The person spoke Friday on condition of anonymity because the team had not disclosed the deal.
Terms were not disclosed but several media outlets reported the extension was worth $205 million.
Until Durant's free-agency flight to Golden State past year, he and Westbrook were OKC teammates for eight seasons.
As Wojnarowski noted, in 2016, Westbrook signed a three-year extension with the Thunder, assuring he wouldn't flee immediately in the wake of Durant's decision.
Pak appeals for peace along LoC after retaliatory fire by BSF
They immediately informed police about the suspicious movement which with the Army and the CRPF launched the operation. The incident had led to parts of the 740-km long LoC witnessing escalation in tensions.
Anthony is one of three players in the NBA (LeBron James, Dirk Nowitzki) with a no-trade clause built into his contract. "Now that he's signed a new contract, I've proclaimed that everyday is Russell Westbrook Day".
If Anthony ultimately chooses to go that route, he will have several options, including exercising his $27.9 million player option for the 2018-19 campaign.
The 28-year-old enjoyed a historic season last year as he averaged a triple-double of 31.6 points, 10.7 rebounds and 10.4 assists. Both George and Anthony can become free agents after this season. If teams can afford to pay a player like Westbrook that much money, why shouldn't they?
Westbrook hasn't addressed any speculation about all that, but made it clear that Oklahoma City is the place he wants to be and he's not going anywhere anytime soon.
Westbrook is one of the biggest stars now in the National Basketball Association. Westbrook agreeing to this move dumps cold water all over the Lakers rumors, and this suggests the Thunder could wind up keeping their core together as well. "I had a feeling he wanted to remain a Thunder". Pictured: Westbrook reacts after scoring against the Houston Rockets in the 2017 NBA Playoffs on April 23, 2017 in Oklahoma City.