htmx 4.0.0 has been released

# htmx 4.0.0 has been released! Source: [https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released) ## [htmx 4\.0\.0 Release](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#htmx-400-release) The htmx team is very happy to announce the release of htmx 4\.0\.0\! This is the culmination of 8 months of work \(plus a[game](https://four.htmx.org/game)\) and we are very happy with the results\. The idea of htmx 4 started to germinate when I decided to create[fixi](https://fixiproject.org/)and, in doing so, got more familiar with the`fetch\(\)`API and async programming in JavaScript\. \(htmx had always used[XMLHttpRequest](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest)due to backwards compatibility issues\.\) One chance evening I was contacted by Christian, who had some interesting ideas around[streaming HTML](https://four.htmx.org/docs#streaming-html)that got me thinking that moving the internals to`fetch\(\)`would simplify things for him and for the library in general\. After a bit of work I managed to get Michael and Alex on board, and we were off to the races\. Development has been very smooth\. We started a port of fixi \+ the htmx test suite\. Over time, we rediscovered why htmx did many of the things that it did and moved our new implementation closer and closer to the old one\. At this point the behavioral differences between 2\.x and 4\.x are relatively small and where they do diverge we have made explicit choices that we feel will put htmx\-based applications in a good spot for being[100\-year web services](https://www.youtube.com/watch?v=lASLZ9TgXyc) Note that we are not marking 4\.0 as[`latest`](https://docs.npmjs.com/cli/v10/commands/npm-dist-tag#purpose)in NPM because we do not want to force\-upgrade users who are relying on non\-versioned CDN URLs for htmx\. Instead, 2\.x will remain`latest`and the 4\.0 line will remain`next`until some point in early 2027\. The website, however, will reference 4\.0\. ### [Major Changes](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#major-changes) As mentioned above, htmx 4, from a users viewpoint, is almost identical to htmx 2\. There are three major changes: - Attribute inheritance is now explicit by default rather than implicit by default \(this is the biggest upgrade item\) - The htmx event names have been standardized & cleaned up\. Some advanced users may need to change the events they listen for\. - History support now does not use`localStorage`by default \(which was a cause of many support headaches\)\. Most people won’t notice this at all\. Internally, we migrated from`XMLHttpRequest`to`fetch\(\)`but that should be transparent for most users of htmx\. #### [Attribute Inheritance](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#attribute-inheritance) In htmx 2 many attributes where “inherited” by default\. This allows you to place attributes on parent elements and their behavior will apply to child elements\. This behavior, which came from the[intercooler\.js](https://intercoolerjs.org/)days, was inspired by CSS and, unsurprisingly, worked out about the same as CSS: powerful but difficult to understand at times\. In htmx 4 attributes are not inherited unless you[explicitly say so](https://four.htmx.org/docs#attribute-inheritance)by adding an`:inherited`after the attribute name: ``` <!-- htmx 2 --> <div hx-confirm="Are you sure?"> <button hx-delete="/item/1">Delete</button> </div> <!-- htmx 4 --> <div hx-confirm:inherited="Are you sure?"> <button hx-delete="/item/1">Delete</button> </div> ``` This will be the largest upgrade burden in migrating from htmx 2 to htmx 4\. To make things easier, we have provided a[command line tool](https://four.htmx.org/docs#upgrade-checker)to find places you need to mark as inherited\. Note that attributes like`hx\-disinherit`, etc\. are no longer required and should be removed\. #### [Events](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#events) The events triggered by htmx 2 had grown organically over the life of the librar and were not particuarly well organized, making it difficult to know exactly which event was fired when\. In htmx 4, all events now follow`htmx:phase:action\[:sub\-action\]`: htmx 2htmx 