The 2005-born protege made his mark at both youth and senior level during the 2023-24 campaign, where he was handed his first-team debut by Jurgen Klopp in an FA Cup fifth-round clash against Southampton.
Koumas scored his first goal for the Reds in that 3-0 win over the Saints, opening the scoring on the stroke of half time before fellow academy graduate Jayden Danns netted a brace off the bench.
The two-cap Wales international also excelled for the juniors with nine goals and five assists in 15 Premier League 2 appearances, as well as four goals in three FA Youth Cup games for the Under-18s.
In the second round of that competition, Koumas netted a hat-trick in a 7-1 obliteration of Arsenal, and he made his first two appearances for Wales in friendlies against Gibraltar and Slovakia in June.
Regarded by the Reds as a serious future talent, the attacker - who primarily plays on the left but is also comfortable down the middle - was involved in his side's pre-season friendlies against Preston North End and Real Betis as he sought to prove his worth to Arne Slot.
Stoke chief hails Koumas's "huge potential" as Liverpool loan confirmed
Following claims that Koumas was set to sign a new deal before spending the 2024-25 campaign on loan with a Championship club, the Reds have now confirmed that the teenager has committed his long-term future to the Merseyside giants and will represent Stoke for the coming season.
Stoke sporting director and former Republic of Ireland international Jonathan Walters talked up Koumas's promise following his arrival, telling the Potters' website: "In Lewis, we are signing a player of huge potential and I'm excited to see what the 24/25 season has in store for him in a Stoke City shirt.
"We are thankful to Liverpool for entrusting us with one of their brightest prospects ahead of other interested clubs. I know he'll be warmly welcomed into the Stoke City family and will get all the support he needs - from staff, teammates and fans alike - to be successful with the Club."
Koumas is not expected to be involved in Saturday's Championship opener against Coventry City, but the teenager should be available to make his debut in Tuesday's EFL Cup opener against Carlisle United.
The Welshman becomes the third Liverpool academy starlet to leave on loan this summer after Luke Chambers (Wigan Athletic) and Fabian Mrozek (Brommapojkarna), while Billy Koumetio left permanently for Dundee on Friday.
In their final two friendlies of the summer, Slot's side take on Sevilla on Sunday afternoon in front of the Anfield crowd, a few hours before they host Las Palmas behind closed doors.