Just as GPT-5.5 dropped, Anthropic announced they've figured out why Claude seemed to get dumber recently — and they've patched it. 🙃
Anthropic blames three separate but compounding changes for the perceived intelligence drop, all fixed as of version 2.1.116 on April 20.
Fixed on the 20th, announced today — and honestly, I'm not convinced it's actually fixed...
The three issues occurred on March 4, March 26, and April 16:
① March 4 — Default thinking duration switched from "long" to "medium."
The reasoning: in high mode, Claude occasionally thought for so long the UI appeared frozen. Internal testing showed medium mode sacrificed only a tiny bit of intelligence while being much faster, so they flipped the default. Users immediately noticed the drop. They reverted on April 7. Now Opus 4.7 defaults to xhigh, and other models default to high.
② March 26 — A cache optimization introduced a bug.
The intent was to clear old thought records after a session had been idle for over an hour, saving tokens. Instead, the implementation cleared them every single turn. Claude progressively forgot what it was doing, manifesting as forgetfulness, repetition, and tool misuse. It also burned through users' quotas faster because the cache never hit. Fixed on April 10.
③ April 16 — To make Opus 4.7 less verbose, a system prompt instruction was added:
"Text between tool calls ≤25 words, final response ≤100 words (unless the task requires more detail)."
Internal benchmarks ran for weeks without issue, so it shipped with Opus 4.7. Later, using a broader evaluation set and testing by removing prompts one by one, they found this single sentence dropped performance by 3% on both Opus 4.6 and 4.7. Rolled back on April 20.
Why it took so long to discover: The three changes affected different user groups and time windows. Combined, they created a vague "Claude seems dumber but I can't pinpoint how" feeling. The second bug was also masked by two unrelated internal experiments — even employees using the product internally couldn't reproduce it. Isolating the root cause took over a week.