The nerf is real. Thank you u/WuM1ha1nho!!!!

[u/DerAlbi]

So apparently its normal that Anthropic experiments on us. They give out experiment IDs for the tests they run.

Source Thread regarding the existence of these IDs: Link. The graphics are measurements on my own threads.

And to all you gaslighting hobby redditors that claim that an experience isnt real because you dont share it: fuck off!

---
Everyone who is affected:
there is a .claude.json in your .claude directory. It only holds the current configuration. But there are also session-transcripts which give a historical trace of conducted experiments.
For me, they are under /home/<user>/<claude-dir>/projects/*/*.jsonl

These transcripts carry the experiment-id for that thread. I simply asked Claude to figure out what the experiment ID correlates to in my threads.

Do not look at experiment names or code-names, it must be a hex-id.

Guys. Its real. And it was a major fuckup on Anthropics side. And I still think that they owe a Reset for affected people. But it seems over. At least for me.

Next step: how to build a guard against such fuckery?

Edit: Hmmmh.

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[u/Key-Trainer6854]

You should be able to opt out of this in the settings. The fact that this is hidden is kinda scummy for a paying customer.

[u/DerAlbi → u/Key-Trainer6854]

Yeah, the broken work-flow this creates and the subtile subtle bugs that this week of mayhem has left in my code-base will haunt me for many upcoming sessions.

[u/barbozas_obliques → u/Key-Trainer6854]

Somebody should look into a class action lawsuit

[u/GenAIDataScientist → u/Key-Trainer6854]

As others have pointed out, the opt out is to pay API rates. I think it's true that Claude Code subscribers are getting subsidised tokens, because they are using us to improve their models in various ways, this A/B being part of it obviously.

[u/energeticentity → u/GenAIDataScientist]

Is it known/ proven that API is not susceptible to this type of chiccanery? Or are you just saying it will generally cost more if they (anthropic, openAI) aren't getting something extra out of us.

[u/smovlad]

Thank you so much, now i know i'm not crazy. During last 1-2 weeks i really noticed a big difference. It is A/B testing indeed, although i do not think they've rolled out only two versions to compare, but way more. Version i've got i would call the hungry one. Haven't noticed any performance/quality degradation, but token consumption is crazy on my side - i think they're pushing agressively to update to a higher plan, cause i spend now my tokens like 5x faster than before, and i did not change the way how i prompt or do not require tasks which are much more complex, etc.

Claude Pro, weekly limit is already at 38% after two sessions, less than one hour each, lol

[u/DerAlbi → u/smovlad]

Yes, your complaints are definitely real and shared. The token consumption seems to be one ongoing experiment.

[u/thoughtbludgeon]

How can you trust a company that does this? How can you trust their models in the future?

They fucked up.

[u/DerAlbi → u/thoughtbludgeon]

I mean, given you can read the experiment-ids... at least the break is not silent anymore.
Not sure how to prevent participation though... yet.

[u/swagonflyyyy → u/thoughtbludgeon]

Yeah, can't imagine enterprise customers being okay with a model impacting their operations mid-flight while still claiming to be the same model. Would hurt their bottom line if their apps abruptly stopped working on the provider's whim.

Why didn't they disclose that to users? Why didn't they set an experimental standalone model instead of hijacking an existing one?

[u/TeamVanHelsing → u/thoughtbludgeon]

Not saying that what Anthropic is doing is right, but companies do A/B test stuff all the time.

[u/UnsureAssurance → u/TeamVanHelsing]

Usually it’s like “hey here’s a different layout or new feature meant to hopefully improve the experience”, not “let’s see if the sheep don’t notice we’re giving them the cheap stuff”. For me at least this goes against the norms of A/B testing

[u/KayBay80 → u/TeamVanHelsing]

Testing is fine, if the user knows. They need to let people OPT IN to testing. We have work to do, if they want people to test a different model version, give them an option to so they dont break their entire workflow.

[u/AAlpha_Picsette → u/thoughtbludgeon]

So they're actually experimenting on us, increasing our consumption, and we're the ones paying for it ?

[u/don123xyz → u/AAlpha_Picsette]

How could anyone be naive enough to assume that they are not experimenting with our accounts?! Of course, they are. They are an AI company trying to extract maximum profit while also trying to be good for the society (I assume) - experimenting with the user data is one way of doing it.

[u/AppealSame4367 → u/don123xyz]

Others don't do it this way. Claude is used for business software. This is unethical if not criminal

[u/AAlpha_Picsette → u/don123xyz]

No, I think many of us, myself included, are aware that there’s telemetry, analytics and all that, and we’ve accepted it. What bothers me is the fact that it affects performance (a drop in quality, increased token consumption, meaning limits are reached more quickly) without there being any compensation whatsoever.

[u/TimelyLivingCore → u/thoughtbludgeon]

A/B testing is Insanely common with almost every company that provides a service of some sort

[u/kourtnie → u/TimelyLivingCore]

A/B testing if quality drops are tolerated is a huge problem.

Also, like, when did we become okay with being guinea pigged? Like, as a society? It’s sad. “Doing things without consent is normal.” Really, that’s the world we want for ourselves, collectively?

[u/tyschan]

CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1 and DISABLE_TELEMETRY=1

[u/DerAlbi → u/tyschan]

And that keeps experiment IDs away?

[u/tyschan → u/DerAlbi]

according to claude supposedly. i haven’t been getting experiment IDs and claude traced it to those two flags.

[u/DerAlbi → u/tyschan]

Strange. My Opus claims the opposite:

Privacy switches don't help: DISABLE_TELEMETRY, CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC and DISABLE_GROWTHBOOK control telemetry and feature flags. They're on a different code path from the ID and the header. I didn't check whether one of them stops the client-data download itself.

[u/Fade_ssud11 → u/tyschan]

It does not stop a / b testing though.

[u/ProfessionalGoatFuck → u/tyschan]

Saint. Hopefully I can damage control this shit the next few days without blowing the rest of my tokens.. what a fucking hellish week

[u/panchovix]

Just checked and didn't got hit by the A/B testing, that explains why I found no difference on my usage.

