... they claim in this blog post: https://ai.facebook.com/blog/cicero-ai-negotiates-persuades-and-cooperates-with-people/
And relevant Twitter thread: https://twitter.com/ml_perception/status/1595070329227206656/photo/1
The AI played on webDiplomacy.net and apparently achieved very good results.
Article in Science: https://www.science.org/doi/10.1126/science.ade9097
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(https://pbs.twimg.com/media/FiJ8FJ7acAEDq8E?format=png&name=900x900)
(https://pbs.twimg.com/media/FiKADMcaYAACYWM?format=jpg&name=900x900)