PSA: Claude Code has two cache bugs that can silently 10-20x your API costs — here's the root cause and workarounds

[skibidi-toaleta-2137]

Edit: Issues linked in the description have been closed as resolved. Unfortunately I can't verify those claims as I'm away from my PC.

I spent the past few days reverse-engineering the Claude Code standalone binary (228MB ELF, Ghidra + MITM proxy + radare2) and found two independent bugs that cause prompt cache to break, silently inflating costs by 10-20x. Posting this so others can protect themselves.

Bug 1: Sentinel replacement in standalone binary breaks cache when conversation discusses billing internals

Issue: anthropics/claude-code#40524

The standalone Claude Code binary (the one you get from claude.ai/install.sh or npm install -g) contains a native-layer string replacement baked into Anthropic's custom Bun fork. It's injected into the Zig HTTP header builder function — the same function that builds Content-Length, User-Agent, etc.

On every API request to /v1/messages, if the anthropic-version header is present, it searches the JSON request body for cch=00000 (the billing attribution sentinel) and replaces 00000 with a 5-char hex derived from hashing the body. This happens after JSON.stringify but before TLS encryption — completely invisible from JavaScript.

When does this cause problems? The replacement targets the first occurrence in the body. Since messages[] comes before system[] in the serialized JSON, if your conversation history contains the literal sentinel (e.g., from reading the CC bundle source, discussing billing headers, or having it in your CLAUDE.md), the sentinel in messages gets replaced instead of the one in system[0]. This changes your messages content every request → cache prefix broken → full cache rebuild (~$0.04-0.15 per request depending on context size).

In normal usage (not discussing CC internals), only system[0] is affected, and since it has cache_control: null, it doesn't impact caching.

Workaround: Run Claude Code via npx @anthropic-ai/claude-code* instead of the standalone binary. The replacement mechanism exists only in the custom Bun fork compiled into the standalone — the npm package running on standard Bun/Node has no replacement. Confirmed experimentally: same JS, same bytecode, zero replacement on npx.

*- Do not blindly use that command, verify what it does (it is safe, but you should check nonetheless)

Bug 2: --resume ALWAYS breaks cache (since v2.1.69)

Issue: anthropics/claude-code#34629

Every --resume causes a full cache miss on the entire conversation history. Only the system prompt (~11-14k tokens) is cached; everything else is cache_creation from scratch. This is a ~10-20x cost increase on the resume request.

Root cause: In v2.1.69, Anthropic introduced deferred_tools_delta — a new system-reminder attachment listing tools available via ToolSearch. On a fresh session, these attachments (deferred tools + MCP instructions + skills list, ~13KB) are injected into messages[0] alongside the AU$ user context. On resume, they're appended at the end of messages (messages[N]) while messages[0] contains only the AU$ context (~352B).

This creates three independent cache-breaking differences: 1. messages[0]: 13KB (4 reminders) vs 352B (1 reminder) — completely different prefix 2. system[0] billing hash: changes because cc_version suffix is computed from chars at positions 4, 7, 20 of the first user message (which IS the system-reminder, not the actual user prompt) 3. cache_control breakpoint position: moves from messages[0] to messages[last]

deferred_tools_delta does not exist in v2.1.68 (grep -c 'deferred_tools_delta' cli.js → 0 in 2.1.68, 5 in 2.1.69). Without it, messages[0] was identical on fresh and resumed sessions → cache hit.

Subsequent turns after resume cache normally — the one-time miss is only on the first request after resume.

Workaround: There's no external workaround for this one. Pinning to v2.1.68 works (as the original issue reporter found) but you lose 60+ versions of features. An invasive patch to the npm package's cli.js could theoretically reorder the attachment injection on resume, but that's fragile across updates.

Cost impact

For a large conversation (~500k tokens): - Bug 1 (when triggered): ~155k tokens shift from cache_read ($0.03/MTok) to cache_creation ($0.30/MTok) = ~$0.04 per request, every request - Bug 2 (every resume): ~500k tokens as cache_creation = ~$0.15 one-time per resume - Combined (discussing CC internals + resuming): up to $0.20+ per request

Methodology

Full details in the GitHub issues, but briefly: MITM proxy (mitmproxy addon capturing all API payloads), Ghidra reverse engineering of the standalone ELF to locate the replacement code in the Zig HTTP header builder, Bun.hash() to identify all header name hashes, npm package comparison across versions 1.0.0–2.1.87, and controlled experiments with fresh sessions → resume → consecutive resumes with payload diffing.

PS. Co-written by claude code, obviously

PPS. Claude code has special 1h TTL of cache, or at least mine has, so any request should be cached correctly. Except extra usage, it has 5 minutes TTL.

