Calibre 2123 was launched in 1977 to equip the Royal Oak III, Reference 4100, whose 35 mm diameter required a smaller calibre than the 2120 (d: 28 mm, h: 3.05 mm). This new mechanism, which oscillated at a high frequency of 28,800 vph, was both 2 mm smaller and 0.2 mm thicker than its predecessor, thus enabling it to add a centre seconds hand, a first for a Royal Oak watch.

Just under 9,000 units were produced between 1977 and 1984, the most productive years being 1987–1981 with an annual average of around 1,800 movements. Major improvements were made in 1979, leading to the creation of the 2123/1 variation (different mainplate, new pull-out piece, barrel bridge, yoke spring, etc.).

Calibre 2123 heralded the long history of Audemars Piguet 11½-ligne (26 mm) selfwinding calibres based on a LeCoultre & Cie blank. In 1983, the second generation kicked off with Calibre 2124, followed by its derivatives 2124/2810, 2124/2815, 2124/2825, 2124/2812, 2125, 2126, 2126/2840 and 2129/2845. The third generation was born in 1996 with Calibre 2224, also accompanied by multiple derivatives 2224/2810, 2224/2815, 2224/2811, 2224/2812, 2224/2814, 2225, 2226, 2226/2840, 2226/2841, 2226/2839, 2127/2827, 2229/2845. It was in turn succeeded by a fourth generation in 2005, starting with Calibre 2325 and its derivatives 2326, 2326/2840, 2326/2841, 2326/2839, 2326/2847, 2326/2848, 2329/2845 and 2329/2846. The filiation between these calibres made it possible in some instances to replace severely damaged movements by one of their direct descendants.

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