From Adrian Wojnarowski of Yahoo Sports
Portland has informed Thomas Robinson that it will not pick up his 4th-year option, sources tell Yahoo. He'll be free agent in summer.— Adrian Wojnarowski (@WojYahooNBA) October 27, 2014
The Blazers will still be eligible to sign the forward to a contract next summer. Because the Blazers have declined the option, Robinson will become an unrestricted free agent.
Robinson's option would have cost the Blazers (or any team they trade him to) $4.7 million in 2015-16.
The 6'9" power forward averaged 4.8 points and 4.4 rebounds in 12.5 minutes per game in 70 appearances last season for the Blazers. He had previously been drafted 5th overall in the 2012 NBA Draft by the Sacramento Kings. He played 51 games for the Kings before being traded to the Houston Rockets for a package that included center Cole Aldridge and point guard Toney Douglas.
The Trail Blazers acquired Robinson last July for the rights to Kostas Papanikolau and Mirko Todorovic, plus two future 2nd-round draft picks.
Update: The Blazers have announced that they've picked up options on the contracts of CJ McCollum and Meyers Leonard.
Erik Gunderson of the Columbian has a nice write-up on the process.