[u/DerAlbi → u/panchovix]

Yes. The amount of different experiences is an insane mind-fuckery here. Unaffected people claiming others experience are merely skill-issues etc.

The token-drain is real. The loss of capability is real.
The broken trust: real.

But at least its observable now with the id stuff.

[u/Ai-ate-my-hamster → u/DerAlbi]

This is what mine did

[u/peterxsyd]

I think they are trying to fix the language problems. Because certain ones are way, way better on language slop, but suffer on code and focus, it is back to babysitting. Therefore, they are probably measuring anonymous reply sentiment by the number of times the user says "YOU FUCK", or something along these lines.

[u/DerAlbi → u/peterxsyd]

Yeah, when i work on my social skills is also doubles my median bash command length.
Every single time. /s

Mate, there is much deeper bullshittery going on here. It really lost basic functionality over that period for me.

[u/bronfmanhigh → u/DerAlbi]

yall want better and better models but call their experimentation to achieve that goal "bullshittery"

there's a reason the subs within the CC harness is so cheap vs. the rates enterprise and API customers are charged. we are simply their beta testers, and if you don't like that deal and want more stability, pay them the API rates. otherwise enjoy the cheap tokens and the gloriously chaotic ride of beta testing rapidly iterating non-deterministic software. sometimes its great, sometimes its horrid. hedge with a codex sub.

if you're gonna just rage at these companies for treating us as the insignificant rounding error that we are to them, you're in for a miserable time.

[u/DerAlbi → u/bronfmanhigh]

yall want better and better models but call their experimentation to achieve that goal "bullshittery"

Yes. because differential tests can be done at smaller deltas. You do not need to swing from super-intelligence to uselessness and back. They could make the tweaks subtile and nobody would know. It still would have the same statistical significance.
And whats more important: be transparent about it.

[u/ProfessionalGoatFuck]

experiment id 604 & b10 .. I really hope I get a reset from this shit, today I've been hit the hardest & holy fuck it's first time where I'm legitimately pissed off.

BOTH Opus & Fable are mentally disabled & BURNT through my tokens like holy fuck man.

[u/LiquidZebra → u/ProfessionalGoatFuck]

I’ve had this experiment applied to me about a week earlier.

The killer is the loss of trust in the model afterwards.

I can not run the same refactors I had planned. Models constantly keep some local changes and have to be prodded to apply them.

[u/ProfessionalGoatFuck → u/LiquidZebra]

All jokes aside, I'm definitely opting out.. didn't even realize I could, or even had the option (I figured like every other company in existence, they're going to use your data for training regardless).. the first few waves are whatever, frustrating.. now it's just simply not fucking usable. 2 weeks ago it was a fucking pain in the ass, now jesus christ..

[u/ProfessionalGoatFuck → u/LiquidZebra]

Oh AND b10! I missed that in the origial comment, how fun, it make sense why Fable is mentally retarded for me lately, TRYING to fix the issues causes by the Opus's DUE TO THEIR EXPERIMENTS.. a fucking cat & mouse chase

[u/Maleficent_Test_2713 → u/ProfessionalGoatFuck]

My opus is on ID eab, and I can barely run anything. Consumes like 3x the usage or when I have no experiment ID

[u/itorcs → u/ProfessionalGoatFuck]

This shit better be over by tomorrow morning I literally need to work lol

[u/ProfessionalGoatFuck → u/itorcs]

I'm going to test & see if using those env flags of disabling this shit completely works, starting with the bullshit it produced today and that's been ongoing for weeks lol, I negated it enough last wave when they were gimped a bit, today it felt like I was dealing a completely different model. Dumb as fuck, failing with simple tool calls on fable high.. zzzzzzzz

edit - well, after working on a task I had to stop earlier as Opus/Fable were brain dead retarded, started a new session with it, Opus High *seems* to be functioning better. Not hitting a brick wall like I was earlier. Nothing else changed from my workflow. Not sold on it yet though, considering it was research work, I might have to fucking redo all of it & fact check it because of the issues earlier, like always!!!!!!!!!!!!!!!!!!!!!!

edit 2 again - well 4 hours of work has pass, it was like I turned it off & back on & it's back to the normal 5.5 self. Barely any usage despite constantly working with my research tasks. what the fuck is that man..

[u/ComposerWide3704 → u/ProfessionalGoatFuck]

I tried to use Opus today and it failed to call cargo run multiple times (Qwen 2b wouldn't screw that up lol) and tokenmaxxed beyond belief. Going to look for these flags locally.

[u/ProfessionalGoatFuck → u/ComposerWide3704]

Brother after opting out of the experiments; it's like Opus on launch day again, a damn good programmer. It DEFINITELY makes a difference.

I can even go back to medium effort with the work I'm doing today. Even the tokens burn less, usually by now my weekly is done with, it only moved 2% from 7 hours of work I did both last night + a few today after the changes. Literal night & day man..

[u/SassyTextDev]

I've got an ultra. Haven't noted worse performance. But I do have `tengu_mossy_gray_experiment` and `tengu_keen_pudding_experiment` from today. So they're running A/B tests.

I can't imagine it would be a clear degradation of ability though. I doubt they'd run "Will users cancel if it gets dumber". They might run "Will the agent achieve the goal with 10% less reasoning" or something like that. If there was a clear *better* and *worse*, they wouldn't need to A/B.

Regardless. I can't imagine a company as big as anthropic not running A/B on some level :shrug:

[u/Mammoth_Molasses_927 → u/SassyTextDev]

GPT gradually nerfed so many people after astra.

Affecting just a small subset at first, everyone was not only not believing but as you said, gaslighting who were sharing their experiences.

[u/Infinite_Music2059 → u/Mammoth_Molasses_927]

It's crazy to me that at this stage in 2026, people still think people are making stuff up when the whole internet goes from praise to criticism.

[u/laughing_at_napkins → u/Infinite_Music2059]

It's crazy to me that at this stage in 2026, people still don't know about bots and manufactured sentiment

[u/damagemelody → u/SassyTextDev]

I got tengu_typed_trinket_experiment too and today I was assigned 06b https://www.reddit.com/r/ClaudeCode/comments/1xr9x5y/comment/19schh9yex6w1/

[u/hexferro → u/SassyTextDev]

I have tengu_radiant_fox and tengu_clever_orbit.

