The singer-songwriter discusses Max Martin's invaluable contribution to "1999," and how Taylor Swift might end up a mixtape guest star of hers someday.

These days, MTV’s TRL is almost unrecognizable. On a recent Tuesday, British pop star Charli XCX is sitting on a mustard-colored loveseat in a room that looks more like a lava-lamp-inspired daytime talkshow set than the windowed Times Square perch of yesteryear, waiting to film an interview. Although it’s currently the middle of the afternoon, the same block of time the original TRL ruled during its heyday, her pre-taped segment won’t air until the early morning a few days later.

Still, there are flashes of TRL’s golden years: For the interview, Charli sits down with Sway Calloway, a frequent face during the show's original run. And on her way to set, Charli runs into and briefly catches up with The Fault in Our Stars actor Nat Wolff, whom she got to know when her song “Boom Clap” was featured prominently in that film -- the kind of impromptu star collision that probably happened with great frequency in the Carson Daly era, when music’s biggest names shuttled in and out of the building to take part in what was once appointment viewing for many teens and pre-teens.

It makes sense that Charli, whose pink-streaked bob today is partially tied up into a spiky top-knot, would stop by: She’s just released a new single, a Troye Sivan collaboration called “1999,” that celebrates turn-of-the-millennium pop culture and references TRL fixtures like Britney Spears (“I just wanna go back, sing ‘Hit me baby one more time,’” goes the song's chorus) and Eminem (whom Sivan also dresses up as in the track’s nostalgia-heavy music video).

It’s the latest track in a free-flowing stream of music the pop star unleashed last year, when she released two acclaimed mixtapes (Number 1 Angel and Pop 2) along with her viral, star-studded “Boys” video, while her third studio album appeared to be in limbo. (Now, Charli says that album, which was never released, is a "book closed.") This year, while opening for Taylor Swift on her record-setting reputation tour alongside Camila Cabello, she shared new tunes on an almost monthly basis. The 26-year-old says she finds the traditional release model for pop music -- anchored by a few choice singles and sporadic, carefully scheduled studio albums -- too constricting for her prolific, collaboration-heavy creative process.

“Whether [my label wants] me to do an album or a mixtape, I’m going to release stuff the way I want to release it,” she tells Billboard from TRL’s green room -- well, it’s actually an all-blue room, decorated with gold cattle skulls on the walls and a giant gold dog statue in the hallway -- as she battles a hangover. The night before, she threw a "1999" release party, raging and performing alongside guests like Kim Petras until the wee hours. She’s been throwing these intimate half-party, half-concert events with frequency since releasing Pop 2 last December, and Charli describes them with great reverence.

“I feel like, for the first time in my career, I really have something to say, and I feel like those mixtapes put me in the center of this community that I’m so proud to be a part of,” she says. “When we’re in that room together, it feels really special, and I don’t think I would have found that had I continued down the path I was going.”

Below, Charli tells Billboard about her free-form approach to releasing music, what it takes to make a pop video event in 2018 and the community of songwriters and rising pop stars she’s trying to foster.

What made you want to work with Troye Sivan on this song? He wasn’t what I was expecting -- and not just because he was only 4 years old in 1999.

Yeah, it's definitely a new vibe for him -- it's kind of a new vibe for me too. I'm just such a big fan of Troye. I think he and Ariana Grande are the best pop stars right now. When “My! My! My!” came out, I was like, “Whoa, this is really good!” I’ve been really obsessed with Bloom. We had spoken vaguely about doing something together before -- like if I ever did a mixtape, I’d have to get Troye on it, and I knew he liked Pop 2. We’ve just spoken about collaborating, and then I got this song played for him, and he really liked it. He was like, “Let’s just do this,” and I was like, “Okay, cool!”

A lot of fans on Twitter believe hitmaker Max Martin worked on this song, but his name doesn’t show up in the official credits. Can you clarify his involvement?

So Oscar Holter, who works a lot with Max, [produced the song] -- he’s amazing, I love him. Me, Noonie [Bao, frequent co-writer], and Oscar were writing at Max’s place, and we did the song and sent it to Max. Max was like, “I’ve got an idea: You should change the lyric in the chorus to ‘I just wanna go back, sing ‘Hit me baby one more time,’” And we were like, “Oh my God, this guy is a fucking a genius!” That came from him, so he not only made the song better, but he also referenced himself in a song he and wrote and produced that [was big] in 1999. I was like, “That’s why he’s the king of pop.”

That seems so un-Swedish of him, to reference his own accomplishments.

Oh, he knows he’s the best. He’s the G.O.A.T., as they say.

During a session for Spotify’s Secret Genius Studios program in June, you played an early version of the song for a small group of fans and said you weren’t sure if you were going to keep it for yourself or pitch it to another artist. How did you make that call?

