Selenium 4, the latest iteration of the popular open-source test automation framework, introduces several significant enhancements over Selenium 3, propelling it to the forefront of modern testing tools. Key improvements include the adoption of the W3C WebDriver protocol, which supersedes the JSON wire protocol, providing more direct and standardized communication between client and server. Selenium 4 also integrates a built-in WebDriver Manager, simplifying the management of browser drivers, and introduces a more optimized Selenium Grid with enhanced support for parallel testing and resource management. Notable new features include relative locators, Chrome DevTools integration for advanced debugging, and an improved Selenium IDE with support for multiple browsers and cloud-based execution. These advancements not only enhance performance and stability but also address previous limitations such as limited support for modern web technologies and synchronization challenges. While Selenium 3 remains popular due to its robust community support, Selenium 4 offers a more streamlined, efficient, and feature-rich automation experience, making it a recommended upgrade for testers seeking to leverage the latest in test automation technology.