From Software Engineer to AI Engineer - Part 1: A whole new world

You are a software engineer. Your craft honed through years of careful practice. Then suddenly, there are these chatbots and agents. Overnight, your colleagues got a new title on LinkedIn: "AI engineer". Some are already SENIOR AI engineers. You're curious about this new world, and might want to catch up and become part of it yourself. If this is you, then join me on this tour through the concepts and patterns that make up the field of AI engineering. We will find that AI application development is mostly 'just' software engineering, applied to one genuinely strange new non-deterministic component: the LLM. During the tour, we build a real application, end to end. Every article adds a new layer. We link the new patterns and words to existing software engineering concepts you already know. Before take-off, I'd like to establish one vocabulary rule used throughout: "the model" means the LLM itself (large language model, like GPT or Claude), and what AI engineers build around it will be referred to as "the application", "the agent" or "the harness". What we're building As I work at a payments company myself, I figured I'd stick to my domain. PayIQ, the application we build, is an assistant for merchants to perform payment operations: issue refunds, defend chargebacks, calculate processing fees. Give it a charge amount and a payment method, and it computes what a refund actually costs (spoiler: more than the refund amount). Ask it whether a chargeback is worth fighting, and it does the expected-value math using your knowledge base. Ask it something it can't responsibly answer, and it asks for what's missing. No guessing, no hallucinations. By the end, PayIQ will have structured outputs that can be consumed by other systems, a tool belt of financial calculators, retrieval over a knowledge base, an agent loop with persistent memory, an orchestration graph with steps the model cannot skip, token streaming behind a FastAPI service, a regression eval suite, and layered injec