The iPhone 5s was the first iPhone model to have a 64-bit processor. Apple introduced it on September 10, 2013, with the Apple A7 system-on-chip, which used a 64-bit ARM-based CPU architecture.
The A7 was a major technical milestone because it was also the first 64-bit processor used in a consumer smartphone. Apple paired the chip with iOS 7, whose system software and built-in apps were prepared to operate in 64-bit mode. The phone also included the M7 motion coprocessor, which handled data from sensors such as the accelerometer and gyroscope.
The iPhone 5c launched alongside the 5s but retained the 32-bit A6 chip from the iPhone 5. The iPhone 6 came later and used the newer 64-bit A8 chip, so it was not the first. The 5s also introduced Touch ID, making its processor upgrade one part of a broader hardware redesign.