Hey, Boris from the Claude Code team here.

Normally, when you have a conversation with Claude Code, if your convo has N messages, then (N-1) messages hit prompt cache -- everything but the latest message.

The challenge is: when you let a session idle for >1 hour, when you come back to it and send a prompt, it will be a full cache miss, all N messages. We noticed that this corner case led to outsized token costs for users. In an extreme case, if you had 900k tokens in your context window, then idled for an hour, then sent a message, that would be >900k tokens written to cache all at once, which would eat up a significant % of your rate limits, especially for Pro users.

We tried a few different approaches to improve this UX:

1. Educating users on X/social

2. Adding an in-product tip to recommend running /clear when re-visiting old conversations (we shipped a few iterations of this)

3. Eliding parts of the context after idle: old tool results, old messages, thinking. Of these, thinking performed the best, and when we shipped it, that's when we unintentionally introduced the bug in the blog post.

Hope this is helpful. Happy to answer any questions if you have.

I appreciate the reply, but I was never under the impression that gaps in conversations would increase costs nor reduce quality. Both are surprising and disappointing.

I feel like that is a choice best left up to users.

i.e. "Resuming this conversation with full context will consume X% of your 5-hour usage bucket, but that can be reduced by Y% by dropping old thinking logs"

Is there a way to say: I am happy to pay a premium (in tokens or extra usage) to make sure that my resumed 1h+ session has all the old thinking?

I understand you wouldn't want this to be the default, particularly for people who have one giant running session for many topics - and I can only imagine the load involved in full cache misses at scale. But there are other use cases where this thinking is critical - for instance, a session for a large refactor or a devops/operations use case consolidating numerous issue reports and external findings over time, where the periodic thinking was actually critical to how the session evolved.

For example, if N-4 was a massive dump of some relevant, some irrelevant material (say, investigating for patterns in a massive set of data, but prompted to be concise in output), then N-4's thinking might have been critical to N-2 not getting over-fixated on that dump from N-4. I'd consider it mission-critical, and pay a premium, when resuming an N some hours later to avoid pitfalls just as N-2 avoided those pitfalls.

Could we have an "ultraresume" that, similar to ultrathink, would let a user indicate they want to watch Return of the (Thin)king: Extended Edition?

I don't envy you Boris. Getting flak from all sorts of places can't be easy. But thanks for keeping a direct line with us.

I wish Anthropic's leadership would understand that the dev community is such a vital community that they should appreciate a bit more (i.e. not nice sending lawyers afters various devs without asking nicely first, banning accounts without notice, etc etc). Appreciate it's not easy to scale.

OpenAI seems to be doing a much better job when it comes to developer relations, but I would like to see you guys 'win' since Anthropic shows more integrity and has clear ethical red lines they are not willing to cross unlike OpenAI's leadership.

I'm also a Claude Code user from day 1 here, back from when it wasn't included in the Pro/Max subscriptions yet, and I was absolutely not aware of this either. Your explanation makes sense, but I naively was also under the impression that re-using older existing conversations that I had open would just continue the conversation as is and not be a treated as a full cache miss.

My biggest learning here is the 1 hour cache window. I often have multiple Claudes open and it happens frequently that they're idle for 1+ hours.

This cache information should probably get displayed somewhere within Claude Code

As some others have mentioned.

I think the best option would be tell a user who is about to resurrect a conversation that has been evicted from cache that the session is not cached anymore and the user will have to face a full cost of replaying a session, not only the incremental question and answer.

(In understand under the hood that llms are n^2 by default but it's very counter intuitive - and given how popular cc is becoming outside of nerd circles, probably smaller and smaller fraction of users is aware of it)

I would like to decide on it case by case. Sometimes the session has some really deep insight I want to preserve, sometimes it's discardable.

Thanks for giving more information. Just as a comment on (1), a lot of people don't use X/social. That's never going to be a sustainable path to "improve this UX" since it's...not part of the UX of the product.

It's a little concerning that it's number 1 in your list.

This violates the principle of least surprise, with nothing to indicate Claude got lobotomized while it napped when so many use prior sessions as "primed context" (even if people don't know that's what they were doing or know why it works).

The purpose of spending 10 to 50 prompts getting Claude to fill the context for you is it effectively "fine tunes" that session into a place your work product or questions are handled well.

// If this notion of sufficient context as fine tune seems surprising, the research is out there.)

Approaches tried need to deal with both of these:

1) Silent context degradation breaks the Pro-tool contract. I pay compute so I don't pay in my time; if you want to surface the cost, surface it (UI + price tag or choice), don't silently erode quality of outcomes.

