The official Pokémon movie website has updated with information on the Pocket Monsters XY anime's new ending theme. Translations follow:

The TV anime "Pocket Monsters XY"'s new ending theme will be done by Little Glee Monster

The new ending theme for the TV anime "Pocket Monsters XY" will be sung by "Little Glee Monster", the vocal group made up of the greatest young singers in the nation!

The song's title is "Gaogao All Stars"!
This new song made its debut during a live concert at UMEDA CLUB QUATTRO in Osaka Thursday March 26th! "Gaogao All Stars" will also be used as the theme song for the short "Pikachu and the Pokémon Musicians"!

Those of you who want to hear the song right away, make sure to tune into the popular show "Oha Suta!", which airs on the TV Tokyo Network at 6:45am! Little Glee Monster will appear live on the episode airing Thursday April 16th! In addition to the very first TV performance of "Gaogao All Stars", the episode will also have the world premiere of a new movie trailer!

Comments from Little Glee Monster:

"It is a true honor to be allowed to sing a Pokémon ending! Also, the fact that we get to be involved with Pokémon, which we've been watching constantly since our childhood, really makes it clear that good things happen as long as we just keep on living our lives."

"Gaogao All Stars" is the kind of song that really makes you want to dance, one that we, our friends and our families all dance to, sing to and just get ourselves caught up in together. We want lots of people to hear it and become happy!!"

A biography on Little Glee Monster:

"Sharpened singing voices that leave marks behind in people's hearts"
A teenage girl vocal unit where the members are 15 years old on average, formed from the greatest singing girls found throughout Japan.

Prior to their debut in October 2014, they were singing at summer festivals and doing joint performances with many major artists.
They were skillfully singing a cappella with powerful voices, wielding crystal clear harmonies as weapons as they appeared time and again on national television, giving them a very visible profile. They released their second single March 4th and have been steadily gaining fans through concerts, the tickets to their solo tour through Tokyo, Nagoya and Osaka selling out the day they went on sale.
In Fall 2015, they will make a 13 stop solo tour through all of Japan.

For further information, see the official Little Glee Monster website

Source: http://www.pokemon-movie.jp/news/?p=1624