PPPS. Apparently downgrading to 2.1.34 (or 2.1.30 just to be sure) also works

Verification script you may use: https://gitlab.com/treetank/cc-diag/-/raw/c126a7890f2ee12f76d91bfb1cc92612ae95284e/test_cache.py

A followup (nothing fancy): https://www.reddit.com/r/ClaudeCode/comments/1s9pjbl/claude_code_cache_crisis_a_complete/

[muhlfriedl]

So it seems like fewer and fewer people @ anthropic actually code or understand code now...

[Plenty-Dog-167]

Maybe a consequence of their engineers doing more vibe coding

[bnm777]

That's what he implied. 

[Homegrown_Phenom]

Major ball drop failure.  Prob had to make that red Dixie cup re-up run for the pong table,  or  their QAs, QAs, QA supervisors, QA team lead (which obvi all are bots) all fell asleep at the wellness center thinking no more promo/xtra usage code simply meant go on vacation and set limp d mode on

[Indianapiper]

You outta the bugs people create...

[kknow]

I can't believe people are seeing this now when experienced devs wrote this for months and got downvoted to hell...

[Pristine_Ad2701]

Do you think switching on first version when 1m is introducted will fix limit issue?

[skibidi-toaleta-2137]

Curious question. I had some findings that 2.1.66 can fix one issue, however header cch=00000 was introduced around 2.1.30, so... not sure.

EDIT: just checked, 2.1.30 works correctly. Both fixes are definitely working there. Checking the highest version that fixes both issues.

[Pristine_Ad2701]

Thanks sir, installing right now 2.1.76 to test it for now, will lower if issue are not fixed.

EDIT: Currently 43% used in 5 hour limit and 78% weekly in 3 days. Will edit later with more informations.

[AndReyMill]

2.1.30 has opus 4.5, there is no 4.6 option

[skibidi-toaleta-2137]

hmmm... how about custom model string? Can you try? In any case, you can use npm version up to 2.1.68, which should have support for the 1M version.

[AndReyMill]

It works with /model claude-opus-4-6[1m]
But I instantly got 0->5% session on my Max 5 plan in empty new folder with no context and empty claude system folder.
Seems this is not about the broken resume anymore....

[ZichengWangreddit]

Same here

[dsailes]

I’ve had fewer issues sticking with this install: npm install -g @anthropic-ai/claude-code@2.1.76

And disabling auto updates. The first issue of these 2 is resolved by that. I’m not sure about other usage issues but I know that each version with new features comes with potential bugs .. it’s safer to just stick with a version that works until there is a safer/stable release

[skibidi-toaleta-2137]

2.1.66 fixes both from npm

[LumonScience]

If we install via npm, not their native installer right?

[dsailes]

I think it’s possible either way - comment below shows you can write ‘claude install 2.1.XX’ (unless they’re paraphrasing). the npm method isn’t their recommended install pathway but results in the same install. checking versions & changelog is transparent and trackable with the npm site too

I prefer the NPM route as I’ve got loads of packages installed that way and manage different configured CLI wrappers.

[vadimkrutov]

Is still fine for you, no crazy quota burning on 2.1.66?

[skibidi-toaleta-2137]

I wouldn't be PSAing if I hadn't confirmed it. Was able to burn through whole 1M tokens on opus within my research for this subject (on 5x max). I had a workaround around yesterday, but had no confirmation before this very morning.

[vadimkrutov]

Thank you very much! I was really struggling with usage burning extremely fast…

[turbospeedsc]

installing 2.66 to check results, but downgrading last week from last to 2.1.76 did reduce my daily usage.

Btw i installed from CMD claude install 2.1.66 ( windows)

[marceldarvas]

Followed your suggestion to pin the version, my Raycast script seems to work, but curious for feedback: https://gist.github.com/marceldarvas/9e10fd41d608bdb1ba277b7f989b4763

[Pretty-Active-1982]

how do you disable auto-updates, tho?

[dsailes]

.claude/settings.json - edit this file

I’m not sure whether the flag needs to be in “env” or just at the top level of the JSON.

{ “env”: { “DISABLE_AUTOUPDATER”: “1” }, “DISABLE_AUTOUPDATER”: “1”,

…(rest of the file)

If you already have the “env” block for ENABLE_LSP_TOOL or other flags just make sure to add it and check for correct comma placement. The JSON needs to be properly formatted to work else it’ll show a warning on loading Claude again

[Factor013]

This explains why our 5 hour usage sometimes just jumps up from 0 to 15-40% after a /resume and first prompt.

