Born in Catalonia, Guiu emerged from the prestigious La Masia academy at FC Barcelona and made an immediate impact when handed his senior debut in October 2023.
Coming off the bench against Athletic Bilbao, he netted just 23 seconds into his appearance, becoming the youngest and fastest debutant to score for Barcelona in La Liga at just 17 years and 291 days old.
Guiu made seven senior appearances for the Catalan giants, including two outings in the UEFA Champions League, before moving to Chelsea.
In his first season in England, he featured 16 times for the Blues and scored six goals - all in the UEFA Conference League - as Chelsea went on to lift the trophy. He was also part of the squad that triumphed in the FIFA Club World Cup in July 2025.
"I'm feeling great and really looking forward to the season ahead," Guiu told Sunderland's official website.
"I see myself as a powerful striker, who can make a difference on and off the ball, and I pride myself on being a natural goalscorer.
"This year is a huge opportunity for me to help take this team where it truly deserves to be, and I can't wait to get started."
Manchester United have firmly rejected Chelsea's attempts to secure winger Alejandro Garnacho through a swap deal, insisting on a cash-only transfer as they look to reshape their squad for the 2025-26 season.
Manchester City have reportedly launched a staggering 250 million pounds offer to bring Cole Palmer back from Chelsea, aiming to shatter the world transfer record and rectify a past oversight, according to reports.
Chelsea have set their sights on a daring move for Liverpool defender Ibrahima Konate, with reports from Spain suggesting the Blues are ready to test the Reds' resolve amid an injury setback in their own backline.
Sunderland have confirmed the signing of DR Congo international Arthur Masuaku, subject to international clearance.
