I don't think this is more challenging than the browser thing. The scope is much smaller. The fact that this is "only" 100k lines is evidence for this. But, it's still very impressive.
I think this is Anthropic seeing the Cursor guy's bullshit and saying "but, we need to show people that the AI _can actually_ do very impressive shit as long as you pick a more sensible goal"
I think this is Anthropic seeing the Cursor guy's bullshit and saying "but, we need to show people that the AI _can actually_ do very impressive shit as long as you pick a more sensible goal"