The Red Sox and ace lefty Garrett Crochet didn’t get a long-term deal done before his self-imposed negotiating deadline on Opening Day. Four days later, they have a deal.

Boston has agreed to a six-year, $170 million contract extension with Crochet that covers the 2026-2031 seasons and includes an opt-out after 2030, a source confirmed to MassLive on Monday night. ESPN’s Jeff Passan was first to report the deal.

The contract, which is the largest contract for a pitcher with Crochet’s service time (between 4-5 years), checks off a major priority for the Red Sox, who gave up four prospects (Kyle Teel, Braden Montgomery, Chase Meidroth and Wikelman Gonzalez) in a blockbuster trade with the White Sox in December. It gives them control over Crochet for at least five seasons after 2025. The deal, which comes with a $28.33 million average annual value beginning next year, has not been announced by the team.

MLB.com’s Mark Feinsand reports that Crochet’s deal includes escalators (up to $2 million in each season) from 2027-2031 based on where he finishes in the Cy Young race.

The Red Sox acquired Crochet — a 2024 American League All-Star who posted a 3.58 ERA in 146 innings in his first season as a starter with Chicago — with just two years of control over him. Since January, the sides have gone back and forth on a potential long-term deal that, at times, looked unlikely to come to fruition. Crochet said repeatedly throughout spring training that he did not want to negotiate after Opening Day. A week before Thursday’s opener, things looked bleak — a reality Crochet acknowledged during an appearance on the “Play Tessie” podcast when he said he was not “thinking there’s much possibility” of getting a deal done. On Thursday in Texas, chief baseball officer Craig Breslow seemed to hint that he was in the same headspace.

“Right now, Garrett is getting ready to throw the first pitch for the 2025 season. I think he has been outspoken about wanting to table conversations and be able to focus on the season,” Breslow said at Globe Life Field. “We absolutely want to respect that and we’re super excited about what he’s gonna do for us.”

Nevertheless, conversations continued, with the sides getting a landmark agreement done five games after the start of the season. Crochet made his Red Sox debut on Opening Day, allowing two runs on five hits while striking out four batters. He’ll pitch again Wednesday in Baltimore.

Crochet, who turns 26 in June, will still earn $3.8 million in 2025, as previously agreed upon with the Red Sox. Boston’s competitive balance tax (CBT) number for this season will not be impacted. The deal buys out one arbitration year (2026) and either four or five free agent seasons, depending on the opt-out. Crochet will still have the ability to opt out in search of a massive payday on the free agent market after the 2030 season, when he is 31.

The Red Sox now have the core of their starting rotation locked up for years to come with Crochet (through 2030), Brayan Bello (through 2029 with a 2030 option), Kutter Crawford (through 2028) and Tanner Houck (through 2027) all under control for at least three more seasons. Boston, which signed Bello and center fielder Ceddanne Rafaela to long-term agreements during spring training last year, is still trying to get deals done with younger players — and could have more news soon. As MassLive reported over the weekend, the Red Sox are also engaged in talks with rookie Kristian Campbell about a long-term extension; at this point, sources characterize an agreement as very possible.