This research brief from AI Hub for Education at Stanford University shares findings from a study that explores how K–12 teachers are using artificial intelligence (AI) in their work. The study partnered with an educational platform and analyzed over 150,000 prompts written by more than 4,400 teachers in October 2024. It focused on two research questions related to teachers’ frequency of usage and input of content. Two major findings were that most teachers relied on one AI assistant rather than specialized tools and the most common tasks included creating teaching materials such as lesson plans and ensuring that the content aligned to academic standards. In addition, the study found that most teachers showed limited use of AI in their day-to-day practice. The brief concludes with implications for developing stronger prompting strategies grounded in high-quality instructional materials, expanding research on teacher and student AI use, and designing more integrated systems to support productive teacher–AI interactions.