OpenAI Codex Subagents Hit General Availability: Custom Agents with Separate Model Configs and System Prompts Per Subtask
simonwillison.net·high signal
OpenAI moved Codex subagents from feature-flag preview to GA on March 16, 2026, enabling developers to spawn parallel specialized subagents with distinct model configurations and system prompts within a single Codex task. Subagent activity is surfaced in both the Codex app and CLI and is enabled by default across all current releases. This productizes hierarchical agent orchestration inside a widely-used coding tool — a direct pattern shift from single-model execution to structured agent delegation.