Apple Inc. QUIC defines a variant of the ACK frame that carries cumulative count for each of the three ECN codepoints (ECT(1), ECT(0) and CE). From this information, the recipient of the ACK frame cannot deduce which ECN marking the individual packets were received with. This document defines an alternative ACK frame that encodes enough information to indicate which ECN mark each individual packet was received with. This information is essential for accurately performing adjustments to congestion window and sending rate of the sender.