Anthony had a Monday deadline to terminate the final year of his contract. He filed the paperwork on Friday, one of the people told The Associated Press on condition of anonymity because no official announcements were made.
Anthony has repeatedly said he planned to explore free agency this summer. Team president Phil Jackson told the All-Star forward after the season he may want to delay the decision and play out the final year of his deal, which would have paid him $23.3 million, but Anthony is going ahead with his previous plans.
He will be eligible to negotiate with teams starting July 1.
Teams such as Chicago, Houston, Dallas and Miami have been mentioned as potential suitors for Anthony, a two-time Olympic gold medalist who led the NBA in scoring in 2012-13.
The Knicks can offer Anthony, whom they acquired from Denver in a blockbuster trade in February 2011, more than $20 million more than any team. But Anthony has said he would be willing to take less than a maximum salary for a chance to win, and Jackson has said he hopes Anthony sticks to that.
Anthony never truly got to experience the full free agency process, signing an extension of his rookie contract in 2006, then extending that deal as a condition of the trade to New York, and has said that is something that interests him.
Now he will have his chance.