[peterfirefly]

No.

https://en.wikipedia.org/wiki/Windows_NT#Development

Windows NT was developed on various different CPUs before the Alpha was a thing. When it was released in 1993, it was released for three CPUs: IA-32, MIPS, and Alpha.

[dcrazy]

Sorry, I had conflated Windows NT development with development of 64-bit Windows as told by Raymond Chen: https://learn.microsoft.com/en-us/previous-versions/technet-...

Raymond also says elsewhere that most WinNT engineers did development on i386, but doesn’t explicitly say what time period he is describing: https://devblogs.microsoft.com/oldnewthing/20250513-00/?p=11...