What is the difference between classic Codenames and Codenames Duet?

In classic Codenames, red and blue teams compete over who will guess all their words first. Each team has a spymaster who gives clues and operatives who try to guess them.
In Codenames Duet, players form two teams as well, but the teams play together against the game. While the teams share the word grid, they each see a different distribution of agents. One team is giving clues to the other and vice versa and they need to find all green agents before they run out of clues.