[BUG] Extremely slow Opus 4.8 and Fable 5, missing 5 minute cache mid work due to slowness.

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Yesterday and today Fable 5 and Opus 4.8 has been extremely slow, a task I run multiple times a day that normally takes Fable less than 10 minutes and Opus 4.8 around 10 minutes took Fable 30 minutes. Checking the same task with Opus 4.8 a few hours later, I gave up after 50 minutes.

Later that night, the speed returned to normal and both Fable and Opus completed the task without issue in the standard time.

Came back this morning, Fable 5 took around 45 minutes for the task instead of the 5 minutes it took late the night before or the 30 minutes it took earlier that night.

Cache Misses:

Another issue surfaced today, Fable 5 was on a continuous task, nothing it was doing should be taking much time, but on multiple occasions it would take so long and essentially freeze resulting in a cache miss and rewrite.

I have tested this on multiple workspaces that had issues early last night, returned to normal late last night, and is now even worse.

What Should Happen?

Fable 5 and Opus 4.8 should not be taking 10 times longer for a single task than normal and should not be taking so long to do a single routine thing that it actually misses the 5 minute cache.

Error Messages/Logs

Steps to Reproduce

If Claude is extremely slow monitor your cache hit / miss. No means to reproduce if claude is not slow, no variation between workspaces.

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

v2.1.211

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_