Hi @Dreaming-Codes - I was able to reproduce this issue.

It seems that xAI is (incorrectly) always returning JSON when you send "response_format": { "type": "text" } to them (OpenAI and other don't behave like this).

We'll stop sending this default value by default.

In the meantime (until we fix + release), please set extra_body during inference to override response_format.

For example, assuming you had a function generate_haiku and the Grok variant is called grok_3_mini_beta...

curl -X POST "http://localhost:3000/inference" \
  -H "Content-Type: application/json" \
  -d '{
    "function_name": "generate_haiku",
    "input": {
      "messages": [
        {
          "role": "user",
          "content": "Write a haiku about artificial intelligence."
        }
      ]
    },
    "extra_body": [{"variant_name": "grok_3_mini_beta", "pointer": "/response_format", "value": null }]
  }'

This works as you'd expect (no JSON).

Thanks for reporting!