Turn★

A turn is a single message exchange in a conversation. It consists of the client payload sent to the API, followed by the model's generated response.

In agent architectures, a single user prompt can trigger multiple sub-turns (e.g. the model calls a tool, the harness executes it and returns the result, the model calls another tool, and finally responds to the user).

You count turns whenever you:

• Measure the speed and efficiency of an agent's problem-solving loop.
• Configure maximum loops (max_turns = 10) in your scripting harness.
• Calculate the token growth rate of your active chat session.

Anatomy of a Multi-Step Turn

When an agent interacts with tools, a single user action translates to multiple API turns behind the scenes:

[ Turn 1.1 ] User: "Fix the type error in user.ts"
            ──► Model outputs: [ Tool Call: view_file "user.ts" ]
[ Turn 1.2 ] Harness returns: [ Tool Result: "export interface User {..." ]
            ──► Model outputs: [ Tool Call: replace_line "..." ]
[ Turn 1.3 ] Harness returns: [ Tool Result: "Success" ]
            ──► Model outputs: "I've fixed the type error. You're ready to compile."

Each sub-turn requires a network request to the provider. Because the API is stateless, every subsequent turn must send the accumulated history of all previous sub-turns, causing the context token size to grow step-by-step.

Field Applications

AI engineers set a strict limit on the number of turns in an agent's execution loop to prevent runaway billing cycles when models fall into loops:

• Code Example (Loop Guardrail):

  def run_agent_loop(user_task, max_turns=8):
      context = initialize_session(user_task)
      
      for turn in range(max_turns):
          response = call_model(context)
          context.append(response)
          
          if not has_tool_calls(response):
              return response # Task completed
              
          execute_and_append_tool_results(response, context)
          
      raise TimeoutError("Agent exceeded maximum turn threshold without finishing.")