What is RCP?

The Runtime Context Protocol (RCP) is an open, versioned event format for AI-assisted engineering. Every supported client — Claude Code and Codex CLI — emits RCP events as you work. Runtime ingests those events into a searchable engineering timeline that powers Replay and Ask Runtime.

Why not just log the chat transcript?

A chat transcript tells you what was said. It doesn't tell you which model was used, what it cost, how long it took, or how one session relates to another. RCP records engineering events — structured facts with a type, a timestamp and a typed payload — instead of free-text conversation.

What Runtime captures today

The current implementation emits session lifecycle events (SessionStarted, SessionEnded) from the Runtime CLI, and model invocation, completion and cost events from the Runtime Gateway as your requests are routed to a model provider. See Event taxonomy for the full picture of what is live versus what is defined in the schema for future work.

Why a protocol, not just a feature

RCP is designed to outlive any single product. It is vendor neutral, versioned, and meant to become a common language for AI-assisted engineering — similar to how OpenTelemetry became the shared standard for application telemetry. Runtime is the reference implementation, not the only possible one.

Continue to Schema reference for the exact envelope and payload shapes.