This study investigates the persuasive influence of political microtargeting using large language models (LLMs), specifically GPT-4. The authors developed a custom web application that integrates self-reported demographic and political data into GPT-4 prompts in real-time, allowing for the creation of personalized messages on four political issues. A randomized controlled experiment with 8,587 participants was conducted to evaluate the effectiveness of microtargeted messages compared to non-microtargeted messages. The results show that while GPT-4-generated messages were generally persuasive, the aggregate persuasive impact of microtargeted messages was not statistically different from that of non-microtargeted messages. The study concludes that the persuasiveness of current LLMs may lie more in their generic, nontargeted messages rather than their ability to tailor messages to individuals. The authors release the experimental dataset, *GPTarget2024*, to support future research on AI-driven political microtargeting.This study investigates the persuasive influence of political microtargeting using large language models (LLMs), specifically GPT-4. The authors developed a custom web application that integrates self-reported demographic and political data into GPT-4 prompts in real-time, allowing for the creation of personalized messages on four political issues. A randomized controlled experiment with 8,587 participants was conducted to evaluate the effectiveness of microtargeted messages compared to non-microtargeted messages. The results show that while GPT-4-generated messages were generally persuasive, the aggregate persuasive impact of microtargeted messages was not statistically different from that of non-microtargeted messages. The study concludes that the persuasiveness of current LLMs may lie more in their generic, nontargeted messages rather than their ability to tailor messages to individuals. The authors release the experimental dataset, *GPTarget2024*, to support future research on AI-driven political microtargeting.