SEATTLE -- Luis Castillo sat atop a head table at T-Mobile Park on Monday, sporting the grin he dons on both good days and bad while raising his pitching fist and flexing his right arm. It’s the trademark pose of the two-time All-Star after a strikeout, but he wasn’t on a mound and instead was celebrating something even more rewarding.

“La Piedra!” teammate Julio Rodríguez shouted from the back of the interview room, moments after Castillo’s massive contract extension with the Mariners was formally announced. The deal is for five years and $108 million, though it can be as rich as six years and $133 million based on a vesting option.

Less than two months after Seattle acquired the starting pitcher from Cincinnati in a Trade Deadline blockbuster, its front office ensured that the prized acquisition will be here beyond this year and next, after which he would’ve been eligible for free agency. At that point, any of the 29 other clubs could’ve courted the 29-year-old on the open market -- so why forfeit the chance to go to the highest bidder and sign here and now?

“The first thing that really caught my attention was the personality of the team,” Castillo said through interpreter Freddy Llanos. “When I came in here and saw firsthand the people here and how tight and competitive this team was, it was one of the things that convinced me the most.”

In Jerry Dipoto’s eyes, Monday’s press conference was a culmination six years in the making. Seattle’s president of baseball operations tried to trade for Castillo when he was a prospect with the Marlins in 2016, and again multiple times after he was dealt to Cincinnati, where he debuted in '17 and blossomed into one of the game’s more impactful righties. Dipoto and Mariners assistant GM Justin Hollander finally landed Castillo on July 30 in a transaction that cost Seattle three of its top five prospects.

At long last, they had their guy, and with him, exclusive negotiating rights over his final 15 months before reaching free agency. Beyond injecting their already above-average rotation with an ace, the Mariners viewed the Deadline deal as the springboard to locking up another cornerstone player.

“You never know which way it's going to go when free agency is right there on the horizon, but we were willing to spend free-agent prices to make it happen,” Dipoto said.

Negotiations began almost immediately after the trade, with Hollander reaching out to Castillo’s agent, Rafa Nieves of Republik Sports, while Nieves was in Europe. Hollander made the club’s intentions clear, outlining that it viewed Castillo as a long-term fixture in Seattle, that it was willing to pay market value to back that assertion and that it’d like to have that conversation sooner than later.

At the time, the Mariners were finalizing a massive contract extension with Rodríguez, and once that megadeal became official, Nieves followed up, saying: “Clearly, this team wants to win, so let's talk about it now.”

Castillo’s contract is quite similar to the five-year, $115 million deal that the Mariners gave Robbie Ray in free agency last December, but Castillo’s camp was set on the chance to earn a sixth year. That’s why the $25 million vesting option for 2028 by reaching 180 innings in ‘27 was included, as well as the $5 million club option should Castillo undergo Tommy John surgery and miss at least 130 days at any point from ‘25-27.

Another win-win: Castillo has the chance to earn the sixth year based on performance incentives, and the Mariners receive some health security, even though Castillo has never suffered a significant arm injury.

“It’s something that we came up with on this one largely because we’ve never done a contract for a pitcher for longer than five years,” Dipoto said. “This contract negotiation for quite a while was centered on the desire to have six years, so this was a way to counter that, was to have the sixth year as an option based on performance. ... And if somewhere between now and then there's [an elbow injury] that should happen that doesn't allow that to happen, then we get another option.”

Castillo becomes the latest Mariner signed to a long-term contract extension before reaching free agency, joining Rodríguez (12 years, $210 million, and possibly longer and richer), shortstop J.P. Crawford (five years, $51 million), starting pitcher Marco Gonzales (four years, $30 million) and reliever Andrés Muñoz (four years, $7.5 million). The club has transitioned from a state of identifying and acquiring talent to locking it up long term.

Moreover, with Castillo and Ray on long-term deals, Gonzales signed through 2024 and Logan Gilbert and George Kirby not eligible for free agency until after ‘27 and ‘28, respectively, the Mariners have a promising rotation in place for the foreseeable future.

“I’m just very happy, very happy that I’m finally able to join this family long term,” Castillo said. “I’ve got to give everything my all, my heart and everything. If we’re prepared to win the World Series, let’s get out there and do it.”