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Main Authors: Duffy, Alexander, Paech, Samuel J, Shastri, Ishana, Karpinski, Elizabeth, Alloui-Cros, Baptiste, Marques, Tyler, Olson, Matthew Lyle
Format: Preprint
Published: 2025
Subjects:
Online Access:https://arxiv.org/abs/2508.07485
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author Duffy, Alexander
Paech, Samuel J
Shastri, Ishana
Karpinski, Elizabeth
Alloui-Cros, Baptiste
Marques, Tyler
Olson, Matthew Lyle
author_facet Duffy, Alexander
Paech, Samuel J
Shastri, Ishana
Karpinski, Elizabeth
Alloui-Cros, Baptiste
Marques, Tyler
Olson, Matthew Lyle
contents We present the first evaluation harness that enables any out-of-the-box, local, Large Language Models (LLMs) to play full-press Diplomacy without fine-tuning or specialized training. Previous work required frontier LLMs, or fine-tuning, due to the high complexity and information density of Diplomacy's game state. Combined with the high variance of matches, these factors made Diplomacy prohibitive for study. In this work, we used data-driven iteration to optimize a textual game state representation such that a 24B model can reliably complete matches without any fine tuning. We develop tooling to facilitate hypothesis testing and statistical analysis, and we present case studies on persuasion, aggressive playstyles, and performance across a range of models. We conduct a variety of experiments across many popular LLMs, finding the larger models perform the best, but the smaller models still play adequately. We also introduce Critical State Analysis: an experimental protocol for rapidly iterating and analyzing key moments in a game at depth. Our harness democratizes the evaluation of strategic reasoning in LLMs by eliminating the need for fine-tuning, and it provides insights into how these capabilities emerge naturally from widely used LLMs. Our code is available in the supplement and will be open sourced.
format Preprint
id arxiv_https___arxiv_org_abs_2508_07485
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Democratizing Diplomacy: A Harness for Evaluating Any Large Language Model on Full-Press Diplomacy
Duffy, Alexander
Paech, Samuel J
Shastri, Ishana
Karpinski, Elizabeth
Alloui-Cros, Baptiste
Marques, Tyler
Olson, Matthew Lyle
Artificial Intelligence
Computation and Language
Computers and Society
Machine Learning
We present the first evaluation harness that enables any out-of-the-box, local, Large Language Models (LLMs) to play full-press Diplomacy without fine-tuning or specialized training. Previous work required frontier LLMs, or fine-tuning, due to the high complexity and information density of Diplomacy's game state. Combined with the high variance of matches, these factors made Diplomacy prohibitive for study. In this work, we used data-driven iteration to optimize a textual game state representation such that a 24B model can reliably complete matches without any fine tuning. We develop tooling to facilitate hypothesis testing and statistical analysis, and we present case studies on persuasion, aggressive playstyles, and performance across a range of models. We conduct a variety of experiments across many popular LLMs, finding the larger models perform the best, but the smaller models still play adequately. We also introduce Critical State Analysis: an experimental protocol for rapidly iterating and analyzing key moments in a game at depth. Our harness democratizes the evaluation of strategic reasoning in LLMs by eliminating the need for fine-tuning, and it provides insights into how these capabilities emerge naturally from widely used LLMs. Our code is available in the supplement and will be open sourced.
title Democratizing Diplomacy: A Harness for Evaluating Any Large Language Model on Full-Press Diplomacy
topic Artificial Intelligence
Computation and Language
Computers and Society
Machine Learning
url https://arxiv.org/abs/2508.07485