OpenAI Decisions API vs Function Calling

// Function calling: the model decides to call a tool and
// builds its arguments. You parse tool_calls and execute it.
{
  "tools": [{
    "type": "function",
    "function": {
      "name": "route_ticket",
      "parameters": {
        "type": "object",
        "properties": {
          "team": { "enum": ["payments", "frontend", "account"] }
        }
      }
    }
  }]
}

// Decision endpoint: pick among finite answers and get a
// probability per option — no tool plumbing, no arg parsing.
{
  "model": "decisions-1",
  "state": "The page renders blank in Safari.",
  "questions": {
    "team": {
      "type": "choice",
      "instructions": "Which team should own this ticket?",
      "criteria": {
        "payments": "Checkout or billing.",
        "frontend": "Rendering or browser behavior.",
        "account": "Login or permissions."
      }
    }
  }
}