Is X99 only comlatible with DDR4?

I am wanting to get the i7 5820k, but do not want to buy a set of DDR4 Ram.

Can DDR3 be used or not?

Cheers

Looked quickly over newegg and it seems they all take DDR4

You need DDR4 with 5820K. Which means you also need a new mobo.

well thats an expensive upgrade. may have to give it a miss

Just wait for prices to come down a bit.