Provided are imidazol [1,5-f] [l,2.4]triazinyl, imidazol [l,2,4]triazinyl, and [1,2,4] triazolo [4,3-f] [1,2,4] triazinyl nucleosides of formula I nucleoside phosphates and prodrugs thereof. The compounds, compositions, and methods provided are useful for the treatment of Flaviviridae virus infections, particularly hepatitis C infections. Formula I Wherein X1 or X2 is indepently C-R10 or N and wherein at least one of X1 or X2 is N.
