The purpose of the paper is to study human-centered knowledge management in start-ups, reveal challenges, its peculiarities, and framework. The technology start-up teams used experiential design thinking, agile and lean approaches to design and validate the hypotheses of minimal viable products and repeatable and scalable business models. The exploratory qualitative research was conducted with 27 cross-functional start-up teams in a period 2019-2023. The research reveals: (1) the necessary knowledge set for start-ups which facilitates entrepreneurial teams to launch new ventures, design products and business models by using human-centered knowledge management framework that includes social-based and technology-based parts for acquisition, creation, sharing/transferring, and application of tacit and explicit knowledge in start-ups; (2) specific set of peculiarities and challenges of KM in start-ups; (3) dominance of the mode “Socialization” in the discovered 3-mode SEI (socialization, externalization, and internalization) knowledge conversion model for early (fuzzy front end) stage of product/business development in start-ups; (4) evidence that conversion “explicit to tacit” knowledge in “Internalization” occurs effectively in combination of explicit knowledge obtained in exploratory prototyping inside of start-up and the knowledge generated by generative AI at the requests of a startup. Practical implication of the research is understanding of framework and challenges of KM in start-ups, and opportunity to use the research results in start-ups management at the fuzzy front-end stage.