I wasn't aware that they'd been around that long. Did they only recently become part of that Gap/B-Republic group? Do they actually have physical store locations (if so they aren't mentioned on the website).
I tend to find that I wear a much smaller size in Gap than I would elsewhere so maybe I should size down to a small in Athleta.
Athleta was just recently acquired by the Gap/B Republic group. Their sizing is not related to these stores. I find that they run true to size for the most part. If anything, their items might be a tad looser than what you might see in other clothing stores, but not much. Their clothes are very well made and comfortable. I've purchased from them several times.