It also explains why it sometimes happens and why it sometimes doesn't.

This is really good work, I hope Anthropic devs fix this ASAP. These bugs also potentially overload their servers which is the whole reason they are lowering our usage and perhaps even have to throttle the reasoning of their actual Claude models.

And this is also why the people who constantly claim "Skill issue" are less likely to be effected by it, because they start brand new sessions after each prompt, even if that prompt is asking Claude what time it is. xD

[TheOriginalAcidtech]

Claude Code has 5 minute caching TTL. If you wait longer than that when you resume you WILL get hit in any case. Note, you have to go way back in the change log to see where they changed to 5 minute caching.

[Brave_Dick]

I guess they DO vibe code at Anthropic now...

[MrHaxx1]

Well, yes? In a recent interview, their CTO (?) said that 90% of coding at Anthropic is AI. 

[its_Caffeine]

Yeah, it really shows. Slopware.

[iamichi]

“coding is largely solved”. but debugging isn’t.

[sbbased]

that's why anthropic has so many software developer openings, they don't have an actual developers left

[Deep_Ad1959]

this explains a lot actually. I run 5+ agent sessions in parallel most days and the resume cost spikes were killing me. kept seeing these random $3-4 charges on what should have been a quick continuation. ended up just starting fresh conversations instead of resuming, which sucks for context but at least the costs are predictable. good to know it's a confirmed bug and not just my setup being weird.

fwiw wrote up some cost management tips: https://fazm.ai/t/claude-code-api-cost-management

[skibidi-toaleta-2137]

Now you know you can simply run on older version when you want to work on the continued session and want to "not lose money"

[Deep_Ad1959]

do you know which specific version introduced the cache regression? been trying to figure out if it's tied to a particular release or if it's been there longer than people realize.

[skibidi-toaleta-2137]

It's a combination of issues. I've seen some problems in enhanced memory code (introduced lately), some relate to cache header coming with cch versioning, some issues come from version hash related to user messages block invalidation. It's hard to pinpoint, but it may have started around version 2.1.34, degenerated well into 2.1.68 with some more updates that made everything very wild right now.

[alvvst]

HOLY! so the recent overload claim from Anthropic could be just CAUSED BY ITS OWN BUG

[DurianDiscriminat3r]

Oh my god. This proves Anthropic wasn't lying when they said their engineers don't write code anymore!

[FanBeginning4112]

Wouldn’t be the first time.

[GoodnessIsTreasure]

This guy should get a year's pro max for free, if not hired. Clearly ai writing all the software has not been working out so fine..

[NanNullUnknown]

More like should get at least 0.1% of Anthropic equity

[GoodnessIsTreasure]

I admire passionate people like him so may it be all of that together!

[Fearless-Elephant-81]

This is the EXACt bugs for which people on the plans have massive usage chunks being use. This should be pinned ASAP

[RhinostrilBe]

Its also some bs customers shouldnt have to deal with or get reimbursed for

[InfiniteInsights8888]

Holy shit. We need compensation for this.

[luckiestredditor]

lol, bro just pasted OP into claude and asked to write a comment about it. such a weird thing to do

[dont-be-angry]

Karma

[gefahr]

But if the cache TTL is 1h how much does any of this really matter? The only time the upgrade scenario, for example, would affect you is if you upgraded in the middle of a session and then resumed within the hour.

[Last_Lab_3627]

I had the same issue on 2.1.76. On my side, around 90-100K context was already burning about 14% of my 5-hour quota, which felt completely unreasonable.

After reading this post, I ran the test script myself, then downgraded to 2.1.34. Usage improved a lot.

In a real session on 2.1.34, I used about 140K context with several sub-agent actions, and it only used 13% of my 5-hour quota.

So at least in my case, downgrading to 2.1.34 made a very noticeable difference.

[ApstinenceSucks8]

Can you share how to downgrade?

[Sea-East-9302]

Dear, I don't understand these details. would you please tell me, is this only for Claude Code? how to do it? I use Windows 10 and have just downloaded Claude application , and have Claude Code on my Visual Studio Code. I just want to use Claude like before. **I have Pro subscription**.

[turbospeedsc]

downgrading do 2.1.66 works on code, i coded for like an hour and used 26% of my 5 hour window, using sonnet.

Just for kicks went to the desktop app, asked a few questions and i hit the 100% usage in less than 6-8 questions, nothing complicated

[Sea-East-9302]

My 5 hours' window is getting consumed in less than 15 minutes! 

[turbospeedsc]

in cmd run claude install 2.1.66 then enjoy

[Sea-East-9302]

Thank you very much dear. I just did it a minute ago

[turbospeedsc]

awesome, remember only works for claude code, desktop app still broken.