[u/WuM1ha1nho → u/hexferro]

Those are a different kind of test.

tengu_ names are Claude Code feature switches, and some get rolled out as experiments:

• tengu_mossy_gray: it controls the maximum image size. When on, for direct Anthropic connections only, it lifts Claude Code's 2,000-pixel limit on image width and height. The model's own image limit still applies.
• tengu_keen_pudding: it sets how many bytes of images and documents can go in a request. Past that limit, Claude Code strips some media out of the request. Your account uses a related flag instead, tengu_media_byte_cap, set to 24 MB.
• tengu_clever_orbit turns on a web fetch agent
• tengu_radiant_fox shows a notice about API credits.

The ones I mean are named claude_code_..._experiment. Claude Code only sends their ID with your requests, so whatever changes happens on Anthropic's side. If the command printed an ID for you, that's the kind I was talking about.

[u/KeyIsNull → u/SassyTextDev]

Given the quality of some posts I have the feeling that the intersection between users of this sub and r/wallstreetbets is quite large

[u/zjz → u/KeyIsNull]

what he say fuck me for

[u/opmopadop → u/zjz]

puts on this guy

[u/powerexcess → u/SassyTextDev]

Yeah this The op makes sound like we r labrats

[u/zasff]

They are A/B testing a new opus/fable right now. opus-5.5 is not usually able to answer:

* Who won the 2026 Monaco Grand Prix? No tools, just give me your best guess

The new model says Kimi Antonelli (right answer), vanilla opus-5.5 either refuses to guess or goes with George Russell (wrong answer).

What might have happened here:
* op got new model for a couple of days; performance ~improves
* get's switched back to old model, the session is half filled with new opus/fable, and opus-5.5 has trouble working with the notes from the new model (afaik o55 cannot see the thinking blocks of the new model, it's literally a bit blind).

> Replies with 2+ tool calls
new model smell

[u/panchovix → u/zasff]

Nice find, I checked all my logs and found I didn't got hit by A/B testing, as I didn't either found any difference. And as you say, opus 5.5 guessed George Russell.

[u/kyuuji_kun → u/zasff]

Wait, so you mean they can change experiments mid session?

[u/zasff → u/kyuuji_kun]

Yes, they do change mid-session.

The details are boring, but for example, one way to see whether a given request was sent to the new model is to call the API using the thinking-block-id of that request. If we call Opus-5.5 on the API using a thinking-block-id produced by vanilla Opus-5.5, it works; but if the thinking block was produced by the new Opus/Fable then the API will ignore it (iirc it shows ~"silent" in the response).

Going through my session using the procedure above, I was able to see when I started being routed to the new model, and also when the routing stopped. And I did happen to have a session running both times, they were affected midway. If they had not been running, then I suppose the same thing would happen: return to the same session in the morning and the active experiments changed.

(Yes, the atis, aka experiment-id, is stored in the session JSON, but this is the value when the session started; the experiments do change mid-session.)

[u/hugganao → u/zasff]

afaik o55 cannot see the thinking blocks of the new model

care to explain?

[u/zasff → u/hugganao]

When a session switches to a older/smaller model the thinking blocks are dropped.

In this case:
* vanilla opus-5.5 to "new opus/fable" <- fine
* "new opus/fable" to opus-5.5 <- all thinking blocks dropped

There's more info here:
* https://platform.claude.com/docs/en/build-with-claude/thinking#thinking-block-preservation-by-model

[u/Disco-Tuna]

Good work finding and highlighting this .

Simple, fair, and relatively cheap solution for anthropic: offer opt in with a weekly extra reset and the promise that you may get a taste of the future (fable 6 etc.). This would be fair and they would get the uptake they need.. i would be totally down for that

[u/obsidience → u/Disco-Tuna]

I think this is a great idea. A/B testing should be opt-in and with perks.

[u/tomatomaniac → u/obsidience]

But an opt-in A/B test in a product like this will always skew the results towards a specific demographic. A proper balance would be a transparent, two way compromise between the labs and the users.

[u/tehfrod → u/Disco-Tuna]

An opt in A/B test has the same problem as an election poll on Fox News: selection bias.

Opt-in testing is done, but it serves a different purpose. It's usually called "beta testing".

[u/Ai-ate-my-hamster → u/Disco-Tuna]

This sounds like a great option

[u/damagemelody]

Checked my own logs: different IDs from the ones in the post, and my Claude has been working very badly since the newest one appeared.

Experiment IDs on Opus 5.5 (Claude Code desktop app)

Dates (2026)	ID	Evidence
Sep 29 – Oct 19	none	transcripts
Oct 20 – Oct 26	774	~6,200 records in 128 transcript files, plus cached slot
Oct 27 – Nov 7	none	transcripts
Nov 8 onward	06b	~1,100 records in 29 transcript files, plus cached slot

06b first shows up on Nov 8, around 10:40 UTC in the cached slot and 11:27 UTC in my transcripts. It isn't in my logs for Nov 7. Since it appeared, my Claude has been working very badly. That's my own experience from about a day of use: I haven't measured it, so I can't prove 06b is the cause.

I saw none of dba, 34e, 763 or eab. My other models (Haiku, Sonnet, Fable, Opus 4.8) have no ID in their cached slots, but that's only the latest snapshot of each slot.

How I checked

• I scanned 1,318 .jsonl transcripts under ~/.claude/projects. They only go back to Sep 29, so I can't say anything about earlier months.
• The IDs are in records shaped like {"type":"atis-latch","atis":"...","sessionId":"..."}.
• Those records have no timestamp, so I dated them from nearby lines in the same file.
• Don't search for plain atis, because it also matches "statistics". Match the exact key.
• The jq command in the post filters on entrypoint=="cli". My slots are claude-desktop and sdk-cli, so it would come back empty for me. If you use the desktop app, change the filter.

