# Dust Expiry: Clean the UTXO set from spam

**URL:** <https://delvingbitcoin.org/t/dust-expiry-clean-the-utxo-set-from-spam/1707>\
**Category:** Protocol Design\
**Tags:** softfork, bitcoin-core\
**Created:** [May 20, 2025, 1:12am UTC](https://delvingbitcoin.org/t/dust-expiry-clean-the-utxo-set-from-spam/1707 "2025-05-20T01:12:51Z")\
**Posts on this page:** 1\
**Showing post:** 1

<div class="post-metadata">

**Author:** ![RobinLinus](https://delvingbitcoin.org/user_avatar/delvingbitcoin.org/robinlinus/32/130_2.png) [@RobinLinus](https://delvingbitcoin.org/u/RobinLinus)\
**Post date:** [May 20, 2025, 1:12am UTC](https://delvingbitcoin.org/t/dust-expiry-clean-the-utxo-set-from-spam/1707/1 "2025-05-20T01:12:51Z")

</div>

# Age-Based Expiration For Dust Outputs

Dust Expiry is a soft-fork proposal which effectively cleans the UTXO set of any spammer’s spam who is not willing to pay an ongoing fee forever.

## Motivation

The UTXO set is full of spam, and it’s a growing problem.

Since 2023—when the inscription spam attacks, BRC-20 token scams, and related wash-trading started—the number **of** UTXOs has doubled:

[![Screenshot 2025-05-19 at 17.47.13 | 570×500, 100%](https://delvingbitcoin.org/uploads/default/original/2X/6/66215372c93d54924c1f9d2de9e8af562d0e5c63.png)](https://mainnet.observer/charts/utxoset-size/)

These spam outputs have increased the size of the UTXO set from 4.6 GB to 11 GB:

[![Screenshot 2025-05-19 at 18.01.42 | 690×409](https://delvingbitcoin.org/uploads/default/original/2X/d/dada14ad5751c66ab935029b5529ae15f2b25afb.png)](https://statoshi.info/d/000000009/unspent-transaction-output-set?orgId=1&viewPanel=8&from=1585897200000&to=1744354799000)

> “Currently half of all UTXOs contain less than 1 000 sats”  
> —[mempool.space research](https://research.mempool.space/utxo-set-report/)

Thus, half of the UTXO set is likely spam-related. Since UTXO spam is permanent and unprunable, it is much worse than spam in the form of auxiliary transaction data.

Thus, we should think about ways to clean the UTXO set of these spam outputs.

## Soft-Fork Proposal: Age-Based Expiration

Introduce a rule that makes very small, very old outputs unspendable. For example, let `T` be a UTXO’s age in years.

Once `utxo_amount - T * dust_limit` is negative, the UTXO expires and becomes unspendable. Expired UTXOs can then be pruned from the UTXO set.

Feedback welcome!

---

_[View the full topic](https://delvingbitcoin.org/t/dust-expiry-clean-the-utxo-set-from-spam/1707)._