It’s about 3 years behind schedule, which when compared to the Patriot Missile, which was entered design in 1969, but did not enter service until 1984, but the S-400 Triumf (NATO designation SA-21 Growler) has officially entered Russian army service.
It is arguably the most capable SAM in service, with a 400 km range, and a significant ATBM capability, as well as an active radar seeker, which was not present in the S-300 (SA-20 Gargoyle).
It claims to have a significant anti-stealth capability, and based on some numbers I ran a few years back, it would appear that the system could detect an F-22 at a range of at least 15 miles, perhaps more, if some of the advances in signal processing and computers work as advertised.
H/t ELP Defens(c)e Blog.
If that's the first instance at which it detects the F-22, then its already dead.
Understand something: I came up with the number from taking 400km, and assuming that was the range for a 10 sq meter RCS (F-15 and B-2).
My guess is that their detection abilities, involving sensor fusion and increased processing power, are a lot more than that.