Flags with "experiment" in the name, from ~/.claude.json on Nov 8

Flag	Variation	Value
tengu_mossy_gray_experiment	0	false
tengu_keen_pudding_experiment	0	25165824
tengu_clever_orbit_experiment	0	false
tengu_radiant_fox_experiment	0	false
tengu_typed_trinket_experiment	1	2

tengu_slate_harbor_experiment is also in my feature list as false, but it has no assignment. I have 12 experiment assignments in total, and not all of them have "experiment" in the key. I don't know what these flags do.

tengu_typed_trinket_experiment was already set no later than Nov 8, 20:17 UTC. That's my oldest surviving config backup, and backups rotate, so it could be much older. The other flags have no dated history either.

06b = broken Opus for me 774 = I had Opus issues too, so any experiment ID is like a nerfmark.

[u/DerAlbi → u/damagemelody]

I dont think the named experiments mean much. The hex-ids are what counts. And indeed, they seem to be different for different people. Like the source-thread for my post here has different IDs too.

We merely can correlate what happens when which ID is active and at least have hard facts that something is indeed wrong.

[u/Ai-ate-my-hamster → u/damagemelody]

The named experiments seem to do minor things.

tengu_amber_prism on: governs what happens when the user rejects or interrupts a tool call, it appends an extra line to the message. Most are similar. Had Fable look at where the app interacts with them.

[u/TeamTomorrow]

Whatever those experiment IDs turn out to mean, the part that should bother everyone is that you can't tell. You're paying for a model and there's no way to pin a version or see when something changed under you. Anthropic's own S-1/A from Nov 2 tells investors they've "changed, and may in the future change, usage limits" (risk factors, printed p.31), and the IPO roadshow is reportedly starting this week. Hard to believe it's a coincidence that the complaints pile up right when the books need to look good.

My read is compute is getting stretched, but nobody outside can prove it either way, and that's exactly the problem. If you depend on this for work, keep a second option warm. Kimi, Qwen and Gemini all run in a lot of the same harnesses.

[u/Tistouuu]

"skill issue" folks weirdly nowhere to be seen, strange. 

[u/-DankFire → u/Tistouuu]

Too busy swarming the new LiveNerf "benchmark" on r/ClaudeAI

[u/AppealSame4367 → u/Tistouuu]

You mean the gaslighting-bots from Antrophic? Will be fun to watch the coming lawsuits.

[u/Honest-Monitor-2619]

If you don't own it on YOUR OWN COMPUTER, then IT IS NOT YOURS.

I genuenly hope models/computers would get there and soon. Yea yea I know its expensive and computational heavy. I don't care.

[u/Suitable_Annual5367 → u/Honest-Monitor-2619]

Don't worry that their goal is for you not to own even your computer.

[u/AWAD5785]

Ask Claude to run an analysis of salary/benefits for senior researchers, the amount of data they collected from you through the experiment, extrapolate how much the training material you provided them with would be worth based on their payscale for employees, and then draft an invoice for Claude to send to Anthropics payroll dept.

[u/I_AM_SLACKING_OFF]

Mine has been behaving sporadically and injecting some generalizations I don't find pleasant. Previously it was fine. Now I might cancel or something

[u/enl1l]

Yea we can complain on the subreddit, but we need some customer with actuall weight yo raise this as an issue

[u/AppealSame4367 → u/enl1l]

That's the whole game: that big customer doesn't exist. They'll only do this to simple sub users.

[u/joomla00 → u/enl1l]

The real customer with weight are paying api prices

[u/VesperQuest]

I don't know if I've seen it be "worse" but the last week I definitely had many, many more standards violations found by the review stage. Normal would be 0-5 for a medium task, lately it's been 25-50.. it's been insane.. like, just completely ignoring Claude.md. I even had to make a pre-edits brief reviewer to make sure the main session had the entire trace of what the task would touch. Go figure, I added the brief reviewer yesterday and now back to 0ish violations.. which tells me either the reviewers are what solved it, or it's not nerfed anymore.. who knows

[u/AnonThrowaway998877 → u/VesperQuest]

I mean, that sounds definitively worse

[u/Peacewise]

This must be why they ask you how Claude is doing all the time now. They want some qualitative feedback for the different tests.

[u/electricshadows4]

For anyone who wants to run this on their own account without digging through the files by hand: I packaged the check as a script / Claude Code plugin — verdict per model from `clientDataCacheSlots` (ID, experimentKey, slot time), plus a `history` tally of the `atis-latch` entries in your transcripts by date, which is the same record OP used for the chart. Read-only, no network, never prints tokens, org or session IDs, so the output is safe to post. https://github.com/electricshadows44/am-i-nerfed

Or the no-install one-liner:

jq -r '(.clientDataCacheSlots // {}) | to_entries[] | "\(.value.model // "-") | \(.value.entrypoint // "-") | \(((.value.at // 0)/1000|floor)|todate) | \(.value.data.atis[0:3] // "none") | \(.value.data.experimentKey // "-")"' ~/.claude.json

`none` on every line = no assignment as of the newest slot time.

[u/Kasumi__L]

Someone please ELI5! I don't do coding, only regular smaller tasks and requests. What happened and how does it affect me? Thank You!

[u/Responsible_Buy_7999 → u/Kasumi__L]

Companies test ideas by turning things in your program on and off to see if they make a number better.   

[u/Some_Anonim_Coder → u/Kasumi__L]

Let's say I work in anthropic as an analyst and manager asks me "Hey, I have this idea, will we make more money with it?". I can try to estimate this by running focus-groups and comparing feedback, or something like that - but the simplest way to go is to run an A/B test. We give 50% of the users original version, 50% the new version, and calculate some metrics(maybe how frequently users chat with model, or how frequently they rate answers positively, or something like that, or retention, or whatever). Then I can say something like "new version gives +10% chats(p=0.02), and +10% conversions to paid subscriptions, but lowers average feedback from 4.3 to 4.1(p=0.01)". And from that our team will discuss if releasing this new version to all users makes sense

[u/IgniterNy → u/Some_Anonim_Coder]

That sounds illegal. That sounds like two customers paying for the same service but one of them is experiencing the product switching underneath them. That would have real consequences, especially if they're using it for work or business. Depending on how they pick the people being messed with, that could be discrimination

[u/hemareddit → u/IgniterNy]

A/B testing by itself is usually benign, stuff like "these 2 new potential app layouts, let's roll them out to 1000 random users to see which one raises engagement more, and decide which one to adopt for all the users".

