SPOILER ALERT: Do not read unless you have seen the April 10 season one finale of “Billions,” “The Conversation.”

The big finish of the first season of “Billions” — the fiery confrontation between Chuck Rhoades and Bobby Axelrod — was in fact the big finish after six months of filming on season one. Brian Koppelman and David Levien, showrunners and co-creators of the Showtime drama with Andrew Ross Sorkin, made a point of making that the last scene lensed.

Just as it was important to stoke anticipation for the inevitable showdown between Chuck and Axe among viewers, it was important to have some tension building up for stars Paul Giamatti and Damian Lewis. Saving that sequence for last allowed both actors to leave it all on the floor — the decimated floor of Axe Capital.

“We really went out of our way to make that the last shot of the season,” Levien told Variety. It was logistically tricky for the production but worth it, Koppelman added of the scenes filmed in mid-December. “It was so satisfying to let those two guys (Lewis and Giamatti) prepare and to build to that moment. It let them play everything else in the entire season to lead up to the moment where they really collide,” Koppelman said.

Going into production last spring, Koppelman and Levien knew the overarching story arc of the season, including the final gloves-off encounter between Axe and Chuck. But getting there was a journey they took with the writers room.

“We had a rough idea of the endpoint when we got started,” Levien said. “We weren’t completely flying blind, but we didn’t have all the answers. We just trusted that the moves we would find along the way would serve this endpoint and we would find a way to deepen it.”

Although Chuck and Axe meet early in the season when the settlement deal goes awry, the actors didn’t really get to stretch out with each other until the finale. “Deferring that face-to-face conflict really paid off in a big way,” Koppelman said.

The finale was penned by Koppelman and Levien and directed by Michael Cuesta, a familiar face to Lewis from “Homeland.” The six-minute final showdown features Lewis and Giamatti circling each other like boxers in a ring. The exchange is deeply personal between the two characters but also veers into a heady verbal tennis match about Axe’s contention that excessive regulation stifles competition (“taxation by other means”), which Chuck dismisses as “Ayn Rand bulls—-.” The memorable line from Axe — “When I pull a deal off the table I leave Nagasaki behind” was written on the spot as the actors went at it, Koppelman said.

Behind the scenes, the pairing at long last of Giamatti and Lewis gave a lift to the entire “Billions” crew. The actors were tired but in high spirits, demonstrating their easy camaraderie. It was a long and memorable day of shooting.

“All of us got sick for the next two weeks from all the adrenaline of riding out that night,” Koppelman said.

The construct of season one meant that Lewis and Giamatti didn’t actually have many scenes together. Koppelman and Levien are mum about whether that will change in season two.

The other source of fireworks in the finale revolved around Wendy, making the episode a fine showcase for the talents of Maggie Siff. First she’s confronted by Axelrod about how the federal prosecutors suddenly know about the police bribery incident involving the Axe Capital exec who went nuts a few episodes back and aimed his automatic weapon at a bunch of deer in his backyard. That came out in the previous episode’s long and long overdue counseling session between Axe and Wendy. Wendy is thrown when Axe produces a dossier of unflattering info about Wendy’s interest in S&M and pictures of their clothing-optional meeting in the bath few a few more episodes back. More than the material it’s the fact that he was clearly amassing dirt on her that enrages Wendy.

After that Wendy has an icy fight with Chuck at their home, which ends with her instructing him: “Pack your s—-.” Then she drives the Maserati that Axe gave her at the start of the episode as thanks for the to Axe Capital to break up with Axe in a way that amounts to a therapy session for herself, after she collects a $5 million bonus for helping Axe get his groove back, professionally speaking. She vindicates herself with Axe by playing a recording of Chuck admitting to stealing her notes from her computer. But she still ends her platonic but unusually close relationship with Axe — snapping the bond that has been the source of much angst for Chuck as well as for Axe’s wife, Lara (Malin Akerman).

“You really feel there’s much unsaid between them,” Koppelman said of the Axe-Wendy relationship.

The sets Wendy up to once again be a pivotal player in the Chuck-Axe hunt next season. The episode ends with her presumably driving off to join the female-led hedge fund that courted her a few episodes back.

For each of the core cast members the finale amounts to a day of reckoning. Chuck has become so obsessed to the point of being willing to burn down the village to save a bridge — or in this case, destroy his marriage to obtain any type of conviction.

Axe is back to tap dancing for capital on the Street — and making sure his arsenal of cash and gold bonds is stashed in his basement. “You never know,” he tells Lara after breaking the good news that they don’t have to flee the country, at least not yet. Lara’s flinch when he tells her to keep the cash at home speaks volumes, especially after her nostalgic adventures with her sister in the previous episode.

Brian Connerty gets an offer that Axe hopes he can’t refuse, to join the seven-figure private sector law community. That scene offered a nice moment for interaction between Lewis and Toby Leonard Moore, who blossomed in the role of Chuck’s frustrated right-hand attorney as the season wore on. And David Constable’s Mike “Wags” Wagner is humbled in his role as Axe Capital’s odious COO, when he’s reduced to carrying the briefing books as he and Axe make the rounds of potential investors.

“It was really important to us that all of these characters have internal lives,” Koppelman said. That gave them a lot of work to do in the finale.

But nobody had a tougher job in episode 12 than production designer Michael Shaw. He had to destroy the Axe Capital headquarters bit by bit to allow director Cuesta and cinematographer Jake Polonsky to capture those dark-hued moody shots of the search for listening devices in Axe’s lion’s den — the visual representation of Axe’s extreme paranoia about getting nabbed by the feds. “He gave us a great progression of destruction,” Levien said. By the final scene, the Axe Capital headquarters is fairly smoldering, adding to the drama of the final face off.

The damage done to the Axe Capital headquarters — an abandoned Olympus medical supply facility in Orangeburg, N.Y. — suggests that Axe and Co. will be moving to new digs next season. Koppelman and Levien refuse to trade in inside information. The writers room for season two is up and running, with three new recruits joining two returning scribes from season one.

As they survey the experience of season one, Koppelman and Levien say they are grateful that they get to do it all again. They admit to some nervousness at the outset about whether the subject matter would be a turn off to anyone but the elite few who manage their own hedge funds and the like.

“There are so many other moves coming for these characters,” Levien said. “It’s great to have the real estate to allow them to go to their various depths.”

Among other observations: