At SHOT Show next month Glock will be introducing Gen4 versions of the G21 (.45 Auto), G32 (.357) and G34 (9mm). They all use the new(ish) dual recoil spring system. From the press release …

GLOCK’s newest generation pistol, the Gen4, brings revolutionary design changes to the world’s most popular pistol. New to the Gen4 family, GLOCK will introduce the G21 (.45 Auto), G32 (.357) and G34 (9X19) Gen4 models at the 2012 SHOT Show in Las Vegas.

The ergonomics of the Gen4 pistol have been refined by adding a Multiple Back Strap (MBS) system to the grip of the pistol. Each Gen4 comes with three difference grip options: a short, medium and large size, enabling the pistol to adapt to each individual shooter’s hand size with the removal and insertion of a single pin. In addition, the grip has also been given a new Rough Textured Frame (RTF) to increase grip traction.

The Gen4 magazine release catch has been enlarged and is reversible for the ambidextrous shooter. To utilize the interchangeable magazine release feature, the Gen4 magazines have two notches cut on each side of the magazine body, allowing users to switch access of the catch to the left or right side of the pistol with no additional parts. Previous magazines will continue to work in the Gen4 pistols as long as the magazine release catch is left in its original position.
Internally, the original recoil spring has been replaced with a dual recoil spring assembly, which noticeably reduces felt recoil while simultaneously increasing the life cycle of the pistol.

Glock 22 Gen4 showing dual recoil spring.