htmx 4.0 ships with fetch-based internals, explicit attribute inheritance, and cautious NPM rollout through 2027

The htmx team released htmx 4.0.0 after eight months of work, rebuilding internals around the fetch API while keeping behavior largely compatible with 2.x. Key changes include explicit attribute inheritance by default, cleaned-up event names, and history support that no longer uses localStorage by default. The project will keep 2.x as NPM’s latest tag until early 2027 to avoid unintended upgrades for CDN users.

The release reflects a broader push toward simpler, standards-based web tooling that modernizes internals without forcing developers into major rewrites. htmx’s cautious rollout strategy highlights how widely used frontend libraries increasingly need upgrade safety as much as new features, especially when CDN and package-manager defaults can affect production apps unexpectedly.