In HTML5, both the <html> and <body> tags are completely optional, as are their closing tags. Since there's no other content on this "page", you don't need to close the header either, so you could replace everything with:
The title tag is required, though (unless you’re in an iframe), and an h1 tag must be closed (unlike, e.g., paragraph and list item tags). So your minimal page looks like:
The world's most inane objection: If you force the validator to HTML5 mode, (as in the first and second links) then you don't need to declare a DOCTYPE, a savings of 16 bytes. Not that you would ever do that for a real document, since it's a dumb idea.