I don't have any first-hand knowledge, sorry. (Not affiliated with ISRG.) Based on some public posts, I believe Let's Encrypt is using Gemalto HSMs, though I'm

I don't have any first-hand knowledge, sorry. (Not affiliated with ISRG.) Based on some public posts, I believe Let's Encrypt is using Gemalto HSMs, though I'm not sure which model or how many of them.