# Is quantum a threat to my coins?

**In short.** Not today. No quantum computer can break Bitcoin’s signatures, and the machines that exist are far from it. If one is ever built, the coins at risk first are the ones whose public key is already on the chain. If you don’t reuse addresses, your coins mostly stay out of that group.

> Not today. What it would take, which coins are exposed, and one thing to check.

You may have heard that quantum computers could one day break Bitcoin. It helps to start with what a coin's lock is made of, and what a quantum computer would have to do to open it. This page goes through what that would take, which coins it would affect, and what developers are doing about it. It ends with one thing you can check in your own wallet.

- Level: Beginner
- Time: About 15 minutes
- Web version: https://few.guide/guides/quantum-coins.html

## What you need

- **Your own wallet**: Any wallet where you hold the keys. The example uses Sparrow.
- **15 minutes**: Reading, plus a look at your address list.

## Step 1. What the worry actually is

Your wallet has a private key and a public key. The public key can be seen. The private key is what lets you spend.

Today nobody can work out a private key from a public key. A big enough quantum computer could, using a method called Shor’s algorithm. That is the worry.

It is about the **signatures** that prove a coin is yours. Mining uses SHA-256 hashing, which quantum computers help with much less.

**Public key** The part of your key that goes on the chain when you spend. It’s safe to show today.

## Step 2. How far away it is

In 2026 Google’s quantum team estimated that breaking one Bitcoin key would take about 1,200 to 1,450 **logical qubits**. On their kind of hardware that means fewer than 500,000 physical qubits.

What exists today:

- The biggest error-correction experiment so far held 96 logical qubits, in short test runs (Harvard and QuEra, 2025).
- The biggest array of physical qubits has about 6,100 (Caltech, 2025). They aren’t error-corrected.

Nobody knows when, or if, a machine big enough will exist. NIST says guesses vary widely. Some people think under ten years, others much longer.

**Logical qubit** A reliable qubit built out of many error-prone physical ones. An attack needs logical qubits, and they are the hard part.

## Step 3. Which coins show their public key

An attacker needs your public key. Most address types hide it behind a hash until you spend from them.

| Address starts with | Public key on the chain? |
|---|---|
| Very old coins (P2PK, 2009–2010) | Yes, always |
| 1…, 3… or bc1q… | Only after you spend from that address |
| bc1p… (Taproot) | Yes, from the moment coins arrive |

For most people, the risk comes from **address reuse**. Once you spend from an address, its public key is public. Any coins still on it, or sent to it later, sit next to a visible key.

About 6 to 7 million BTC is on addresses like that today, roughly 30 to 35% of all coins, depending on who counts. Much of it is ordinary reused addresses. About 1.7 million is very old coins from the early years.

Using a new address every time also helps your privacy today, quantum or not.

## Step 4. What developers are working on

Bitcoin can be upgraded by soft fork, like SegWit in 2017 and Taproot in 2021. For quantum, nothing is agreed yet. These are the main written proposals:

- **BIP-360 (P2MR).** A new address type like Taproot that never shows a public key while coins sit in it. Draft, added to the BIP list in February 2026.
- **BIP-361.** A plan to phase out old-style signatures after a quantum-safe type exists, over about five years. Draft, added in April 2026.
- **Quantum-safe signatures.** Still research. One draft, SHRINCS, was posted in August 2026. Its signatures are much bigger than today’s, and it is marked experimental.

None of these has an activation date. If a change is ever agreed, it arrives as new node software that people choose to run. Running your own node is how you follow along and choose.

**Watch for scams.** Quantum headlines get used to sell “quantum-safe” tokens and apps. You don’t need to buy anything.

## Step 5. One step for today

Check one wallet for reused addresses. It takes about 10 minutes.

- Open your wallet’s list of addresses. In Sparrow, that is the Addresses tab. Other wallets have a similar list.
- Look for an address that still has a balance and has sent coins before.
- If you find one, send those coins to a new receive address in the same wallet. New to sending? Do a small test first, like in [steps 12 to 18 of the SeedSigner guide](https://few.guide/guides/seedsigner-sparrow.html?step=12).
- From now on, use a new receive address every time.

No reused addresses? Then you’re done for now.

Your seed words stay where they are. Never type them anywhere because of a quantum headline.

## Sources

- [Google Research, March 2026](https://research.google/blog/safeguarding-cryptocurrency-by-disclosing-quantum-vulnerabilities-responsibly/): under 1,200 / 1,450 logical qubits, under 500,000 physical
- [Babbush, Gidney, Boneh and others](https://arxiv.org/abs/2603.28846): resource estimates for breaking secp256k1
- [Harvard and QuEra in Nature, Nov 2025](https://www.nature.com/articles/s41586-025-09848-5): fault-tolerant architecture, up to 448 atoms
- [qbitcount](https://qbitcount.com/history/2025-harvard-quera-96lq.html): that experiment held 96 logical qubits at once
- [Caltech, Sep 2025](https://www.caltech.edu/about/news/caltech-team-sets-record-with-6100-qubit-array): 6,100-qubit array, published in Nature
- [NIST](https://www.nist.gov/cybersecurity/what-post-quantum-cryptography): nobody knows when; some think under 10 years
- [NIST IR 8105](https://nvlpubs.nist.gov/nistpubs/ir/2016/NIST.IR.8105.pdf): Shor breaks elliptic curve keys; hash functions much less affected
- [ChainQuery quantum exposure, 18 Oct 2026](https://chainquery.com/reports/quantum-exposure): 7.12M BTC, 1.71M in P2PK
- [Glassnode](https://research.glassnode.com/measuring-bitcoins-quantum-exposed-supply/): 6.04M BTC (30.2%) exposed
- [BIP-360 (P2MR)](https://github.com/bitcoin/bips/blob/master/bip-0360.mediawiki): Draft, merged 11 Feb 2026
- [BIP-361](https://bitcoin.org/bip/361/): Draft, Informational, merged 14 Apr 2026, phases over about 5 years
- [SHRINCS draft spec](https://github.com/SHRINCS/shrincs-bip/blob/main/SHRINCS.md): 548–5,777 byte signatures, experimental, security proof TODO
- [Sparrow quick start](https://sparrowwallet.com/docs/quick-start.html): the Addresses and Receive tabs

Checked on 24 Oct 2026 against the Google and Nature papers, the BIP and SHRINCS drafts, ChainQuery and Glassnode. Exposure counts differ by method, so we give a range. Proposals change, so check the BIP pages for the latest.