He highlighted winning the URC last season as “a phenomenal achievement” but suggested “the future is definitely bright in the second row” at Glasgow, with Scott Cummings, Max Williamson, Alex Samuel and Jare Oguntibeju competing for places.
Gray has amassed 79 Scotland caps and featured once for the British and Irish Lions during their 2013 tour of Australia.
At pro-team level, he also won the French Top 14 final with Toulouse.
Glasgow head coach Franco Smith added: “Richie has been a fantastic servant to this club, both on and off the field.
“When I first came in, he very quickly adapted to the intensity of our training sessions as well as also adapting elements of his game.
“It will be sad to lose him, but this is a massive opportunity for him at this stage of his career. I know from experience what an opportunity like this means as you’re coming to the end of your career and I’m very proud of the way he has gone about his business.”