It brings to an end Rees’ 13-year association with the Liberty Stadium region.
Rees has been a loyal servant to Ospreys head coach Steve Tandy, but will seek pastures new when the current campaign comes to an end.
“I’ve been talking to Steve since last year about the future direction of the Ospreys, about what this group needs, and about my own hopes and aspirations,” said Rees.
“I’m very aware I’ve been in this environment for a long time and have been on the field talking to some of the squad for 10 years or more, particularly those I worked with when they were coming through the development pathway. That’s a long time for them to be hearing my voice.
“We are an open and honest group of coaches and our discussions over the last 12 to 18 months reflected that.
“I believe this is the right call for all parties, allowing Steve to bring in a fresh voice and for me to take on a new challenge that will allow me to continue developing.”
Tandy paid tribute to Rees, thanking him for his service to the Ospreys.
“Gruff has been amazing in the Ospreys environment for so long and has contributed immensely to the cause,” said the former flanker.
“He’s played a huge part in the development of so many players who have gone on to represent the Ospreys, Wales and the British & Irish Lions.
“He has been immense in terms of the support he has given me personally. We’ve been talking for a long time about the future and been completely honest about what the best next step is.
“He’ll be missed by everyone at the region when he leaves but, understandably, he is entirely committed to ensuring that between now and the end of the season he does all he can to help us improve on our current fortunes before moving on to his next challenge.”
Rees added: “The years have absolutely flown by and it’s only natural I have strong ties with the region now.
“I’m really excited about the future of the Ospreys, with some good signings coming in for next season and the young talent coming through.
“For now I’m firmly committed to helping improve our fortunes, starting with an exciting back-to-back European challenge and then going into the local derbies.
“I’m proud of the small part I’ve had in developing regional and national players and for the relative success we’ve enjoyed here over the years.”