When Troye said he liked it, I was like, “Cool, I like it too!” Sometimes it’s hard to have perspective on your own work, especially because I’m a psycho who listens to my music on repeat once I’ve recorded it. You lose all perspective on whether it’s good, whether it’s hooky only because you’ve listened to it a million times. So when he was like, “This is good, I want to be a part of it,” It was like, “All right, cool!” I think it’s important to have some people that you can always trust to tell you, “This is good, this is bad.” He was that for me.

Is there someone in your life who takes on that role regularly?

Yeah, there are a couple of people. [Producer] A.G. Cook is definitely one of those people for me. I admire him, and we have a good relationship, so he can tell me something and laugh at me, and I won't be offended -- it's never personal. It's just a fun conversation to have, so I love going back and forth with him, and he always has really funny responses. [When I played him] “5 in the Morning,” he was like, “This is a song that should be in James Bond movie,” and then we played the intro to a James Bond movie on mute and played “5 in the Morning” [over it], and it really worked! And Twiggy -- she's my childhood best friend and we work together as well -- she has really good taste, so I play her stuff too.

The first time we spoke, you said nobody in the industry really knows what they’re talking about when it comes to these decisions -- some of the same people who urged you to keep “I Love It” for yourself didn’t think “Fancy” was going anywhere.

Especially now, even more so than when we spoke about it before. It's so crazy now -- there's no formula to pop music or successful music. It's so about a moment. A lot of people don't know what they're doing. I guess the best people who are going to be able to tell you whether your song's good are kids -- they're the ones who are going to listen to it more.

Do you think you'll do more fan focus groups in the future?

That was fun, because they're super intelligent and give me really good feedback. [My fans] also put me onto stuff like CupcakKe. So that's why it's good for me to do that. But last night, it was such a small little space -- that feels like my version of a focus group, just with champagne. It's fun to do those performances where you can see everyone and party with them and play new stuff.

In addition to your mixtapes last year, you also put out a bunch of standalone songs this summer. As you experiment with non-traditional release models, how do you decide which tracks get a music video or an official “push,” whatever that means in 2018?

The video thing, it depends on how much money I can persuade my label to give me. [Laughs] And then it's a group decision between the people I mentioned. A.G. will tell me if something's good or bad, but me and Twiggy will talk about it like, “Will the label be on board?” All of that boring stuff. I used to be very open about the music I made and play it for everyone and anyone. I'd send it even if I didn’t really like the song.

I’ve learned not to do that. The songs you don’t like just don’t exist, because more often than not, the songs that you hate the most will be the one where everyone’s like, “That’s the single, let’s put that one out!” And then you’re stuck singing fucking “Break the Rules.” So now I only show people songs that I really love, so if they’re like, “This is the one,” it’s cool.

You’ve talked about your dislike of “Break the Rules” in the past, but you also performed that song every night that you opened for Taylor. I was going to ask if this tour helped you reconnect with your older hits, but I guess that answers my question.

I do feel “Fancy” a lot at the moment. When I put that song out, I wasn’t really aware of how big it was because I was so in it, and I had so much other shit going on around that song. It was crazy. I just didn’t really get a chance to sit back and go, “Oh, this is amazing,” and now when I got to play that on this tour, I was like, “Wow, this song is a big deal!”

You mentioned the idea of creating a “moment” with a song earlier, and I’m realizing that must be a big part of deciding what gets the proper single treatment: What’s the tagline? For the “Boys” video, it’s shirtless celebrities playing with puppies and eating pancakes. For “1999,” it’s you and Troye recreating Titantic. There’s a pitch there.

That’s when I’ve been successful in persuading people to give me money to make a video. I was like, “Well, I’m gonna fucking put Joe Jonas, G-Eazy, Charlie Puth and Wiz Khalifa in this video, so you gotta give me fucking money to do it, let’s go!” I felt like I had to hustle the label, but it was fun.

Is there a scenario in which “1999” blows up or hits certain success markers and Atlantic suddenly turns to you and goes, “Okay, great, let’s put out a proper album, can you send over 12 songs?”

I mean, maybe. Whether they want me to do an album or do a mixtape, I’m going to release stuff the way I want to release it. I think that’s moving toward something more structured, but I don’t care if shit sells. I think that’s what’s been really nice for me over the past two years: I’ve learned that commercial success doesn’t give you happiness. [Having released] Pop 2 and Number 1 Angel, which weren’t commercially successful projects, I just feel so much more connected to my fanbase and so happy about going on stage and performing those songs.

I feel like, for the first time in my career, I really have something to say, and I feel like those mixtapes put me in the center of this community that I’m so proud to be a part of. I've always enjoyed making music and performing, but -- and this sounds fucking cheesy -- it just feels magical being on stage. I feel like last night, or when I do a Pop 2 show, the room just feels like a safe space full of people who are from different places, who identify however they want to identify, who feel different on the inside or outside -- whatever. It’s a room full of amazing people who have different stories who may not always feel comfortable outside of that room. But when we’re in that room together, it feels really special, and I don’t think I would have found that had I continued down the path I was going.

