LLM-Native APIs: How the Runtime behind REST Changed Fundamentally in 2026

Introduction For over a decade, the runtime behind a REST endpoint made a set of assumptions that were safe to make. A request maps to a single, predictable operation. The response shape is known before execution begins. Each request is self-contained — no memory of what came before (stateless). Business logic is deterministic: same input, same output, every time These assumptions held because they matched the workload. CRUD operations, relational queries, rule-based decisions — all of these are