Topic on Talk:S.T.A.L.K.E.R.: Shadow of Chernobyl
I can confirm DX8 is not used in the STALKER games by using DgVoodoo 2, which, by default, puts a watermark on the screen when a given renderer is used. I only used the DX8 and DX7 DLLs for dgVoodoo2, and while the game defaulted to static lighting, the watermark did not appear - so definitely DX9. The R1 renderer, the one used when static lighting is selected, could still be using DX8-level shader models since DX9 also supports them, but that's speculation on my part.