Bitcoin Has Changed More Than You Think: What Forks Mean for BTC’s Security and “Original” Bitcoin

A renewed dispute among prominent Bitcoin voices has reopened a question that has followed the network since its major 2017 splits. The argument is not whether the protocol changed. Several upgrades have altered transaction handling, scripting, and validation without replacing its mining algorithm.

Instead, the dispute concerns which changes preserve Bitcoin’s identity and which create separate chains with different security assumptions. Mr. Hodl challenged claims that 2017-era UTXO forks all retained the original network’s SHA-256 mining system.

He said Bitcoin Cash and Bitcoin SV kept SHA256d, while several other derived networks adopted different proof-of-work algorithms. That distinction matters as mining rules determine which hardware can secure blocks and whether a new chain competes directly for the same miners.

Bitcoin Kept SHA256d While Consensus Rules Evolved

The main network still uses double SHA-256, or SHA256d, to hash 80-byte block headers during proof-of-work mining. However, retaining that system did not mean the protocol remained frozen.

Segregated Witness, or SegWit, activated in August 2017 and changed how transaction witness data was handled under consensus rules. The upgrade also addressed transaction malleability, increased effective block capacity, and provided a stronger technical foundation for systems such as the Lightning Network.

Taproot later expanded scripting and signature capabilities while remaining backward compatible through a soft fork. Bitcoin Core 0.21.1 included Taproot activation logic before the upgrade became active in 2021.

Those changes separate two ideas that are often treated as identical. The mining algorithm stayed largely intact, while transaction and scripting rules continued evolving around it.

2017 Bitcoin Forks Split Across Different Mining Algorithms

That distinction became especially important after the 2017 split. Bitcoin Cash separated at block 478,558 on August 1, 2017, following disagreements over scaling and block capacity. Although BCH introduced incompatible consensus rules, it retained Bitcoin’s double-SHA256 mining system.

Bitcoin SV later split from Bitcoin Cash and also continued using SHA256d for block production. However, other Bitcoin-derived networks took a more radical path. Their choices changed not only the mining process but also the hardware base and security environment inherited from the original chain.

Bitcoin Gold, for example, adopted Equihash as part of an ASIC-resistant design, which changed the type of hardware best suited to securing the network. Bitcoin Diamond switched to X13, while Bitcoin Private also relied on Equihash-related mining software.

Those changes reduced direct competition for SHA-256 hardware, but they also moved those projects away from the established mining ecosystem supporting $BTC security.

Why Economic Consensus Decides Which Chain Is Bitcoin

While consensus software determines whether blocks and transactions are valid, it cannot independently decide which incompatible chain should retain the Bitcoin name. Within a single ruleset, nodes enforce validity, while accumulated proof of work helps participants converge on the accepted blockchain.

Once competing networks adopt different rules, however, that decision extends beyond mining power alone. Instead, users, miners, developers, exchanges, wallets, businesses, and node operators collectively influence which version receives broader economic recognition.

That distinction has become relevant again amid debate over BIP-110, a proposed temporary soft fork designed to restrict certain forms of arbitrary transaction data. Importantly, the BIP process makes clear that publishing a proposal does not establish community consensus, since adoption ultimately depends on Bitcoin users.

Against that backdrop, Adam Back has argued that groups supporting contentious rule changes can separate into another chain rather than redefine the economically dominant network. His argument reinforces the broader point that technical rules can create a fork, but economic consensus ultimately determines which chain retains Bitcoin’s dominant identity.

“Original” Bitcoin Means More Than Unchanged Code

The history of these forks shows that a chain can preserve SHA256d while changing other consensus rules. It also shows that the main network can adopt meaningful upgrades without abandoning the proof-of-work mechanism underpinning $BTC security.

“Original Bitcoin,” therefore, is not defined by completely unchanged code or miner preference alone. Its identity combines compatible consensus rules, accumulated proof of work, and the economic network choosing which rules it will enforce.

The practical conclusion is clear from the record. Bitcoin has changed, but its dominant chain kept the mining system central to $BTC security while allowing other consensus features to evolve.