When-issued (WI) trading refers to transactions in a Treasury security that has been announced but not yet settled. It establishes the market's consensus yield before the auction takes place.
When a new Treasury issue is announced (typically several days before the auction), dealers begin trading it on a "when, as, and if issued" basis. The when-issued yield:
When-issued trading serves an important price discovery function:
The when-issued market is most active in the hours leading up to the auction. The "1:00 PM level" (just before the typical 1:00 PM ET auction cutoff) is the standard reference point for calculating the tail.
When-issued trading carries settlement risk — if the auction doesn't proceed or terms change, WI trades may be canceled. In practice, this risk is negligible for standard Treasury auctions.