Hi,

im reading about specular aliasing because of mip maps, as far as i understood it, you need to compute fetched normal lenght and detect now its changed from unit length. I’m currently using BC5 normal maps, so i reconstruct z in shader and therefore my normals are normalized. Can i still somehow use antialiasing or its not needed? Thanks.

That is the approach suggested in the original Toksvig whitepaper, but it's not the only way to do it. These days it's quite common to pre-compute the modified roughness value, and "bake" that into your roughness map. Since roughness maps are fairly ubiquitous now that almost everyone has moved to microfacet specular models, you can basically get your specular AA for free by baking into the roughness map.