The Grand Seiko 9S85 and 9S86 family are modern automatic “hi-beat” movements. The family was developed in the 2000s as a return to the Hi-Beat tradition of Grand Seiko models like the famous 45GS, 61GS, and 19GS of the 1960s. The movement design is also used by Credor and Prospex, under the 8L name.
The first modern Hi-Beat movement from Seiko was the limited-production “Super Hi-Beat” Cal. 8L88. Introduced at Baselworld in 2006, this movement ran at 12 Hz (43,200 A/h) and was used in the Credor GBBX998.
Cal. 9S85 was introduced in 2009 as the first modern Hi-Beat movement for Grand Seiko and was joined in 2014 by Cal. 9S86, which adds an independently-adjustable 24 hour GMT hand. They operate at the traditional Hi-Beat rate of 10 Hz (36,000 A/h).
The 9S movements are finished to the standard of the modern Grand Seiko 9S family and feature many technological advancements. They were the first movements to use MEMS technology for ultra-fine finishing of the escape wheel and pallet fork, and they use proprietary Spron alloys for the hairspring (Spron 610) and mainspring (Spron 530).
In 2019, Seiko introduced a lower-finished version of Cal. 9S85 for the Prospex SLA025 Hi-Beat dive watch. This Cal. 8L55 is otherwise similar. Grand Seiko also introduced a V.F.A. version of Cal. 9S85 tuned to deliver -1/+3 seconds accuracy.
A new generation, the Grand Seiko 9SA family, appeared in 2020. These new “80 hours” movements are hi-beat automatics with a longer power reserve, free-sprung balance, and double-impulse escapement.