text: Filled with jazz solos and politically-charged lyrics, it appers to be a companion piece to Butterfly, rather than a standalone record.
  All of the tracks are untitled, save for the date they were recorded.
  Strangely, its appearance seems to have been prompted by basketball star LeBron James.
  The sportsman tweeted Lamar's record label boss Anthony Tiffith following the rapper's incendiary Grammy Award performance - in which he debuted a verse that alluded to the 2012 death of 17-year-old Trayvon Martin - demanding "you have to release those untitled tracks ASAP!"
  Tiffith replied he would think about it and, earlier this week, hinted at the release in an Instagram post: "I've decided to drop a project one day this week. I won't say what day or who." He later posted that fans should thank James for the new release.
  Untitled Unmastered appeared at around 04:00 GMT on all major streaming services including Spotify, Apple Music and Google Play.
  It features a cameo from singer Cee Lo Green, while Alicia Keys' five-year-old son Egypt allegedly produced the sprawling, eight-minute Untitled 07, which ends with a lo-fi recording of Lamar improvising lyrics to amuse his friends.
  The musician recently told hip-hop site 2 Dope Boyz he was sitting on a vault of material which didn't make the cut for To Pimp A Butterfly.
  "I got a chamber of material from the album that I was in love with where sample clearances or something as simple as a deadline kept it off the album. But I think probably close to 10 songs that I'm in love with that I'll still play and still perform that didn't make the cut."
  Fans will already be familiar with some of the songs, which Lamar has performed on US TV. Among them is Untitled 03, originally unveiled on late-night chat show The Colbert Report, which deals with religion, success and the exploitation of his music.
  Curiously, the studio version fades out before the song's original, angry coda, written as a response to the Black Lives Matter movement: "What the Black man say? Tell em, we don't die / We multiply."
  But the album doesn't shy away from political commentary, with Lamar chanting: "The government mislead the youth / And welfare don't mean well for you."
  The Compton-born performer was the most-nominated artist going into this year's Grammys, shortlisted in 11 categories.
  He took home five prizes on the night - including best rap album - but lost out on the main prize, album of the year, to Taylor Swift's 1989.
  To Pimp A Butterfly also had some high profile fans, including US President Barack Obama who named the song How Much A Dollar Cost, a parable with parallels to the Biblical story of the Good Samaritan, as his favourite song of 2015.
  Lamar is due to headline the BST festival in London's Hyde Park this summer.
target: Rapper Kendrick Lamar has released a surprise eight-track album, Untitled Unmastered, comprising outtakes from the Grammy-winning To Pimp A Butterfly.