On November 15, 2016, Bitcoin reached a pivotal moment in its technical evolution as miners officially began signaling for Segregated Witness (SegWit), the most significant protocol upgrade since Bitcoin’s inception. The activation window opened following the release of Bitcoin Core version 0.13.1, which formally introduced SegWit code into the reference client, setting the stage for a transformation that would reshape the network’s capacity and capabilities.
TL;DR
- SegWit signaling window opened on November 15, 2016, via Bitcoin Core 0.13.1
- 95% miner approval required across a 2,016-block retarget period for activation
- ViaBTC, controlling roughly 9% of network hash power, opposed the upgrade
- SegWit promised ~70% transaction capacity increase and a fix for transaction malleability
- The upgrade represented nearly 5,000 lines of code developed over almost a year
The Road to SegWit Signaling
Segregated Witness was first proposed by Bitcoin Core and Blockstream developer Dr. Pieter Wuille at the Scaling Bitcoin conference in Hong Kong in December 2015. Wuille began coding the solution in November 2015, collaborating with Eric Lombrozo, Johnson Lau, and several other Bitcoin Core contributors. The result was approximately 5,000 lines of code that fundamentally restructured how Bitcoin transactions are validated.
The upgrade went through rigorous testing, including three dedicated SegWit test networks and successful deployment on Bitcoin’s main testnet by May 2016. Compact blocks were also developed and integrated into Bitcoin Core 0.13.0 to mitigate latency and bandwidth concerns ahead of the rollout.
What SegWit Actually Does
At its core, SegWit separates digital signature data from the core transaction data in Bitcoin blocks. This seemingly technical change carries profound implications. By moving signature data outside the base transaction structure, SegWit effectively increases the block size limit without requiring a hard fork. Estimates based on typical transaction patterns suggested the network could support roughly 70% more transactions if all wallets adopted SegWit addresses.
Beyond raw capacity, the upgrade eliminates transaction malleability — a long-standing issue that complicated wallet development and made certain smart contract constructions unreliable on Bitcoin. Eric Lombrozo, Co-CEO of Ciphrex and a key SegWit contributor, described it as “the biggest extension of the protocol to date” in comments to Bitcoin Magazine.
The 95% Threshold Challenge
Under BIP9 activation rules, SegWit required at least 95% of blocks mined during any single 2,016-block difficulty period (approximately two weeks) to signal support. This supermajority threshold was deliberately set high to ensure broad consensus before enforcing new protocol rules.
Signaling began on November 15, meaning the earliest possible activation would come in mid-December 2016. However, the path was not without obstacles. ViaBTC, a relatively new but growing Chinese mining pool controlling approximately 9% of network hash power, publicly stated it would not signal support for SegWit. Given that even a single pool controlling more than 5% of hash power could theoretically block activation, ViaBTC’s opposition introduced genuine uncertainty into the timeline.
A Network at a Crossroads
The SegWit signaling launch coincided with Bitcoin trading at approximately $711, according to CoinMarketCap data from November 15. The broader cryptocurrency market showed Bitcoin with a market capitalization of $11.38 billion, Ethereum at $10.22 with a market cap of $878 million, and Litecoin at $3.89. The total market reflected a maturing ecosystem where technical governance decisions carried significant financial implications.
The debate over SegWit also highlighted a deeper tension within the Bitcoin community between different visions for scaling. While Bitcoin Core’s roadmap prioritized SegWit and layer-two solutions like the Lightning Network, alternative implementations like Bitcoin Unlimited gained support among some miners who preferred a simpler block size increase. This divergence would ultimately lead to the creation of Bitcoin Cash in August 2017, but in November 2016, the community was watching the signaling period with bated breath.
Why This Matters
November 15, 2016 marked the beginning of one of Bitcoin’s most consequential governance experiments. The SegWit activation process tested whether the network could coordinate a major technical upgrade through voluntary miner signaling, rather than centralized decree. The outcome would determine not just Bitcoin’s transaction capacity, but its trajectory as a platform for increasingly sophisticated financial applications. Though full activation would take months longer than the most optimistic projections — eventually activating in August 2017 — the signaling window that opened this day set in motion changes that continue to shape Bitcoin’s technical landscape.
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.