Diffuse hemispheric gliomas, H3G34R/V-mutant (DHG-H3G34), are uniformly lethal malignancies lacking targeted therapies. These gliomas uniquely originate from interneuronal precursor cells, and leveraging this interneuronal lineage origin for mechanistic and therapeutic insights is a pressing need. Here, we elucidate the cell state composition of DHG-H3G34, resolving a cellular hierarchy along continuous interneuron lineage development. In the developing human brain, interneuron lineage precursors form characteristic histological patterns organized in streams of progenitor cells surrounding nests of migratory interneurons, and we find these same spatial patterns to be mirrored in primary DHG-H3G34 tumors. We integrated these findings with genome-wide CRISPR-Cas9 screens, which revealed the majority of dependencies to be genes upregulated in interneuron lineage progenitors, highlighting these as a driver of DHG-H3G34. We validated the essentiality of these lineage-associated targets in patient-derived in vitro and in vivo models. Among these, CDK6 emerged as a targetable dependency, and we demonstrated enhanced sensitivity of DHG-H3G34 tumor cells to CDK4/6 inhibitors and a CDK6-specific degrader. Inhibition of CDK6 shifted cells towards more mature interneuron-like cell states, reduced tumor growth, and prolonged survival of patient-derived xenografts. Concordantly, a patient with progressive DHG-H3G34 under second line therapy was treated with a CDK4/6 inhibitor, and exhibited stable disease for 17 months. Collectively, we identify interneuronal progenitor-like states, organized in characteristic developmental spatial niches, as a distinct vulnerability consistently upregulated in DHG-H3G34 tumors, and provide initial evidence for CDK6 as a clinically actionable target particularly relevant for its interneuronal developmental biology. At time of import, last updated (by provider) on: Aug 01 2024 Contributors: ; [Rebecca F Rogers, Gustavo Alencastro Veiga Cruzeiro, Lynn Bjerke, Alan Mackay, Mariella G Filbin, Ilon Liu, Yura Grabovska, Chris Jones] (inherited)