David (and Patrick),
this is what Patrick mentions in the first sentence: He is not asking about RASTER CALCULATOR tool (your link above) but about the CALCULATOR raster function (Calculator function—ArcGIS Pro | Documentation ) - and here the Doc says two things:
So to clarify, I made a test:
Without Spatial Analyst or Image Analyst Licenses i got:
With Spatial Analyst activated the raster function I tested worked.
With Image Analyst activated the raster function I tested worked.
So the short term answer is: It does require one of both Extensions and thus the documentation on the Calculator function page should also state:
But thank you for notifying us, Patrick. We'll have it adjusted
As a workaround for you, Patrick, if you really only want to to an arithmetic PLUS of two rasters: The Arithmetic function will not require Spatial Analyst or Image Analyst.
Guenter