Imagine you are at a crossroads in a complex project and you need quick answers on how to grapple with a problem. It is quite likely that you might turn to an online knowledge community for answers, one hosted by your company, or perhaps Stack Overflow, Quora, or Reddit. These communities have come to play a central role in knowledge exchange, in many corners of the economy and society, but they depend on voluntary participation from users just like you and me. Our recent research indicates an intriguing shift is now taking place: generative AI technologies, such as OpenAI's large language model (LLM) ChatGPT, are disrupting the status quo. Increasingly, users are gravitating toward these new AI tools to obtain answers, bypassing traditional knowledge communities.

ChatGPT generates believable text about nearly any subject, but there is a big difference between "believable" and "correct." ChatGPT, similarly to other LLMs, is trained on large swaths of publicly available data, in large part scraped from online forums such as Stack Overflow and Reddit. Given differences in the volume of available data, ChatGPT's performance naturally varies by topic and may in turn affect communities to different degrees. We observed ChatGPT's impact on Stack Overflow participation varies significantly across topics, aligning with its expected performance based on available training data. Those topics related to open-source tools and general-purpose programming languages (for example, Python, R) appeared to experience larger declines in participation and contribution than proprietary and closed technologies, such as those employed for enterprise server-side development (for example, Spring Framework, AWS, Azure).