GPT-5.4 Equals Opus 4.7 on 20-Task Coding Sprints
Both models built a full Laravel/React project with 20 tasks in 34-38 minutes without context exhaustion; GPT-5.4 Codex delivered equal or superior code quality via deeper details and rigorous checks.
Completing Production-Ready Code Under Constraints
Test both models on a detailed MD prompt specifying 20 Laravel/React tasks (e.g., routes, seeders, controllers with gates)—equivalent to 30 minutes of dev work. Use high reasoning mode for consistency. Opus 4.7 finishes in 34 minutes on 1M-token context (Cloud Code CLI). GPT-5.4 Codex takes 38 minutes on 258K-token limit ($20 OpenAI plan), leaving 12% context and 26% of 5-hour limit. Neither hits limits for this stack, proving half-hour agentic coding viable even on smaller windows—though heavier stacks risk overflow.
Opus shows clearer terminal progress: visible checklist of done/in-progress tasks. Codex lacks this, requiring manual log scanning, but offers superior dashboard (clickable queues, stage updates, activity tables vs. Opus's static view).
Superior Reliability Trumps Raw Speed
GPT-5.4 excels in end-to-end discipline: batches operations larger, runs type checks and route/action regenerations repeatedly—yielding robust integration. Opus fragments into many small writes/updates, faster per step but weaker on holistic quality.
Code outputs match closely due to prompt's specificity (pre-includes syntax/logic), but Codex edges ahead: seeds activities alongside customers (Opus omits), adds gate authorizations with authorize() trait. Minor Laravel variances (e.g., Codex uses older but functional syntax) don't break functionality. Looser prompts amplify gaps—Codex generates deeper, more surprising code (detailed in premium analysis).
Trade-offs: Codex costlier operationally from extra checks, but produces reliable results worth it. Opus quicker/direct but risks integration slips.
Use Codex Over Opus for Agentic Coding
Don't switch from GPT-5.4 Codex to Opus 4.7—Codex matches speed, often betters quality/reliability. Opus 4.7 improves on 4.6 (faster, per prior test) but trails Codex consistently. Prioritize Codex for production coding agents; its checks ensure deployable code despite UI quirks.