OpenAI API adds a 12-hour prompt caching option

OpenAI's API changelog for October 20, 2026 says developers can now choose 12-hour prompt caching in the API (labelled for v1/responses). It keeps shared instructions, tools and context cached longer, so cached-input pricing applies even when requests are hours apart. OpenAI says 12-hour cache writes cost 2.5x the input token price.