Research Scientist: Publishes papers, pushes state-of-the-art. Tests mathematical rigor and novel problem solving. You'll likely need a PhD.
ML Engineer: Builds and deploys models. Tests system design, coding, and production ML. You'll need strong software engineering skills.
Applied Scientist: Applies ML to business problems. Blends ML knowledge with domain expertise. Common at Amazon, fintech, healthcare.
AI Engineer: The role. Builds LLM applications using APIs, RAG, and agents. Tests prompt engineering and system integration.