Simmons has spent nine years with the Reds, making 112 Super Rugby appearances for the franchise.
However, with young second-rows Izack Rodda and Lukhan Tui having impressed and the likes of Harry Hockings and Angus Blyth coming through the ranks, Queensland will allow their 71-cap Wallaby to leave.
Reds head coach Nick Stiles said: ““These conversations are never easy, especially with players who have been with Queensland since they started and who have given their all for the state and the organisation.
“However, we believe that the future lies with the players who started the game in Samoa [against the Blues] last weekend and with other emerging second-row talent that has come through our under-20s programme.
“The reality is that all Australian Super Rugby teams have to make decisions based on future priorities, as well as salary cap limitations. Rob will leave us at the end of the year with our best wishes and gratitude for the long service he has given Queensland.”
The Reds have also agreed to release Leroy Houston from the second year of his contract for personal reasons. Houston rejoined Queensland from Bath last year, in the hope of furthering his international career.
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