<p>China faces the significant challenge of achieving its 2030 carbon intensity target, and the development of high-end producer services (HPS) is expected to be an important driving force. To better understand the impact mechanism of HPS agglomeration on urban carbon intensity, this study conducts an empirical analysis using panel data from 274 prefecture-level cities from 2006 to 2023. Based on revealing the spatiotemporal evolution characteristics of HPS agglomeration and urban carbon intensity, a spatial econometric model was used to explore the impact of HPS agglomeration on carbon intensity from the perspectives of spatial spillovers and city-size heterogeneity. The empirical results indicate that the average HPS agglomeration and carbon intensity in Chinese cities both gradually decrease, whereas the degree of spatial differentiation continues to expand. Both carbon intensity and HPS agglomeration exhibit significant positive spatial autocorrelation. The results of the spatial Durbin model show that HPS agglomeration contributes to the reduction in carbon intensity at the national level. For every 1% increase in HPS agglomeration, local carbon intensity decreases by 0.048%, but the carbon intensity of neighboring cities increases by 0.013%. In terms of city size, HPS agglomeration can promote a reduction in carbon intensity in large and mega-cities and medium-sized cities, but has no significant effect on small-sized cities. On the basis of these empirical findings, this paper proposes three specific suggestions: policymakers should vigorously increase the speed and scale of HPS development, explore differentiated HPS development paths that match the size of cities, and build an HPS development pattern based on urban agglomeration as the spatial carrier.</p>