Block-cloning.
See here.
It doesn’t matter how large a file is. The main bottleneck (over SMB) for a copy operation is the number of files (i.e, metadata operations). A single 100-GiB file will copy instantly, even if facilitated via SMB.
The higher the number of files in the copy operation, the slower the process. Unlike with traditional “copying”, the sheer size will have almost no affect on performance if block-cloning is used.