The iPhone has been 64 bit since 2013 and Android 2014, but Windows phones have been lagging in support for this instruction set, with the OS running in 32 bit mode even though the Snapdragon chips are 64 bit.

Now there is some indication the OS may finally moving towards the future, with a job posting on careers.microsoft.com suggesting the change should take place in the Redstone wave.

The job post for a senior program manager says:

The silicon ecosystem is always evolving.   Windows across all device categories is readying for the introduction of 64 bit computing with the ARM instruction set (ISA).   Bringing a new ISA to market involves working both broadly and deeply across Microsoft from devdiv to WDG to Server to Office and others depending on the scope of product target.   Many hard system problems need to be discovered and solved to be successful.   The role also requires deep engagements in the silicon ecosystem too.

…

Responsibilities include:
Building the plan for ARM64 aligned with the Redstone wave
Identify the “big rocks” we need to move, solve, make it happen
Build the all up view of where we are, drive the schedule
Work to ensure the necessary hardware is planned for and delivered on time
Drive performance and compatibility goals, define and drive to key metrics

There has also been other evidence that Microsoft is working on and testing “Windows 10 Mobile ARM64” already.

Moving the OS to 64 bit would allow Windows 10 Mobile to address more than 3 GB of RAM and potentially allow ambitious projects such as the “x86 compat subsystem for Windows on ARM based on x86-to-ARM just-in-time (JIT) emulator” which would allow users to run x86 apps on ARM chips.

One of the first applications may however be on the server farm, with the Microsoft Datacenter Compute Infrastructure (DCI) team hiring Systems ARM64 Architect Engineer.

We would however expect Microsoft’s next flagship to also support this technology, and I expect disappointed if it does not.