Selenium 3 vs Selenium 4: Key Differences Explained

Introduction to Selenium 3 and Selenium 4

Selenium 3, released in 2016, brought stability and language binding improvements to the Selenium ecosystem. However, it still relied heavily on the JSON Wire Protocol for client-server communication, introducing performance overhead and inconsistencies across browsers.

Selenium 4, officially released in 2021, marked a significant milestone. It introduced W3C WebDriver standard compliance, making browser automation faster and more reliable. It also modernized Selenium Grid, added new APIs, and improved support for modern web elements like Shadow DOM and relative locators.

Selenium 4’s primary goal is to offer a streamlined, W3C-compliant automation experience that aligns closely with evolving browser technologies.

Architectural Changes: JSON Wire Protocol vs W3C WebDriver Standard

One of the most fundamental differences between Selenium 3 and Selenium 4 lies in the underlying communication model.

Selenium 3: JSON Wire Protocol

• In Selenium 3, test scripts written in languages like Java, Python, or C# communicated with browser drivers using the JSON Wire Protocol.
• Each command sent by the client library was converted into JSON format and transmitted to the browser driver (e.g., ChromeDriver, GeckoDriver).
• The browser then parsed this JSON payload, executed the corresponding actions, and returned a response.

While this worked effectively, there was a mismatch between Selenium and browser protocols, leading to extra conversion steps, latency, and occasional inconsistencies—especially when interacting with new browser features.

Selenium 4: W3C WebDriver Protocol

• Selenium 4 is built on the W3C WebDriver Standard, which is now the universal communication protocol used by all major browsers.
• Since Selenium 4 and modern browsers speak the same protocol, the communication is direct and faster, eliminating translation overhead.
• This shift enhances stability, ensures predictable behavior, and provides better cross-browser compatibility.

In practice, testers see fewer flaky tests and faster execution times—especially noticeable in large automation suites.

Updated WebDriver APIs and Locator Strategies

Selenium 4 modernized its API surface to make WebDriver more intuitive and expressive.

New Methods and Commands

Selenium 4 introduces several new methods that improve interaction with web pages:

• getRect() – Combines getSize() and getLocation() to provide element position and dimensions.
• newWindow() – Allows creation of a new browser tab or window without relying on JavaScript.
• DevTools APIs – Enables direct access to Chrome DevTools Protocol (CDP) for network tracking, performance metrics, and capturing console logs.

Example:

driver.switchTo().newWindow(WindowType.TAB);

driver.get("https://example.com");

Enhanced Locators

Selenium 4 introduces Relative Locators (previously called Friendly Locators) to improve readability and robustness in element identification.

Example:

WebElement emailField = driver.findElement(By.id("email"));

WebElement passwordField = driver.findElement(RelativeLocator.with(By.tagName("input")).below(emailField));

Supported relative locators include above(), below(), toLeftOf(), toRightOf(), and near(). These make tests more human-readable and resilient to UI layout changes.

What’s New in Selenium 4: Key Features & Enhancements

Selenium 4 isn’t just an incremental update—it redefines how testers interact with browsers.

• W3C Compliance: Ensures smoother communication with modern browsers.
• Improved Selenium Grid: Grid has been completely rewritten with a distributed architecture supporting Docker, Kubernetes, and cloud setups.
• New Window and Tab Management: Allows easier handling of multi-tab workflows.
• Native Support for Chrome DevTools Protocol (CDP): Enables capturing network requests, performance logs, and console outputs directly.
• Better Debugging: Screenshots for every test failure, enhanced logging, and detailed error messages.
• Improved Support for Modern Web Components: Handles Shadow DOM elements and CSS pseudo-elements more effectively.

Example: Capturing Console Logs with CDP

DevTools devTools = ((HasDevTools) driver).getDevTools();

devTools.createSession();

devTools.send(Log.enable());

devTools.addListener(Log.entryAdded(), entry -> {

    System.out.println("Console log: " + entry.getText());

});

This API gives testers deeper visibility into application performance and browser-side events—something that was previously possible only with external tools.

