Seymour Stowers-Smith captained St Andrew's College to its first New Zealand First XV Championship in 2026.
The Christchurch school defeated Tauranga Boys' College 34-24, strengthening the teenager's credentials across both rugby codes.
Fox Sports reports that the Sydney Roosters will retain Stowers-Smith for the 2027 season.
The brother of New Zealand Warriors forward Tanner has already featured in the Roosters' SG Ball and Jersey Flegg pathways.
In two SG Ball appearances, the rangy second-rower recorded four tackle breaks, 90 post-contact metres and 195 running metres.
That equated to just under 100 metres per match with the Steeden during 125 minutes, making him a difficult defender to contain.
His continued development gives the Roosters another emerging prospect after losing Angus Crichton, Joseph Manu, Joseph Suaalii and Mark Nawaqanitawase to other opportunities.
With Crichton moving to Rugby Australia next season, Stowers-Smith could develop behind the scenes before pushing for an NRL debut.
Tanner has become an important interchange forward for the Warriors, averaging just under 120 metres this season.
He is scheduled to face Newcastle this weekend, with the Warriors chasing a preliminary-final meeting against Penrith.