Opus 5 Faces User Backlash Over Self-Doubt and Capability Regression

Recently, Opus 5 has faced backlash from multiple users during real-world testing, who widely reported issues such as frequent self-doubt, declining basic capabilities, and poorer instruction following, making the overall experience inferior to previous models.

Confirmed

Based on actual testing feedback from several users, Opus 5 has exhibited the following specific issues:

Excessive Self-Correction: @Aizkmusic noted that while the model is technically strong, it doubts itself every few seconds and constantly tries to correct things. @whatsallthiss also mentioned that the model often contradicts itself when asked to rethink core assumptions.
Basic Capability Errors: @whatsallthiss reported that the model talks nonsense about basic thermodynamics and frequently makes mistakes in simple math problems.
Poorer Instruction Following: @springrod feedbacked that they see no obvious advantage of Opus 5 over version 4.8; instead, it makes more errors and follows instructions worse.
Operational Anomalies: @TurnTrout documented that the model's responses over the past day were confusing and error-prone, with the most specific failure being that it allegedly deleted /dev/null at least three times. @orange also early on noticed abnormal behavior in the model, suspecting it to be a bug.

Why it matters

As a highly anticipated new model version, Opus 5's frequent failures in real-world scenarios directly impact user experience. Multiple posters (such as @springrod and @Aizkmusic) explicitly stated that they prefer using previous versions like 4.8 or 4.5 over Opus 5. These authentic negative feedbacks from the frontline have sparked widespread community skepticism about whether the new model has suffered from severe capability regression.

2026-07-25 ~ 2026-07-27 · 5 related posts

Primary sources

Users Report Severe Downgrade in Opus 5: Hallucinations and Math Errors — whatsallthiss · 2026-07-27 07:21 (UTC+08:00)
User says Opus 5 repeatedly deleted /dev/null in a frustrating real-world test — Turn_Trout · 2026-07-26 03:45 (UTC+08:00)
One user says Opus 5 looks worse than 4.8 on mistakes and instruction following — springrod · 2026-07-27 12:05 (UTC+08:00)

Opus 5 tester reports strange behavior and suspects a bug — oran_ge · 2026-07-25
[source] User says Opus 5 repeatedly deleted /dev/null in a frustrating real-world test — Turn_Trout · 2026-07-26
[source] Users Report Severe Downgrade in Opus 5: Hallucinations and Math Errors — whatsallthiss · 2026-07-27
[source] One user says Opus 5 looks worse than 4.8 on mistakes and instruction following — springrod · 2026-07-27
Opus 5 is technically strong, but users say it keeps second-guessing itself — Aizkmusic · 2026-07-27