Aspects of the present disclosure provide for opportunistic uplink transmissions within a slot. In some examples, after scheduling all regular uplink transmissions within a current slot, a base station (e.g., gNB) may identify a set of unused uplink resources within the current slot and generate and transmit unused resource information identifying the set of unused resources to the user equipment (UE) within the cell served by the base station. If a particular UE is configured to operate in an opportunistic mode, the UE may utilize the unused resource information to generate and transmit an opportunistic uplink transmission within the set of unused uplink resources.