Originally posted by Santa Drummer
After

d4 d5
c4 c6
Nc3 dxc4
e6 b5

is it safe to hold out on c4 as black? I cant seem to find a counter for white

It's the Noteboom variation of the semi-slav. Black often winds up a pawn ahead and intends to push them on the queenside. But it's sharp because white counterattacks in the center and has chances at weakening them. eg.
1. d4 d5 2. c4 c6 3. Nf3 e6 4. Nc3 dxc4 5. e4 b5 6. a4 Bb4 7. Bd2 a5 8. axb5 Bxc3 9. Bxc3 cxb5 10. b3 Nf6