From Wikipedia,

Diplomacy is an American strategic board game created by Allan B. Calhamer in 1954 and released commercially in the United States in 1959. Its main distinctions from most board wargames are its negotiation phases (players spend much of their time forming and betraying alliances with other players and forming beneficial strategies) and the absence of dice and other game elements that produce random effects.

From IEEE Spectrum,

Now that DeepMind has taught AI to master the game of Go—and furthered its advantage in chess—they’ve turned their attention to another board game: Diplomacy. Unlike Go, it is seven-player, it requires a combination of competition and cooperation, and on each turn players make moves simultaneously, so they must reason about what others are reasoning about them, and so on.

“It’s a qualitatively different problem from something like Go or chess,” says Andrea Tacchetti, a computer scientist at DeepMind. In December, Tacchetti and collaborators presented a paper at the NeurIPS conference on their system, which advances the state of the art, and may point the way toward AI systems with real-world diplomatic skills—in negotiating with strategic or commercial partners or simply scheduling your next team meeting.

When will AI first be revealed to be superhuman at the board game Diplomacy?

This question will resolve positively on the first date during which a credible public document reveals that a computer program has obtained superhuman performance at the board game Diplomacy, according to the then-current standard official rules (with no modifications, including any official suggestions), and with no handicaps or limitations that are not ordinarily present in tournaments. For the purpose of this question, a demonstration of superhuman performance will require at least one of the following conditions to be met,

1. The AI has won a first-place spot on a well-known international Diplomacy tournament. Eligible tournaments currently include WorldDipCon, and the Online Diplomacy Championship.

2. Some highly-regarded ranking of Diplomacy players ranks the AI higher than any human player.

3. A statement by a group of highly credible researchers indicates that they have obtained superhuman performance on Diplomacy to a very high degree of confidence.