Sessions

session.set({ model })

How a local SDK session explicitly binds its default model instance

`session.set({ model })`

Local SDK sessions do not have a model by default.

You must explicitly call:

await session.set({
  model: openai.responses("gpt-5"),
});

Why it works this way

The local SDK behaves more like an embedded execution shell:

the agent handles path, tools, services, and session storage
the caller decides which live model instance should be used

That makes the local SDK more flexible, but it also makes the caller responsible for model readiness.

What happens if you skip it

Execution fails because the session has no default model.

This is one of the most common runtime mistakes in local SDK usage.

What about remote sessions

Remote sessions do not currently support setting the model this way from the client side.

Session Overview

Understand the central role of Session in the Agent SDK and the most common usage sequence

session.prompt()

Add a new user input into a Session actor and get back a turn handle

Table of Contents

session.set({ model })Why it works this way What happens if you skip it What about remote sessions