What happens when you run "quarkus dev"?

Running quarkus dev starts the application in Dev Mode, but the sequence of what actually happens under the hood is more involved than a normal application launch, which is why it can offer live reload without a manual restart.

1. Quarkus performs an initial build-time augmentation, same as any other build, producing a first runnable version of the application.
2. The application starts and begins serving requests, while a file-watcher process monitors source directories for changes.
3. On the next incoming HTTP request after a source file changes, Quarkus pauses that request, triggers an incremental recompilation and re-augmentation of only what's needed, then resumes handling the request against the updated code.
4. The Dev UI becomes available (default /q/dev), exposing extension-specific developer tooling, current configuration values, and a live view of registered beans and endpoints.
5. If continuous testing is enabled, affected tests re-run automatically in the background as source or test files change.

The key detail interviewers often look for is that recompilation is triggered lazily, on the next request, rather than eagerly the instant a file is saved — which avoids wasted rebuild work if several files are saved in quick succession before the next request actually arrives.