What replaced the L901.0
The original Lange 1 launched in 1994 with the Cal. L901.0, the first new Lange caliber after the post-reunification revival of the manufacture. By the 2010s the L901.0 had served for over twenty years; A. Lange & Söhne announced its successor in 2015. The L121.1 retains the asymmetric Lange 1 dial layout (off-centre time, big date, sub-seconds, power reserve) but rebuilds the movement from scratch with an in-house balance, twin mainspring barrels for 72 h reserve, and a redesigned big-date module.
The instantaneous big date
The Lange 1's outsize date ("Großdatum"), inspired by the Semper Opera House calendar in Dresden, has been the watch's signature complication since 1994. The original L901.0 used a creeping change (the date crept over a few minutes around midnight). The L121.1 introduces a fully instantaneous mechanism: both date discs (units and tens) jump simultaneously at midnight in less than 1/100 of a second, driven by a constant-force spring that releases at the stroke of 12. This solves the long-standing complaint about the slow date change of the original.
In-house balance and twin barrels
A. Lange & Söhne developed its own in-house balance wheel for the L121.1, eccentric-poising and free-sprung, paired with a proprietary overcoil hairspring. The escapement remains a Swiss lever, but every component (escape wheel, pallet fork, balance, hairspring) is now manufactured at the Glashütte facility. The twin mainspring barrels, mounted in series, raise the power reserve to 72 hours (up from 72 h on the L901.0 incidentally; here the gain is in torque stability across the reserve, not headline figure).
Finishing standard
The L121.1 is finished to the standard Lange has set since 1994: untreated German silver three-quarter plate (oxidises to a warm patina if exposed), hand-engraved balance cock (each engraving slightly different across pieces), screwed gold chatons holding key jewels, polished bevels and inward angles. The movement is visible through the sapphire caseback. Total finishing time per movement runs in the dozens of hours; this is the floor of "haute horlogerie" finishing alongside Patek and the higher Vacheron / AP movements.
Where it sits and what it costs
The L121.1 powers the standard Lange 1 since 2015, and (with module variants) the Lange 1 Daymatic, Lange 1 Tourbillon Perpetual Calendar, and several Anniversary editions. Retail for the steel-back-only Lange 1 in white gold is approximately EUR 41,000; rose gold around EUR 45,000; platinum in the high 60s. Service intervals are recommended at five-year intervals; service is exclusive to A. Lange & Söhne in Glashütte. The L121.1 sits at the same finishing tier as Patek's 215 PS and Vacheron's top manual movements.
