Portland had until early January to fully guarantee the deal for the season. Anthony, 35, signed a non-guaranteed contract last month.
Anthony was named the Western Conference Player of the Week last week after averaging 22.3 points, 7.7 rebounds and 2.7 assists to help the Blazers go 3-0. It marked the first time he was named a player of the week since the 2014 season, while he was a member of the Knicks.
Head coach Terry Stotts said Friday that the time was right to fully guarantee Anthony's contract.
"I don't think it changes anything," Stotts said. "I think it sent a good message to him and the team and the rest of the league that he's here to stay. He's shown that he can really help us, and there was no point waiting til January 9th. As far as how it changes things going forward, it probably doesn't change much at all."
Stotts told ESPN Radio's Spain and Company on Thursday that he has been impressed with Anthony's conditioning after being out of action for a year.
"We put a kind of limit/restriction on the first game or two just because we didn't want to extend his minutes not knowing what shape he was in," Stotts said. "But now he's playing 32-35 minutes, he played 37 minutes the other night. And for him to be out of NBA basketball for a year and be able to come in and play productive minutes for 35 minutes in an NBA game, to me, was remarkable."
Anthony poured in 20 points in 36 minutes in Wednesday night's 127-116 win over the Sacramento Kings. He is averaging 16.9 points, 5.9 rebounds and 1.8 assists per game this season.