Silo

Interface: AgentSessionUpdate ​

Defined in: packages/sdk/src/agents-service.ts:745

Beta

One session/update notification from a Chat session, lightly normalized. The Agent Client Protocol streams a turn as a sequence of these: assistant text, agent "thinking", tool-call rows, plan updates, and more.

A consumer must tolerate kind values it does not recognize — agents emit different subsets and vendors add their own (recon §3). Switch on the kinds you render and ignore the rest; never treat an unknown kind as an error.

Everything a Chat UI must draw to render a transcript is a modelled field: text / content for the message kinds, toolCall for tool_call and tool_call_update, plan for plan. raw is for what is deliberately left out — see its own note.

Properties ​

kind ​

ts
readonly kind: string;

Defined in: packages/sdk/src/agents-service.ts:751

Beta

The Agent Client Protocol sessionUpdate discriminator, e.g. "agent_message_chunk", "agent_thought_chunk", "tool_call", "tool_call_update", "plan", "available_commands_update".

text? ​

ts
readonly optional text?: string;

Defined in: packages/sdk/src/agents-service.ts:758

Beta

Text payload for the streaming-text kinds (agent_message_chunk, agent_thought_chunk, user_message_chunk); undefined for every other kind — and also for a text kind whose block is not text, in which case read content.

content? ​

ts
readonly optional content?: AgentContentBlock;

Defined in: packages/sdk/src/agents-service.ts:765

Beta

The whole content block a streaming-text kind carried, of which text is the "text" shorthand. Read it when you want to render an image or a resource link an agent sent as a message rather than dropping it. undefined for every non-message kind.

messageId? ​

ts
readonly optional messageId?: string;

Defined in: packages/sdk/src/agents-service.ts:772

Beta

Stable id for the run of chunks this update belongs to. Consecutive same-kind chunks share one — synthesized by Silo when the agent omits messageId, which real agents do (recon Finding 7), so a consumer can group a streamed sentence into one bubble without minting ids itself.

toolCall? ​

ts
readonly optional toolCall?: AgentToolCall;

Defined in: packages/sdk/src/agents-service.ts:778

Beta

The tool call, for kind "tool_call" and "tool_call_update"; undefined otherwise. Key rows by AgentToolCall.toolCallId and patch in place — an update carries only what changed.

plan? ​

ts
readonly optional plan?: readonly AgentPlanEntry[];

Defined in: packages/sdk/src/agents-service.ts:784

Beta

The agent's plan in full, for kind "plan"; undefined otherwise. The agent reissues the entire list every time, so replace the plan you are showing rather than appending to it. May be empty.

raw ​

ts
readonly raw: Readonly<Record<string, unknown>>;

Defined in: packages/sdk/src/agents-service.ts:805

Beta

The raw Agent Client Protocol update object — the escape hatch, for the kinds and fields this surface does not model.

What is deliberately not modelled, and why: available_commands_update (an agent's slash commands — a menu, not a transcript row), usage_update (token counts, which no agent reports the same way), current_mode_update (already surfaced as AgentSessionConfigOption.currentValue), session_info_update (already surfaced as AgentInfo.title), and vendor extensions such as claude-agent-acp's _meta. None is needed to draw a transcript; all are readable here.

raw tracks the protocol, not this SDK's semver. A field inside it can change shape, or vanish, when an agent or its adapter changes — no SDK major required, and that has already happened three times inside one sprint. Read it defensively, and if you find yourself needing it for something every Chat UI must render, that is a gap in this surface worth reporting. Treat it as read-only.