This is not a course on using chatbots. It teaches you to build AI features that a business can trust. You'll design the support assistant for Paystream, a Nigerian mobile wallet, using its help centre, 900 labelled support tickets and graded answers from two assistant versions. You'll learn how models work and why they make confident mistakes, call them safely from Python with keys kept out of code, write prompts as versioned specifications, and validate every output against a schema. You'll compare a small model, a large model and a classic text classifier on the same tickets, build retrieval and measure its hit rate, show how grounding with citations and refusals changes answer quality, and check an LLM judge against human grades before trusting it. Finally, you'll redact personal data, defend against prompt injection, cost the options, and write a launch recommendation the evidence supports. Every number in the lessons comes from running the code; live model calls are optional and shown with the Anthropic SDK.