Abstract AMPA‐type glutamate receptors (AMPARs) lacking an edited GluA2 subunit are calcium permeable (CP), and contribute to synaptic plasticity in several hippocampal interneuron types, but their precise role in neocortex is not well described. We explored the presence of CP‐AMPARs at pyramidal cell (PC) inputs to Martinotti cells (MCs) and basket cells (BCs) in layer 5 of developing mouse visual cortex (postnatal days 12–21). GluA2 immunolabelling was stronger in MCs than in BCs. A differential presence of CP‐AMPARs at PC‐BC and PC‐MC synapses was confirmed electrophysiologically, based on measures of spermine‐dependent rectification and CP‐AMPAR block by Naspm using recordings from synaptically connected cell pairs, NPEC‐AMPA uncaging, and miniature current recordings. CP‐AMPAR expression in BCs was in addition correlated with rapidly decaying synaptic currents. Computer modelling predicted that this reduces spike latencies and sharpens suprathreshold responses in BCs, which we verified experimentally using dynamic clamp. The synapse‐specific expression of CP‐AMPARs may thus critically influence both plasticity and information processing in neocortical microcircuits. This article is protected by copyright. All rights reserved