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Enhancers are key regulators of mammalian gene expression, yet how they interact with promoters in space (contact vs. action-at-a-distance) and in time (transient vs. stable) remains poorly understood. Recent studies suggest that enhancers can activate promoters across distances exceeding 200 nanometers, challenging classical contact models, but limited spatiotemporal resolution has obscured the mechanistic details of enhancer-promoter (E–P) interactions and their link to transcription. Here, we engineered a synthetic biology platform optimized for the simultaneous visualization of E–P 3D distance and nascent transcription using super-resolution live-cell imaging. By applying five complementary approaches integrating imaging, 3D genomics, and gene expression data across cell lines, we estimate that transcriptional activation is mediated by ∼25-42 nanometer contacts on the seconds timescale. Our results support a transient contact mechanism for E–P-mediated gene activation.