This is consistently reproducible in completions API with `gpt-5-chat-latest` model:

``` curl 'https://api.openai.com/v1/chat/completions' \ --header 'Content-Type: application/json' \ --header 'Authorization: Bearer <your-api-key>' \ --data '{ "model": "gpt-5-chat-latest", "messages": [ { "role": "user", "content": [ { "type": "text", "text": "How many times does the letter b appear in blueberry" } ] } ], "temperature": 0, "max_completion_tokens": 2048, "top_p": 1, "frequency_penalty": 0, "presence_penalty": 0 }' ```