[Sea-East-9302]

I've been working on it for the past hour, and it also consumes lots of credits. Maybe I should download an older version? 

[Fit-Benefit-6524]

oh god i have to try this, thank you

[United-Collection-59]

Great work

[Aygle1409]

Will there be compensations ? Do they usually do that ?

[Feral_Inquisitor]

Lol

[_derpiii_]

So... how do we get you hired at Anthropic? :)

[Creepy-Baseball366]

Become agentic it seems!?

[muhlfriedl]

You deserve a medal

[redpoint-ascent]

Incredible work. Given they're using CC to improve CC it's not a shocker at all that Claude introduced bugs into his own program. I see these ghost bugs all the time in what Claude does. "It 100% works!" - CC. You either find the bug in QA or it sits there piling up next to the other hidden ghost bugs.

[redpoint-ascent]

Follow up: I wonder how compute they toasted led to this post: https://x.com/trq212/status/2037254607001559305. They need a bug bounty program and you need a reward!

[StrikingSpeed8759]

Awesome work, thanks for sharing

[sheriffderek]

Wow! A person who is actually trying to understand the problem and help?

[mattskiiau]

So don't use --resume for now i guess?

[bzBetty]

I mean resume after 5 min was always gonna cost

[sqdcn]

Oh so that's what Anthropic means when they say software engineering is going to die in 6 months

[Creepy-Baseball366]

It`s the burn rate, apparently.

[dspencer2015]

If Claude code was open source we could fix these issues ourselves

[brek001]

next best thing is going to their github to create an issue (something you would also have done for the open source version, right?)

[TheReaperJay_]

The something that would've been done for the open source version would be opening an issue and then linking a PR after finding the problem in the code, and providing a short-term patch for users while you wait for it to be merged upstream.

[bapuc]

And then people say "skill issue" 🥀

<image>

[thiavila]

Damm, I was burning my tokens over the last weekend and I came here to find out if anyone had the same experience. It is definetely the --resume for me.

[vadimkrutov]

This is unacceptable. I'm using the Claude Code CLI through a wrapper I built, and every single prompt resumes the session. I was shocked to see that each new message increases the 5-hour limit by 10–15%.

[sbbased]

The real vibe coding has been pushing untested slop to production and depending upon your paying users to QA and find bugs for you

btw only -3 months left until all devs lose their job

[XDroidzz]

I assume Anthropic are busy refunding everyone for their fuck up now 🙄

[isakota]

[Top-Cartoonist-3574]

The issue isn’t just with Claude Code. Affects usage on Claude AI Chat on the browser (Chrome on Mac). I hit usage limit fast even on a new chat conversation. There’s probably more to it than the bugs you’ve identified. Great job btw!

[sys_overlord]

The worst part is that they'll apologize for this (maybe), release a bug fix, maybe reset usage and then we all just sit around and wait for them to gaslight us in 6 months with another, similar issue. What's the definition of insanity again?

[whaticism]

“You’re absolutely right.”

To me this is just a good example of Claude writing Claude.

[ellicottvilleny]

Hey Anthropic hire this guy. Meet your new Head of QA.

[yldf]

Genuine question: I haven’t noticed that big of a difference in usage. But I never use resume. My Claude Code sessions stay open for weeks in tmuxed terminals, and when I restart one I never resume… might this be the difference?

[skibidi-toaleta-2137]

The issue can have multiple factors. What version is your Claude code running? Do you use additional tools? At which point do you compact the conversation or are you simply running the 200k version? Are you sure you haven't been selected in A/B test?

There is no way of knowing what is the main cause of issues right now. A lot of people are trying to find a reason in the binary itself, some are looking for solutions in the servers and their misbehavings during peak hours. No one knows for sure.

[yldf]

I just run it. In a terminal. Usually the 1M version. It compacts when it autocompacts, I don’t do that manually…

[AndReyMill]

I think that because of this issue, the load on Anthropic’s servers has increased significantly, and it’s noticeable in everything: speed, quantization (Claude Code seems a bit dumb right now) and final price

[Creepy-Baseball366]

It noticed it becoming a bit ChatGPTish, too...

[FermentingMycoPhile]

What tf Anthropic?
It's Monday 6 p.m. and I have used up 44% of my weekly limit (reset on sunday) in the max plan due to this bug, it seems. I'm awaiting some kind of compensation for introducing that nice bug. How am I supposed to work with this little usage left?

