Bitcoin is often touted as a censorship-resistant network, a key feature that attracts users. However, the Bitcoin developer community is currently embroiled in a heated debate over the removal of a spam filter that limits non-monetary data to 83 bytes per block. Some opponents argue that this change could potentially allow the posting of illegal content, such as child pornography, on the blockchain, potentially making Bitcoin illegal in many jurisdictions.
Summary
- The ongoing “spam wars” have led to a shift from Bitcoin Core to Bitcoin Knots, with concerns that the Bitcoin blockchain could become a hub for illicit content like child pornography.
- The issue of illegal content on the blockchain was raised years ago, but was dismissed prior to plans to remove the spam filter.
- Supporters of the change argue that the removal of the filter in version 30 (v30) would enable new possibilities, allowing users to store different types of data on-chain. Those opposed could opt to use alternative versions of Bitcoin Core or other node software.
Bitcoin Core vs. Bitcoin Knots
The monitoring and verification of blockchain data is carried out by nodes, with each block having the capacity for up to 83 bytes of non-monetary data, such as images, through an OP_RETURN script. This feature is often referred to as a spam filter, as it aims to keep the Bitcoin network focused on monetary transactions. Removal opponents fear that eliminating the filter could lead to network congestion.
On the other hand, some developers advocate for the removal of the spam filter to increase the arbitrary data limit to approximately 2 megabytes per block. They argue that this change would eliminate restrictions and censorship, opening up possibilities for sharing various types of data like images, videos, and documents.
I truly detest politics.
Thus I have little patience for those who try to impose traditional governance models onto Bitcoin.
If you don’t like anarchy, you’re free to leave.
— Jameson Lopp (@lopp) August 26, 2025
From a technical standpoint, images and other non-monetary data already exist on the Bitcoin blockchain as forever unspent transaction outputs, contributing to blockchain bloat and slower transaction speeds. The proposal to remove arbitrary data limits was put forth by Peter Todd earlier this year.
Bitcoin Meditations Series
1.
Satoshi Asked Core & Knots:
My children, how does Bitcoin last an Eternity?Core said: by becoming Many Things!
Knots said: by refusing to be anything else… pic.twitter.com/FdfssMOroR
— Zatoichi🌊 (@Zatoichi42) August 24, 2025
The proponents of the spam filter removal are predominantly aligned with the Bitcoin Core software community, the oldest and most widely used node program. With consensus reached, Bitcoin Core version 30, which expands the OP_RETURN space to the entire block, is set for release in October 2025. Given the prevalence of Bitcoin Core software in block verification, the Bitcoin network is likely to see an influx of arbitrary data post the October update. Meanwhile, opponents of the filter removal tend to use Bitcoin Knots nodes.
A comment on whether this process was “rushed”.
As someone who has both authored and merged mempool policy changes for the last 4 years, I’d say this is par for the course.
– The original PR was discussed around 2 years ago (of course, echoing arguments that were made 10 years…
— gloria (@glozow) June 9, 2025
Despite ongoing debates and some Bitcoin Core users transitioning to Bitcoin Knots, the removal of the spam filter is on track for October 2025. Proponents suggest that dissatisfied users can stick to older software versions or explore alternative options.
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The dispute took a personal and aggressive turn, with personal attacks prompting Gloria Zhao, a prominent Bitcoin Core developer, to temporarily deactivate her account. Critics accused Bitcoin Core devs of favoring Citrea, a zero-knowledge Layer 2 rollup protocol, enabling Ethereum-like functions on the Bitcoin blockchain. Bitcoin Mechanic, a Bitcoin dev, claimed to be blocked on GitHub after criticizing Bitcoin Core’s strategies.
Someone pushing for a major change to Bitcoin is affiliated with a company whose current exploit of Bitcoin was the motivation for the change.
Pointing this out on the github discussion has resulted in me being banned. https://t.co/VAaNByBE5o pic.twitter.com/5yYXgtWAti
— Mechanic #FixTheFilters #300kb (@GrassFedBitcoin) April 28, 2025
The resistance to Peter Todd’s proposal stems from the significant influence of Bitcoin Core, responsible for the majority of Bitcoin blockchain data at the time of the proposal. Amid escalating conflicts, over 15% of the Bitcoin Core community opted for Bitcoin Knots.
Illegal content concern
The debate was reignited by Bitcoin Mechanic on Aug. 31, warning of “unforeseen consequences” following the spam filter removal, potentially allowing illegal content like child pornography on the blockchain post the Bitcoin Core v30 update. Supporters of Bitcoin Core argue that other blockchains without spam filters have not faced such issues.
With Bitcoin’s immutable and censorship-resistant ledger, illegal content could persist indefinitely, transforming Bitcoin into a repository for illicit material. While monetary data remains neutral, arbitrary data could be subject to discrimination based on its content, according to Bitcoin Mechanic.
Bitcoin Mechanic acknowledged that “disgusting content” was previously uploaded to the blockchain in 2013 in hex form. However, the current structure allows users to avoid association with such data by refraining from using inscriptions. In contrast, illegal content potentially uploaded post the Bitcoin Core update would be in a different format.
“Why would anyone want to store child pr0n in the blockchain”?
Because getting other people to store it for you is vastly preferable to storing or hosting it yourself. Particularly if the storage medium is widely distributed among people otherwise engaged in a morally defensible…
— Mechanic #FixTheFilters #300kb (@GrassFedBitcoin) August 31, 2025
The issue of child pornography on the Bitcoin blockchain is not new, having been discussed extensively in 2017. With the increase in data per block, concerns arise regarding the potential for nations to ban Bitcoin due to the association of running a node with storing illicit content. Legal implications require expert analysis, while morally, the Bitcoin community deems such content unacceptable.
Core will pretend they didn’t see this video.
With Core’s changes, Bitcoin risks being exploited to store illegal material (like CP).
That gives governments the perfect excuse to outlaw Bitcoin or make running a node illegal.
Core devs @glozow –
Your choices determine if… https://t.co/pTMgabnddW— Joyce (@BitcoinWifey) September 1, 2025
The contentious nature of the debate is not uncommon in the decentralized and community-driven Bitcoin space. With the impending Bitcoin Core update, the true extent of the issue will unfold in the coming months.
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