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Muhammad Moeed
Muhammad Moeed

Posted on • Originally published at moeed.app

Claude Code slow or worse? How to diagnose and fix it in 2026

#claude #ai #tutorial #devtools

If Claude Code has felt slower or less capable this spring, you were not imagining it. Anthropic confirmed in an official post mortem on April 23, 2026 that three product changes stacked between March and April caused real, measurable quality drops. All three were reverted by April 20.

This is the short version. The full guide is on my blog: Claude Code Slow or Worse? How to Diagnose and Fix It (2026).

What actually happened

Change Landed Reverted
Reasoning effort dropped from high to medium March 4 April 7
Cache eviction bug fired every turn March 26 April 10 (fixed)
System prompt "25 words between tool calls" April 16 April 20

All resolved in v2.1.116. Anthropic reset usage limits as an apology.

Three quick checks

1. Are you on the fixed build? 

claude --version
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Update if you are below v2.1.116. Fast mode now defaults to Opus 4.7 as of v2.1.142 (May 14).

2. Run /doctor

It catches about 80 percent of "Claude is broken" cases. Stale install, wrong API key, broken MCP server, outdated CLAUDE.md, silently failing hook. Fix anything yellow or red before blaming the model.

3. Check status

status.claude.com

If it is red, stop and come back later.

Six fixes for the rest

  1. Start fresh sooner. Long sessions lose attention to context bloat. Run /compact every 30 to 45 minutes or restart.

  2. Write a real CLAUDE.md. Project context that belongs in every session. Keep it under two pages.

  3. Use /fast only when speed matters. Same intelligence as standard Opus 4.7, six times the cost.

  4. Put quality constraints at the end of your prompt. Attention weight is higher there.

  5. Shrink your MCP surface. Every connected server eats tokens before you type.

  6. Full restart. Kill Claude Code, wait 10 to 15 minutes, start again.

The diagnostic tree 

version >= 2.1.116?      no → update
/doctor clean?           no → fix it
status.claude.com clean? no → wait
session > 45 minutes?    yes → /compact or restart
> 3 MCP servers?         yes → disconnect what you do not use
still bad?               → restart, then file a GitHub issue
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Most people stop at one of the middle steps.

The full guide covers what each platform change did, the cost trade off of fast mode, when to file a GitHub issue, and a longer FAQ: Claude Code Slow or Worse? How to Diagnose and Fix It (2026).

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