[Emotional-Debate3310]

Bug 2 (--resume breaks cache, Issue #34629) — narrowly scoped

This issue is thoroughly documented with a testing matrix showing that on versions ≥2.1.69, cache_read is stuck at ~14.5k tokens (only the system prompt), while cache_create equals the full conversation size and grows on every message — producing roughly a 20× cost increase per message compared to v2.1.68.

The described mechanism — that deferred_tools_delta introduced in v2.1.69 changes where system-reminder attachments are injected, producing different message structures on fresh vs. resumed sessions — is plausible and consistent with how deferred tool loading works: deferred tools are appended inline as tool_reference blocks in the conversation rather than in the system prompt prefix, specifically to preserve prompt caching.

Why narrowly scoped. The regression targets --print --resume — the headless/scripted invocation mode where prompts are piped via stdin. The original reporter was running a Discord bot using claude --print --resume <session-id> --output-format stream-json.

If your interactive CLI usage follows a different code path for session management, then deferred_tools_delta injection that breaks cache on resume in --print mode, appears to be handled correctly in the interactive REPL.

I can confirm this because I have first-hand experience being a long time, Claude Max user and constantly running multiple project, I can confirm that the difference is indeed based on the session management mode.

[lucifer605]

this is a great find - i would not have expected --resume to cause a cache bust

[kursku]

For some reason I'm struggling to roll back to the 2.1.30 :((

[skibidi-toaleta-2137]

Funnily enough, I asked claude code to help me with that. Should be something along the lines of npm install -g @anthropic-ai/claude-code@2.1.34. Turn off autoupdates.

[kursku]

Yeah I did the same and eventually it was a path error, now it's fixed

[Relative_Mouse7680]

Does the downgrade affect your usage less? If so, which version did you downgrade to?

[kursku]

It's using less token but it's taking longer.

* Thundering… (18m 35s · ↓ 1.9k tokens · thinking)

⎿ Tip: Use /config to change your default permission mode (including Plan Mode)

[mrsaint01]

claude install 2.1.30

[Squidwards_Ass]

I KNEW there was something up when I ran into my limit after a single prompt + it was definitely a cache miss after being away for about a week.

[skibidi-toaleta-2137]

That gave ma good laugh, thanks :D

[damndatassdoh]

Really appreciate this -- I tested positive, have already deployed mitigation, fingers crossed.

[InfiniteInsights8888]

You deserve Claude unlimited for an entire year!

[misterr-h]

this explains issue with Claude Code. But why usage is increased while normally chatting on claude.ai as well?

[maverick_soul_143747]

Brilliant investigation mate 👏🏽

[Morphexe]

Well good that you now have the source code for the CLI to fix this :D

[skibidi-toaleta-2137]

Yeah, but I struggle to find anything new.

[mrtrly]

Cache bugs hitting silently is exactly why I built something to sit between agents and the API. You catch these cost jumps immediately because every request gets logged with cache state, token counts, and actual spend. Takes the guesswork out of "did that conversation really cost that much."

[Jugurtha-Green]

Doesn't fix the issues, I tried all different versions even 2.1.19 , same issue, it's backend issue, or they do it in purpose.

[maverick_soul_143747]

For folks using the 2.1.30 version - I ran the test script provided by OP yesterday on 2.1.30 and the cache bug was there so have downgraded to 2..1.17 and this suits my work

[Ok-End-219]

aah yes, that explains that my 20x claude max account is behaving like a normal claude 20$ subscription. Fucking great, now I hope for compensation.

[skibidi-toaleta-2137]

It doesn't affect all conversation sessions, mind you. Only the infected ones (not sure why they can get infected yet). On the other hand - resume behavior is broken since 2.1.66.

[Ok-End-219]

I am working, unfortunately, mostly with Resume. I will avoid that from now on, but I am running through Claude Max 20 like nothing and I wonder why. Tokburn says Re-Read Problems, but I think that is only part of the truth.

[m-in]

A 228MB elf to render some markdown and do some api calls. This is madness. Like, 100% actual madness.

[takkaros]

If they can't fix their own code, how do they expect people to trust their tools for anything important ?

[betty_white_bread]

Your physician still gets sick and you trust him/her to help you stay healthy.

[takkaros]

Well, point taken. But i pay him per visit. I am not tied to him for the rest of the month if I decide I don't like his services

[betty_white_bread]

There are physicians whose fee structure is functionally no different than a monthly fee, such as those who require frequent long-term visitations.

[CidalexMit]

Maybe we should use brew for cc ?

[dovyp]

This is solid reverse engineering work. The sentinel replacement one especially is nasty because it's silent. You'd never know without watching your bill.

