It comes as a surprise that power poppers Hellogoodbye formed more than a decade ago. Forrest Kline — chief songwriter, lead singer and sole remaining original member — started the band in 2001 as he was finishing high school. He never expected to be featured on MTV’s The Real World, have smash radio singles like “Here (In Your Arms),” play festivals like Bamboozle and Reading, or tour with the likes of Hanson.

“God no,” Kline said when asked if he expected the longevity. “It was totally just a goof, a high school hobby. There was never any intention of doing this full-time, but once you get into it, it just kind of snowballs. We just found ourselves where there was a possibility, and we went for it.”

The band rocketed to relative fame on the strength of its unabashedly youthful, exuberant tunes. A self-titled EP and first full-length effort, Zombies! Aliens! Vampires! Dinosaurs! charmed listeners as singles “Baby, It’s Fact” and “Oh, It Is Love” stormed radio and TV waves in the mid-aughts.

A four-year layover existed between Zombies! and Hellogoodbye’s sophomore, still punctuation-laden effort, Would It Kill You?. In the meantime, the demise of the group’s old label led Kline and company to release the album on their own.

“We had a lot of options, but the record was done and we knew what we wanted to do,” he said. “We didn’t want to portray it the wrong way, and it felt right just to do it ourselves.”

That independence has let the band do things its own way, like recently choosing to put Would It Kill You?  up as a free download on its website.

“We’re shifting focus onto what we are doing next,” Kline said. “At this point, now that it’s been out for a year and we’re shifting into a new gear, I just want people to hear it.”

The record is decidedly more grown-up — but still sunny and bright — than the admittedly adolescent Zombies!, the result of a half-decade of living and learning.

“Most of those first two releases were written while I was in high school or shortly after. I was a whole new person when I followed that material up. I grew up five or six years’ worth, got married, had a real life and responsibilities,” Kline said. “I, as a person, went through a lot that contributed to that.”

Musicially, a new approach that relied more on instruments than technology helped match that growth.

“I always tear everything down conceptually and start again,” Kline said. “I used to work a particular way. I threw away the programs and built a studio in my garage to make real recordings, kind of start from the ground up.”

True to form, he’s finding a new formula for the next album, which should be recorded over the summer. He has debuted several new tracks at Hellogoodbye’s recent shows, like tonight’s free outdoor concert on the University of Oklahoma campus, which find an intersection between the band’s earlier, propulsive power pop and more recent beachy melodies.

“On this one, it’s a progression of that, but I’m kind of mixing the two. I’m doing the programming again,” Kline said. “I fell back in love with rhythmically based things. The last record was based more on melody, and switching it back around is really fun to do.”