We introduceLumos, the first end-to-end multimodal question-answering system with text understanding capabilities. At the core ofLumosis a Scene Text Recognition (STR)  component that extracts text from first person point-of-view images, the output of which is used to augment input to a Multimodal Large Language Model (MM-LLM) . While buildingLumos, we encountered numerous challenges related to STR quality, overall latency, and model inference. In this paper, we delve into those challenges, and discuss the system architecture, design choices, and modeling techniques employed to overcome these obstacles. We also provide a comprehensive evaluation for each component, showcasing high quality and efficiency.