The Orioles declined Mountcastle's $7.5 million club option for 2027 on Monday, Jake Rill of MLB.com reports.
It was a lost 2026 season for Mountcastle, who was limited to only eight games because of a fractured foot and strained oblique. Mountcastle is healthy now and will turn just 30 in January, but he's had trouble staying on the field and being productive the last few years, so his free-agent market will likely be modest.