Why Codex Usage Drains Faster: Prompt Cache Hit Rate

Melvin Vivas · X post · 2026-08-22 · Open on X

Topics: LLMOps, Deployment & Monitoring, AI Dev Tools & Productivity · Level: intermediate

Summary

Melvin shares an OpenAI Codex update from Tibo (@thsottiaux): some users drained their Codex rate limits faster because the prompt-cache hit rate dropped that week. The lesson is that cache hits count heavily toward how much usage a coding agent burns.

Key points

• OpenAI saw a lower cache hit rate for some Codex users that week than in the stable weeks before.
• A lower cache hit rate can make usage limits drain faster.
• Hitting the prompt cache consistently is a big part of keeping agent usage cheap.
• OpenAI says it is working on a fix.

Resources mentioned

• Tibo (@thsottiaux) · person · x.com · free
  X account of the OpenAI Codex team member who posts Codex updates and usage-limit announcements.
  Also in: Codex Tip: Ask Codex to Organize Your Recent Chats (Melvin Vivas on X · notes), An X research bot built with Hermes (Melvin Vivas on X · notes), Codex safeguards against accidental destructive actions (Melvin Vivas on X · notes), Run OpenAI Codex with Open-Source and Local Models (OSS Mode) (Melvin Vivas on X · notes) and 1 more
• 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