I supposedly have to do the plugs on my wife's car, but I'm going to leave them for another 30K.
They are ruthenium-iridium alloy with the fingernail GND electrode.
Should be good for 100K easy. So they stay in. Subaru of America should should be prosecuted for a shakedown on this 60Kmi plug replacement scam!
There are a couple of good videos on youtube on doing this job
This guy used autolites - they looked fine, and he said he noticed no loss in performance or fuel mileage
and they are 1/2 to 1/3rd the cost of the ripoff NGK.https://www.youtube.com/watch?v=5L1gSGqYQ6E
Subaru has traditionally used Denso or Champion - not NGK. When the dealer used NGK on a tuneup on one of my wifes older subaru, the car ran poor - I had to pull them and put in the proper K20 PRU-11 Nippon Denso and then it ran great again. Not a NGK fan, had FAILS on most everything that used them or that I "downgraded" to NGK aver many decades.