Can I buy a Delta cabin upgrade for just one traveler on a shared reservation?

What this answer depends on

• Delta post-purchase paid cabin upgrades through the stated eligible Delta/Delta Connection booking process
• The selected flight segment is the unit identified in Delta’s upgrade explanation, while all customers on the reservation are included for that selection. Do not assume that upgrading one flight upgrades every connection, or that one traveler can be removed from the displayed offer by changing a seat-map selection. The public rule does not establish a self-service one-person exception.
• Delta distinguishes Preferred Seats within Main Cabin from upgrades to a different cabin. A front-of-cabin location or other seat attribute is not, by itself, evidence of a cabin upgrade. Read the product name in the offer and compare it with the booked cabin before paying.
• Delta’s help page contains different timing formulations for paid-upgrade availability. This guide therefore does not publish a single last-purchase deadline. Look for the offer in the current booking and ask Delta about timing when necessary. An absent offer is not proof that the higher cabin is sold out, and a visible seat map is not a guaranteed purchasable upgrade.
• Delta’s stated paid-upgrade process includes all customers on the reservation for the selected flight segment.
• Delta Preferred Seats are within Main Cabin and are distinct from cabin upgrades.
• The Delta seats-help page contains differing paid-upgrade timing formulations, so no universal purchase cutoff is adopted.