Head coach Steve Tandy is giving a debut to Leicester wing Hamer-Webb while simultaneously restoring Costelow at fly-half.
The twin calls — one ushering in a new cap, the other reviving an international career — are part of the fall-out from Wales’ attempt to arrest a miserable run that has seen them concede 102 points in defeats to England and France and slip to 23 losses in their past 25 Tests.
Up front, Tandy has also adjusted his pack, with two further changes.
Dragons lock Ben Carter is promoted from the bench to start alongside captain Dafydd Jenkins, replacing Adam Beard after the latter’s costly mistake against France led directly to a try for Matthieu Jalibert.
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Television pictures showed Tandy reacting furiously as the error unfolded.
Scarlets back-rower Taine Plumtree comes in for Olly Cracknell, adding size and mobility on the blindside, while Aaron Wainwright shifts across to number eight in a positional reshuffle intended to sharpen the balance of the back row.
Gloucester lock Freddie Thomas, Cardiff flanker James Botham and Scarlets full-back Blair Murray are poised for their first involvements of this year’s championship from the bench.
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Hamer-Webb, uncapped at senior level until now, will become the 1,221st men’s international when he steps onto the Principality Stadium turf.
Alongside him, Costelow returns to the No 10 jersey for the first time since the 24-19 defeat to Japan in Kitakyushu in July 2025, replacing Dan Edwards after a seven-match stretch in which Edwards started and Jarrod Evans regularly provided cover.
“We feel this is the best team to take on Scotland,” said Tandy.
“With a six-day turnaround, you want some freshness as well going into the game.”
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Freshness arrives in both youth and renewed faith.
Hamer-Webb’s elevation follows an impressive integration into the squad since leaving Cardiff for Leicester at the start of the 2025-26 campaign.
A former Bath wing who represented England at age-grade level, he qualifies for Wales through his mother and now steps straight into the starting XV in place of Ellis Mee.
“Gabe has impressed me in the way he's attacked training, the way he's adapted and the way he's settled into the squad,” said Tandy.
“His training efforts have been outstanding.
“When you dig into his background at Leicester, even when he wasn't in the team, everyone said he was an amazing team player.
“He also kept pushing, he never gave up and then when he had his Leicester opportunity he took it with two hands.
“Now this opportunity has come up and it's thoroughly deserved.”
If Hamer-Webb represents promise, Costelow embodies opportunity reclaimed. The 25-year-old Scarlets playmaker is given a chance to reassert control in a pivotal role as Wales search for fluency and composure after two heavy defeats.
His recall forms part of an all-Scarlets midfield combination designed to spark cohesion and attacking clarity.
“This is our third game of the championship and we want to build on our performance,” said Tandy.
“We want to see more consistent moments and back-to-back moments, which we feel if we get, we'll be closer to getting the outcome we want from games.”
Wales’ 13 successive Six Nations defeats underline the urgency.
Their last home victory in the tournament came against Scotland in February 2022, and the 57,744 crowd that watched the loss to France was the lowest attendance for a Wales home Six Nations fixture in Cardiff.
Scotland arrive buoyed by a 31-20 win over England in Edinburgh.
Wales: Rees-Zammit; Hamer-Webb, James, Hawkins, Adams; Costelow, T Williams; Carre, Lake (capt), Francis, Jenkins, Carter, Plumtree, Mann, Wainwright.
Replacements: Elias, Smith, Griffin, F Thomas, Botham, Hardy, J Evans, Murray.
Wales: Rees-Zammit; Hamer-Webb, James, Hawkins, Adams; Costelow, T Williams; Carre, Lake (capt), Francis, Jenkins, Carter, Plumtree, Mann, Wainwright.
Replacements: Elias, Smith, Griffin, F Thomas, Botham, Hardy, J Evans, Murray.
