The Bangor born prop put pen to paper on a deal that will keep him at the Liberty Stadium until 2012 just days after Andrew Bishop also committed his long term future to the Ospreys, taking the total number of players who have agreed to extend their time with the region in recent months to 14.
24 year-old Griffiths arrived at the Ospreys from Caernarfon RFC in the summer of 2003 ahead of the first ever season of regional rugby, and made his debut as a replacement in a 35-21 away defeat to Leinster in September of that year. Capped at all age levels by Wales, he has made a total of 51 appearances in an Ospreys shirt, 18 of which came last season making it his best campaign yet.
Speaking after signing his new contract, Cai said:
"The Ospreys are the leading region in Welsh rugby, it's a forward thinking and ambitious set-up that clearly has an exciting future and its fantastic that I'm going to be able to play a part in that over the next four years. There are some outstanding props in the squad, I'm competing with Adam Jones for the shirt and then you've also got Duncan Jones and Paul James as well as some great youngsters coming through but that is the kind of environment you want to be involved with, where you are having to work hard and are being tested every day in training.
"It's great to be a part of the Ospreys squad, working with guys likes these, competing with them and learning from them can only make me a better player in the long run and help me towards nailing down the number three jersey with the Ospreys and if I can do that, then with Wales as well, this has to be my long term aim."
Ospreys Coach Jonathan Humphreys added:
"It's good news that Cai has signed a long term contract, as one of the best young props in the Magners League he has a bright future ahead of him. Props traditionally get better with age, so at 24 he is still learning, but he has the right attitude and commitment to hard work to have a real impact. His versatility and ability to play on both sides will certainly benefit the squad over the next four years, and I expect to see him contesting the number three shirt with Adam Jones, really pushing him hard for the starting spot."
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