A mechanism for speculative packet transmission including a credit-based flow control interconnect device to initiate speculative transmission of a Transaction Layer Packet if the number of available flow control (FC) credits is insufficient for completing the transmission. The sending device initiates a speculative transmission of packets to the receiving device even though the packet for transmission requires a number of FC credits greater than the available FC credits. If the additional FC credits required to complete the packet transmission become available to the sending device before the transmission is completed, the packets are then fully transmitted by the sending device. Otherwise, if the additional FC credits required do not become available prior to completion of the transmission, then the sending device aborts the transmission without utilization of the FC credits. The sending device may initiate speculative packet transmission only if a particular minimal amount of FC credits is available.