Solar expert Dr. Leif Svalgaard says the last X class flare was Dec 13th, 2006. The flare today is the first Solar Cycle 24 flare reaching X class level.
Flare classifications: Each category for x-ray flares has nine subdivisions ranging from, e.g., C1 to C9, M1 to M9, and X1 to X9.
Peak (W/m2)between 1 and 8 Angstroms
|B||I < 10-6|
|C||10-6 < = I < 10-5|
|M||10-5 < = I < 10-4|
|X||I > = 10-4|
Live updates on the WUWT solar page
h/t to Leif Svalgaard