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Draft — not yet ratified. This document is published for review. It describes the intended 1.0 behaviour, its wording is not final, and nothing here is covered by a compatibility promise until a version is frozen. Do not cite it as a stable reference.
This page defines the event patterns of the core protocol: the ways a producer composes events into a stream. Every transport carries all of these patterns; transports differ only in how events are framed and delivered. The direction of the protocol is fixed. Events flow from producer to consumer; the consumer speaks exactly once per exchange, by sending the run input that opens it. A producer MUST NOT require any mid-run message from the consumer — a run that needs outside input ends, and the answer arrives on the next run: through an interrupt and its resume entries, or through a frontend tool call left unanswered and answered in the next input’s messages.

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Streaming

Long values arrive a piece at a time: a *_START opens an item, content events extend it, a *_END closes it — or a chunked shorthand compresses the three. Text messages, tool calls and reasoning messages all stream this way. See Streaming Messages.

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Snapshot and delta

Values that evolve — agent state, activities, the conversation itself — are carried as a snapshot that replaces and deltas that amend, with deltas expressed as RFC 6902 JSON Patch. See Snapshots and Deltas.

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Interrupt and resume

A run that needs something from outside — an approval, a missing value — ends with an interrupt outcome, and the run that continues from it carries the answers in its input. See Interrupts and Resume.

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Adding patterns

All protocol features are built from these patterns. A protocol revision that adds a pattern defines it on this page. Transports carry new patterns without changes, because patterns are expressed entirely in terms of events and the run input.