Methods, systems, and devices for wireless communication are described. The payload size for uplink transmissions of unscheduled control information may vary and, in some cases, may be dynamically determined. A user equipment (UE) may determine a payload size or may select a payload size from a set of predetermined sizes. A base station may independently determine the same payload size or it may blindly detect the payload size upon receiving the uplink (UL) transmission. Or the base station may indicate the payload size to the UE. Additionally, UL grants issued to the UE may take one of several forms (e.g., different downlink control indicator formats), and characteristics of the grant may indicate information about resources assigned by the grant, including a location of the resources among various transmission opportunities or whether the grant is for multiple subframes.