The free games releasing in July for Games with Gold was confirmed by Larry Hryb (Major Nelson) today on Twitter.
A leak of the lineup was circulating earlier this week, but now we know for sure that following games will be free in the month of July:
On Xbox One:
The Banner Saga 2 (July 1-31)
Tumblestone (July 16-August 15)
On Xbox 360:
Tom Clancy's Rainbow Six Vegas 2 (July 1-15)
Tron: Evolution (July 16-31).
— / Larry Hryb / (@majornelson) June 28, 2016
Both of the Xbox 360 titles will also be available on the Xbox One thanks to the Backward Compatibility program.