Apple tells developers that existing app updates will need to be 64-bit by June 1st
Forcing developers to include 64-bit support should remove some of the pressure from iOS, since apps now have to load 32-bit runtimes to be backward-compatible. The new rules though, won't affect any iPhone model older than the Apple iPhone 5s. It was the latter that first brought 64-bit processing to a smartphone.
Apple gave developers a heads up about the change in October, offering a 6-month warning on the 64-bit requirements for new apps. Today's warning gives developers working on updates to their apps, a similar warning.
source: Apple via AppleInsider