During his studies in the 1970’s at Eastman School of Music in Rochester, American marimbist Leigh Howard Stevens (1953 -) developed the Stevens grip which is also called the Musser-Stevens grip or the Stevens technique. It was the first double-mallet grip to get a thoroughly documented description when Stevens published his book Method of Movement for Marimba in 1979. As Stevens describes it in his book, the grip is a child of the Musser grip. What separates it from the Musser grip is most notably the vertical hand position and the manipulation of the inner mallet where the mallet does not go under the thumb when playing larger intervals but instead is held between the outer phalanxes of thumb and index finger and the shaft end is moved from the base of the thumb towards the base of the middle finger.
The Stevens grip is together with the Burton grip the most used double-mallet grip today; it seems more common on terraced bar layouts like that of the marimba than on the flat bar layout of the vibraphone. Below are two images of the grip.