A shabby workaround…
The same text that you would normally put in the “Instructions” field of a GPT in the configure tab can just be pasted as a starting prompt in an ordinary ChatGPT 3.5 session. (not using the GPTs feature)
You won’t have actions. You won’t have the quick start buttons. You won’t have an easily shareable link to a GPT. You won’t have a GPT that appears in the GPT Store.
BUT… your GPT will be able to answer more than a dozen prompts before announcing you’ve used up your quota for the day. On a paid account. Sigh.
GPTs are basically just prompt grounding with a bit of glue to actions.