photos Project Extension downloaded from the Mac App Store. With these extensions, apps like Shutterfly can integrate photo printing services into Apple's own Photos app so users don't have to leave the app to build their photo books.
For classic landscape-style books, Apple sells softcover books starting at $9.99 in a medium size, and increasing to $49.99 in hardcover and extra large size. Calendars are $19.99 each, cards start at $0.99, and posters for panoramic shots are also available for $12.99-$17.99. These prices should remain intact until the service shutters in the fall.