ESPN's Adrian Wojnarowski first reported the trade on July 11.
The Thunder are receiving Chris Paul, first-round picks in 2024 and 2026 and the right to swap first-rounders in 2021 and 2025.
Shams Charania of The Athletic and Stadium broke down the protections on those picks:
Wojnarowski added Westbrook and his agent worked in tandem with Thunder general manager Sam Presti to get him to Houston.
The move comes after Paul George's unexpected trade to the Los Angeles Clippers in July.
Kawhi Leonard signing with the Clippers was a little surprising, but they were still one of the three remaining finalists to land him this offseason. Nobody thought George would join him in Los Angeles.
Losing George significantly lowered the Thunder's playoff ceiling, which was already a question coming off back-to-back first-round exits since the George trade. Trading Westbrook and embracing a full-scale rebuild was naturally one option Oklahoma City had to seriously consider.
Wojnarowski reported July 6 the Thunder were in contact with Westbrook's representatives about possibly moving him elsewhere: "The two sides have 11 years of history together, and both understand that the time has likely come to explore trade possibilities for Westbrook, league sources said."
From a sentimental standpoint, this will be a clear blow for fans in Oklahoma City.
With Westbrook, Kevin Durant and James Harden leading the way, the Thunder reached the 2012 NBA Finals, losing to the Miami Heat in five games. The franchise looked to be on the verge of building a dynasty.
All three players are now gone and OKC never advanced past the Western Conference Finals since the 2011-12 season. That was probably going to remain the case if Westbrook had stayed and played out the duration of his career with the Thunder, but this definitively ends an era for the team.
Looking at the situation pragmatically, the upside of losing George is it allowed the Thunder and Westbrook to reach a mutually beneficial decision about their respective futures.
Westbrook is owed $171.1 million over the next four seasons and will make $47.1 million alone in 2022-23, assuming he opts in to the final year of his contract.
That deal made it hard enough to assemble a title contender around Westbrook and George. The Thunder were then still in the luxury tax even after taking George out of the mix.
Now, Presti has a clean slate to start over.
Westbrook presumably has a better shot at winning a championship as well. At the very least, he should be able to get out of the first round with the Rockets.
To call this a win-now move for Houston is stating the obvious, but Westbrook's age, contract and performance bring additional layers of urgency.
His incredible athleticism is one reason he can put up triple-doubles on a nightly basis. As he continues to get older, it's fair to wonder how much longer he can keep that up.
At 6'3" and 200 pounds, Westbrook isn't built like LeBron James. Along with that, he doesn't appear capable of adapting his game to cater to an inevitable physical decline.
Westbrook shot 29 percent from three-point range in 2018-19, the fourth time in five years he connected on fewer than 30 percent of his three-pointers. NBA.com's player-tracking data paints an even worse picture. He hit 32.2 percent of his catch-and-shoots and 31.4 percent of his pull-up jumpers.
That aforementioned urgency stems from the fact the version of Westbrook the Rockets are getting now simply may not be the same player in two or three years. He isn't going to age gracefully if he remains unable to improve as a shooter.
Houston might only have a small window to maximize Westbrook's on-court value before his production and contract combine to become serious issues.
Head coach Mike D'Antoni successfully balanced Paul and James Harden for the most part, and now he'll need to do the same with Westbrook and Harden.
The Rockets were met with some level of skepticism when they acquired Paul to join Harden. Both players had grown accustomed to being their team's primary playmaker, and Paul's more methodical style was antithetical to Houston's uptempo offense.
The pairing worked out initially as the Rockets were a game away from the 2018 NBA Finals. But then they lost to the Golden State Warriors in six games in the second round this past season, followed by rumors of friction between Paul and Harden.
Swapping Paul for Westbrook might leave the Rockets better off, and they acquired Westbrook without giving up Clint Capela, Eric Gordon or PJ Tucker. Losing one or more of those three would've further depleted a roster already lacking in depth.