Which macOS version was the first to be 64-bit only, dropping 32-bit app support?

The first macOS version to drop support for 32-bit apps and support only 64-bit applications was macOS Catalina.

Apple released macOS Catalina, version 10.15, on October 7, 2019. It followed macOS Mojave, which was the final macOS release capable of running 32-bit applications. Catalina completed a transition Apple had been signaling for years: software intended to run on the Mac had to use the 64-bit architecture.

The change affected older applications, plug-ins, drivers, installers, and components that had never been updated. When users upgraded, Catalina could no longer launch those 32-bit programs. Apple had already begun warning users about the transition in earlier releases, and macOS High Sierra and Mojave displayed compatibility notices for aging software.

This is sometimes confused with Apple’s later move from Intel processors to Apple silicon. Catalina was still an Intel-only release; macOS Big Sur introduced support for Apple’s ARM-based M1 Macs. Catalina also retained the familiar 10.x numbering, while Big Sur became macOS 11. The 64-bit-only change therefore describes application compatibility, not the processor transition.