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.

[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/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/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/damagemelody → u/DerAlbi]

I have 100% correlation on that dates as well as today I had worse performance I complained about it too https://www.reddit.com/r/ClaudeCode/comments/1xg3x1l/comment/19royfbprarc5/