Large language models Protocols

Function calling, now also called tool calling, lets an application describe external functions to a model, which then decides whether to emit JSON arguments for one of them — the route by which models reach data and actions outside their training data.

GPT Actions let a custom GPT call external APIs, turning a user's request into the JSON input an API needs. Introduced by OpenAI on 6 November 2023, they grew out of the plugins beta and rely on OpenAPI schemas plus authentication settings.

Open Responses is an open specification and ecosystem, based on the OpenAI Responses API, that gives applications one shared schema for calling models, streaming results and composing agentic workflows across providers.

OpenEnv is an open framework and community hub from Hugging Face for building reinforcement-learning environments as containerized services that expose an agent interface, MCP and the Gym training protocol. It was contributed to the Agentic AI Foundation in October 2026.