Servo 0.4.0 introduces a record 558 commits from June, bringing numerous web platform features and DOM APIs. Key additions include experimental support for 'attr()', new image and 'calc()' functionalities, and expanded media query support like '@media (device-width)' and '@media (orientation)'. Several new DOM APIs are now available, such as console.dir(), customElementRegistry, textStream(), and pointer event handling.

Security updates are significant, with Servo's JavaScript runtime, Spider Monkey, updated to fix several vulnerabilities. Specific CVEs and MFSA advisories are mentioned. Improvements in real-world compatibility are noted, with sites like lichess.org, Zulip, and Speedtest showing enhanced readability due to better variable font handling.

Work in progress includes a more powerful 'attr()' implementation, enhanced Web GPU support, and advancements in accessibility. Notably, Servo is developing a wrapper C API to enable embedding Servo as a prebuilt shared library, overcoming Rust's lack of a stable ABI. This aims to simplify integration for developers.