All four build agents with tool calling, RAG and MCP, so features are not the decision. What separates them is what each one demands of the runtime you already operate — and for the JVM pair that demand is a Spring Boot major version.
Four orchestration frameworks let you wire up the same workflow — and the feature lists nearly match. The thing that decides which one survives production is invisible there: where your agent's state actually lives.
Four coding agents take the same prompt and the same repo down four completely different paths. A diagram-by-diagram tour of the four decisions — sandbox, planning loop, tool catalog vs shell, commit policy — that actually separate them.
Three of 2026’s fastest-growing open-source agents look almost identical on a feature list — and behave like completely different species the moment you run them. A diagram-by-diagram tour of where the architectures diverge.