2) The workaround (external context files re-primed on return) eats the exact same cache miss, so the "savings" are illusory — you just pushed the cost onto the user's time. If my own time's cheap enough that's the right trade off, I shouldn't be using your machine.

Just wanted to say I appreciate your responses here. Engaging so directly with a highly critical audience is a minefield that you're navigating well.

Thank you.

I leave sessions idle for hours constantly - that's my primary workflow. If resuming a 900k context session eats my rate limit, fine, show me the cost and let me decide whether to /clear or push through. You already show a banner suggesting /clear at high context - just do the same thing here instead of silently lobotomizing the model.

Is having massive sessions which sit idle for hours (or days) at a time considered unusual? That's a really, really common scenario for me.

Two questions if you see this:

1) if this isn't best practice, what is the best way to preserve highly specific contexts?

2) does this issue just affect idle sessions or would the cache miss also apply to /resume ?

Then you need to update your documentation and teach claude to read the new documentation because here is what claude code answered:

Question: Hey claude, if we have a conversation, and then i take a break. Does it change the expected output of my next answer, if there are 2 hours between the previous message end the next one?

Answer: No. A 2-hour gap doesn't change my output. I have no internal clock between messages — I only see the conversation content plus the currentDate context injected each turn. The prompt cache may expire (5 min TTL), which affects cost/latency but not the response itself.

  The only things that can change output across a break: new context injected (like updated date), memory files being modified, or files on disk changing.                                                                                  
                                                                                                                                                                     

A similar thing happens if I ask claude code for the difference between plan mode, and accept edits on.

Then Claude told me the only difference was that with plan mode it would ask for permission before doing edits. But I really don't think this is true. It seems like plan mode does a lot more work, and present it in a total different way. It is not just a "I will ask before applying changes" mode.

We at UT-Austin have done some academic work to handle the same challenge. Will be curious if serving engines could modified. https://arxiv.org/abs/2412.16434 .

The core idea is we can use user-activity at the client to manage KV cache loading and offloading. Happy to chat more!!

This just does not match my workflow when I work on low-priority projects, especially personal projects when I do them for fun instead of being paid to do them. With life getting busy, I may only have half an hour each night with Claude to make some progress on it before having to pause and come back the next day. It’s just the nature of doing personal projects as a middle-aged person.

The above workflow basically doesn’t hit the rate limit. So I’d appreciate a way to turn off this feature.

Why does the system work like that? Is the cache local, or on Claude's servers?

Why not store the prompt cache to disk when it goes cold for a certain period of time, and then when a long-lived, cold conversation gets re-initiated, you can re-hydrate the cache from disk. Purge the cached prompts from disk after X days of inactivity, and tell users they cannot resume conversations over X days without burning budget.

> that would be >900k tokens written to cache all at once

Probably that's why I hit my weekly limits 3-4 days ago, and was scheduled to rest later today. I just checked, and they are already reset.

Not sure if it's already done, shouldn't there be a check somewhere to alert on if an outrageous number of tokens are getting written, then it's not right ?

Resuming sessions after more than 1 hour is a very common workflow that many teams are following. It will be great if this is considered as an expected behaviour and design the UX around it. Perhaps you are not realising the fact that Claude code has replaced the shells people were using (ie now bash is replaced with a Claude code session).

This sounds like one of those problems where the solution is not a UX tweak but an architecture change. Perhaps prompt cache should be made long term resumable by storing it to disk before discarding from memory?

reasonably, if i'm in an interactive session, its going to have breaks for an hour or more.

whats driving the hour cache? shouldnt people be able to have lunch, then come back and continue?

are you expecting claude code users to not attend meetings?

I think product-wise you might need a better story on who uses claude-code, when and why.

Same thing with session logs actually - i know folks who are definitely going to try to write a yearly RnD report and monthly timesheets based on text analysis of their claude code session files, and they're going to be incredibly unhappy when they find out its all been silently deleted

How does the Claude team recommend devs use Claude Code?

1) Is it okay to leave Claude Code CLI open for days?

2) Should we be using /clear more generously? e.g., on every single branch change, on every new convo?

You created this issue by setting a timer for cache clearing. Time is really not a dimension that plays any role in how coding agent context is used.

So you made this change completely invisible to the user, without the user being able to choose between the two behaviors, and without even documenting it in the (extremely verbose) changelog [1]? I can't find it, the Docs Assistant can't find it (well, it "I found it!" three times being fed your reply with a non-matching item).

