Isn't the Function Calling feature meant for this purpose? It guides the LLM to output according to the given schema. The name of the feature is a little misleading.

https://platform.openai.com/docs/guides/gpt/function-calling

Function Calling is fine-tuned to a certain output format, but it very often strays from that format. My function-calling-handling code has a mess of edge case handlers that catch when GPT-4 is calling functions incorrectly.

It’s not though, they even say it in their docs that sending a schema does not guarantee that the model will actually adhere to the scheme or even produce valid JSON

Surprisingly the function calling mechanism doesn't appear to use this trick - apparently it's still possible to get the wrong JSON structure back from it occasionally.

They recently added logit biases, so that's a start.

It's limited to 300 logit biases at a time. Knowing GPT4's vocabulary is ~100k tokens it's not nearly enough to get reliable guided generation. Although it could work in some cases, and another advantage of this work is that we can determine that before generating.