OTel kind of has both today. Most languages support autoinstrumentation via either an agent, libraries, or both. So for example, if you've got a big Spring Boot

OTel kind of has both today. Most languages support autoinstrumentation via either an agent, libraries, or both. So for example, if you've got a big Spring Boot app, it'll instrument requests/responses and DB calls for you. Some languages also have lightweight "sprinkle some spans on it" things you can put in code, like Java method annotations. But none have truly automatic "span for every method call" instrumentation.