Deprecated Features and Backward-Compatibility Considerations

While Selenium 4 maintains backward compatibility with Selenium 3 scripts, a few features have been deprecated or replaced:

DesiredCapabilities → Options Classes:‍

Selenium 4 encourages the use of ChromeOptions, FirefoxOptions, etc., instead of the older DesiredCapabilities.

ChromeOptions options = new ChromeOptions();

options.addArguments("--start-maximized");

WebDriver driver = new ChromeDriver(options);

• Legacy Grid Components Removed: Selenium Grid Hub and Node configurations have been replaced with a unified, scalable design that supports distributed execution.
• RemoteWebDriver Enhancements: Remote sessions now use W3C-compliant commands, so mixed protocol issues between client and server are eliminated.

Despite these changes, most Selenium 3 scripts continue to run seamlessly after minor updates to driver initialization.

Upgrading from Selenium 3 to Selenium 4: Migration Path

Migrating from Selenium 3 to 4 is relatively straightforward but requires some attention to dependencies and configurations.

Steps for Migration

1. Update Dependencies:‍

Update the Selenium version in your build configuration (e.g., Maven pom.xml).

 <dependency>

    <groupId>org.seleniumhq.selenium</groupId>

    <artifactId>selenium-java</artifactId>

    <version>4.21.0</version>

</dependency>‍

2. Refactor DesiredCapabilities: Replace instances of DesiredCapabilities with browser-specific Options classes.

3. Verify W3C Compatibility: Ensure all browser drivers (ChromeDriver, GeckoDriver, EdgeDriver) are updated to their W3C-compliant versions.‍

4. Leverage New APIs: Gradually refactor scripts to use new methods like RelativeLocator and newWindow().

5. Upgrade Selenium Grid (Optional): If you’re using Selenium Grid 3, move to Selenium Grid 4 for enhanced parallel test orchestration.

The migration process ensures better maintainability, faster execution, and future-proofing for upcoming Selenium releases.

Performance, Grid & Parallel Testing Improvements

Selenium 4’s reengineered Grid architecture is a major upgrade over Selenium 3.

Selenium 3 Grid Limitations

• Complex setup involving Hub and Node configurations.
• No native support for containerization or distributed execution.
• Limited observability and manual session management.

Selenium 4 Grid Enhancements

• Single JAR Architecture: Both Hub and Node functionalities are bundled into a single executable.
• Docker & Kubernetes Support: Easily deploy scalable test environments in containers.
• Enhanced Observability: Includes built-in monitoring endpoints and session traceability.
• Parallel Execution: Improved load balancing and session queuing reduce test runtime drastically.

This makes Selenium 4 Grid a true enterprise-grade solution for large-scale testing environments.

Tool-Based Cloud Testing & Cross-Browser Coverage

While Selenium Grid 4 simplifies distributed testing, maintaining an in-house grid can still be resource-intensive. This is where cloud-based testing platforms like BrowserStack Automate come into play.

BrowserStack Automate provides instant access to over 3,500+ real browsers and devices, allowing Selenium 3 and Selenium 4 tests to run in parallel across multiple environments—without setup or infrastructure maintenance.

Benefits:

• Run Selenium tests on real devices, not emulators.
• Test across multiple browser versions simultaneously.
• Integrate easily with CI/CD tools like Jenkins, GitHub Actions, and Azure DevOps.
• Analyze detailed logs, video recordings, and screenshots of test runs.
  

By combining Selenium 4’s new APIs and BrowserStack’s real device cloud, teams can achieve faster feedback cycles, improved accuracy, and wider test coverage.

Summary of Differences & Which Version to Use

This table shows the summary of key differences between Selenium 3 and 4:

For new projects, Selenium 4 is the clear choice—it aligns with modern web standards, provides better performance, and supports advanced automation features.

Conclusion

Selenium 4 represents a significant leap forward in test automation. Its shift to W3C compliance, new relative locators, CDP integration, and revamped Grid architecture deliver tangible improvements in reliability and speed.

For existing Selenium 3 users, migration is straightforward and worthwhile. And by combining Selenium 4 with platforms like BrowserStack Automate, teams can extend testing beyond local setups to real browsers and devices at scale—ensuring faster, more consistent, and production-grade automation.

In short, Selenium 4 isn’t just an upgrade—it’s the evolution of browser automation for the modern web.