Reigning American League Cy Young winner Blake Snell agreed Thursday to a record-setting five-year, $50 million contract extension with the Tampa Bay Rays, league sources familiar with the deal told ESPN.

Snell, 26, rode an otherworldly final two months of the 2018 season to a 21-5 record and a 1.89 ERA, the lowest for an AL starter since Pedro Martinez in 2000. Over his final 16 starts, the left-handed Snell used a devastating four-pitch mix to post a 1.25 ERA over 93⅓ innings.

The contract beats previous records for extensions to players with less than three years of service in both total value (Gio Gonzalez's $42 million deal from the Washington Nationals in 2012) and average value (Luis Severino's $10 million a year from the New York Yankees this winter).

Snell was not arbitration eligible as a player with two-plus years of service, either, and he topped Corey Kluber's previous record of $38.5 million without giving the Rays a team option.

Tampa Bay will keep Snell for one projected free-agent season and do so via an anomalous deal -- five years for a young player that does not include any club options. The Rays do get the benefit of Snell's prime seasons, and he will reach free agency after his age-30 season.

The Rays rocketed to a surprising 90-win season in 2018 and harbor playoff aspirations this season in large part because of Snell's ascent. One of the Rays' nine first-round picks in the 2011 draft, Snell is the only one to carve out a substantive career -- though it's trending well enough to make up for the team's other eight misses.

Snell spent parts of seven years in the minor leagues and was there as recently as 2017. Last season -- his first full season in the majors -- exceeded all expectations with 31 starts, 180⅔ innings, 221 strikeouts and an opponents' batting line of .178/.254/.300.

As the Rays tinkered with, and eventually relied upon, the strategy of using a so-called opener, Snell at times was the lone exception, beginning games and racking up quality starts. He'll enter the 2019 season alongside free-agent signee Charlie Morton and right-hander Tyler Glasnow as the only three penciled into the Rays' rotation.

Although they've eschewed starting pitching the past two seasons, the Rays have a history of extending young starters. From Chris Archer to Matt Moore to Wade Davis to James Shields, Tampa Bay has tried to keep its best homegrown pitchers.

The Rays aren't hesitant to go for higher-risk signings than Snell, either. They've also guaranteed $24 million this week to rookie utilityman Brandon Lowe, who signed a six-year deal. Snell, Lowe and center fielder Kevin Kiermaier are the only Rays signed beyond the 2020 season, and they're expected to enter the 2019 season with the lowest payroll in baseball.

Before agreeing to the deal, Snell had expressed disappointment earlier this month that Tampa Bay renewed him -- or assigned him a salary ($573,700, a raise of just $15,500) without his approval -- when other pre-arbitration award winners had received significant bumps in compensation.