GPT-5 HAS A HIDDEN SYSTEM PROMPT

Summary from the TLDR AI newsletter

GPT-5, when accessed via the OpenAI API, has its own hidden system prompt that is independent from the system prompt users specify in their API calls. It is very resistant to sharing the details of this secret system prompt. The prompt seems to specify a level of 'oververbosity' where the assistant prioritizes direct answers with minimal extra content and keeps explanations short unless users ask for more.