When standard exchanges do not fit
The replacement showed up before you sold.
The standard 1031 exchange (called a delayed exchange) follows this order: sell the relinquished property first, then identify and close on a replacement within the 45 and 180 day windows. That works for the majority of transactions. But sometimes the right replacement property comes up while your current property is still on the market, and waiting is not realistic. The deal will go to someone else.
A reverse 1031 exchange flips the order. You acquire the replacement property first, then sell the relinquished property within 180 days. The catch is that the IRS does not let you actually own both properties at the same time during an exchange (that would defeat the like-kind structure), so the exchange uses a special intermediary called an Exchange Accommodation Titleholder (EAT) to hold legal title to one of the two properties during the exchange period.
Reverse exchanges are more expensive and complex than delayed exchanges. They require lender pre-approval (since the EAT, not you, holds title), additional legal structure, and tighter timing on the relinquished property sale. For the standard delayed-exchange playbook, see the Austin 1031 main guide. This page covers reverse-specific mechanics.