So I’m really grateful that I found that moment in my life as an artist. It’s put everything into perspective for me. I love doing what I’m doing now, so I don’t want to sacrifice my musical vision just for the sake of maybe being on the radio. It’s more important for me to just stay true to who I am and to those people in that room. I’m getting emotional — woah. I’m hungover too, so maybe that’s it.

Pop 2 did feel like a turning point for you, not just because of the great critical reception. I think it clarified what kind of artist you are to others -- and maybe yourself, it seems. Like, if they didn’t get it before, they got it now.

I know what you mean. It's a good cherry on top of all the other stuff I've been doing, especially because I'm not structured in the way I release things. Pop 2 was an explanation of that because Pop 2 itself is messy as fuck -- there are 10 collaborations on it, the production is crazy, the lyrics are repetitive and weird at points. That was very representative of me as an artist and who I am as a person, so it was cool.

Two of the songs you put out this summer -- “No Angel” and “Girls Night Out” -- are fan favorites that you've performed live for a few years now. What did it mean to you to finally put them out?

I did it for my fans. Obviously they leaked or were on the Internet -- I don’t really know. I’ve been playing them live. Every day people were like, “Release ‘No Angel!’ Release ‘Girls Night Out!’” It got to the point where I was doing these monthly drops and was like, “I should do this and give these songs proper artwork and mini-moments or whatever.” I’m really happy I did. I feel like that’s done now: book closed. And I’m so proud of those songs. I’m also really happy that people are hassling me for only one song now, which is more manageable than three.

So you don’t have a handful of songs you’re saving for a regular album anymore.

Honestly, I would say, maybe aside from one other song, I’ve pretty much released all the music that I have now. Not ever, but music that’s finished and ready to go? It’s out. I’m a clean slate now. I don’t really know what I’m going to do next. I’ll do something, but I don’t know what that is yet. There’s no scoop, unfortunately! But I like that -- it could be anything.

Pop 2 featured a lot of collaborations, but there are some artists you work with regularly: MØ, Tove Lo. How do you recognize that these artists are your kind of people -- artists you’ll have lasting creative partnerships with?

If they're a good person, it's really just that. I don't care how talented you are, if you're a dick and not a nice person, I'm just not going to work with you. Music is such a huge part of my life, and everyone around me is creating or working in some way — I just don't want to spend my energy on people who are not nice. If we're friends in real life and you wanna make music, we can, and it's gonna be fun. That’s really it.

This is more of an observation than a question, but early on in your career, your songwriting accomplishments helped sell your solo work: Like “I Love It” and “Fancy”? Check out her album! But lately I’ve noticed a shift where your songwriting is now helping newer artists get their foot in the door, like ALMA and XYLO: Like Charli XCX? She co-wrote this song of theirs! Getting a Charli co-write has become a big stamp of approval for a certain kind of new artist.

You're right, and I'm honored. Even though it is the next generation, I want to be in it with everyone. I don't want to be considered this [untouchable entity], I don't have an ego about that shit. I want to just go into the studio with them and hit them up. We can all work together and be really collaborative — that's really fun for me. I do write with a lot of new people, and I'm really inspired by a lot of them. Have you heard of this girl L Devine?

I just heard her song “Peer Pressure” the other day, I really like it.

She’s really good. I think some of my backing vocals are on that song, I don’t really know.

Did you co-write that one?

No, I just heard it and was like, “I really want this song, this is a really cool song.” So I cut the vocals and then heard her version and was like, “Fuck, she sounds really good, she wrote it, she should have the song. I can't just take this girl's song. She sings it better than me, it's like her vibe.” And so I [told her], “Hey, I really like this song and sung it, sorry, but it's amazing!” I think they maybe used a couple of [vocal parts], but I was just a fan of the song. She's such a great writer, and the video's really good. We were DMing. She's so good, actually, she's maybe going to be a really big deal.

You’ve got a bit of a pop matchmaker vibe going — this artist should sing this song.

I really love curating, and that's what I've learned from the mixtapes too. I think I'm quite good at it, and I really enjoy bringing artists together, so it's fun for me.

Now that you've done the reputation tour, is there a world in which Taylor or Camila could hop on your next mixtape? I would love to hear what Taylor would sound like on a sick twisted SOPHIE beat like “Vroom Vroom.”

I think there is a world where that's possible, but I don't know if we're quite in that world right this second. But SOPHIE's going to be the biggest producer in the world, so it probably is possible soonish. Gaga first, then Camila and maybe Taylor. The thing is, I can imagine SOPHIE producing “Blank Space.” That makes so much sense to me, like a SOPHIE edit of “Blank Space” would not be super far out. Taylor would sound incredible with SOPHIE drums.