4`htmx:beforeRequest``htmx:before:request``htmx:afterRequest``htmx:after:request``htmx:beforeSwap``htmx:before:swap``htmx:afterSwap``htmx:after:swap``htmx:configRequest``htmx:config:request`In addition, the following changes were made: - Most error events collapse into[`htmx:error`](https://four.htmx.org/reference/events/htmx-error)\. HTTP error responses fire[`htmx:response:error`](https://four.htmx.org/reference/events/htmx-response-error)\. - The`htmx:xhr:\*`events are removed\. htmx 4 uses`fetch\(\)`\. - The`htmx:validation:\*`events are removed in favor of native browser form validation\. The full table is in[What’s New in htmx 4](https://four.htmx.org/docs/whats-new-in-htmx-4)\. The command line upgrade checker flags old event names in`hx\-on`attributes and in your JavaScript where it can find them\. #### [History](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#history) History support has always been included in htmx, allowing you to implement back\-button aware actions with simple attributes\. In htmx 2, a cache in`localStorage`was used to snapshot pages for restoration\. Unfortunately a large source of issues was that this snapshot could include DOM mutations by 3rd party JavaScript libraries\. When the page was restored, those mutations remained by the underlying JavaScript logic was not\. htmx 4 does not cache pages in`localStorage`\. On back navigation htmx re\-fetches the page and swaps it into`<body\>`, or into the`\[hx\-history\-elt\]`element if one is present\. This allows 3rd party JavaScript libraries to “just work” in most cases and, with good request caching, is very fast\. If you want local caching instead, we now ship a very complete[`hx\-history\-cache`](https://four.htmx.org/extensions/hx-history-cache)extension restores history from`sessionStorage`and is designed to integrate well with scripting solutions like Alpine\.js, etc\. ### [New Features](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#new-features) There are two big new features in htmx 4, both of which we are really excited about: #### [Morph Swaps](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#morph-swaps) We now support[morphing swaps](https://four.htmx.org/docs#morphing-swaps)out of the box with htmx\. I created[idiomorph](https://github.com/bigskysoftware/idiomorph)and nearly included it in htmx 2\.x but decided against it\. In htmx 4, Michael has done great work improving on that algorithm and integrating it seamlessly into htmx\. #### [`<hx\-partial\>`](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#hx-partial) Another major new feature is the`<hx\-partial\>`tag\. This tag is similar to[out\-of\-band swaps](https://four.htmx.org/docs#out-of-band-swaps), but is much clearer when you want do something beyond just replacing a single element with a new version of itself: ``` <hx-partial hx-target="#messages" hx-swap="beforeend"> <div>New message</div> </hx-partial> <hx-partial hx-target="#count"> <span>5</span> </hx-partial> ``` #### [Extensions](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#extensions) Much of the excitement in htmx 4 is in the extensions\. Switching to`fetch\(\)`internally let us rething how extensions can and should work, and sparked the creation \(and recreation\) of many new extensions, for example: - `hx\-preload`\- preload content \(e\.g\. on`mouseover`\) to speed requests up - `hx\-download`\- native, fetch\-based file downloads - `hx\-alpine\-compat`\- smooths over compatibility issues between htmx and[Alpine\.js](https://alpinejs.dev/) - `hx\-history\-cache`\- caches history in`sessionStorage`, provides Alpine\.js compatibility Additionally, there are three new or updated streaming HTML extensions: - [`hx\-sse`](https://four.htmx.org/extensions/hx-sse)streams over`text/event\-stream`\. - [`hx\-ws`](https://four.htmx.org/extensions/hx-ws)streams and sends over WebSockets\. - [`hx\-multipart`](https://four.htmx.org/extensions/hx-multipart)streams over`multipart/mixed` Finally, we decided it was time to try our hand at our own small front\-end scripting solution that tightly integrates with htmx\.