This study presents a fractional-order investigation of the thermal performance of magnetized blood-based octa-hybrid nanofluids flowing through stenosed arteries in the presence of heat generation and thermal radiation effects. The mathematical model is formulated within the Caputo fractional derivative framework to analyze the combined influence of arterial constriction, magnetic field strength, thermal radiation, nanoparticle interactions, and memory-dependent fluid behavior on blood flow and heat transfer. By incorporating the Caputo fractional derivative into the governing momentum and energy equations, the model effectively captures the hereditary and memory characteristics of the fluid, which are not adequately represented by classical integer-order models. The transformed governing equations are solved using an appropriate analytical technique to obtain velocity and temperature distributions under various physical conditions. Particular attention is given to the effects of the fractional-order parameter, magnetic parameter, thermal radiation parameter, stenosis severity, nanoparticle volume fraction, and heat generation/absorption parameter on the thermal and flow characteristics of the nanofluid. The results reveal that the inclusion of octa-hybrid nanoparticles substantially enhances the effective thermal conductivity of blood, resulting in improved heat transfer performance. It is further observed that increasing the heat generation parameter significantly elevates the fluid temperature, whereas heat absorption suppresses the thermal field. Additionally, thermal radiation contributes to an increase in temperature distribution within the arterial region, thereby enhancing thermal transport. The magnetic field and fractional-order parameter are also found to play crucial roles in regulating flow resistance and temperature profiles in the stenosed artery. The findings demonstrate that fractional-order modeling provides a more realistic description of complex bio-thermal transport processes in magnetized blood-based octa-hybrid nanofluids. This study offers valuable insights into thermal management in diseased arteries and may contribute to the development of biomedical applications such as targeted drug delivery, hyperthermia treatment, thermal therapy, and advanced cardiovascular nanofluid technologies.