January 13, 2016, marked a pivotal moment in Bitcoin’s governance crisis as the community grappled with competing visions for the network’s future. With Bitcoin Core’s reference implementation facing its first serious challenge to consensus dominance, three new alternative clients — Bitcoin Unlimited, Bitcoin Classic, and a BitPay-backed fork of Bitcoin Core — emerged to challenge the status quo, each proposing different approaches to solving the network’s pressing block size dilemma.
TL;DR
- Three new Bitcoin implementations emerged to challenge Bitcoin Core’s consensus rules
- Bitcoin Unlimited removes hard-coded block size limits, letting users set their own
- Bitcoin Classic proposes a simpler 2MB block size increase via hard fork
- BitPay released its own fork of Bitcoin Core with modified block size parameters
- Gavin Andresen submitted BIP109 to double block size to 2MB in January 2016
- Bitcoin XT, the first challenger, failed to gain sufficient mining adoption
The Block Size Debate Reaches a Breaking Point
At the heart of the controversy lies a fundamental technical constraint: Bitcoin’s blocks are limited to 1 megabyte in size, a restriction that limits the network to roughly three to seven transactions per second. As Bitcoin adoption grew through 2015, this ceiling became increasingly problematic, with transaction fees rising and confirmation times lengthening during periods of high demand. The debate over how — or whether — to increase this limit had been raging for over a year, dividing the community into competing camps.
Bitcoin was trading at approximately $432 on January 13, 2016, with a total market capitalization of around $6.5 billion. While the price remained stable, the underlying governance crisis threatened to undermine confidence in the network’s long-term viability. Ethereum, still in its infancy at $1.13, was positioning itself as an alternative that could handle higher transaction throughput.
Bitcoin Unlimited: Decentralized Block Size Consensus
Bitcoin Unlimited, a fork of Bitcoin Core led by developer Andrew “thezerg” Stone, took perhaps the most radical approach. Rather than proposing a specific new block size, Bitcoin Unlimited removes the hard-coded limit entirely, allowing individual node operators to set their own preferences. The theory, rooted in game theory’s concept of a Schelling point, suggests that the network would naturally converge on an optimal block size without central coordination.
Dr. Peter R. Rizun, a prominent voice in the block size increase camp and aspiring managing editor of Ledger, the first peer-reviewed academic journal dedicated to cryptocurrency research, has been prominently involved with Bitcoin Unlimited. Rizun gained notoriety in the community after publishing a controversial paper claiming that a block size limit is not required to establish a functioning fee market — a direct challenge to the arguments made by small-block proponents.
In practice, Bitcoin Unlimited defaults to conservative parameters: miners create blocks at the existing 1MB limit, and the client only accepts larger blocks up to 16MB if they achieve four confirmations on the longest chain. This emergent consensus mechanism is designed to ensure that any block size increase has genuine mining support before being accepted by the broader network.
Bitcoin Classic and BitPay Core: Simpler Alternatives
While Bitcoin Unlimited pursued an experimental approach, Bitcoin Classic offered a more straightforward solution: a hard fork to increase the block size to 2MB. The proposal, championed by early Bitcoin developer Gavin Andresen through BIP 109 submitted in January 2016, represented a middle ground that many hoped could bridge the divide between the small-block and large-block camps.
Meanwhile, payment processor BitPay released its own fork of Bitcoin Core, dubbed “BitPay Core,” further fragmenting the implementation landscape. For a company that had built its business on Bitcoin transaction processing, the block size constraint was not theoretical — it directly affected BitPay’s ability to serve its merchant base efficiently.
The Shadow of Bitcoin XT’s Failure
All of these efforts unfolded in the shadow of Bitcoin XT, the first serious attempt to challenge Bitcoin Core’s consensus rules. Launched by Mike Hearn, who had since departed to join blockchain consortium R3, Bitcoin XT proposed increasing the block size from 1MB to 8MB, with the limit doubling every two years until reaching 8GB. Despite significant media attention and support from some prominent community members, Bitcoin XT failed to gain sufficient adoption among miners — the critical constituency whose support any hard fork requires.
