Inaki Williams has ended speculation about his future by signing a new contract with Athletic Bilbao that runs through June 2025, the club announced on Wednesday.
A reported Liverpool target, the Spanish forward's previous deal would have expired in 2021.
According to the club, Williams' release clause will be set at €80 million and "will progressively increase" to €108m.
"Today is a very happy day for me because I've extended my commitment with this club for another eight years," Williams wrote on Twitter. "I've always said that I am where I want to be. I've grown here as a player but especially as a person. Everyone that belongs to this club knows that if there is a word that defines it, it is family, and those of you who know me know that family for me comes first.
"Alongside you, I will continue to laugh, cry, work the hardest and give my all for this shirt in every game and every training session. I thank the club, the coaches, the best fans in the world and my teammates, who make me feel the most fortunate footballer in the world for playing alongside them."
The 23-year-old, a youth product of Athletic, broke into the first team in 2014 and has one cap for Spain.
He scored 10 goals in 2014-15, his debut season, and in 32 starts for Athletic in all competitions the following campaign, he had 15 goals and set up five more.
The forward scored five goals in 38 league appearances to help Athletic finish seventh in La Liga last season. This year, he has scored four times and assisted on three goals in 19 league games.