This projects to be even more significant considering Doolittle is likely to be accumulating saves by then.
The deal adds to an already remarkable path taken by the 27-year-old, who, in three years' time, has transitioned from a top first base prospect to one of the game's best relievers.
"It means everything that the organization thinks of you like that, that you're someone they want to keep around and think you can be a part of teams here for years to come," said Doolittle. "I think if you factor in the road I took to get here, everything I went through to be able to put on this uniform, it's really special to know I'll be a part of this organization for awhile."
Details of the deal are not known, but the A's likely checked out of the conversations with a decent discount in exchange for guaranteeing such a lengthy pact to a reliever with such little service time. Doolittle, in his third year of Major League action, entered the season with 1.122 years of service.
Should he finish the year with Super Two eligibility, he'll be able to cash in on escalators in his contract based on games finished. And should he appear in a combined 100 games between 2018 and 2019, his 2020 option becomes a mutual option.
The A's initially approached Doolittle about a deal in early spring, and it resulted in a "pretty smooth negotiating process," according to Farhan Zaidi, assistant GM/director of baseball operations.
"Sean's been in the organization a long time, obviously, and is a guy we've gotten to know on a personal level, and we just have a ton of faith in the type of person he is off the field and on the field," said Zaidi. "I think the resilience he's shown in his career, having transitioned from being a position player to pitcher, that's shown us a lot. And then we've seen what everyone else has seen of him the last two years. He's been one of the best relievers and setup men in all of baseball. I think every team would want to be able to have that guy around as long as possible."
Since making his debut June 5, 2012, Doolittle has totaled 125 innings, tying him with Kansas City's Greg Holland for most by an American League reliever in that time. Moreover, only two AL relievers (Glen Perkins, Jake McGee) have a better WHIP than Doolittle's 0.99 over that stretch.
Doolittle has made 122 total appearances, posting a 3.10 ERA while averaging 9.3 strikeouts, compared to just 1.7 walks, per nine innings. This year, he's 0-0 with a 3.12 ERA and one save in eight appearances.
"I think we're all as happy for him as we are for ourselves," said Zaidi. "We were all talking the other day about when he was first in camp as a first baseman a couple years after being drafted and had one of the most impressive Spring Trainings that we can remember. He really looked like the team's first baseman of the future. And then to go through what he's gone through since then, obviously, to sort of come out the other side as a big leaguer and now one who's going to be here for a long time, I'm sure he's excited about it, and we're happy to be able to reward him."
"If you had said to him a few years ago this is what you're looking at, he'd probably kind of be puzzled," said manager Bob Melvin. "It's been a quick path for him, but certainly well-deserved, and a terrific person on top of it. Nothing he does really surprises me now."
Doolittle grew up an army brat, calling several cities home along the way. But during the time he spent in Merced, Calif., he was introduced to the A's, attending a handful of games with brother Ryan -- also a pitcher in Oakland's organization.
Doolittle still peeks up to their old seats on the third-base line each time he takes the field for stretch.
"This was my first exposure to baseball of any kind, and for it to come full circle was cool enough," he said, "and now to know I have a little security and will be wearing the green and gold for several years is exciting.
"There are still plenty times I can't believe I actually did what I did. The way things worked out, it just makes everything that much better. I don't take a single minute I have up here for granted. I try to work my butt off and have as much fun with everything as I can and take it all in."
Only three active relievers have received extensions of four-year durations, and two of them are established closers in Craig Kimbrel and Joe Nathan with much more service time under their belt.
"Apparently they have a lot of faith in me I guess," Doolittle said, smiling. "That was one thing that you can't help but notice is there hadn't really been a precedent set for this, especially for a reliever. I try to put as much work behind the scenes to be sure I'm healthy and always ready to go. I don't like having to spend days where I'm unavailable in the bullpen."
"I think the way we think about relievers is anyone who gets important outs in the bullpen is important, and I actually think the player markets have started to reflect that," said Zaidi. "We don't necessarily know what inning he's going to be pitching, but we know he's going to be getting important outs, and that's not always going to be the ninth inning.
"There was definitely a personal aspect of this deal as a guy that's been in the organization as long as he has and gone through everything he's gone through. That's the type of person and player that, as an organization, we want to invest in."