Teachers must, in one way or another, address issues of Artificial Intelligence (AI) and generative AI (GAI). The urgency became even more acute when the chatbot ChatGPT was launched in November 2022, changing the conditions for teaching and learning in schools, creating tensions within the educational system. The aim of the study is to deepen understanding of teachers' experiences of how generative AI, specifically ChatGPT, shapes teaching and education in secondary and upper secondary schools. The theoretical framework is cultural-historical activity theory. Focus group interviews were performed on two occasions with 15 Swedish teachers. The reflexive thematic analysis resulted in three themes, elucidating tensions and contradictions: Navigating professional autonomy and institutional support in a new teaching landscape; Transforming relationships in the age of AI; and Rethinking the purpose of education in a dynamic educational context. Cultural-historical activity theory regards tensions and contradictions as prerequisites for transformation and development. Therefore, there is potential that generative AI and ChatGPT can become useful educational tools if teachers can negotiate and manage the uncertainties, and learn how to integrate the tools successfully into their teaching.