Which movement is used in the Audemars Piguet Royal Oak Extra-Thin “Jumbo”?

Created in 1970, Calibre 2121 is a derivative of Calibre 2120 (1967), also powering an aperture-type date display. This additional function raised its thickness to 3.05 mm, making it the world’s thinnest mechanical selfwinding movement with a central rotor and date.