Comment by ryandsilva

A couple of tradeoffs I don't see mentioned here for HTML vs MD: - HTML is significantly less token-efficient - Difficult to provide precise feedback on plans HTML, much easier to do this in MD.

Both of these tradeoffs set Anthropic up for success. Using HTML as our medium will increase token usage, and I'd bet they're investing in tools to mark up HTML (part of Claude Design) which will help improve lock-in. Either coincidence or brilliant strategy.