I am 99% sure that the 3-burner Spirit II and the current "larger" Spirit - whether 3 or now 4 burners, all still use the same grate size as the original Genesis, Silver/Gold, etc. And the orginal 2-burner Spirits used the same grates as the Silver A. I believe that changed with the Spirit II 2 -burner where the grate was deeper front to back but narrower left to right. I think that configuration has continued with the newest "smaller" 2 or 3-burner latest Spirits.
But, I have been known to be wrong - especially on April 14!!