OpenAI has introduced a more unified API endpoint, POST /v1/responses, alongside the established POST /v1/chat/completions, to better support agents that invoke tools, execute tasks, and process multimodal content. The Chat Completions API centers on a "messages" data structure, where the client must submit all context each round and manage conversation history, including tool calls and their results, as shown in a weather query example using model "gpt-5.6". This approach is intuitive for chat scenarios but has an engineering shortcoming: context management is primarily handled by the client, which must continuously maintain and replay historical messages as conversations grow. The Responses API instead treats model output as a single "response" that may include text, reasoning, tool calls, images, or structured results, centered around a single "task response." In the Responses API example, the request uses an "input" field instead of "messages" for the same weather query. The introduction of Responses does not mean Chat Completions are obsolete; rather, it provides a more appropriate abstraction for the complex workflows of agents.