Nusach Ari means, in a general sense, any prayer rite following the usages of Rabbi Isaac Luria, the AriZal, in the 16th century.
The Ari and his immediate disciples did not themselves publish any prayer book, though they established a number of characteristic usages intended to be used as additions to the existing Sephardic rite.
[1][2] In alteration of this concept, especially in 18th/19th-century Hassidism the claim emerged that a superior Nusach Sefard[3] would reach a believed "thirteenth gate" (Shaar ha-Kollel) in Heaven.
In the 18th century, Rabbi Schneur Zalman decided to undertake the task of compiling a prayer book which amalgamated Kabbalistic-Hasidic teachings (including his own) with what he considered to be the most correct version of the Lurianic Sephardic rite.
For this reason, a number of non-Hasidic rabbis (see Mitnagdim) disapprove of the adoption of these different rather recent 18th/19th-century devised customs by Ashkenazi Jews.