Google image URLs allow arbitrary upscaling via size parameter

i noticed that Google profile image URLs accept a size parameter (s96, s512, etc.) [1]. if you increase it to something large like s9999, the server returns a much higher-resolution image even when that size was not originally uploaded.

example: https://lh3.googleusercontent.com/a/default-user=s9999

i am curious what the underlying system is here... are they doing real-time upscaling?

[1] https://developers.google.com/people/image-sizing