Sessions

Platform advisor roster entry: a model the session's primary thread may consult mid-turn. At most one per roster; the entry occupies the roster name anthropic.advisor.

Specification for an Agent. Provide a specific version or use the short-form agent="agent_id" for the most recent version

Reference to an agent plus optional configuration overrides. Each provided field replaces the agent's value for the caller's use; the agent resource is unchanged.

A hard spend ceiling. The session stops issuing new model requests once the tracked list cost reaches max_list_cost.

Prompt-cache creation token usage broken down by cache lifetime.

Confirmation that a session has been permanently deleted.

An incremental update to an event that is still being streamed. Deltas are best-effort and may stop early; when the buffered event with id == event_id is produced it carries the complete content. A model request that ends early (an error or interrupt) produces no buffered event — its terminal span.model_request_end closes the preview. Only sent on stream connections that opt in via event_deltas; never appears in event history.

EventDeltaType enum

Mount a file uploaded via the Files API into the session.

Mount a GitHub repository into the session's container.

Parameters for attaching a memory store to an agent session.

Resolved coordinator topology with a concrete agent roster.

A coordinator topology: the session's primary thread orchestrates work by spawning session threads, each running an agent drawn from the agents roster.

An entry in a multiagent roster: an agent ID string, a versioned agent reference, or self.

Evaluation state for a single outcome defined via a define_outcome event.

Cumulative count of server-executed tool invocations, broken down by tool.

A Managed Agents session.

Resolved agent definition for a session. Snapshot of the agent at session creation time.

Mid-session agent configuration update. Only tools and mcp_servers are updatable. Full replacement: the provided array becomes the new value. To preserve existing entries, GET the session, modify the array, and POST it back.

Resolved coordinator topology with full agent definitions for each roster member.

Timing statistics for a session.

Emitted when an UpdateSession request changed at least one field. Carries only the fields that changed; absent fields were not part of the update. The new configuration applies from the next turn.

Cumulative token usage for a session across all turns.

Periodic snapshot of the session's cumulative usage and tracked list cost.

Opens a preview of a buffered event. Carries the previewed event's type and id only. Followed by zero or more event_delta events with the same event id, normally concluded by the buffered event carrying that id. If the producing model request ends without that event (an error or interrupt mid-stream), its terminal span.model_request_end closes the preview. Only sent on stream connections that opt in via event_deltas; never appears in event history.

Regular text content.

A mid-conversation system message event. Carries system-role content that is appended to the session as a role: "system" turn.

Event sent by the client providing the result of an agent-toolset tool execution. Only valid on self_hosted environments, where sandbox-routed tools are executed by the client rather than the server.