Windows 8.1 worked fine in "just" 1Gb (my tablet ran it with that, it was a very smooth environment.)
People were expecting Windows 10 to be the "7" to 8.0s "Vista" (boy, is that a confusing sentence.) I think Windows 10 though is the second coming of Vista. I'm hoping "what comes after Windows 10" (I'm not sure how the marketing will go) to be rather more memory efficient.
Technically Windows 10 runs in 1Gb, it's running on the same tablet right next to me. But it crawls. All the smoothness of 8.1 is gone.