public ChatSession startChat() {
    return new ChatSession(this);
  }
Returns a new {@link ChatSession} instance that can be used to start a chat with this model.

<p>Note: the returned {@link ChatSession} instance is NOT thread-safe.
java-vertexai/google-cloud-vertexai/src/main/java/com/google/cloud/vertexai/generativeai/GenerativeModel.java