今年5月31号过期，可以订美国境内48个州的I和Z舱头等舱往返票，必须在今年5月31号之前完成旅行。

https://thriftytraveler.com/guides/credit-card/delta-companion-ticket/

Companion Certificate is valid for one round-trip First-Class, Delta Comfort+® or Main Cabin ticket with the payment of applicable taxes and fees detailed below and the purchase of certain adult round-trip fares on published routings within the 48 contiguous United States.

booking Class: Seats are limited in First-Class to I, Z class of service, in Delta Comfort+® to W, S class of service, and in Main Cabin to L, U, T, X, V class of service.

Travel Dates: Travel must be completed by the certificate expiration date stated in the customer SkyMiles® Wallet.