4L25 is one of a family of high-end automatic watch movements from Seiko. The other closely-related members of this family are the 4L75 and 6L35, and it is believed to be the design basis for the Soprod A-10. Seiko only produced 4L movements from 2006 through 2013 and the 6L35 in 2018.

Seiko introduced the 4L family in the late-2000's as a thin and compact yet upscale automatic movement. The 4L25 was used in a new line of Seiko-branded dress watches priced higher than the main brand had ever dared, at ¥189,000 (about US$1,600 in 2007). These watches, SARA001/SARA003/SARA005, SARA007/SARA009, and SARA011/SARA013, featured high-end touches like a guilloche dial, signed crown, and sapphire crystal. Yet they were too expensive and did not sell well. They appear in the Seiko catalog only between 2006 and October 2008.

Seiko went on to use the 4L in their upscale Credor range in the Credor Signo GCBW999/997 and GCBW995/993 and Credor Node GCBW991/989. Apart from more elaborate decoration, the 4L75 and 4L25 appear very similar. These models sold for over ¥260,000, appearing in April 2007 and removed from the catalog by April 2013.

This cost is partially due to the high-end 4L movement, which was designed by Seiko Instruments as a competitor and drop-in replacement for the ETA 2892. The 4L family is a radical departure for Seiko It was their thinnest-ever automatic movement at just 3.6 mm as well as one of their smaller automatics at 25.6 mm. Both dimensions, along with the location of dial feet, date, and crown, were chosen to match the ETA 2892. Additionally, the 4L family uses a conventional geared bidirectional winding system rather than Seiko's familiar Magic Lever system and Incabloc shock protection instead of Seiko's Diashock. It is likely that these changes were an additional effort to attract Swiss customers.

Seiko Instruments apparently sought to enter the ebauche market, providing the 4L movement to Swiss makers for finishing and re-branding. Although extremely hesitant to discuss this arrangement, Soprod introduced their A-10 movement in 2004, which obviously shared its architecture with the 4L. It is very likely that this was the initial ebauche customer for SII. Soprod's statement that the A-10 is “calibrated 2892” has caused confusion that this movement is related to the ETA, but a glance at the layout disproves this. But the September 2007 acquisition of Soprod parent STM Holdings by Peace Mark of Hong Kong derailed the arrangement Seiko was unwilling to allow a Chinese company access to its products and intellectual property. Still, Seiko continued producing their 4L to 2013 and Soprod's A-10 remains in production, now under Festina.

It appears that the poor sales of the SARA line, the elimination of the only ebauche customer, and the availability of other movements, notably the 6R family, led to the quick demise of the 4L movements.

In 2018, Seiko introduced a new movement, 6L35, in the new SARA015. This movement appears very similar to the 4L family with just a few differences. An extra jewel is fitted (now 26), the anti-shock mechanism is now Seiko's in-house design rather than the Swiss Incabloc arrangement and the balance studs are gold rather than silver.

The 4L family operates at 28,800 A/h and features hacking and hand winding.

• 4L25
  • Seiko SARA001/SARA003/SARA005, SARA007/SARA009, SARA011/SARA013
• 4L75
  • Credor Signo GCBW993/GCBW995, GCBW997/GCBW999
• 6L35
  • Seiko Presage SARA015

• Seiko 4L/6L Family
• Seiko 4L25 Manual
• Seiko 4L75 Manual
• The Curious Case of the Seiko SARA and 4L25
• The "new" Seiko 6L35 caliber introduced in the Presage SJE073J1/SARA015, or is it?, Musings of a Watch Addict, March 31, 2018