Kai Toedter upgraded the HAL Explorer dependency from version 1.2.3 to 2.1.0 in the spring-projects/spring-data-rest repository, focusing on enhancing API exploration and HAL support for users. He managed this change by updating the Maven pom.xml configuration, ensuring backward compatibility for existing REST clients while introducing new HAL features. The work involved careful dependency management using Java and XML, with attention to minimizing disruption during the upgrade. Although the scope was limited to a single feature and did not include bug fixes, Kai’s contribution improved user experience and contributed to the project’s release readiness through clear, lightweight documentation.