I could be wrong, but I think every 950 XL is dual SIM.
I'm curious if only the unlocked 950 has dual SIM or if dual is even available in the US.
There are single sim and dual sim versions of both the Lumia 950 and the Lumia 950 XL. All in black or white. Plus AT&T version. 10 SKUs so far.
I do not have enough posts to post links yet.
Please change the word "dot" to actual dots below.
Microsoft Lumia 950 (Single SIM)
wwwdotmicrosoftdotcom/en/mobile/phone/lumia950/
Microsoft Lumia 950 Dual SIM
wwwdotmicrosoftdotcom/en/mobile/phone/lumia950-dual-sim/
Microsoft Lumia 950 XL (Single SIM)
wwwdotmicrosoftdotcom/en/mobile/phone/lumia950-xl/
Microsoft Lumia 950 XL Dual SIM
wwwdotmicrosoftdotcom/en/mobile/phone/lumia950-xl-dual-sim/
Unless the phone is specifically marketed as the "Dual SIM" variant (especially in the USA), it is safest to assume that the model only supports a single SIM.
I sure hope that Microsoft offers the Lumia 950 Dual SIM in the USA. Having both business and personal SIMs on the same phone would be awesome. I also hope they offer both colors. For whatever reason, microsoftstore.com only shows one version of the 950 (black?).