3.5. I actually just tried the same prompt in playground > text-davinci-003 and it wrote the front end in htmx without any endpoint code, then when prompted it provided endpoint code.

Still looks to be missing something aside from just the api key...

    <script>
      htmx.on('load', () => {
        const apiKey = '<your-api-key>';
      });
    </script>

...maybe 4 is way better. I thought I had a Plus account but it looks like API only.

Edit: Just tried 4 and it is better in the sense that it writes a more complete app for you, but it strangely separates the sections of the front end into discrete textareas w/ code, so if you are new to front end it'll be confusing for sure. "Where do I put all this" "oh actually it all gets run together; specifically these two sections of code are concatenated and placed in the body area of the first code section."

It also writes the endpoint code in Python and Flask by default, but with one more prompt it seems to have fixed all that.

I really wonder why 3.5, the common public interface, did what it did, when "actually writes code for more languages by default" isn't exactly on the Plus features list.