The synthesis of amphiphilic linear-hyperbranched block copolymers with a linear poly(ethylene oxide) (PEO) segment and a hyperbranched poly(carbosilane)s (PCS) block in a rapid three-step strategy is described, combining oxyanionic polymerization with carbosilane chemistry. A linear precursor block copolymer was synthesized via anionic polymerization of ally] glycidyl ether onto a commercial hydroxyl-terminated PEO, using its cesium alkoxide as macro-initiator. The resulting linear AB or ABA-type di- or triblock copolymers serve as polymer cores for the subsequent hydrosilylation polyaddition of an AB(2)-type carbosilane monomer. Di(allyl)methylsilane or methyldi(undec-10-enylsilane) were employed, using Karstedt's catalyst as Pt-0-species. Due to the high reactivity of allyloxy groups in catalytic hydrosilylation reactions, the slow monomer addition technique, previously used for the controlled polyaddition of AB(2)-monomers, was not necessary in this case and complete conversion of all core allyl groups is achieved. Both the molecular weights of the hyperbranched block and the linear block were varied. The resulting polymers exhibited molecular weights up to 40,100 g/mol with rather low apparent polydispersities between 1.10 and 1.47. Phase segregation of the block copolymers was investigated by differential scanning calorimetry, demonstrating strongly segregated nanophases for all block copolymers. Transition electron microscopy showed unusual anisotropic morphologies in solution, which depended both on the length of the hyperbranched block and the nature of the carbosilane monomer used.