GIRM: 53 “The Gloria is a very ancient and venerable hymn in which the Church, gathered together in the Holy Spirit, glorifies and entreats God the Father and the Lamb.  The text of this hymn may not be replaced by any other text.  The Gloria is intoned by the priest or, if appropriate, by a cantor or by the choir; but it is sung either by everyone together, or by the people alternately with the choir, or by the choir alone.  If not sung, it is recited either by all together or by two parts of the congregation responding one to the other." 
 
STL: 149.  “While the through composed settings of the Gloria give clearest expression to the text, the addition of refrains is permitted, provided the refrains encourage congregational participation. “
Here at the Cathedral of St. Mary, we vary the Mass setting at the change of seasons.  Currently, we are singing the Heritage Gloria and the Mass of Renewal.  On the third Sunday of the month at the 8:00 a.m. Mass, beginning in the Fall, the English chant version of the Gloria will be sung.  On most occasions, unless otherwise directed, the Gloria is sung through-composed by everyone throughout.