I think the truth is sort of halfway between yall.

Hallucinations in tool call results _do still exist_, but basically everyone asks for a JSON schema for the tool call and uses that to validate and re-prompt the LLM until it emits something with a valid schema.

That all goes out the window when a string field has a “hidden” schema in that only particular strings are valid, but that restriction isn’t in the JSON schema. I have had failures when I want a field to be specifically formatted Markdown or something.

We’ll probably see something that handles this better in the future like jsonnet or Cue or dhall that has some execution capabilities so you can write a custom validator beyond what JSON schema supports.