Module 06: Update Types

Comprehensive coverage of all SessionUpdate types in ACP.

What You’ll Learn

All SessionUpdate types and when they appear
Dispatching on update types with instanceof
Building rich UIs that show agent activity

The Code

The client registers a sessionUpdateConsumer and uses instanceof to handle each type:

AcpSyncClient client = AcpClient.sync(transport)
    .sessionUpdateConsumer(notification -> {
        SessionUpdate update = notification.update();
        if (update instanceof AgentMessageChunk msg) {
            System.out.print(((TextContent) msg.content()).text());
        } else if (update instanceof AgentThoughtChunk thought) {
            System.out.println("[Thought] " +
                ((TextContent) thought.content()).text());
        } else if (update instanceof ToolCall tc) {
            System.out.println("[Tool] " + tc.title() +
                " | " + tc.kind() + " | " + tc.status());
        } else if (update instanceof ToolCallUpdateNotification tcUpdate) {
            System.out.println("[ToolUpdate] " +
                tcUpdate.toolCallId() + " -> " + tcUpdate.status());
        } else if (update instanceof Plan plan) {
            System.out.println("[Plan] " + plan.entries().size() + " entries:");
            plan.entries().forEach(entry ->
                System.out.println("  - " + entry.content() +
                    " [" + entry.status() + "]"));
        } else if (update instanceof AvailableCommandsUpdate commands) {
            System.out.println("[Commands] " +
                commands.availableCommands().size() + " available");
        } else if (update instanceof CurrentModeUpdate mode) {
            System.out.println("[Mode] " + mode.currentModeId());
        } else if (update instanceof UsageUpdate usage) {
            System.out.printf("[Usage] %d/%d tokens%n", usage.used(), usage.size());
            if (usage.cost() != null) {
                System.out.printf("  Cost: %.4f %s%n",
                    usage.cost().amount(), usage.cost().currency());
            }
        }
    })
    .build();

Update Types Reference

Type	Content	Typical Use
`AgentMessageChunk`	Incremental response text	Main output, streamed word by word
`AgentThoughtChunk`	Agent’s thinking process	Show reasoning in a collapsible panel
`ToolCall`	Tool execution start	Show tool name, kind, and status
`ToolCallUpdateNotification`	Tool progress	Update status of in-progress tool
`Plan`	Agent’s planned steps	Show step list with priorities and completion
`AvailableCommandsUpdate`	Slash commands	Populate command palette
`CurrentModeUpdate`	Mode change	Update UI mode indicator
`UsageUpdate`	Token usage and cost	Show context window usage bar

This module extends Module 05 by handling every update type rather than just messages.

Source Code

View on GitHub

Running the Example

export GEMINI_API_KEY=your-key-here
./mvnw exec:java -pl module-06-update-types

Next Module

Module 07: Agent Requests — handle file read/write requests from agents.

Projects

AgentWorks

Agento

Supporting Projects

Migration

06 update types

Module 06: Update Types

What You’ll Learn

The Code

Update Types Reference

Source Code

Running the Example

Next Module

​Module 06: Update Types

​What You’ll Learn

​The Code

​Update Types Reference

​Source Code

​Running the Example

​Next Module

Module 06: Update Types

What You’ll Learn

The Code

Update Types Reference

Source Code

Running the Example

Next Module