Per both sources, the Thunder and Harden could not agree to a contract extension, and OKC management chose to flip the 4th year guard from Arizona State for assets before the season began.
Reportedly, the Thunder will receive Kevin Martin, Jeremy Lamb, two future first rounders (UPDATE: Yahoo! reports that the firsts are Dallas 2013 and Toronto 2013) and a future second round pick (UPDATE: Yahoo! reports as Charlotte's 2013) in exchange for Harden, Daequan Cook, Lazar Hayward, and Cole Aldrich.
This trade could prove to weaken Oklahoma City, and, while it helps the Rockets, Houston should still be no threat to the Clippers in the standings. Depending on how sorely Harden is missed and on how Martin plays, the Thunder could potentially regress from last season, opening the door for the Clippers to leapfrog OKC in the standings.
Hat tip to 82-0 who had it first in the fanshots.