Codex is OpenAI's AI coding agent platform — available as a CLI, desktop app, and VS Code extension. It scores 69/100 on AgentRanks' architecture rubric and leads on Terminal-Bench 2.0 with GPT-5.5.
Codex features 8 parallel sub-agents for high-volume editing, achieving 82.7% on Terminal-Bench 2.0 — the highest score of any coding agent. Its architecture emphasizes speed over depth: 240+ tok/s generation, 2.5x faster than Opus-based agents. Codex uses OpenAI's models exclusively (GPT-5.5, GPT-5.4, GPT-5.3-Codex).
Speed (18/20): Codex's tool system is optimized for rapid code generation. Terminal-Bench 2.0 leader at 82.7%.
Multi-Agent (16/20): 8 parallel sub-agents for concurrent task execution. Strong but less sophisticated than Claude Code's Coordinator mode.
$20/mo (Plus/Pro). Higher tiers for heavy usage. Codex uses OpenAI models — GPT-5.5 API costs $6/$25 per 1M tokens.
Codex is locked to OpenAI models and has a weaker memory system (8/15) than Claude Code (15/15). Its architecture score of 69 trails Claude Code's 94.