---
key: process.codex-cheap-worker-launch
title: 2026-07-21 — Launch Codex cheap workers via `codex exec`, not `spawn_agent` (#542)
status: active
since: '2026-07-21'
supersedes: none
superseded-by: none
rule: For bounded tool-bearing selector/recon work, launch a Codex worker with `codex exec -m gpt-5.4-mini -c model_reasoning_effort=low -s read-only`; `spawn_agent` buys parallelism but no cost savings.
signals: 'codex exec · `--ephemeral` · `spawn_agent` · `gpt-5.4-mini` · `gpt-5.1-codex-mini` HTTP 400 · `model_reasoning_effort` · `~/.codex/models_cache.json` · paths: `~/.codex/models_cache.json` · issues: #542'
mechanics: Local `codex` CLI on this ChatGPT-authenticated host. Tested 2026-07-14.
---

The native `spawn_agent` interface currently exposes no model or effort selector, so it parallelises at
full cost. Launch a separate worker instead:

```
codex exec --ephemeral --color never -m gpt-5.4-mini -c model_reasoning_effort=low -s read-only -C <repo> "<hard-capped scope contract>"
```

GPT-5.4-Mini is the current supported small/cost-efficient profile on this host; the older
`gpt-5.1-codex-mini` guess fails with **HTTP 400**. Keep `low` whenever any shell/MCP/web tool is
exposed; reserve `minimal` for explicitly tool-free synthesis over already-supplied bounded evidence.
On model rollover, inspect the visible entries in `~/.codex/models_cache.json` rather than guessing
names, then update this record once verified.