Ops Development & AI Practice

Sep 27, 2026 · Artificial Intelligence

OpenAI API Evolution: Completions to Responses — Why Open Source Still Uses Chat Completions

This article traces OpenAI's API evolution across six generations from Completions to Responses API, explains why the open-source ecosystem remains anchored to Chat Completions despite official advances, compares architectural trade-offs between stateless and stateful paradigms, and provides a practical selection guide for engineers building heterogeneous model gateways or agent systems.