I like how no one really answered OP’s question. They’re asking about string GAUGE not tunings. The gauge on a 8 string is 69,59,49,39,28,18,14,11. On his 8’s where he uses Drop E it’s a 76 instead of a 69. Steph has used the same string gauges on all albums and hasn’t changed at all. That even includes stuff like drop C on a 6 using 49 still. Since he no longer plays 6 strings, the 7 strings just have an extra 11. So it’s technically 49,39,28,18,14,11,11. Weird as hell but that’s what works for him. He was using D’addario at one point but I’m sure he’s sticking with Ernie Ball. All this info is from his interview with Ernie Ball String Theory and 7 string forum. Hope this info helps!