Low cache hit rate when Codex integrates with GPT-5.5

[pyfdtic]

What version of Codex CLI is running?

0.125.0

Which model were you using?

gpt-5.5

What platform is your computer?

WSL2

What terminal emulator and version are you using (if applicable)?

Windows Terminal

What issue are you seeing?

When Codex integrates with the GPT-5.5 model, its cache hit rate is very low, which causes costs to be consumed rapidly.

In contrast, OpenCode integrated with GPT-5.5 has no such problem and maintains a high cache hit rate.

Besides, Codex paired with GPT-5.4 also achieves a high cache hit rate normally.

What steps can reproduce the bug?

We tested Codex integrated with GPT-5.4 and GPT-5.5 respectively. By checking the session logs of both versions, we can see there is a significant difference in the frequency of cached_input_tokens.

What is the expected behavior?

The expected behavior is that Codex with GPT-5.5 should maintain a normal high cache hit rate, consistent with the performance of Codex + GPT-5.4 and OpenCode + GPT-5.5, to avoid excessive and rapid cost consumption.

Additional information

No response

[github-actions]

Potential duplicates detected. Please review them and close your issue if it is a duplicate.

• Usage limits exhausting too fast #20292
• Quota usage is extremly high for basic tasks #20227
• Quotas draining like crazy: burnt 100% of my 5h limit in 10 min on Business #20153
• Weekly limits dropping too quickly #20169
• Pro weekly usage limit depletes unusually fast on 5.5, worsened by unstable context compaction #19585

Powered by Codex Action

[etraut-openai]

Thanks for the feedback. We track cache miss rates closely on the server, and we don't see any anomalous behavior related to Codex and gpt-5.5. It's possible that the session you analyzed wasn't representative.

[etraut-openai]

We're receiving similar reports from other sources, so I'm going to reopen this issue until we're able to reconcile these reports with our server-side stats.

[kkondaurov]

Can confirm. Codex Desktop on Mac OS with an API key.

Other users in our org with API keys also have this problem, although they're TUI/OpenCode users. So it's probably not about the harness.

Had to switch back to 5.4, where caching is totally fine. On my personal subscription, 5.5 is totally fine.

@etraut-openai I can share session ids with cache misses if it helps.

[hsir]

Yes, I also confirm this. I am using the API Key billing, not a subscription. Whether using the CLI or the desktop version, when using GPT-5.5, the cache hit rate is almost always 0%. Once I switch back to GPT-5.4, the cache ratio returns to normal, at 90% or higher. I didn’t make any changes other than switching the model in Codex settings. I even checked the request body JSON shape, nothing wrong at all. I think there must be something wrong in OpenAI server

[AetherMagee]

Can confirm too, GPT-5.5 cache hit rates are close to zero in both Codex and Opencode for me. GPT-5.4 is doing fine with otherwise identical configs.

[etraut-openai]

If you're seeing this problem, please use /feedback to upload the session and post the session ID here. Thanks!