I agree with you. And sadly, there's nothing we can do about it because it's an arms race. People will try to exploit loopholes to get more benefits and companies will try to prevent exploits--sometimes by making the service worse for normal users.

In this specific case, Anthropic can avoid keeping the cache if it detects this kind of prompt (i.e., if max tokens < some number).

How do a few extra requests with the same prefix make it more expensive for everyone else?

Keeping a conversation with a very large model active requires hundreds of GB of memory. If my conversation can never be swapped out, like when I go to lunch or take an afternoon walk, that's several hundred GB not available for other users. If everybody does that, Anthropic needs even more infrastructure than the quarter trillion dollars in infra they're already using.

The idea here is that your conversation is being swapped out for no good reason. The session is still active, as the subagents continue to make progress.

How is this comparable to going to lunch or taking a walk?

Is that actually happening, though?

Yes https://github.com/izeigerman/claude-thermos/blob/main/src%2...

CC actually prompts Claude about this by default in the ~20k system prompt and instructs it to avoid 300s timeout and to be mindful of the 300s cache expiration.

CC also will also block sleeps longer than eg 300s; the harness handholds the model quite a bit.

But you pay for cache writes, it's not like you're abusing anything, you're simply choosing to call a billed API for the explicitly intended purpose of writing/refreshing cache.

If you keep this running for hours without doing anything, it will drain your limits and API. The use case of keeping the main thread cache warm while subagents work is very genuine and legitimate.

The prefix cache is a resource shared by all users. This is basically a tragedy of the commons.

If true, I suspect Anthropic will begin suspending accounts that use it.

I highly doubt that.

Keeping your cache warm is a good thing, caching saves compute and electricity.

Cached input is cheap for a reason, it is in everyone’s mutual interests to maximise cache hit rates.

If that was true then Anthropic would have built this functionality in themselves.

They did. On any long running query with large context, tell Claude “give me a status report every 4 minutes to keep the cache warm”. It’s entirely happy to oblige and usually says “good idea, that will keep costs down”

Compute is also a resource shared by all users. When your prompt isn’t cached, your input needs to go through prefill; which is compute-bound.

The cache is discounted for a reason. They WANT you to use it.

They could always just extend the cache timeout beyond 5 minutes themselves. They don't do that because it is an expensive resource and there is a trade-off bewteen saving computation and reserving VRAM. Running a tool like this will force them to do one of the following:

1) Start charging for VRAM reservations.

2) Charge _other_ customers more.

3) Eat the cost themselves.

They charge you for cache writes already. There's a price assigned to it. Even if you're on subscription, it counts against your usage (very easy to observe with a big cache miss).

Anthropic (and now OpenAI too for 5.6) prompt caching is not free.

Holding your cache in VRAM for 5 minutes or 3 hours have very different costs to them.

"They already charge me to park my car, why can't I leave it there for a year for the same price as 1 week?"

So why is it 5 minutes at both peak and off peak hours? If they can guarantee 5 minutes at peak hours for everyone, why is it only 5 minutes at off peak?

I don’t think your understanding works.

you use more memory?

Eh, I assume Anthropic prices queries somewhere in line with their actual costs. If they don't, and they misalign incentives instead, that's kinda on them.

From the README:

> Detect the danger window. When the main lineage goes idle and a subagent is actively running, the main prefix is at risk of expiring.

So, this is not demanding to be at the front of the queue, it's just paying someone to take the place you already had in the queue, when you want to take a leak.

A subagent running doesn't mean that much, though. I often walk away while the subagents are chewing.

The defaults seem sensible. This isn't keep-alive-forever by default solution.

You’re already paying for the subagent, why should you pay twice? (Once for subagent, and again for waiting for the subagent). That’s double billing.

You PAY for cache writes. Holding the prefill in VRAM for a certain period of time is part of what you're paying for.

Right, but also using the cache refreshes/extends it, which means you can pay for a write once, then have it extended for very cheap (1 token).

You dont have to repay per hour? It seems like that is a design issue - Like yes we will keep these in whatever cache you want, but you will have some sort of renewal period

hey guys dario’s here!

There's no need for insults.

No? You still pay for cache reads... Actually this is actually MORE expensive than just redoing prefill if your context is below 100k.

This has nothing to do with queueing.

Cached input tokens cost 10% of uncached. So if you’re model runs for 45 minutes, generates 300k output tokens and asks you a question, it costs 10x more if you wait 5.01 minutes to answer.

Sure, you may be willing to pay 10x more (or get 10x less for your subscription). But the time limit is arbitrary and has nothing to do with other peoples’ workloads. So I think your point is a non sequitur.

> But the time limit is arbitrary and has nothing to do with other peoples’ workloads

No it has to do with others workloads, now you keep their cache for longer so others will get less. And no its not arbitrary, they run out of memory, if more people do this they will have the dial it down further or run out of capacity.

Explain to me how “every gets 5 minutes, 24/7, regardless of load” is remotely compatible with your statement?

Are you imagining this a fixed MRU where duration scales with usage? Becasue that is not at all what Anthropic documents: https://platform.claude.com/docs/en/build-with-claude/prompt...

You would not get more than 5 minutes if you were the only user in the world. You would not get less at their peak hours.

1) To be clear, it costs you 10x more for uncached input tokens _for the next call_, which are still 5x cheaper than output tokens.

2) Now imagine Anthropic or OpenAI now charge your per minute of reserved VRAM time. It would be more fair if they did. Would you still want to run a tool like this?

Totally agree that if the economics changed, the economics would change.

> has nothing to do with other peoples’ workloads.

Because ram/memory is free and not in demande at all these days?