Anthropic chose HTML artifacts over Markdown because they load 5 times faster...
https://www.slideserve.com/aaron_ward92/what-s-a-practical-html-artifact-layout-for-a-code-review-with-3-findings
Anthropic chose HTML artifacts over Markdown because they load 5 times faster and handle complex layouts smoothly. This means teams spend less time waiting and more time collaborating. With over 4