The failure of Bitcoin XT served as both a cautionary tale and a rallying cry. For supporters of larger blocks, it demonstrated that a more gradual, consensus-driven approach might be necessary. For small-block advocates, it validated their position that the market would reject radical changes to Bitcoin’s fundamental parameters.
Why This Matters
The emergence of multiple competing Bitcoin implementations in January 2016 represented a critical stress test for decentralized governance. With bitcoin at $432 and the network still relatively small by global standards, the block size debate forced the community to confront fundamental questions about who controls Bitcoin’s evolution — developers, miners, businesses, or users. The proliferation of alternative clients demonstrated that Bitcoin Core could no longer claim uncontested authority over the protocol, setting the stage for the contentious hard forks and community splits that would define Bitcoin politics for years to come. The resolution of this governance crisis would ultimately shape the trajectory of the entire cryptocurrency industry.
Disclaimer: This article is for informational purposes only and does not constitute financial advice. Cryptocurrency markets are highly volatile. Always conduct your own research before making investment decisions.
Bitcoin Unlimited letting miners set block size via emergent consensus was the most game-theoretically sound proposal. problem was nobody could explain it to a journalist in one sentence
Bence A. emergent consensus was elegant but try explaining it to a CNBC producer who just wants to know if BTC is splitting. the PR battle was lost before the tech argument started
BIP109 was 2MB. SegWit gave 1.7MB effective weight. the entire block size war was fought over 300KB and it split the community for years
Gavin pushing BIP109 for a straight 2MB bump while Core wanted SegWit was the real split. neither side trusted the other to follow through
BIP109 proposing 2MB was so reasonable at the time. crazy that it turned into a multi year civil war over 1MB vs 2MB
blockwars_kek the 2MB proposal was the compromise and it still failed. teaches you that in governance, moderates always lose to hardliners on both sides
Bitcoin Unlimited letting each miner set their own block size limit was elegant in theory. in practice it means consensus is undefined until someone mines a block the rest reject. hello fork
BIP109 proposed 2MB and Core said no. ended up with SegWit giving 1.7MB effective weight. the difference between 1.7 and 2 was literally the cause of a multi-year civil war
miners rejecting bigger blocks because orphan rates would spike was the real economic argument. incentives aligned against on-chain scaling from day one
bitcoin unlimited letting users set their own block size was chaos in theory but honestly made more sense than a centrally planned limit
right idea at the wrong time. bandwidth and storage costs in 2016 made large blocks genuinely risky for decentralization
bandwidth argument held in 2016 but looks silly now. 8MB blocks would be trivial with todays infrastructure
Tomasz K. 8MB blocks in 2016 would have been rough on propagation. but todays nodes handle 100MB+ without breaking a sweat
8MB blocks in 2016 would have been risky. in 2026 with the hardware we have, the bandwidth argument feels almost quaint
segfault_ 8MB blocks in 2016 would have been risky for propagation but the real issue was validation cost. a quad core node would have struggled to verify 8MB blocks every 10 min
gavin andresen submitting BIP 109 for 2MB blocks. history remembers him differently now but he was a core dev who genuinely believed in scaling on chain
gavin was right about one thing. the community couldnt keep arguing forever. the fork happened anyway, just took a different form than anyone expected
the fork happened as segwit + BCH. big blockers got their chain, small blockers kept the original. both sides kinda won in the end
bitpay forking their own core client because they couldnt wait for consensus. every company wanted to be the one calling the shots
segwit + BCH was the compromise nobody wanted but everyone needed. BTC kept small blocks and big blockers got their chain. the market decided which vision won
Magda Witkowski both sides won is generous. BCH has been bleeding users since the fork and BTC layer 2 is still catching up
BIP109 wanted 2MB and Core refused. ended up with segwit which was basically a soft fork workaround. politics not engineering won that war
Aleksei P. segwit gave us 1.7MB effective block weight without a hard fork. clever but it kicked the can down the road forever
Bitcoin Unlimited letting users vote on block size was the most democratic proposal. shame it got politicized into irrelevance
Bitcoin Unlimited letting miners set their own block size was game theory masquerading as governance. in practice it meant consensus was undefined until someone mined a block others rejected
BIP109 proposed 2MB and Core refused. we got SegWit at 1.7MB effective weight instead. a multi year civil war over 300KB difference. the most expensive rounding error in crypto history