Mark Otto has announced the first alpha of Bootstrap 6, five years after version 5. The release is a major overhaul of the open-source toolkit for websites and web applications. Existing projects will require migration work.

Bootstrap was created by Twitter and released as open source in 2011. The project reports more than 1.75 billion installations. It recorded 394 million npm downloads from 2015 through its tenth anniversary. W3Techs measured Bootstrap on 13.8 percent of all websites in August 2026, down from 15.3 percent in December 2025. Tailwind CSS has gained ground in new projects and ranked ahead of Bootstrap in a 2021 developer satisfaction survey.

Bootstrap 6 supports Chrome and Edge from version 130, Firefox from version 132, and Safari from version 18. Bootstrap 5 still supported Chrome and Firefox 60 and Safari 12. The newer baseline enables automatic light and dark mode switching and native dialog windows. Layouts can also align to their surrounding elements. Colors, spacing, and border radii can mostly be changed through CSS variables at runtime, so developers no longer need to recompile the framework for those adjustments.

The class naming scheme also changes. For example, `.d-md-none` becomes `.md:d-none`, and `.col-lg-6` becomes `.lg:col-6`. Accordions use standard HTML elements and no longer require JavaScript. Dialogs also rely on a browser standard. Documentation is supplied as the plain-text files `llms.txt` and `llms-full.txt` for AI coding assistants. The repository includes Skill files with guidance for AI agents, including instructions for migrating to version 6.

Bootstrap 5 will continue to receive support for now. The maintainers plan a 5.4.0 release before announcing an end date for the 5.x support period. Otto attributed the long development pause to his work on the company Pierre. He expects version 7 to arrive more quickly.