Unfortunately I cannot answer that question. I've purchased 3 pair and they all have the rubber strips on the heel.
you can't tell by the description for sure. The ones I bought do have the gel on the heel.
When I'd asked SmartWool this question, I'd learned: it's by manufacture date - all current ones have the gel. So, "closeouts" MAY have greater likelihood of not having the gel. (It's not related to size or color.)