Idea: Auto-append router decision + rationale to model context window

[jrkropp]

Idea: Auto-append router decisions to the conversation context

Problem
When the router chooses which model to use (e.g., GPT‑4, GPT‑5), that choice and reasoning are hidden from the model itself. This causes issues:

• The model doesn’t know which version it is, or why it was selected.
• User requests like “use a more advanced model” get misinterpreted as a content request instead of a routing request.
• Routing choices lack continuity across turns, reducing consistency in long conversations.

Proposal
Each time the router selects or switches models, it should automatically insert a short developer/system message into the context. This message includes:

1. The model name (e.g., gpt-5).
2. The reason for selection in plain language (e.g., “Upgraded to GPT‑5 for complex reasoning needs.”).

Benefits

• Makes the model aware of its own identity and routing history.
• Ensures user meta-requests (“switch to a simpler model”) are understood and acted on.
• Improves consistency across turns by persisting model selection context.
• Provides transparency and a smoother user experience.

Example

ResponsesBody: {
  "model": "gpt-5",
  "input": [
    {
      "role": "user",
      "content": [
        {
          "type": "input_text",
          "text": "Use a more advanced model please."
        }
      ]
    },
    {
      "role": "developer",
      "content": [
        {
          "type": "input_text",
          "text": "[Router Decision]: Switched to gpt-5 because the user requested a more advanced model."
        }
      ]
    }
  ],
  "instructions": "Respond in chat‑optimized bolded Markdown.",
  "stream": true,
  "store": false,
  "truncation": "auto",
  "reasoning": {
    "effort": "minimal",
    "summary": "auto"
  },
  "parallel_tool_calls": true,
  "user": "a28e8ee4-1f0c-48da-a21f-a6b869fef275",
  "tools": [],
  "include": [
    "reasoning.encrypted_content"
  ]
}

--- Example Model Response ---

You’re now on GPT‑5, the most advanced model available.
I’ll handle your requests with the highest level of reasoning and clarity.