Tier 2 narrows

Tier 2 of the quantum runway narrows, but the box is not open

Updated 20 October 2026

That is a narrower tier. It is not an opening.

What the runway counter actually counts

The quantum runway counter on the site tracks the dollar value of bitcoin held in address types whose public key is, or could become, a clean target for a future Shor run. Two tiers are usually listed. Tier 1 is the obvious one: legacy P2PK outputs whose public key sits naked on the chain from the moment the coins were sent. Tier 2 is the subtler one: coins whose key is exposed only because the owner has spent from the address at least once, in any format where the spend reveals the underlying public key.

Up to now the counter has lumped those two tiers together when it prints a single number, and the lumped number has been the headline. As of the 20 October 2026 tick the lumped figure is around 8.4 billion dollars at a notional sixty thousand dollar coin. That is the number the dashboard shows. It is also the number that, in the long run, overstates the urgency. The interesting movement this month is not in the lumped headline but in the way the second tier is being carved by wallet behaviour and by tooling, and that movement is downward.

To be precise about the chain of custody mechanic: a coin is in Tier 2 only when a transaction spending from its address has been confirmed and the public key is now part of the witness data or script data on chain. A coin that has been received but never spent is, at the address level, still in the hashed state. The hash closes the box, in the sense the site has used that phrase since the first run of the runway counter. A future Shor run against a hashed address has to invert the hash first, which is a separate and considerably larger ask than running Shor on a key that is already on chain in the clear. Tier 2 coins have, in plain language, been opened once by their owner, and that opening is what the runway counter is counting.

Why the second tier has been shrinking

Three movements matter, and they are not speculative. They are observable in the chain and in wallet release notes from the second half of 2025 through to this October.

First, address rotation has become the default behaviour of every wallet that ships an automatic change output to a fresh address. The pattern is older than this site, but its share of the network has climbed. When a wallet spends a UTXO, returns the change to a new address, and never reuses the new address, the new address is hashed and the chain of custody mechanic of the second tier does not extend to it. The wallet effectively rolls the box back into the closed state for the change. What the counter still records is the spent UTXO. The counter has not recorded the new address, because the new address is still hashed, and the runway counter is, by design, an address-type counter rather than a balance counter.

Second, wallet providers have rolled out, in stages through 2025 and into 2026, optional migration paths that take a user from a legacy address type to a SegWit or Taproot address type and then sweep the legacy balance across. These are not consensus migrations. They are client-side sweeps. A sweep consumes the legacy UTXO as an input and pays the same private key a new output at a different address type. The legacy UTXO is spent, the public key is exposed one last time on chain, and the balance arrives at a hashed address at the destination. From a Tier 2 perspective the legacy UTXO leaves Tier 2 by being spent. It does not enter Tier 2 from the perspective of the new destination.

Third, watch-only wallets, and the wallet providers behind them, have been tightening which addresses they will display. The post-quantum story for watch-only has not been settled, and the site has covered that in pieces on the watch-only window. What is settled is that the window does not count as an opening. A watched address is a watched address. A watched key is a watched key. Neither spend reveals a public key to the chain. The chain of custody mechanic of the second tier is therefore indifferent to whether the owner is running a watch-only stack or a signing stack. The tier ticks up only on confirmed spends, not on local key import.

What this means in the runway counter is that the second tier has been losing coins faster than Tier 1 has been losing them, and Tier 1 does not move much. Tier 1 is mostly the early P2PK coinbases from 2009 and 2010. The taproot opens the box on arrival piece and the Satoshi coins piece on the site have covered the lower bound there. Tier 1 is structural. Tier 2 is behavioural, and behaviour is moving.

What the narrower tier changes, and what it does not

A narrower Tier 2 changes two things and leaves three things alone.

It changes the order in which a future quantum adversary would have to think. The box model on the site is consistent. The hash closes the box. The signature opens it. A quantum adversary that wants to spend a coin must have both a valid ECDSA or Schnorr signature and a valid script. For Tier 1 coins the box is already open at the address level. For Tier 2 coins the box was opened by the owner's first spend, was closed again at the new change address, and will only reopen when the next spend of the new change address confirms. A shorter Tier 2 means fewer address types that are currently in the open-by-owner state, and therefore a smaller immediate target set for an adversary who can already run Shor against keys in the clear.

It also changes the slope of the runway counter. The headline number on the site has not been moving linearly. It has been stair-stepping. A narrower Tier 2 means the next stair step down, when it comes, is shorter.

What it does not change is the box mechanic for the address types that remain. A box that is open by virtue of a confirmed spend is open in the same way that a box opened by a key the owner has lost is open: a future quantum run against the exposed public key can reconstruct a private key, and a future quantum run against the hashed address can be left for later, when and if the qubit budget allows. The custody mechanic is identical in both cases. The quantum adversary's task is to recover a private key. The chain does not care why the public key is exposed.

What it also does not change is the position of the long horizon. The runway counter prints years to threshold under assumptions that have not been updated this month, and the assumptions are not what this post is about. The site has covered the runway counter's qubit budget assumption, the threshold crossing, and the standard objections to the threshold figure in earlier pieces. The narrower tier affects the numerator. It does not, by itself, change the denominator.

Finally, what it does not change is the box state of any specific user reading this. A box is open or closed based on the address type and the spend history of that specific UTXO, not on aggregate statistics. The runway counter is a system-level number. It is not a personal number. A reader who has spent once from a P2PKH address and is now holding change at a fresh P2WPKH address is, at the change address, hashed. The owner of the spent UTXO is, for the spent UTXO, open. The runway counter does not reconcile this for the owner. The owner reconciles it for themselves, by inspecting the address type of every UTXO they currently hold, and by deciding whether the address type is one whose chain of custody mechanic has, at any point in its history, exposed the public key.

How to read the counter after the carve

The carved counter, from this tick forward, prints two figures. The lumped figure remains, for backwards compatibility with the older pieces on the site. The carved figure prints Tier 1 and Tier 2 separately. The carved Tier 2 figure is the one to watch for movement in the next two ticks.

For a custody mechanic post the practical reading is the following. A user with a balance entirely at hashed, never-spent address types is not in the counter. A user with a balance partly at hashed, never-spent address types and partly at address types whose UTXOs were spent at some prior point is in the counter for the spent UTXOs and out of the counter for the unspent change. A user holding a balance at legacy P2PK coinbases is in Tier 1 and the counter cannot help them.

The site is not a sweep tool and is not recommending a sweep. A sweep is a custody decision and belongs to the owner. What the site is doing is printing the narrower number, and pointing out, in the same terse register it has used since the first runway counter tick, that a narrower number is not a smaller box. A narrower Tier 2 is a smaller set of open boxes. Each open box in the set is as open as it was before the carve. The runway counter has not opened any box. The runway counter has, if anything, given the owner a more accurate picture of which of their own boxes are open, and that picture is, in the terse framing of this beat, exactly the picture a custody mechanic post ought to print.

The box is not open. The address is hashed, or it is not. The runway counter is a measurement, not a key. Never paste a seed into a watch-only field.

This post is descriptive of chain and wallet behaviour. It is not a recommendation to sweep, to migrate, or to alter any custody arrangement. A sweep is a custody decision and belongs to the owner.