Law & Order: Special Victims Unit reached a rare television landmark on Thursday night, airing its 600th episode on NBC and prompting a celebration that creator Dick Wolf described as a once-in-television-history event.

After the milestone episode wrapped, Wolf gathered the current cast and crew for a dinner party, joined by Wolf COO Peter Jankowski and Christopher Meloni. In a speech opening the night, Wolf stood and told the group, "This has never happened, and it will never happen again."

In an era when reaching 100 episodes is considered a major accomplishment, Mariska Hargitay admitted she never imagined the show would reach 600. But Wolf did, she said, and that vision became part of the speech she delivered that evening to what she calls her SVU family.

"It really doesn't feel totally real, which, in a way, is exactly how it should feel, because it's as if we all get to live in this dream of what you thought might be possible someday," Hargitay told Wolf. She added that if someone had described a 600-episode series to her, she would have assumed it was "running on fumes," yet SVU remains "healthy, that's muscular, that's fresh, smart, honest, and just so damn important."

Hargitay, who has worked with Wolf since the Universal Television series debuted in 1999, said the word "family" gets thrown around loosely, but on this set it is genuine. "I go to work and we hug, and it's real. It feels like you're going to a good dinner party when you go to work on Monday," she said, noting many cast and crew members have been there from the start.

She grew emotional describing the set's atmosphere, one she said guest stars consistently praise when they arrive and depart. "I love making a space where people feel safe enough to try, to risk, to play," she said. "This is someone's life. This is serious, and these are important stories. I'm so grateful."

The milestone episode, written by showrunner Michele Fazekas and directed by Brenna Malloy, follows jury consultant Gwen Sharpe, played by J. Smith-Cameron, as she persuades Benson to reopen an old case that sent a man to prison for a 1998 rape and murder. Revisiting the file, Benson realizes she originally worked the case alongside Stabler, played by Meloni.

Stabler is initially hesitant, having failed to follow up on leads that could have exposed the truth and having cut Benson out of the interrogation, but he ultimately joins her on a road trip to put the right person behind bars. When Captain Renee Curry points out that Stabler is no longer her partner, Fin, played by Ice-T, replies, "It doesn't matter. Some partnerships don't end, even when they do."

The storyline forces both characters to confront how they have changed since their years working together. Benson tells Stabler, "I let you shut me out.. I have to live with the fact that I didn't do the right thing because I was new, that I didn't follow my instinct because I thought you knew better." For the first time, she fully uses her voice with him, and the story suggests their partnership endures regardless.

Hargitay said the episode ran nearly 12 minutes over time. "This was a big one. We were writing and rewriting and playing, and we had to shoot some scenes before we knew exactly what a scene was going to be," she said. "But it's an embarrassment of riches."