>  1 BTC might actually make sense and not be so arbitrary—as it will be an easy number for people to track and understand what coins they can move or are moving at any given time.

I very much agree that keeping things easy for people should be a high priority.  As opposed to a % of the block reward or subsidy, one suggestion is to use something like the halving we use for the subsidy.  Start with a maximum of 1 or 2 BTC per block and reduce the amount by half on the same 210,000 block schedule as the subsidy halving.  People seem to get that concept well and I think it would work here too.  Alternatively, we could use the same schedule but do doubling.  Start with a very small number like 1M Sats and then build to a bigger number in the future.  This takes away the incentive for an early attacker and means the bigger prizes for the quantum attackers would come in a period when there is massive competition from the quantum world and much more economic uncertainty for an individual quantum attacker.

I must admit that this does create a bit of quandary regarding property rights and that does bother me, but if the decision is to do something to slow down the attackers this, does seem like a reasonable approach.  Also, by spreading this out over several decades and restricting block space access, it means that there will likely be numerous quantum attackers, and they will be competing with each other not only for the private keys but also for the prized spot in each block (good news for fees).  

From: bitcoindev@googlegroups.com <bitcoindev@googlegroups.com> on behalf of Isabel Foxen Duke <isabel.duke@gmail.com>
Date: Monday, February 23, 2026 at 1:51 PM
To: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
Subject: Re: [bitcoindev] Hourglass V2 Update

>  [1 BTC] can be replaced with something else. For example, if things are based on the coinbase reward, then these rules can be wired into consensus. Which means, that if the current block reward is 3.125 BTC plus fees, then P2PKs can be limited to be X% of the coinbase, and not more than that.

I don't mind this idea — however, I worry it could add complexity from a user experience perspective. 1 BTC might actually make sense and not be so arbitrary—as it will be an easy number for people to track and understand what coins they can move or are moving at any given time. Hyper-simplicity has UX and comms benefits.      

-Isabel

On Tuesday, February 17, 2026 at 9:11:45 AM UTC-4 Garlo Nicon wrote:

> My primary complaint is that 1 BTC per block is somewhat arbitrary.

> Hourglass V2 further restricts the output amount to a maximum of 1 bitcoin per block, or roughly 144 bitcoin per day. This is far less than the 450 coins per day introduced by the current block reward subsidy, and should effectively mitigate the market impacts of quantum attacks on P2PK coins.

It can be replaced with something else. For example, if things are based on the coinbase reward, then these rules can be wired into consensus. Which means, that if the current block reward is 3.125 BTC plus fees, then P2PKs can be limited to be X% of the coinbase, and not more than that. It would still be arbitrary, but it would be more aligned with the explanation from the BIP, that it is all about how many coins are introduced into circulation, or assigned to miners.

Or, if it would be based only on the basic block reward, without fees, then when all coins will be mined, P2PKs will automatically expire, because there won't be any amount, which is less than zero satoshis. Because things can be based on fees, but then, a large miner with many coins, could game the system, and turn some of his own coins into fees, only to unlock more P2PK coins.

pon., 16 lut 2026 o 23:11 Jameson Lopp <jameso...@gmail.com> napisał(a):

Bitcoin is ultimately a system of rules that are enforced by those who use the system and hold the keys to spend UTXOs. As such, if a sufficiently large cohort of economic power within the system is interested in protecting itself against massive liquidation events from malicious actors who arguably are not the rightful owners of UTXOs, the incentives are in place for them to do something about it.

I like Hourglass V2 a lot more than V1. My primary complaint is that 1 BTC per block is somewhat arbitrary. It would be interesting to point to the on-chain statistics of what P2PK UTXO spend volume we have seen in recent years.

Additionally, in the context of my own migration BIP, Hourglass V2 could be complementary to the concept of offering a ZK quantum safe spending option for folks who fail to migrate UTXOs to quantum safe scripts before a set deadline, given that these old P2PK outputs do not belong to HD wallets and thus the owners would be incapable of constructing a ZK proof of HD wallet ownership.

On Fri, Feb 13, 2026 at 5:12 PM Light <bitco...@lightco.in> wrote:

Bitcoin should not have an in-protocol plunge protection mechanism, and certainly not one that artificially restricts people's ability to spend their coins. I encourage you to withdraw this proposal, for the sake of bitcoin's integrity and utility as a p2p electronic cash system.

On Tue, Feb 10, 2026, at 3:47 PM, Mike Casey wrote:
> In response to feedback, the Hourglass proposal to mitigate against
> potential mass liquidation of P2PK funds has been enhanced to further
> limit spend amounts from such outputs to only 1 bitcoin per block.
> https://github.com/cryptoquick/bips/blob/hourglass-v2/bip-hourglass-v2.mediawiki
>
> Prior discussion of the original Hourglass proposal:
> https://groups.google.com/g/bitcoindev/c/zmg3U117aNc/m/lDCMs9j7EAAJ
>
> Thoughts & feedback welcome!
>
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