You can be certain that any EF 24-105 f/4L lens for under a $1000 is going to be grey market lens whether it says so in the description or not. B and H Photo and Video carries both US and Overseas versions. The Grey market lens is $100 cheaper (1149 vs 1049). I recommend that you only buy from one of the big retailers (Beach, Adorama or direct from Amazon.com) to be certain that you know which you are getting. If you do buy grey market, buy a domestic after market warranty. Independent retailers are notorious for giving poor service and so your risk is much higher not matter what the online ratings say. They have ways of coercing people into removing unfavorable ratings. The after market warranties from the secondary retail sites can be as worthless as the product so do not believe that it is any protection from a bad retailer. Make sure that you pay with a credit card so that you can stop payment if you don't get what you were promised.
Purchased directly from Amazon.com and received a US retail box with USA / Canada warranty card. I got very lucky with this purchase as I just happened to check my Wish List on Oct 24 1013 and saw the price on this 24-105 dropped to $700 the lowest price over the last 5 years as per CamelCamelCamel.com
Some people think f4 is not good enough to go with 24-105mm, so they prefer 5D mark iii body only to the whole package. This 24-105 len maybe come from the 5D iii package, which possibly makes it cheaper than the retail price.