Jon Lester’s $25 million mutual option for 2021 was declined Friday by the Chicago Cubs, completing a $155 million, six-year contract and allowing the 36-year-old left-hander to become a free agent.

Lester is owed a $10 million buyout: $2 million on each Dec. 31 from 2022 through 2026.

Lester was 3-3 with a 5.16 ERA in 12 starts this year with 42 strikeouts and 17 walks. He earned a prorated $5,555,556 from his scheduled $15 million salary.

He was 77-44 with a 3.64 ERA in 171 starts over six seasons with the Cubs and was 3-3 with a 2.44 ERA and .201 opponents’ batting average in the postseason.

Chicago also claimed infielder Max Schrock off waivers from the St. Louis Cardinals and assigned left-hander Rex Brothers outright to Triple-A Iowa.

The 26-year-old Schrock hit .275 for Triple-A Memphis in 2019 with 20 doubles, two homers, 31 RBs and 12 steals, then batted .176 (3 for 17) this year for the Cardinals with a home run in 11 games.

Brothers was 0-0 with an 8.10 ERA in three relief appearances for the Cubs.