Gatsby 5 introduces a feature called partial hydration, which optimizes web performance by only loading JavaScript code necessary for interactive components on a webpage, known as client components. Implemented using React Server Components (RSC), this approach reduces the size of code bundles and decreases the time until a page becomes interactive, thereby improving user experience and increasing page load speed. Users can adopt partial hydration by either cloning the gatsby-partial-hydration-starter or following setup instructions with an existing project, marking interactive components with "client export" to see the feature in action. This method enhances metrics such as Lighthouse scores by reducing Total Blocking Time (TBT) and unnecessary JavaScript execution, aligning with the latest React community standards.