You may be hearing about a new US variant, sometimes called "The Columbus Variant", and some really sloppy science reporting. Here's the paper on it.
Yes, there is a set of variants that have become common in the US, and yes, they do share some of the same mutations as the UK variant. (The US family is now named 20C-US and includes several related variants.)
It does not seem to be a game changer in transmissibility based on the left-hand chart below. You'll see the blue variant spread quickly to 10% of samples...then didn't grow its share at all for two months. The orange variant, likewise, jumped from 3% to 12% to 19%...and then declined to 18%.
This is very different than the B.1.1.7 variant, which tends to go more like 3%, 20%, 80% in consecutive months. It is very difficult to determine when growth is from higher transmissibility vs a few super-spreader events in areas with growing outbreaks.
But...don't be surprised if there's a lot of hype in the next few days about the "US variant" or the "Columbus variant". It's a real thing, but it's not at all clear if if's more transmissible, and if so, how much.