As with the Nexus 5, Google is going to sell two versions of the new flagship device. There will be one Nexus 6 SKU for the Americas and another for the rest of the globe. Each will have the LTE bands that work for carriers in that region, with the usual overlapping on 3G and 2G. There are a ton of bands too.
GSM: 850/900/1800/1900 MHz CDMA: not supported WCDMA: Bands: 1/2/4/5/6/8/9/19 LTE: Bands: 1/3/5/7/8/9/19/20/28/41 CA DL: B3-B5, B3-B8
Both versions are well-equipped for sure, but check out that monstrous list of LTE bands on the American SKU—a full dozen LTE bands. It even has band 12 for T-Mobile and tri-band for Sprint Spark. And let's not forget the coming Verizon support in there too.