Injectable hydrogels that rapidly gel at physiological temperature are highly desirable for minimally invasive biomedical applications, yet existing systems often lack independent control over gelation kinetics and mechanical properties. Bottlebrush architectures provide a powerful handle to decouple molecular design from macroscopic material responses. Here, we report a hydrogel made from thermo-responsive core-shell bottlebrush with a hydrophilic PMAA core and responsive PDEGMA shell that enables rapid gelation at 37°C. Thermal analysis reveals reversible, architecture-dependent lower critical solution temperatures, with temperature-induced transitions occurring without macroscopic phase separation—consistent with an architecture-driven physical gelation mechanism. Vial inversion studies demonstrate rapid gel formation at physiological temperature. Rheological investigations quantify the influence of backbone length and shell thickness on gel strength and mechanical stability. This work highlights how core-shell bottlebrush architecture can be exploited to engineer injectable hydrogels with tuneable network formation offering a versatile design strategy for soft materials.