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Every session appends what happens to one durable log: the turns it accepted, the text the model produced, the tools it called, the memory it saved and the runtime that ran it. The log is what opencomputer sessions tail --json prints, what useAgent reduces to messages, what the dashboard’s session view shows, and what GET /sessions/<id>/events returns.

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Shape and ordering

Each event is one JSON object: seq is the cursor. A read with after=<seq> returns events with a greater seq, in ascending order, up to 500 at a time; repeat from the last seq you received until a page is empty, and keep polling from there to follow a live session. Because the log is durable and seq only grows, a consumer that stops can resume from its cursor without missing anything, and a page that overlaps one already read is harmless: apply events whose seq is greater than what you have applied. The React hook and the CLI work this way. Events at or below the cursor never change. New types can appear; treat an unknown type as informational and keep reading.

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Event types

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Session lifecycle

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Turns

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Public failures

A failure’s data is a stable code, a fixed message for that code, and at most one parameter. The runtime’s own error text is never sent; a failure no rule recognizes is agent_failed.

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Messages

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Tools

The exact fields come from the runtime’s tool record; read them as optional and key a tool call on callId when it is present. The memory tools (memory_save, memory_read, memory_list) appear here like any other tool; the save itself is reported separately.

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Memory

Delivery is best-effort. A save commits independently of the event: a runtime that loses its connection can commit without ever reporting it, and the same event can be reported once or twice after a reconnect. Treat the event as a hint to re-read the document, and also re-read when attaching, reconnecting and completing work. See Document memory.

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Model and usage

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Outbound requests

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Runtime

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Agent renders

One turn can carry several renders, one per model step. The debug inspector in the playground shows the same data.

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Reading the log

From the CLI, with one NDJSON record per event:
From an application, poll the events route or attach useAgent, which turns message.received, message.delta and message.completed into messages, turn.* and session.* into isRunning and ended, and memory.saved into memorySaves; every event, these included, also reaches onEvent.