A compound of the Formula or a pharmaceutically acceptable salt thereof, wherein: XisN; Y is C or N; R 1 is: (a.) (C 1 -C 3)alkyl-R 2, R 2 is phenyl, pyridyl, C 3 -C 8 cycloalkyl, or C 5 -C 7 cycloalkenyl, wherein R 2 is unsubstituted or substituted by 1 to 3 R 2a; each R 2a is independently halo, (C 1 -C 3)alkyl, or (C 1 -C 3)fluoroalkyl; or (b.) (C 1 -C 6)alkyl, wherein said alkyl is unsubstituted or substituted by 1 to 6 fluoro; R 3 is (C 1 -C 3)alkyl or (C 3 -C 6)cycloalkyl; R 4a is H or (C 1 -C 3)alkyl; R4b is H or NH 2; R 5a and R 5b are independently H or (C 1 -C 6)alkyl, wherein said alkyl is unsubstituted or substituted by 1 to 6 substituents independently selected from fluoro or hydroxyl; or alternatively, R 5a and R 5b together with the nitrogen atom to which they are attached form ring C 5 which is an azetidinyl, pyrrolyl, piperidinyl, piperazinyl, or azepinyl ring, wherein ring C 5 is unsubstituted or substituted by 1 to 3 substituents which are independently halo, hydroxyl, (C 1 -C 3)alkyl, or (C 1 -C 3)fluoroalkyl; each R 6 is independently halo, (C 1 -C 3)alkyl, (C 1 -C 3)fluoroalkyl, or cyano; and the subscript t is 0, 1, 2, or 3; and with the proviso that the compound is not: 4-amino-5-(5-hydroxypyridin-2-yl)-5-methyl-2-(8-(3,3,4,4,4-pentafluorobutyl)-[1,2,4]triazolo[1,5- a]pyrazin-6-yl)-5,7-dihydro-6H-pyrrolo[2,3- d]pyrimidine-6-one; 4-amino-5-(5-hydroxypyridin-2-yl)-5-methyl-2-(8-(4,4,4-trifluorobutyl)-[1,2,4]triazolo[1,5- a]pyrazin-6-yl)-5H-pyrrolo[2,3- d]pyrimidine-6(7 H)-one; or 4-amino-5-cyclopropyl-5-(5-hydroxypyridin-2-yl)-2-(8-(4,4,4-trifluorobutyl)-[1,2,4]triazolo[1,5- a]pyrazin-6-yl)-5 H -pyrrolo[2,3- d]pyrimidine-6(7 H)-one. XisN; Y is C or N; R 1 is: (a.) (C 1 -C 3)alkyl-R 2, R 2 is phenyl, pyridyl, C 3 -C 8 cycloalkyl, or C 5 -C 7 cycloalkenyl, wherein R 2 is unsubstituted or substituted by 1 to 3 R 2a; each R 2a is independently halo, (C 1 -C 3)alkyl, or (C 1 -C 3)fluoroalkyl; or (b.) (C 1 -C 6)alkyl, wherein said alkyl is unsubstituted or substituted by 1 to 6 fluoro; (a.) (C 1 -C 3)alkyl-R 2, R 2 is phenyl, pyridyl, C 3 -C 8 cycloalkyl, or C 5 -C 7 cycloalkenyl, wherein R 2 is unsubstituted or substituted by 1 to 3 R 2a; each R 2a is independently halo, (C 1 -C 3)alkyl, or (C 1 -C 3)fluoroalkyl; or is unsubstituted or substituted by 1 to 3 R 2a; each R 2a is independently halo, (C 1 -C 3)alkyl, or (C 1 -C 3)fluoroalkyl; or (b.) (C 1 -C 6)alkyl, wherein said alkyl is unsubstituted or substituted by 1 to 6 fluoro; R 3 is (C 1 -C 3)alkyl or (C 3 -C 6)cycloalkyl; R 4a is H or (C 1 -C 3)alkyl; R4b is H or NH 2; R 5a and R 5b are independently H or (C 1 -C 6)alkyl, wherein said alkyl is unsubstituted or substituted by 1 to 6 substituents independently selected from fluoro or hydroxyl; or alternatively, R 5a and R 5b together with the nitrogen atom to which they are attached form ring C 5 which is an azetidinyl, pyrrolyl, piperidinyl, piperazinyl, or azepinyl ring, wherein ring C 5 is unsubstituted or substituted by 1 to 3 substituents which are independently halo, hydroxyl, (C 1 -C 3)alkyl, or (C 1 -C 3)fluoroalkyl; each R 6 is independently halo, (C 1 -C 3)alkyl, (C 1 -C 3)fluoroalkyl, or cyano; and the subscript t is 0, 1, 2, or 3; and with the proviso that the compound is not: 4-amino-5-(5-hydroxypyridin-2-yl)-5-methyl-2-(8-(3,3,4,4,4-pentafluorobutyl)-[1,2,4]triazolo[1,5- a]pyrazin-6-yl)-5,7-dihydro-6H-pyrrolo[2,3- d]pyrimidine-6-one; 4-amino-5-(5-hydroxypyridin-2-yl)-5-methyl-2-(8-(4,4,4-trifluorobutyl)-[1,2,4]triazolo[1,5- a]pyrazin-6-yl)-5H-pyrrolo[2,3- d]pyrimidine-6(7 H)-one; or 4-amino-5-cyclopropyl-5-(5-hydroxypyridin-2-yl)-2-(8-(4,4,4-trifluorobutyl)-[1,2,4]triazolo[1,5- a]pyrazin-6-yl)-5 H -pyrrolo[2,3- d]pyrimidine-6(7 H)-one. 4-amino-5-(5-hydroxypyridin-2-yl)-5-methyl-2-(8-(3,3,4,4,4-pentafluorobutyl)-[1,2,4]triazolo[1,5- a]pyrazin-6-yl)-5,7-dihydro-6H-pyrrolo[2,3- d]pyrimidine-6-one; 4-amino-5-(5-hydroxypyridin-2-yl)-5-methyl-2-(8-(4,4,4-trifluorobutyl)-[1,2,4]triazolo[1,5- a]pyrazin-6-yl)-5H-pyrrolo[2,3- d]pyrimidine-6(7 H)-one; or 4-amino-5-cyclopropyl-5-(5-hydroxypyridin-2-yl)-2-(8-(4,4,4-trifluorobutyl)-[1,2,4]triazolo[1,5- a]pyrazin-6-yl)-5 H -pyrrolo[2,3- d]pyrimidine-6(7 H)-one.