When I query multisampling I see it is set to 8 by default. When I set it to 0, both triangles are aliased as expected.
I was under the impression that FXAA was a software based solution based on this discussion: How to anti-alias in vtkRenderWindow - #6 by lassoan
Either way, FXAA is visually unappealing to me. Like looking through smudged glasses. I know, I am picky. But it’s hard to downgrade from the beautifully crisp multisampling of VTK8.