What happened: The Seattle Mariners claimed right-handed pitcher Isaac Mattson off waivers from the Pittsburgh Pirates. Seattle immediately placed Mattson on its 40-man roster to absorb the bullpen addition. The move ends Mattson's three-season tenure in the Pittsburgh organization.

Why it matters: Mattson provides Seattle with immediate bullpen depth as front offices manage 40-man roster flexibility ahead of the offseason. For the Pittsburgh Pirates, exposing Mattson to waivers clears space on their own 40-man roster as winter roster reshaping begins.

What to watch: Seattle will determine Mattson's bullpen role as clubs prepare for upcoming winter roster deadlines.