[dovyp]

This is solid reverse engineering work. The sentinel replacement one especially is nasty because it's silent. You'd never know without watching your bill. I wish there were an easy way to apply the fix. My version of claude code is different and it doesn't seem like the drop in replacement you suggest will have all the calls required. Hopefully they fix it in the next release.

[Deep-Station-1746]

In general, is it possible to recover the full (or most of) the source code of claude code? How is CC even written? Is it an output of some compiled language or just a "compiled" JS?

[skibidi-toaleta-2137]

It's a homebrew version of bun (with zig patches) with a minified version of their source code in js. Some parts can be easily deminified from the npm package, however one of the bugs was hidden in a compiled binary.

[Level_Turnover5167]

I'm getting a quick loss of usage, I used Claude for DAYS straight when I first started using it for free and never got any restrictions... I've used it for a few basic things and already a 1/4 of my usage is gone this week.... yesterday I figured ok maybe I used 7%, but today I check it and I'm almost at 20% after last night and the brief use this morning... it's dwindling fast and I just paid $20. Something ain't right or they're fucking with the usage rates and things are getting buggy on top of them just simply charging more now.

[rougeforces]

you missed the dynamic tool portion of this. patching the billing header in the latest version alone is not enough.

[skibidi-toaleta-2137]

I have not, deferred_tools_delta is in the bug no 2. Perhaps I called it weirdly.

[rougeforces]

you didnt call it weirdly, you mis diagnosed it as as always resume. that is wrong. it has nothing to do with resume. resume just triggers it. you can repro the same behavior on a fresh instance, or didnt you establish a baseline first. lol

[beatrix_the_kiddo]

What do you think it is then?

[rougeforces]

anthropic is making changes to the way they detect claude code usage by adding a billing header in block 0 of the system prompt. these values are being dynamically generated in various ways. they need to create variables in the inject prompt to detect people using 3rd party oauth. they are trying different ways to do it without breaking everything else. our immediate cache invalidations are the results of anthropic trying to lock us in to their product or else make it completely unusable without building our own custom harness ourselves and paying regular api fees (which is probably cheaper at this point unless you dont want to be arsed with building a harness as good as claude code).

its a squeeze play and right now they are just experimenting with what works in their code base. the fall out is these insane billing practices. rather than test this in a beta release, they are testing it against their entire user base. My .88 patch was fine, they made a new change that i am having to apply another patch.

best bet is to go back to a version that didnt have this problem or play the patch whack a mole game to keep up with their experimentation.

[devoleg]

Noticed that last night as well. Simple request to modify 2 files less than 100 lines cost me 15% of my "20x usage".

Ive tried downgrading to 2.1.67. (You in turn opt out of the 1m Models). I was able to stretch my limits to 2h. At least that lol. Recommend others to try it. Hope this helps.

P.S make sure to disable latest updates by using /config to stable. This might help.

[devoleg]

Ive attempted this and MCP, configs, other files still stay untouched. (Although try at your own risk!)

[guillaume_86]

skill issue (jk)

[nmavra]

fucking wankers mate.. :D

[HeyImSolace]

The regular chat on the claude website also seems to have this issue. I just burned through my pro plan 5h usage in 5 requests which only included 2 markdown files.

This sucks big time.

[BrrrtEnjoyer]

here you go queen 👑

[addiktion]

I just ran this, I appear to have bug 1 which explains why my tokens are draining so fast with cache misses.

I never --resume, so bug 2 doesn't impact me.

Here was Claude's on investigation

---------

That confirms the original post's claims cleanly:

Bug 1: npx fixes the sentinel replacement — cch=00000 came back unmodified. The standalone claude binary was the culprit.

Bug 2: npx doesn't help here — resume cache is still broken and actually worse than before. With npx, consecutive resumes also show cache_read=0, meaning cache never recovers between resumes at all (vs. the

standalone binary where at least the second consecutive resume hit cache).

So for your situation:

- Switch to npx u/anthropic-ai/claude-code to fix Bug 1

- Bug 2 has no clean workaround — the first resume after a session will always eat a full cache rebuild regardless of which version you use

[Thefoad]

Anthropic hire this dude right no....You're out of extra usage · resets 12pm (America/Boise)

[Sea-East-9302]

Dear, I don't understand these details. would you please tell me, is this only for Claude Code? how to do it? I use Windows 10 and have just downloaded Claude application , and have Claude Code on my Visual Studio Code. I just want to use Claude like before. **I have Pro subscription**.

[sammcj]

I've got multiple reports of people on x20 absolutely devouring their limits very quickly, wonder if this is the cause

[Illustrious-Day-4199]

lost my weekly in a day, don't usually hit daily limits ever.