I frequently debug issues while keeping my carefully curated but long context active for days. Losing potentially very important context while in the middle of a debugging session resulting in less optimal answers, is costing me a lot more money than the cache misses would.

In my eyes, Claude Code is mainly a context management tool. I build a foundation of apparent understanding of the problem domain, and then try to work towards a solution in a dialogue. Now you tell me Anthrophic has been silently breaking down that foundation without telling me, wasting potentially hours of my time.

It's a clear reminder that these closed-source harnesses cannot be trusted (now or in the future), and I should find proper alternatives for Claude Code as soon as possible.

[1] https://code.claude.com/docs/en/changelog

It is too suprising. Time passed should not matter for using AI.

Either swallow the cost or be transparent to the user and offer both options each time.

I actually have a suggestion here - do not hide token count in non-verbose mode in Claude Code.

Isn't that exactly what people had been accusing Anthropic of doing, silently making Claude dumber on purpose to cut costs? There should be, at minimum, a warning on the UI saying that parts of the context were removed due to inactivity.

From a utility perspective using a tiered cache with some much higher latency storage option for up to n hours would be very useful for me to prevent that l1 cache miss.

Boris, wait, wait, wait,

Why not use tired cache?

Obviously storage is waaay cheaper than recalculation of embeddings all the way from the very beginning of the session.

No matter how to put this explanation — it still sounds strange. Hell — you can even store the cache on the client if you must.

Please, tell me I’m not understanding what is going on..

otherwise you really need to hire someone to look at this!)

So this explains why resuming a session after a 5-hour timeout basically eats most of the next session. How then to avoid this?

That is understandable, but the issue is the sudden drop in quality and the silent surge in token usage.

It also seems like the warning should be in channel and not on X. If I wanted to find out how broken things are on X, I'd be a Grok user.

How big is the cache? Could you just evict the cache into cheap object storage and retrieve it when resuming? When the user starts the conversation back up show a "Resuming conversation... ⭕" spinner.

You need to seriously look at your corporate communications and hire some adults to standarise your messaging, comms and signals. The volatility behind your doors is obvious to us and you'd impress us much more if you slowed down, took a moment to think about your customers and sent a consistent message.

You lost huge trust with the A/B sham test. You lost trust with enshittification of the tokenizer on 4.6 to 4.7. Why not just say "hey, due to huge input prices in energy, GPU demand and compute constraints we've had to increase Pro from $20 to $30." You might lose 5% of customers. But the shady A/B thing and dodgy tokenizer increasing burn rate tells everyone inc. enterprise that you don't care about honesty and integrity in your product.

I hope this feedback helps because you still stand to make an awesome product. Just show a little more professionalism.

what about selling long term cache space to users?

or even, let the user control the cache expiry on a per request basis. with a /cache command

that way they decide if they want to drop the cache right away , or extend it for 20 hours etc

it would cost tokens even if the underlying resource is memory/SSD space, not compute

> We tried a few different approaches to improve this UX: 1. Educating users on X/social

No. You had random developers tweet and reply at random times to random users while all of your official channels were completely silent. Including channels for people who are not terminally online on X

I drop sessions very frequently to resume later - that's my main workflow with how slow Claude is. Is there anything I can do to not encounter this cache problem?

Wasn’t cache time reduced to 5 minutes? Or is that just some users interpretation of the bug?

Sorry but I think this should be left up to the user to decide how it works and how they want to burn their tokens. Also a countdown timer is better than all of these other options you mention.

> tokens written to cache all at once, which would eat up a significant % of your rate limits

Construction of context is not an llm pass - it shouldn't even count towards token usage. The word 'caching' itself says don't recompute me.

Since the devs on HN (& the whole world) is buying what looks like nonsense to me - what am I missing?

The entire reason I keep a long-lived session around is because the context is hard-won — in term of tokens and my time.

Silently degrading intelligence ought to be something you never do, but especially not for use-cases like this.

I’m looking back at my past few weeks of work and realizing that these few regressions literally wasted 10s of hours of my time, and hundreds of dollars in extra usage fees. I ran out of my entire weekly quota four days ago, and had to pause the personal project I was working on.

I was running the exact same pipeline I’ve run repeatedly before, on the same models, and yet this time I somehow ate a week’s worth of quota in less than 24h. I spent $400 just to finish the pipeline pass that got stuck halfway through.

I’m sorry to be harsh, but your engineering culture must change. There are some types of software you can yolo. This isn’t one of them. The downstream cost of stupid mistakes is way, way too high, and far too many entirely avoidable bugs — and poor design choices — are shipping to customers way too often.