(I work at OpenAI.) This document is a preview of the underlying format consumed by ChatGPT models. As an API user, today you use our higher-level API ( https://platform.openai.com/docs/guides/chat ). We'll be opening up direct access to this format in the future, and want to give people visibility into what's going on under the hood in the meanwhile!
The "chat format" looks simple, extensible, and clean. The JSON format shown in https://github.com/openai/openai-python/blob/main/chatml.md looks ad-hoc, confusing, and (as noted by others) likely to lead to mistakes and injections.