Opus 5.5's reasoning took a sharp turn on November 3, analysis of 1,400 Claude Code sessions finds
Is Opus 5.5 nerfed? Thinking patterns changed on November 3
Shane Melaugh had Gemini 4 Argon analyze 1,400 Claude Code sessions and found that on November 3, Opus 5.5's reasoning patterns changed sharply even though the model name stayed the same. Reasoning volume in "high" mode dropped steeply. A test on a real bug showed high mode rushing in and failing for three hours, while xhigh thought briefly and found a fix in minutes.
The model name didn't change, but the way it does reasoning took a sharp turn.
- PhunkyPhil
I don't have any evidence/study to substantiate this but I have the feeling there's a _massive_ amount of fiddling with the quant/functionality of the models at different stages of the release cycle and account freshness.
Every time a new model drops it feels wildly powerful, then regresses to some sort of generic SOTA level we've been used to over the last 6 months.
I remember my first coding prompt with, I think it was sonnet 4.6, on a fresh account and it was shocking how much it successfully did off a single prompt - I haven't found that with any other model at any other time and I suspect it was because they put me at the top of the priority list to get a "wow" reaction.
Regression after a release is pretty well-agreed upon, but I'm wondering if they secretly have a huge amount in the tank they aren't releasing. Either as a card to play in the future, or because they can't keep up with demand. I've heard anecdotes of people working with these companies saying that the public models aren't even close to their actual capabilities... Anyone have any opinion on this?
- PaulKeeble
The local Qwen 3.8 27B might not be anywhere near as smart as Claude's models but I never wake up one morning and wonder if I am part of some test model to see if I will accept something somewhat less capable or not trained as well in the tools I am using day to day. Its also not suddenly going to start refusing to test the security of my system or scanning the code for vulnerabilities or continuing to back engineer that old binary the company lost its code for years ago.
It is something I also appreciate with some of the other labs like deepseek who publish the checkpoint they are running on and still sell you the old one for a period of time as well.
Its obnoxiously anticonsumer to be constantly chopping and changing what a model represents on customers who are paying them an awful lot more to be on the frontier models.
- losvedir
Anyone with evals picking up a real signal? I've learned not to trust "vibes".
The only one I'm familiar with testing Opus 5.5 specifically over time is https://github.com/ninjahawk/livenerf and it's not showing anything.
- rzk
It seems to be an A/B testing experiment:
https://www.reddit.com/r/ClaudeCode/comments/1xr9x5y/the_ner...
- benwills
I noticed Fable decline in quality a couple weeks ago. And I've noticed Opus drop over the last week, even after bumping to a default of Extra High reasoning for almost everything.
Tonight has been maddening with the kinds of absurd mistakes it's repeatedly making. It's so frustrating.
I'm the kind of person that wants something to be consistent and reliable. And Anthropic has been great, except for in this way. Which is enough of a recurring frustration (about every couple months this year) that I genuinely can't wait for other options to catch up. Then I'll be leaving as soon as I can.
I just don't know how long that will be.
- drknownuffin
I've noticed I've been running into more safety guard rails the last few days. I've been using fable 5.1 for scientific lit search (e.g., on topic X, give me a table with links to the top 20 papers, and then major criticisms and rebuttals with direct links to the papers, etc.) to just save me time in getting acquainted with a new sub-topic. The last couple of days it's not just been dropping me from 5.1 to opus 5.5, but all the way to opus 5, stating that it's for safety reasons.
- ricardobeat
I noticed the same, and posted about it three days ago.
Opus is suddenly fumbling basic tool calls and failing to finish tasks even at high, where I had been permanently using it on low effort with success since it came out. It is very frustrating.
My guess is they quantized it and/or reallocated DC capacity to train a new model, this has happened before.
- Zambyte
It blows my mind how people still build their workflows around depending on services like these, with how easy it is to just self host and forget about all of this. You can buy a GPU that can run Qwen 3.8 flash next for about 9 months worth of the highest tier Claude Code subscription. You'll never have to worry about token limits, the model changing out from under you, getting banned, etc.
- 0xb0565e486
Feeling like it's better on my end :shrug:
On some long running conversations it seems to better understand the end goal, follow the constraints we have established.
- jascha_eng
Sadly this thing stopped running a few weeks ago, the propduct half life is truly low these days otherwise wed have some data to rely on: https://marginlab.ai/trackers/claude-code/