No, you don't use a space: "xit name" (http://ex-vi.sourceforge.net/ex.html)

If ex is not your favorite editor, use EX<ESC><ESC> (at least, that is what I think Wikipedia claims. I'm sure any decent TECO user never exits their editor, browsing the web in a browser macro)

[I also checked ed and edlin. They had two commands for exiting: w writes and exits, q quits]