The faq points 30 & 31 say it use multisampling (up to 32 samples per pixel) for AA, and the winding at each sample is calculated analytically from the curve.
From other searching, it seems no other vendor supports that extension.
My original target was iOS, so this was unavailable. I did experiment with their algorithm, but 4x MSAA was slow and had poor quality compared to Core Graphics, which was my reference.