The Abbey of Solesmes web site shows the first volume of a new Antiphonale Monasticum (description in French) available.
The three-volume set is to be a successor to the 1934 Antiphonale: it is designed for Benedictine communities, presenting the Office in chant “in a renewed form conforming to the liturgical principles promulgated by Vatican II”: that is, consistent with the Liturgia Horarum, and approved by the CDW in February.
The first volume includes the Ordinary parts of the Office and the seasonal propers, while the remaining volumes will present the offices for feasts and saints’ days. Hymns are not included, as they are in the already published Liber Hymnarius.
The editors of the book have placed a fifteen-page article about it on-line (sorry, it’s in .doc format), describing the principles and choices guiding the work. There are some changes in notation, particularly in the abandonment of certain markings invented early in the 20th century: the dot or mora vocis, the vertical episema, and the horizontal episema. The result is that a lot of rhythmic interpretation that once seemed standardized will now be left to the discretion of the chant master.
If you’re interested in getting a copy, please note: some people are reporting that credit-card sales are not being accepted (successfully) by the Solesmes web site, but if you request direct billing, the order does go through.