It seems to me that SSFC are juggling the starting XI much less than last season so I thought I'd run the numbers through the first eight games.
Unique starting XI: 8
Unique players who have started: 17
Players who have started all 8 games: 5 (Frei, Yedlin, Marshall, Alonso, Martins)
Mean starting XI churn: 1.7
Standard deviation: 1.0
Players w/ MLS game time: 20
I'm defining churn by the number of players who are in the lineup for a given game but were not in the lineup for the previous games. Unfortunately I don't have the numbers for last year to compare these to, but I'll try to track them throughout the season. Even though we haven't seen a lineup repeated I think the median and mode churn of 1 confirms my impression that Sigi is using a pretty stable lineup. Whether that's a cause or result of the great record is up for debate. I suspect it is some of both.