a2a-multi-turn

A2A Multi-Turn Conversations

Before writing code

Fetch live docs:

1. Fetch https://a2a-protocol.org/latest/specification/ for multi-turn and input-required handling
2. Web-search site:github.com a2aproject A2A multi-turn input-required for multi-turn protocol details
3. Web-search site:github.com a2aproject a2a-samples multi-turn for conversation examples
4. Fetch SDK docs for multi-turn task handling patterns

Conceptual Architecture

What Multi-Turn Means in A2A

Multi-turn conversations allow agents to have iterative exchanges within a single task. The server agent can request more input from the client, creating a back-and-forth dialogue before reaching a final result.

The input-required State

The key mechanism for multi-turn is the input-required task state:

Client sends message → Task created (submitted)
Server processes → working
Server needs more info → input-required (with a message explaining what's needed)
Client sends follow-up → working (task continues with same taskId)
Server completes → completed

How It Works

1. Initial request: Client sends message/send or message/stream without taskId
2. Server processes: May transition to input-required if it needs clarification
3. Server response: Returns the task with input-required state and a message explaining what's needed
4. Client responds: Sends another message/send with the same taskId and the requested information
5. Server continues: Resumes processing with the additional context
6. Repeat or complete: May request more input or reach a terminal state

Context Preservation

Within a multi-turn task:

• All messages are associated with the same taskId
• The server maintains the full conversation history
• Each new message from the client adds to the context
• The server can reference previous messages when processing

Patterns

Clarification Loop

Agent asks for clarification when the request is ambiguous:

User: "Book a flight"
Agent: (input-required) "Where are you flying from and to? What dates?"
User: "NYC to London, March 15-22"
Agent: (input-required) "I found 3 options. Which do you prefer? [options]"
User: "Option 2"
Agent: (completed) "Booked! Confirmation #ABC123"