APFS does have snapshots and at least the local TM backups heavily use them (it takes a fraction of a second to perform a local TM backup). TM backups to disk a

APFS does have snapshots and at least the local TM backups heavily use them (it takes a fraction of a second to perform a local TM backup). TM backups to disk also seem to be organised as snapshots and have become much much faster in the recent macOS versions, so I don't think it does only copy changed blocks (but I can't be sure). What I would love for APFS to have thought is block-level deduplication. Seems like an obvious fit for an SSD-optimized COW system anyway, surprised they haven't implemented it.