I used that API. It was literally autocomplete — if you wanted it to answer a question, you had to start with, say:

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Translate into German:

Q: "Good Morning" A: "Guten Morgen"

Q: "<the thing you actually wanted to translate>

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And even then it might answer with "Good Morning" in five different languages.

InstructGPT is what turned GPT-3 into the ChatGPT-3.5 model.