The article explores whether large language models (LLMs) have a legal duty to tell the truth. It argues that LLMs, which generate responses that are often plausible, helpful, and confident but may contain factual inaccuracies, misleading references, and biased information, pose cumulative, long-term risks to science, education, and shared social truth in democratic societies. These subtle mistruths can degrade and homogenize knowledge over time. The authors propose that LLM providers should be required to mitigate careless speech and better align their models with truth through open, democratic processes. They define careless speech as speech that lacks appropriate care for truth, and examine the existence of truth-related obligations in EU human rights law and related legal frameworks. They find that current frameworks contain limited, sector-specific truth duties and propose a pathway to create a legal truth duty for LLM providers. The article also discusses the concept of careless speech, its harms, and the need for legal duties to address these issues. It concludes by proposing the creation of a legal duty to minimize careless speech for providers of general-purpose LLMs and derived commercial applications.The article explores whether large language models (LLMs) have a legal duty to tell the truth. It argues that LLMs, which generate responses that are often plausible, helpful, and confident but may contain factual inaccuracies, misleading references, and biased information, pose cumulative, long-term risks to science, education, and shared social truth in democratic societies. These subtle mistruths can degrade and homogenize knowledge over time. The authors propose that LLM providers should be required to mitigate careless speech and better align their models with truth through open, democratic processes. They define careless speech as speech that lacks appropriate care for truth, and examine the existence of truth-related obligations in EU human rights law and related legal frameworks. They find that current frameworks contain limited, sector-specific truth duties and propose a pathway to create a legal truth duty for LLM providers. The article also discusses the concept of careless speech, its harms, and the need for legal duties to address these issues. It concludes by proposing the creation of a legal duty to minimize careless speech for providers of general-purpose LLMs and derived commercial applications.