Picking models for orchestrator and subagent roles in Codex

Melvin Vivas · X post · 2026-09-26 · Open on X

Topics: AI Agents, Tool Use & MCP, LLM Fundamentals, AI Dev Tools & Productivity · Level: intermediate

Summary

After testing GPT-6 Sol, the creator is staying with a Codex multi-agent setup: Astra as the orchestrator and Luna as subagents. His reason is that Sol costs too much to run as a subagent and is not smart enough to be the orchestrator. The lesson is to choose a model for each role based on cost and intelligence.

Key points

• Multi-agent setup in Codex: one orchestrator model plans and delegates the work, and subagent models carry out the tasks.
• The creator's preferred setup is Astra as orchestrator and Luna as subagents.
• GPT-6 Sol was rejected for both roles: too expensive for a subagent and less intelligent than Astra as an orchestrator.
• Subagents run many times, so cost matters most there. The orchestrator makes the key decisions, so reasoning quality matters most there.

Resources mentioned

• OpenAI Codex · tool · openai.com · paid
  OpenAI's coding agent. In the diagram it writes code, fixes review findings and drives the build loop. The creator also used it to make this video.
  Also in: An agent bot that installs and drives Codex on its own (Melvin Vivas on X · notes), Asking a Coder bot to install Codex (Melvin Vivas on X · notes), Sign in with ChatGPT: Setting Usage Limits for Each App (Melvin Vivas on X · notes), Codex Cloud Environments Must Be Saved & Published Before Use (Melvin Vivas on X · notes) and 240 more
• Luna · tool · openai.com · paid
  The other model/agent the classifier routes tasks to; the post doesn't describe it further.
  Also in: GPT-6.1 Sol May Beat Luna for Subagents (Melvin Vivas on X · notes), GPT-6 Sol Ultra Subagents Use Up Limits Fast (Melvin Vivas on X · notes), GPT-6 Sol vs Opus 5.5 in a Livestream Comparison (Melvin Vivas on X · notes), DigitalOcean Serverless Inference Now Serves OpenAI GPT-6 Models (Melvin Vivas on X · notes) and 14 more
• GPT-6 Astra · tool · openai.com · paid
  The model announced in the quoted launch post, pitched as the developer's most capable model for work, coding, science and cybersecurity, and able to operate a computer.
  Also in: Customizing Your Coding Setup with Pi Coding Agent Extensions (Melvin Vivas on X · notes), Pi Agent Council: Ask Multiple LLMs in Parallel and Compare Their Advice (Melvin Vivas on X · notes), Use GPT-6.1 Sol by Default, Save Astra for Emergencies (Melvin Vivas on X · notes), Dots in ChatGPT: always-on AI agents that you hand responsibilities to (Melvin Vivas on X · notes) and 49 more

Try this

• When building a multi-agent setup, compare models separately for the orchestrator and subagent roles, weighing cost against intelligence.