Self-assembled 1D block copolymer nanoparticles (micelles) are of interest for a range of applications. However, morphologically pure samples are often challenging to access, and precise dimensional control is not possible. Moreover, the development of synthetic protocols that operate on a commercially viable scale has been a major challenge. Herein, we describe the preparation 1D fiber-like micelles with crystalline cores at high concentrations by a one-pot process termed polymerization-induced crystallization-driven self-assembly (PI-CDSA). We also demonstrate the formation of uniform fibers by living PI-CDSA, a process in which block copolymer synthesis, self-assembly, and seeded growth are combined. We have demonstrated that the method is successful for block copolymers that possess the same composition as that of the seed (homoepitaxial growth) and also where the coronal chemistries differ to give segmented 1D fibers known as block co-micelles. We have also shown that heteroepitaxial growth allows the formation of scaled-up block co-micelles where the composition of both the core and corona was varied. These proof-of-concept experiments indicate that PI-CDSA is a promising, scalable route to a variety of polydisperse or uniform 1D nanoparticles based on block copolymers with different crystalline core chemistries and, therefore, functions.