Issue with Structured Outputs: Model generates repetitive/concatenated JSON objects instead of a single response

Hi everyone,

I am encountering a persistent issue where the model generates multiple, repetitive JSON objects in a single response, corrupting the expected format.

The Setup: I am using JSON Schema (Structured Outputs) to manage a pizza ordering assistant. The goal is to receive a single JSON object per turn.

The Problem: Instead of stopping after the first valid JSON object, the model continues generating the same object (or slightly varied versions) multiple times in a row within the same output block. This results in a stream of concatenated JSON objects (e.g., {...} {...} {...}) rather than a single valid JSON, causing the parser to fail.

What I have tried so far (unsuccessfully):

  1. Changed Temperature: I tried adjusting the temperature (e.g., lowering it to 0.2 and testing other values), but the repetition persists.

  2. Switched Models: I was originally using gpt-4o-mini (referred to as 4.1-mini in my logs), but I also tested with gpt-5-mini , and the behavior remains exactly the same.

Has anyone faced this looping behavior with Structured Outputs recently? Is there a specific parameter or instruction in the system prompt needed to force a stop after the first object?

Thanks in advance for any help.