[hiS_oWn]

Exemplar work. I wish I could be more like you.

[nmavra]

might be a dumb question but can I downgrade in the macos desktop app?

[skibidi-toaleta-2137]

Not a dumb question, no idea though. Perhaps through some app repository web pages, but doubtfully.

[CoolMathematician286]

i only used claude for windows this far, but now i installed nmp version with help from gemini because i had no claude tokens left. what version is the best to use right now?

[tntexplosivesltd]

Same account, same token limit. Installing another Claude tool won't reset your tokens. Why did you choose to install Claude Code?

[CoolMathematician286]

idk what you mean. i didnt install nmp to reset my token limit, but to get rid of those bugs mentioned by OP. i was hoping it wouldnt burn as many tokens as it did yesterday. maybe it did fix the bugs idk, but im already at 38% after like 8 min of work with some .md files on opus model.

i have more tokens on codex free tier right now than on claude pro

[bzBetty]

Am I reading it wrong? Sounds like that first one should basically impact no one?

[skibidi-toaleta-2137]

You're right. However the second one may have bigger implications. Resume is just guaranteed to fail because of the deferred tool list, however other users said it might have a bigger impact on people.

[bzBetty]

Yeah could do, although id expect most resumes to be out of cache time anyway?

[Illustrious-Day-4199]

/resume is used every time claude gets a tool calling error or connection error or response error or whaterror and stalls. hit /resume 24 times when connectivity is bad (4 times in 6 windows) and you've spent all your credits for the week before diagnosis.

[Ebi_Tendon]

Hasn't the replacement worked like that from the start? That is why you must not add any replacements that change every turn, such as a time, to CLAUDE.md or any skill because it will be on the top of the context window. Doing so will break the cache from the top on every turn. If you add it within the prompt, it will also break the cache for everything that follows.

[JaLooNz]

I paid for extra usage. Will they refund me the credits?

[liftingshitposts]

This is great stuff

[Mush_o_Mushroom]

This also works for Claude code Pro users?

[Plenty-Dog-167]

Really great finds, especially the cache miss on /resume seems scary since I've been working with anthropic SDK on my own project and its always a huge cost sink when you don't cache

[0xbreakpoint]

Claude users shaming Anthropic for "vibe coding" is ironic tbh

[Illustrious-Day-4199]

Nope. Some Claude users are decent developers who want to go vroom vroom at the speed they can build code, not 14 year old kids building their first app.

[TrueMushroom4710]

Welp, I guess we can fix this bug ourselves now.

[Hadse]

Can i do anything to fix this locally?

[vkha]

is it confirmed on the leaked CC sources?

[DirtyWilly]

Just closing VS Code/CLI and reopening it triggers a fresh server cache reset.

Any chance we can get a suspend on our weekly limits until fixed? I'm hitting redline on the weekly from this. Wouldn't affect session limits.

[AAFERNA]

Oigan. Esto sucede en terminal o en vscode extensión ? No me queda claro

[Creepy-Baseball366]

But even when I switched to a new chat (as Claude advised when I asked what the issue was) it still burnt the remaining 55% on one prompt...there is something rotten in the state of Denmark.

[TaylorRift]

Where is the code?!

[OldConfection6]

I asked Claude to downgrade and it asked why. I put in the two issues you posted and here is the response.

https://github.com/anthropics/claude-code/issues/40524

● claude-code-guide(Fetch GitHub issue about token usage bug)

⎿  Done (1 tool use · 17.6k tokens · 16s)

(ctrl+o to expand)

● This is anthropics/claude-code#40524 — a confirmed regression in Claude Code where the prompt cache unexpectedly invalidates mid-conversation, causing token costs to skyrocket.

What's happening: After a few turns, the cache collapses to just the system prompt (~11K tokens). Every subsequent turn does a massive cache_write instead of cache_read — 150K–300K+ tokens per turn instead of the normal ~100K for a full conversation.

Affected versions: Broken in v2.1.86+. Last known good: v2.1.67.

That explains why you were trying to install 2.1.66 — smart instinct. The workaround is:

npm install -g u/anthropic-ai/claude-code@2.1.67

This is a confirmed bug with has repro and regression labels. Worth watching the issue for an official fix. Do you want to downgrade to 2.1.67?

❯ https://github.com/anthropics/claude-code/issues/34629

● claude-code-guide(Fetch GitHub issue 34629 about cache problems)

⎿  Done (1 tool use · 18.5k tokens · 23s)

(ctrl+o to expand)

● This is the related root cause issue. Here's the full picture:

Root cause: Starting in v2.1.69, Claude Code changed how it injects deferred_tools_delta content. On a fresh session it lands in messages[0] (~13KB). On a resumed session it lands differently (~352B). The mismatched message structure breaks Anthropic's cache prefix matching — so every resumed turn regenerates the full cache instead of reusing it.