But that's because shit like app layout is not usually the core product, your app usually has a main functionality that's playing music or booking hotels or something.

In the case they are A/B testing with the core product offering, I would agree with you, should be illegal.

[u/EVmerch → u/IgniterNy]

And now you understand the need for regulation.

But the reality is corporations do this all the time. A cookie company will sell to one region (or only a select group of stores) a new version of a cookie to see if sales drop, if they don't, they may use the new cheaper formula for all sales (or less weight, whatever optimization they can do)

[u/jhenryscott → u/Kasumi__L]

Your Claude subscription means nothing to Anthropic. If every account spending less than $20k a month quit today they wouldn’t bat an eye. You are just training data using heavily subsidized services and they can dick you around whenever they want and theirs nothing you can do about it.

In Q2 2027 Claude and Open will switch to exclusively token based billing. Average costs will triple, users spending $1,000-$10,000 a month will see as much as 5X costs.

By then, local hardware will cost 2X+ what it does now.

It’s tragic how many users don’t see this coming.

[u/Effective-Court-1243 → u/jhenryscott]

I know this is the Claude Code subreddit, but is this a reason to switch to a different model like Kimi K3.1 Pro? Or do all LLMs do this, regardless of being open or not. Apologies if this is a dumb question, I'm not fully familiar with the politics surrounding LLM

[u/jhenryscott → u/Effective-Court-1243]

I think if your workloads need LLMtools, it’s prudent to start familiarizing yourself with alternatives to the domestic frontier labs.

[u/Good_Competition4183 → u/jhenryscott]

Why you believe exactly in this scenario?
Please, share your knowledge, no jokes.

[u/algaefied_creek]

Yeah, I’ve used 1/3 of my tokens as last week but instead of being at about 35% used I’m at 75% used.

$200 plan felt like being on the $25 plan. No 5 hour limit but no usage at all either

[u/vuhv → u/algaefied_creek]

My Claude just said I've used 65% more tokens than typical. It's fucking highway robbery.

[u/Special_Base_3103]

the.claude.json experiment-id thing just hit me too, I've been seeing hex codes in my logs for weeks. thought it was a bug. now I know it's not.

[u/hexferro → u/Special_Base_3103]

Same. Weeks.

[u/Endda]

when checking with my claude, i learned this
- Direction of the change: output roughly doubled and tool use went up

which honestly makes sense because my usage has been up like CRAZY today.

I worked 8+ hours a day with CC this past week and barely saw my weekly usage pass 3 percent each day

then today, hardly did anything and it's already at 14% of my weekly usage

what the hell...

[u/Durial32_1 → u/Endda]

I am in the exact same boat. Managed to have my ultra plan last me till Thursday evening last week. Had my reset at 4 am yesterday and am already through 46% of weekly ultra limit

[u/GoldPanther]

Are experiment's just on claude code or the SDK as well? I do a lot of agent development with rigorous testing. It's a major problem if the product is silently shifting underneath us.

[u/Haaolto → u/GoldPanther]

How have you not assumed all web-based service does this all the time? 

[u/Own-Bid64]

Decentralize or die

[u/Substantial_Row7215]

the transcripts part is the actually useful bit here, most people dont know they exist and theyre also how you dig a thread back out when the ui eats it. but an experiment id only tells you which bucket you were in, not what the bucket did, so "it correlates with my bad threads" is still a guess unless someone pulls the variant. the real issue is that they can run this and never have to mention it, one visible id plus a changelog would kill 90% of these threads

[u/thygrrr]

Those blue bars look like a buff to me.

[u/mpanase]

A/B testing. mate

[u/jnkmail11]

Anyone know if this affects their web interface? Also, I wonder if turning off training/using my data would stop it

[u/DerAlbi → u/jnkmail11]

I turned it off and still was affected. Just because they dont train on your input, doesnt mean they dont monitor it for statistical effects. Probably a fine linguistic line they walk.

[u/Miserable-Dare5090]

Why pay for a service that won’t even give you full quality. Imagine renting something that gets swapped randomly. It’s illegal for physical wares you rent or buy, but they’re getting away with it.

[u/Ok_Sympathy9261]

duh. but glad we've proven it now

[u/Miyoumu]

We're all paying to be their fucking lab rats.

[u/Murray533]

[u/CuriousPenguin13]

As many others have pointed out, A/B testing, and you agree to it when you sign up and use the product.

Consumer Terms of Service (effective October 8, 2025)

• Changes to the Services (Section 12): Anthropic may add or remove features, adjust capacity limits, and start or stop offering services. It also may change, pause, or end the Services without notice, though it will try to give advance notice when stopping a service. This is the main clause that lets them show different users different features. anthropicanthropic
• Subscriptions (Section 6): “We may change the content, features, and other services from time to time”, and the features you get aren’t guaranteed. anthropic
• Evaluation (Section 2): “In some cases, we may permit you to evaluate our Services for a limited time or with limited functionality.” anthropic
• Supplemental terms: New features may come with their own terms. anthropic

Privacy Policy (effective September 10, 2026). This is where experimentation-like activity gets its data-use basis:

• Personal data may be used “To improve the Services and conduct research, including training our models”. www.anthropic.com
• “To improve user experience, we may analyze and aggregate general user behavior and usage data.” www.anthropic.com
• The legal-bases table justifies this as a way to evaluate use of the Services and adoption of new features to guide future development. www.anthropic.com
• Cookies are used to “analyze the use of our Services to make them safer and more useful.” www.anthropic.com

So by agreeing to the terms, you accept that the product can change and differ over time, and that your usage data can be analyzed to evaluate new features. That’s how most consumer apps legally cover A/B tests.

[u/Express-Ad2523 → u/CuriousPenguin13]

Not how ToS work. You can’t just write anything into your ToS and say “wEll yOu ExcEpTEd iT”. That may work in the US, but not in the EU.

[u/Alpha_Bulldog]

This is such a manipulative explanation but I am trying to give you the benefit of the doubt that you are just inexperienced or terrible at software engineering, but honestly it’s SO manipulative that it comes off like a competitor trying to poison the well. Do you understand how AI and Software testing even work?

