---
title: "What changes to an OpenAI prompt can break prompt-cache reuse?"  
description: "What changes to an OpenAI prompt can break prompt-cache reuse?"  
author: "Ruslan Galiev"  
published: 2026-10-16  
updated: 2026-10-16  
canonical: https://www.mindstick.com/forum/162500/what-changes-to-an-openai-prompt-can-break-prompt-cache-reuse  
category: "OpenAI API"  
tags: ["OpenAI API", "Prompt Caching", "AI Development"]  
reading_time: 1 minute  

---

# What changes to an OpenAI prompt can break prompt-cache reuse?

I’m testing a long, mostly fixed system prompt with the OpenAI API, followed by a different user message each time. I’m trying to work out which edits to that shared prefix make the prompt cache miss: for example, adding a timestamp, changing a small instruction, or reordering sections.

Has anyone measured this in a real application? I’d be interested in what you log to tell a genuine cache hit from normal variation in response time.


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Original Source: https://www.mindstick.com/forum/162500/what-changes-to-an-openai-prompt-can-break-prompt-cache-reuse

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