[`hx\-live`](https://four.htmx.org/extensions/hx-live)is inspired by Alpine\.js,[jQuery](https://jquery.com/)and[hyperscript](https://hyperscript.org/), and makes front end scripting pleasant and fun\. It even supports what we are calling DOM\-based, HATEOAS\-friendly reactivity\. There is a new[`htmax\.js`](https://four.htmx.org/docs/htmax)bundle in the distribution which packages htmx with the most popular of these in a single file if you don’t want to think about which ones you want to pick\. ### [Upgrading](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#upgrading) For a complete upgrade guide see[What’s New in htmx 4](https://four.htmx.org/docs/whats-new-in-htmx-4)\. As mentioned earlier, we are providing an upgrade tool to help you: ``` $ npx [email protected] upgrade-check -- ./templates File extensions: .html, .php, .js, .ts, .jinja, .jinja2, .j2, .erb, .hbs Use --ext to add more (e.g. --ext .vue --ext .svelte) Scanning 1 file(s)... Found 8 issue(s) in 1 of 1 file(s). templates/index.html:1: [inheritance] hx-headers needs :inherited suffix (descendant on line 3 has hx-delete) (this looks like a CSRF token; without :inherited the header does not reach child elements and the server rejects the request) templates/index.html:2: [inheritance] hx-target needs :inherited suffix (descendant on line 3 has hx-delete) templates/index.html:2: [inheritance] hx-confirm needs :inherited suffix (descendant on line 3 has hx-delete) templates/index.html:3: [renamed-attr] hx-disable -> rename to hx-ignore (hx-disable now means 'disable during request') templates/index.html:4: [removed-attr] hx-vars is removed -> use hx-vals with js: prefix templates/index.html:4: [removed-attr] hx-prompt is removed -> load the hx-prompt extension to keep the same syntax templates/index.html:9: [old-event] old event name "htmx:afterRequest" -> "htmx:after:request" templates/index.html:9: [old-api] htmx.addClass() is removed -> use element.classList.add() ``` We are also shipping an[agent skill](https://four.htmx.org/docs/editor-support#ai-coding-assistants)to assist in upgrading ### [Installing](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#installing) htmx 4\.0 can be installed via a package manager referencing version`4\.0\.0`, or can be linked via a CDN: ``` <script src="https://unpkg.com/[email protected]/dist/htmx.min.js"></script> ``` or[Downloaded](https://unpkg.com/[email protected]/dist/htmx.min.js) ### [LLMs](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#llms) Like it or not, a lot of people are using LLMs and we are providing the following skills files for LLMs: - [`htmx\-guidance`](https://raw.githubusercontent.com/bigskysoftware/htmx/v4.0.0/dist/skills/htmx-guidance.md)\- core htmx skills for developing with htmx 4 - [`htmx\-debugging`](https://raw.githubusercontent.com/bigskysoftware/htmx/v4.0.0/dist/skills/htmx-debugging.md)\- diagnosing htmx issues during dev - [`htmx\-extension\-authoring`](https://raw.githubusercontent.com/bigskysoftware/htmx/v4.0.0/dist/skills/htmx-extension-authoring.md)\- writing and debugging htmx 4 extensions - [`htmx\-upgrade\-from\-htmx2`](https://raw.githubusercontent.com/bigskysoftware/htmx/v4.0.0/dist/skills/htmx-upgrade-from-htmx2.md)\- migrating a codebase from htmx 2\.x to 4\.x \(Let’s leave aside if releasing a new version of a library in the LLM era is a good or bad thing\!\) ### [Conclusion](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#conclusion) We hope you enjoy htmx 4\. htmx 2 will continue to be supported indefinitely so don’t feel any pressure to upgrade\. I’d like to thank the following people for all their help with this release: - [Michael West](https://github.com/MichaelWest22)\- Incredible teammate & grug\-brained developer - [Christian Tanul](https://github.com/scriptogre)\- Inspired htmx 4 & lead the streaming & live extensions - [Alex Petros](https://github.com/alexpetros)\- For keeping the ship on an even keel - Stephen Mitchell \- The genius behind the[game](https://four.htmx.org/game) - Stu Kennedy \- Our WebSockets expert - André Ahlert Jr\. \- Providing IDE & Editor Support - Dien Hoa Truong \- For kicking the tires on early htmx 4 and helping fix many bugs ### [Upgrade Music](https://four.htmx.org/announcements/2026-08-28-htmx-4.0.0-is-released#upgrade-music) Wouldn’t be an htmx update without upgrade music: