=== AP Decoding The _WSJT-X_ decoders for JT65, QRA64, and FT8 include optional procedures that use naturally accumulating information during a minimal QSO. This _a priori_ (AP) information increases sensitivity of the decoder by up to 4 dB, at the cost of a slightly higher rate of false decodes. For example: when you decide to answer a CQ, you already know your own callsign and that of your potential QSO partner. The software therefore "`knows`" what might be expected for at least 57 message bits (28 for each of two callsigns, 1 or more for message type) in the next received message. The decoder's task can thus be reduced to determining the remaining 15 bits of the message and ensuring that the resulting solution is reliable. AP decoding starts by setting AP bits to the hypothesized values, as if they had been received correctly. We then determine whether the remaining message and parity bits are consistent with the hypothesized AP bits, with a specified level of confidence. Successful AP decodes are labeled with an end-of-line indicator of the form `aP`, where `P` is one of the single-digit AP decoding types listed in Table 1. For example, `a2` indicates that the successful decode used MyCall as hypothetically known information. [[FT8_AP_INFO_TABLE]] .FT8 AP information types [width="35%",cols="h10,