III−V nanowire heterostructures can act as sources of single and entangled photons and are enabling technologies for on-chip applications in future quantum photonic devices. The peculiar geometry of nanowires allows to integrate lattice-mismatched components beyond the limits of planar epilayers and to create radially and axially confined quantum structures. Here, we report the plasma-assisted molecular beam epitaxy growth of thin GaAs/GaAsN/GaAs core−multishell nanowires monolithically integrated on Si (111) substrates, overcoming the challenges caused by the low solubility of N and a high lattice mismatch. The nanowires have a GaAsN shell of 10 nm containing 2.7% N, which reduces the GaAs bandgap drastically by 400 meV. They have a symmetric core−shell structure with sharp boundaries and a defect-free zincblende phase. The high structural quality reflects in their excellent optical properties. Local N% fluctuations and radial confinement give rise to quantum dot-like states in the thin GaAsN shell, which display remarkable single photon emission with a secondorder autocorrelation function at zero time delay as low as 0.05 in continuous and in pulsed excitation.