Imac 2012 27" WAITING DIY OWC, FUSION DRIVE OR NOT?

Hello everybody,
I have a question about the fusion drive please.
If I get an Imac 27" with a Fusion Drive is going to be a Unique HD with all together or it's going to be a Regular HD + a SSD 128Gb ?
Since I'm planning to order later a DIY from OWC to add a bigger SSD it's pretty important that I get that answer because if the Fusion Drive is a composition of 2 parts I will simply trash the 128 SSD to put the OWC SSD losing $200. In that case I guess it's better if I simply go with a regular 1TB HD and wait till the DIY Kit will be released so I can save $200 and get the SSD place empty just waiting for the OWC SSD to be placed.

Let me know,
Sorry for my english in advance
Thank you very much for the help!

Ps: There are some rumors about a possible release date for that DIY Kit from OWC?

I can pay OWC to do all the dirty work in case, isn't a problem at all, but my question ether way is going to be relevant because if the SSD is a separate part I will get a $200 component sitting somewhere with no use at all after the OWC SSD upgrade.

Let me know,
thanks.