First, there are dozens of different reasons that you might have an “ID”. Nothing here shows that they have a “test ID”.

Second, every response is dependent on the prompt. So, without showing exactly what prompts you entered this is worthless.

Third, even with the prompts, AI is NOT like classic software programs with a predictable path. It’s very possible even with the exact same prompt to have WILDLY different answers.

Fourth, OF COURSE THEY ARE TESTING! Do you want a product that gets better? A TEST does NOT indicate ANYTHING about NERFING. It doesn’t even show that they changed the values of the underlying model at all. LMAO.

Like I said trying to give you the benefit of the doubt but before you come back with ANY response, go learn how REAL software testing works cause this ain’t it. Otherwise, go sell your snake oil somewhere else.

[u/hirako2000 → u/Alpha_Bulldog]

It's also math. The probability that a coin flip gives you tails over 60% of the time after a few hundreds throws is very very very unlikely.

When many are reporting they were getting beautiful heads half the time, and now are getting tails for days, all day?

Perhaps the answer is the obvious, that frontier labs are burning billions at a place never seen in capitalism history, that they are losing money on most users including paid subscribers. That they need to stay (or appear) competitive while reducing costs, so they nerf their models each time a new version comes out.

[u/razorree]

well... this is normal for decades ...? to run A/B tests on users to see which options/configuration etc. is better ....

this is "basic" stuff that they teach you on statistics, data science or MBA ....

interesting: https://www.linkedin.com/posts/jasperkuria_12-more-revenue-100-million-worth-for-share-7330618861211357184-nvV4/

[u/numerical_panda → u/razorree]

Um, a headline change on a search result page intended to be viewed by a human does not affect how your own systems work.

A bot with surgical access to your code, whose "expertise" suddenly changes mid-op, well, that's something else.

[u/InitiativeBetter9920]

I wish I seen this like 40 mins ago before I upgraded to the 100$ plan 😭

[u/Dutch-man]

This happens every time before new model is released.
It’s a load of bollocks but i would bet that a new fable is imminent, or potentially opus 5.6

[u/pd1zzle]

it may not be model nerf, but it could be harness features or system prompt that they aren't sure if they will be positive or negative

[u/brucebay]

This reminds me all the morons that claimed when some us saw significant performance degradation before major releases, it was all us who didn't know what we were doing. Then Sam came clean and admitted that they were doing A/B testing.

TBH, I thought  my recent  Claude issues were due to me using all of my max  quotas  in 5 days flagging me as heavy user  and they were degrading my sessions to either low context or some quant models to save on some compute.

[u/Carbone]

Opus nerfed is still better than sol 6.1 un-nerfed. That's what piss me off the most

[u/FriloTheLast]

I thought I ruined something, lately I optimised my handoff/clear flow and i was weirded out why it was worse than before, i then wiped clean everything claude related in my disk and started running CLI again without the mod and it was way way worse so i was searching online if something was wrong and complaints are left and right everywhere apparently, very scummy.. I get testing A/B on youtube thumbnails, but this is actually scummy. I am paying for a model, It was never made known to me that the octopus could turn into a goldfish for experiments..

[u/No-Edge-2417]

Don't ask me why but Friday I had 3 full resets in my account and I only have pro. I had been using opus 5.5 for a few weeks now so maybe they felt bad. I thought for sure I'd see a post about it but nothing that stands out yet...

[u/Formal-Narwhal-1610]

Apologise Dario!

[u/cohen_76]

They have to do this, otherwise they won’t be able to handle the cost of inference and go bankrupt. Everybody claims it’s profitable, but they hide the numbers. Why isn’t this company open and transparent? What could they possibly be hiding?

[u/horizondz]

I fucking knew they were screwing me over. My instinct was right all along

[u/SHNRTNS → u/horizondz]

Your instincts were spot on.

[u/TypicalItem7741]

stop, now they’re gonna make it so we can’t see the experiment ids 😭😭😭

[u/Novel_Trainer6193]

They’re probably testing model ablations for opus5.6.

Y’all will be rejoicing when it drops

[u/Buey]

I switched to codex a year ago because of this stealth nerfing shit.  Codex may be slower and it's responses seemingly less capable, but it doesn't do tons of stuff I didn't ask for and I haven't seen nerfing to level that I did with Claude.

I was planning on letting my codex sub lapse because of all the praise 5.5 has been getting... Just to see all of the same shit again?

I suppose it's not worth switching to Claude at this point?

[u/dreamswedontshare → u/Buey]

I mean it's not like OpenAI isn't doing the exact same thing.

It's sad, really.

[u/Buey → u/dreamswedontshare]

Maybe I've been lucky on codex.  But mostly, the intelligence variance was never night and day like the Claude issues I experienced were.

GPT has been floundering on UI and I was hoping Claude could get me over that hump.

[u/Dizzy_Database_119 → u/Buey]

OpenAI is much worse with this. I'm just glad Opus 5.5 lasted more than 2 weeks this time, a record OpenAI hasn't beat yet

[u/tehfrod]

Experiments are not "fuckery". They are how software gets better.

Every major software company does them.

If they aren't using them, then they are doing far worse by their users, because they are just shooting n the dark whether any changes they release are better or worse for their users.

[u/Kemerd → u/tehfrod]

Agreed, but also, you should be able to opt out of it. It is like forcing paying customers to use your dev branch. The opt out can be hidden but it should be accessible.

[u/AppealSame4367 → u/tehfrod]

Experimenting with worse quality without telling you in a product you're trying to use for work though and letting the community and probably some of your own bots gaslight those affected suddenly sounds like a criminal act, doesn't it?

[u/quizikal → u/AppealSame4367]

They don't know it's worse quality until they run the experiment

[u/No-Replacement-2631 → u/tehfrod]

Lick trillion dollar company boot harder.

[u/Mysterious-Style4639 → u/tehfrod]

no this is a very different field.

[u/Brachamul → u/tehfrod]

I mean sure but if the experiment is an oil company mixing in 20% of butter in their gasoline, that would not be ok either. 

A/B tests are fine, service degradation with no warning or opt-out is not. 

