[VWWHFSfQ]

At this point they'll be stuck on old git for all of eternity unless they just roll their own archive/compress step out of band so the old hashes still work. Yikes.

[rfoo]

New git has a flag for keeping the old behavior, so it's not as bad.

[groestl]

They could also brownout the implied contract over a longer timespan.

[jeffbee]

They could use the old behavior for archives in which all the inputs predate the changeover.