K4 (also titled Bremen Radio 1971, Live at Bremen Radio, and Live on Radio Bremen) is a bootleg album of an early Kraftwerk lineup featuring Michael Rother and Klaus Dinger of Neu!, performing on Radio Bremen on June 25, 1971 as a three-piece with Florian Schneider. The distribution features five tracks, and names them (though no reason for the names is given). K1 is sometimes identified as Vom Himmel Hoch and K4 could be Stratovarious.
- "Heavy Metal Kids"
- "K2 (Ruckzuck)"