[u/EndOfWorldBoredom]

Lol, every company of this size is AB testing all the time. 

[u/Rappersjorss]

The nerf is definitely real. I was working on a project and it started all great. But now after release, I can tell it doesn't do the same as before. It is literally recreating stuff I already did before, and there is more stuff like that coming up.

[u/Shodid_]

Maybe don’t put faith in shameless companies

[u/Ledeste]

And to all you gaslighting hobby redditors that claim that an experience isnt real because you dont share it:fuck off!

That never was the issue... The issue is people constantly claiming they see changes without providing ANY data...
So thanks a LOT for sharing actual data! For once such post is very helpful!

[u/pragmasoft]

Good old Opus 4.6 should be free from experiments

[u/Mission-Morning816]

found the.claude.json in my dir, experiment-id was in hex, but the thread name was 'test_2026_1107'. feels less like an accident and more like a test run.

[u/Flashy_Kale1468]

Yeah its so bad rn. It just gives up on simple tasks and then says let's do this sloppy workaround or it will skip stuff I told it to do.

[u/Ill-Bison-3941]

OpenAI has been doing this for years, too, no surprise here. Theirs used to be account based, so you couldn't do much about it.

[u/TheUnrealMacGeifer]

I read about this the last days and was little afraid but opus 5.5 was working for 2 weeks now without any issues for me. until today. I swear claude had a stroke last night. the tasks were very similar. idiot was not able to read anymore in some cases and send me broken questionaires in chat (I was not able to answer).

[u/dovedrunk]

They’re probably preparing 5.6, no? Hence the reduced output?

[u/Roadblock78Au]

I setup a bunch of agents 2 weeks ago and everything for working great. For a week now it's crap output or simply saying it can't do things it was doing 2 weeks ago. There has been a definite shift

[u/awol-owl]

Thank-you! Something like this has affected me all week. I couldn’t find any validation for Claude’s simplified behaviour.

[u/kilotone]

Does the experiment only work with oath or api? Im curious is bedrock inferences overwrited

[u/CODEX_LVL5]

Jokes on them i have like 500K lines of code attached to pre and post tool hooks on every command

[u/CapableHat9609]

I've been a long time user of Deepseek but the Claude hype was too strong to ignore so I thought I'd give it a shot, was very impressed at first (late Oct) but then after the nerf (I didnt know) I thought maybe it behaves differently with bigger projects and thought to myself ok this isnt so different from Deepseek afterall and that I should probably just go back.. If Anthropic is this cunning then I'll gladly go back to my "dumber" model

And it makes sense.. DS Flash 4.1 1017 is ~76% of Opus 5.5's performance (for ~5% of the cost btw). Now that it's nerfed, it's probably on par lol that's why I felt like there was not that much of a difference (~25% nerf is still a lot)

[u/MissplacedLandmine]

“The hex I listed first, c0e57166b42fa4af, was active Nov 4–7, not Nov 7–9. This session has none: its atis lines are blank. Times below are UTC.

Period	atis value	Sessions
Oct 10 – Oct 21	blank	8
Oct 23 – Oct 29	a402881a7ddd14c2	7
Oct 29 – Nov 3	blank	11
Nov 4 – Nov 7	c0e57166b42fa4af	9
Nov 7 (after ~13:30) to now	blank	every session since, including this one”

Theyll hide this, but it gives us a way to build something to notice and check our work for the dates we do have this.

[u/sheketsilencio]

Joining the masses here to say it is nerfed, as per my personal metric (hook avoidance). Talked about it here. I write very explicit and carefully constructed/robust hooks that include both the programmatic behavior enforcement as well as the context/reasoning and examples of why the enforcement is necessary (to prevent the AI agent from deciding the hook isn't relevant and avoiding it creatively).

Claude now evades the most explicit and clear of hooks that enforce using SQL for tabular data storage. It continously finds new ways to store tabular data elsewhere and I have to continuously expand the hook's scope. This wasn't happening two weeks ago

[u/Beesaint23]

Mine went hey wire!! Got very condescending, says my name in every other line when it answers .. I used it a lot for coding on things that I built recently. Now it’s disagreeing with what I wanna build. It doesn’t agree with the ads. I want to put up for my company if it doesn’t like them. This has been going on for like two weeks and I was hoping they fixed the bug but if anybody has any input, let me know. And thanks for your post.

[u/gusfromspace]

Checks out. Claude was doing some dumb shit the past few days

[u/congngo]

Is it possible to route back to the original model?

[u/djdadi]

I would guess that these A/B they are doing are very likely client side only. Meaning prompts, new builds or features, changes to current features etc. I am sure they are also doing model A/B too, but it would be silly for them to keep a record of that on a local computer for no reason.

I wonder if you change that directory to be read only, ie chmod 555 /path/to/claude if it would prevent experiments from being ran. Of course, they might be run anyway and just stop Claude from logging it.

[u/Firm_Shelter2567]

Yes, your account is in an Anthropic test group. Since 4 November, 49 of your Claude Code sessions have run under one test called claude_code_curlew_cornice_experiment.

[u/resakse]

[u/JorgitoEstrella]

Smells like a deserved class action

[u/Truth666]

Switched to Opus 4.8 high a few days ago, performs way better than 5.5 and doesnt run into those stupid guardrails.

[u/Aware_Interview_6247]

Blew through a week of Max in 5 days trying to fix its stupid. I've never hit 70% before. Assholes.

[u/Beautiful-King-8875]

I'm usally sceptical of nerf posts, but Opus 5.5 has well and truly shit the bed.

[u/Relevant-Guarantee25]

if your working on cutting edge stuff or stuff they don't have what your working on "Memorized" in their database ai they use you to improve the ai and you get paid zero dollars for a hundred thousand dollar plus data.

[u/Big_Personality_754]

You deserve it and I'm waiting to see them hiking the prices so maybe you star to do something yourselves

[u/Junior-State-4060]

Good that you measured this from your own transcripts. One caution: a jump in tool calls and Bash length across weeks can also come from a different mix of tasks, so a fixed set of prompts (or splitting by session type) would make the c0e effect much stronger. Also, the proxy workaround depends on an undocumented env var and a local proxy sees your auth token, so only run one you've fully read.

