Speaking of the regular One M8, the Dual SIM model doesn’t bring any novelties besides the added support for two SIM cards. So it’ll be the same 5-inch slab of metal powered by a Snapdragon 801 processor, and running Android KitKat with Sense 6.0 UI. Oh, and it will have the same "groundbreaking UltraPixel Duo camera" (HTC's words, not ours).
It looks like the One M8 Dual SIM will be available in only one color version: gunmetal grey. HTC didn’t say if it’s planning to release the new handset in other markets, but we know that this should be introduced in Russia - most probably pretty soon.
It’s unlikely that we’ll see the HTC One M8 Dual SIM being sold in the US. Anyway, we'll let yo know if we hear anything on this.
source: HTC (translated)