Anthropic switched to HTML artifacts for internal planning and code reviews...

https://spark-wiki.win/index.php/What_is_the_Claude_Side_Panel_Live_Preview_for_Artifacts_and_Why_Does_It_Matter%3F

Anthropic switched to HTML artifacts for internal planning and code reviews because they load 5 times faster than Markdown files. This speed boost means teams can review designs and reports without waiting, keeping everyone in sync. Plus, with 4