The 32-year-old has made 516 official appearances for Athletic, the fifth-highest total in the club’s history, and remains under contract until 2028.
Williams has no plans to decide when he will retire yet, but he is certain that his playing career will end at San Mamés.
“Here I retire. I don't want to wear any other shirt than the Athletic shirt,” Williams told RNE.
The forward recently stepped away from international football with Ghana after representing the country at two World Cups, allowing him to concentrate fully on Athletic Club.
He also ruled out playing for another club during the remainder of his career, describing the prospect as “impossible”.
“I am very proud to have been part of this and when the club considers that I am no longer an important piece for the team, I will step aside,” he said.
Williams has already seen close friends such as Óscar de Marcos bring their playing careers to an end. De Marcos, along with former Athletic players Mikel Balenziaga and Iker Muniain, spoke about remaining connected to the club after retirement.
Williams expects to follow the same path when his own playing days eventually finish.
“The day I leave, I will go to San Mamés with my son to watch new legends grow,” he said.
For now, however, the Athletic captain remains focused on adding to his remarkable record with the club and helping them challenge for honours in La Liga and the Copa del Rey.
Williams also sees himself as having an important role within the dressing room, particularly when it comes to advising younger players.
His younger brother Nico is among those to receive his guidance, with Iñaki warning him about the effect social media can have on footballers.
“Social media is the dumping ground of society. Anyone comes in, says whatever they want and then it becomes a bigger and bigger ball,” he said.
“I always tell Nico that if social media takes away your sleep, get off social media and you will live more peacefully.”
Having experienced the pressures that come with playing for Athletic, Williams believes his responsibility extends beyond his performances on the pitch.
His commitment to the club is now clear: whenever retirement eventually arrives, he intends to remain at San Mamés as a supporter rather than represent another team.