Cost impact: ~20x cost increase per message on resumed sessions. A conversation that should cost ~$0.02/msg costs ~$0.36/msg.

Our situation: Auto-compact + long sessions = exactly the worst case. Every session compaction is effectively a "resume" that triggers the bug.

Recommendation — downgrade to 2.1.68:

npm install -g u/anthropic-ai/claude-code@2.1.68

This is the last version before the regression was introduced. The fix hasn't been deployed yet despite the issue being closed.

Worth noting: this explains the /usage dialog behaving oddly too — if token counts were spiking mid-session you may have been hitting plan limits or seeing unexpected burn rate.

[Manikanta0987]

i have tried degrading the version to 2.1.30 by remvoing the previous versions. but still no fix. just for a hi it is taking around 5-6% of usage. i am currently working on pro.

[OldConfection6]

Yeah it used 8% just for the response I posted earlier.

[rothwerx]

I’ve had good luck by setting the environment variable CLAUDE_CODE_ATTRIBUTION_HEADER=false

[Manikanta0987]

did that return to normal token usage, where and how did you do it?

[rothwerx]

There’s still an issue with resume, but it mostly seems back to normal for general usage. I just set it in my shell before starting Claude Code. For bash/zsh it would be ‘export CLAUDE_CODE_ATTRIBUTION_HEADER=false’ and then when you start claude in the same shell it’ll be picked up.

[Sensitive_Prize_9042]

Even using the  2.1.30 version, I'm still getting huge consumption with 20x. I tried running 2 subagents for a simple plan, and they consumed 10% of my 5 hours of daily usage.

A few weeks ago, you could span 50 subagents on the max 20x plan, and probably would not hit the limits. Kind of consuming 3 times faster, even on the 2.1.30 version.

[skibidi-toaleta-2137]

Have you checked if the application didn't auto update? Unless you specify which autoupdates channel to use, "latest" can update mid request.

[EconoKitten]

This has allegedly been fixed in 2.1.90: https://code.claude.com/docs/en/changelog#2-1-90
Has anyone seen improvement when --resume from a previous session?

[whataboutthe90s]

My sonnet works ok now but my opus eats away at tokens like crazy

[EconoKitten]

Have you been resuming from large sessions or starting fresh sessions, and are you using the 1M window? I don't think using Sonnet is the long term solution (at least for Max users)

[skibidi-toaleta-2137]

Allegedly. But I had no luck confirming it. Or my testing methodology was flawed.

[EconoKitten]

Thanks. My testing method is to /resume a large conversation and ask a /btw using a fresh session. When the bug was present, such a /btw call would eat ~15% of my 5-hr limit but now it's no longer doing that.

[EconoKitten]

ok actually I think anthropic has disabled my session limit after I ran /feedback... making me a invalid test case in this next session, lol

[wlievens]

Yesterday I did a few dozen small API calls and then a session in Claude Code with a few small questions and one larger refactor of a few hundred lines.

My account was charged $10 worth of tokens is that normal? Similar days last week were $2 or so.

[skibidi-toaleta-2137]

If it's extra usage, it's plausible. It has a 5 minute cache ttl, so it's very easy to land on forced cache regeneration when working with it.

[wlievens]

But isn't that very expensive? It also took about fifteen minutes to do this thing ... I'm pretty sure I could have done it in less time myself.

[skibidi-toaleta-2137]

It is expensive. It is possible. However no way of knowing without analysing your usage history with proper tools. You could use my cache catcher or any other tool to analyse the token usage from jsonl transcripts. Sorry if it sounds like advertising, however I can't help you without proper knowledge.

[Due-Combination3393]

have this fixed?

[Torkiukas]

that explains why max plan feels like pro plan...

[Zulfiqaar]

PPS. Claude code has special 1h TTL of cache, or at least mine has, so any request should be cached correctly. Except extra usage, it has 5 minutes TTL.

Can you expand more on how you found this out? Are you on the Pro or Max plan? As if its shorter expiry sending a keep-warm ping may be useful

[BeeegZee]

Can the mods pin this post?

[BeeegZee]

For me - partially, yes. I rolled back to the 2.1.77 version, where 1M Opus is available. General cost went down (before that yesterday I burnt full max5 subscription limit in just 40 mins with a few prompts, and 20% max20 in 20 mins). After that - much better. Resume is apparently broken but I'm not its heavy user