Many sector-level cooperative initiatives involving both national governments and non-state actors were launched around the 2021 Glasgow climate conference (COP26). However, there have been questions about whether and to what extent these initiatives could substantially contribute to achieving the Paris Agreement’s goal to limit global warming to 1.5 °C. To this end, this paper examines the prospects of the 14 Glasgow sector initiatives by investigating their aggregate mitigation ambition under current national signatories and the institutional robustness of each initiative. We find that the additional emission reduction ambition of the current national government signatories would, even if fully implemented, only fill about a quarter of the emissions gap in 2030 between the aggregate of existing national targets (nationally determined contributions: NDCs) and the required emission levels consistent with keeping warming below 1.5 °C, while the institutional robustness varied considerably across the initiatives. We also find that most national government signatories did not mention Glasgow initiatives in their updated NDCs submitted after COP26. Expansion of the national government participation, national government signatories’ incorporation of the initiatives’ goals into their updated NDCs by setting quantifiable domestic targets, and enhanced institutional capacity are key to successful emission reduction outcomes.