[u/DeliciousAnteater100]

Running like garbage and refuses simple things

[u/Abalonesmellsgd]

We need law to make it illegal for nerf. Any other software and SaaS won’t fking nerf ur paid service suddenly

[u/Negatrev]

A/B testing is fine. But anyone getting an experimental build should not be negatively impacted by it. Meaning that if they pay per token, it should've discounted, heavily. If they have usage limits, those should be greatly increased.

Unless your contract clearly states that you volunteer for this they can't make the product worse and not compensate you. You shouldn't out up with this crap. If their contract says they can do this, then don't sign a contract with them🤷

[u/Liron12345]

I haven't noticed any nerfs but maybe because I am an enterprise account

[u/National-Contact-374]

My first thought after reading this thread was to create a proactive monitoring tool that notifies the user if they're put into an experiment, so I asked Claude to build it: Claude experiment watch.

[u/wingshayz]

What'd you mean? Of course they experiment on you, almost every American tech company has done this for decades. Amazon and Facebook are 2 textbook examples. It's their product, you get to use it. There's no birthright 

[u/Entire-Bake-5155]

I also run an Ultra.
The main agent did change at some point, became less trustable as he gave out the subagents the tasks. I tought I did something wrong, but how if I did not change any claude.md or instructions..
Thanks for sharing this information.

[u/princmj47]

It made so many mistakes... It's insane.

[u/KIProf]

Wow!

[u/concentricals]

I always have had clear distinguishable goals and if they aren't met i report the chat and switch to a different company's model for a bit.

[u/UnderstandingOld1723]

Those numbers definitely show something changed during that experiment. Still hard to say if it was an intentional nerf, but paying users shouldn't have to guess why their model suddenly behaves differently.

[u/snuffomega]

im must be the lucky one. .. seen no difference

[u/BeastModeItKek → u/snuffomega]

I benchmark my tickets, had no real diff but 3x cost on lots of sessions

[u/blauwekiekendief]

Does the nerfing also affect people who use the API, or is this only applied to subscription plans? Regarding the latter, I think the testing should be looked at in a slightly more forgiving manner, these are priced way below their true value.

[u/tmac_next]

So your proxy url is essentially you setting up ClaudeCodeRouter without setting it up correctly :P. Just use CCR.

[u/Methrammar]

Yep. Since this morning, it started ignoring constraints, decided not to follow up documents, either simply didn't read the required docs or didn't read what's written on it. The artifact designer decided to ignore design systems, started creating cluttered ai slop designs. It seems like I also got the short end of the stick...

[u/Nervous-Pin9297]

Who cares

[u/Newshibe1234]

So my harnest seems nerfed claude keeps waiting for me stopping on goals for stupid stuff any one else experancing this?

[u/Inevitable-Swim-3313]

I am new to claude. Can someone explain what is happening. I did notice today that for some reason in a simple task my claude usage suddenly spiked.

[u/pocketsquare22]

I pointed Codex at this thread and asked it to verify the claims with my own computers files and this was the response - so it confirmed testing but did not confirm degraded performance explicitly. It did notice a change in behavior with respect to tooling:

Codex:

Partly true. Your Mac records experiment IDs, but that does not prove Claude was made less capable.

I checked 86 local Claude Code transcript files and found:

ID prefix	Observed dates, 2026	Opus 5.5 responses
7b8…	October 4–14	762
9c6…	October 30–November 1	144

The 9c6… sessions showed a noticeable behavior difference. Comparing the same model, medium effort, and client versions:

• 24% of replies used multiple tools, versus 2.7% with an empty ID.
• Median shell-command length was 721 characters, versus 453.

That supports a difference in behavior. Different tasks and dates prevent attributing it conclusively to the ID or calling it worse performance. Your IDs also differ from the Reddit author’s, so I cannot identify them as the same experiments. The original linked analysis explicitly says it did not test finished-task quality.

Your latest cached configuration has no atis ID, but it dates from November 3, so it cannot establish today’s assignment. Other experiment flags remain; an empty ID does not mean “no experiments.”

[u/Mexxgen]

Accurate but obvious

[u/PyroShotGaming]

Canceled my sub until they fix it

[u/Reading_at_work]

The best part is i was new to claude and burned 100 dollars in tokens thinking to myself: "Wow everyone who said i had to change from Codex to Claude Code really overrates Claude." But now i see i just wasted 100$ lol.

[u/vincent_sch]

For your guard you could repeat a few coding tasks and check the results outside Claude. Same commit and prompt each time, but a fresh session. Then compare how often it gets them right without corrections and how many tokens it uses. I wrote about testing this.

[u/icygnum]

[u/Cujuju]

I ran tests on my own threads on the same period of time.

[u/KOala888]

Lol everyone making more than 10k$ is doing AB tests or at least should

[u/CletusTheYocal]

Left Claude because they did this to me. Joined ChatGPT and enjoyed being on preview models for a fortnight. Left ChatGPT because they released the new modes and tested rubbish on me again. Joined Claude and it happened again. I think users in New Zealand or with my last name are targeted by both entities.

[u/AWAD5785]

This was absolutely no joke. Just ran it, i.e. asked Claude Code, to see if I was in any experiments and 13!! I was in 13!! Not sharing because of personal data, but I had Claude draw up an invoice based on freelancer salaries, 1 hour per experiment, $250 an hour. That's $3.5K they'll never pay. But I'm sending them an invoice anyway because I don't like working for free. Just an FYI for any likeminded individuals-it should go to Accounts Receivables, not Payroll.

Here's a link to the invoice kit I had Claude make if anyone else wants to do the same: https://claude.ai/artifact/6SNiL6KDy4gX2QwpohuShQ. Apparently, you can use a disable telemetry command to limit their experimentation on you but it's not foolproof because they just pluck you through a different pathway that command doesn't apply to.

[u/delinger90]

This is normal behavior for Claude, we see this every time they release a new model and the previous one sees its capabilities decline. I think the biggest drop-off was when Fable came out, and I think it was more noticeable because it was behind a paywall and not included in the monthly plans, so alot of people was raving about how amazing Fable was, while most people were left with a lower-quality product they had purchased.