Thundercat on How Kendrick Lamar's New Project 'Completes the Sentence' of 'To Pimp a Butterfly'

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Thundercat poses in the press room with the award for best rap/sung collaboration for “These Walls” at the 58th annual Grammy Awards at the Staples Center on Feb. 15, 2016, in Los Angeles.

Kendrick Lamar dropped a new project called Untitled, Unmastered around midnight ET on Friday (March 4), and as is now more or less custom, it was a complete surprise -- even to some of his closest collaborators.

Billboard caught up with Stephen "Thundercat" Bruner, fresh off a Grammy win for his work on Lamar's 2015 album To Pimp a Butterfly (along with the awards garnered by the album itself, "These Walls," which featured Bruner, Anna Wise and Bilal, won best rap/sung collaboration), to talk about the unexpected release, which features the prolific bassist and songwriter throughout.

How long did you know this was in the works?

I didn't realize until recently -- they kind of hid it from everybody. Every now and again, I'll go to the studio -- I feel like Kendrick's always just working. He's always in the process of coming across something. He just kind of puts things out as he feels. I didn't realize until maybe a day before that he was going to put the music out. I walked in the studio -- they had been recording stuff -- and then there was this sidebar about how to release it. I was just like, "Oh shoot." I was kind of shocked.

Have you listened to it?

Yeah, I listened to it right before it came out. I knew about a couple of the songs that were a little older, but at the same's still surprising every time I hear it.

Which ones are you on?

I'm on "untitled 02," "untitled 03," "untitled 04," "untitled 05," "untitled 07," and "untitled 08." I wrote "untitled 08."

"untitled 07" is the one with that extended stripped-down part, right?

I remember that -- there was a lot of silliness that would happen in the studio. It's like, you never know what someone's paying attention to. But I remember when we came up with that. We were just kind of sitting there, kind of spent from having recorded a lot of stuff, and we came across that. Every once in awhile everyone gets a chance to see Kendrick's comedic side -- you can hear it on this record, how he has the ability to be that guy too. I was laughing so hard [which is audible on the track], just because of how far the idea was going...I was sitting there, like "What the hell?"

Kendrick calls the album "Demos from To Pimp A Butterfly. In raw form. Unfinished. Untitled. Unmastered." Is it safe to say that these are more or less outtakes from the album? That they were recorded in the same sessions?

Well, not all of them -- I think he just kind of did what made sense to him, listening to music that was in and around To Pimp A Butterfly.  ["Untitled 3"] is from a while ago. I remember "Blue Faces" ["untitled 08"] -- that song that was like, mostly me and Mono/Poly -- was more from the beginning of me and him working together. We wrote it at the house and brought it to him. Overall, he mixed it up a bit, that's the best way to describe it. The old, and a bit of the new. It still feels very much like To Pimp a Butterfly, but there's still a bit of the newer Kendrick in there too, what's happened since the album.

I don't know the full scope of what he did -- there was definitely a lot of music there already, too. I just know that the best thing ever was walking into that one session and realizing that he was going to put out new music -- that just excited me a bit.

I know you guys spent so much time together in the studio -- how much more material like this do you think there is?

Oh, there's a lot more. That's why I was saying, there was work that was going on in and around it. The songs I remember -- it's all these little reminders of why he is who he is.

What song do you like the best?

There's one line in the album [on "untitled 5"] that genuinely messes with me, when he said "Why would you want to see a man with a broken heart?" I was just like, wow. I had never heard that song [in its entirety] and then me hearing that for the first time -- it just reminded me of how great Kendrick really is. His ability to convey ideas is like, unmatched. It just hit me really hard. I was like, "Yeah, why would you want to see that?" That's why they call him King Kendrick -- he's pretty amazing.

I also feel like this record is maybe even more jazz-ish than TPAB.

Yeah, absolutely. Everybody's had a chance to see where his influences lie. There's definitely a big jazz influence on the album -- he'll always be that guy. He wears everything on his sleeve. The jazz influence -- it's too heavy in his music. He'll always be able to use that as a reference. He'll always be able to see that.

So you mentioned you've been in the studio with him recently -- making new music?

Absolutely, making music. It kind of varies, which I'm really happy about. I play bass, but also do some production. There are different facets to it -- sometimes somebody will think I'm playing bass, and it's a song I wrote, or somebody will think I wrote a song and it's just me playing bass. He has lots of different influences -- with this stuff, he definitely completed the sentence of To Pimp a Butterfly. I think that's what happened with this album. It's the complete statement of TPAB.

Did you get any sense of what made them want to release it right now?

I don't know what made it right now, but it's like, he's always ticking. I think what he showed with this album is that his mind is always on the music.