BIP-148: The User Activated Soft Fork That Changed Bitcoin Governance

BIP-148 is a Bitcoin Improvement Proposal that described a User Activated Soft Fork (UASF) mechanism to force the activation of Segregated Witness (SegWit) on Bitcoin.

Proposed in March 2017, BIP-148 mandated that nodes running the software would reject any block that didn’t signal support for SegWit after August 1, 2017.

The threat of a chain split driven by users (rather than miners) ultimately pressured miners into signaling SegWit support, establishing a powerful precedent for user sovereignty in Bitcoin governance.

BIP-148 specified that:

• Starting August 1, 2017 (block timestamp), BIP-148 nodes would reject any block that did not signal support for SegWit (BIP-141) via version bit 1
• This was a “User Activated Soft Fork” – driven by node operators and users, not miners
• The goal was to force SegWit activation after months of miner stalling.
  

Origin & History

• 2015–2016: SegWit was developed as a solution to Bitcoin’s scaling debate. It required 95% miner signaling (via BIP-9) to activate.
  
• Late 2016–Early 2017: Miner signaling for SegWit stalled at ~30%.
  
  Many miners, particularly those aligned with Bitmain, opposed SegWit — some because it would disable covert ASICBoost optimization, others because they preferred a block size increase.
  
• 2017 (March 12): Shaolin Fry (pseudonym) proposed BIP-148 — a radical approach where nodes would reject non-SegWit-signaling blocks after August 1.
  
• 2017 (April–July): The UASF movement gained momentum. The #UASF hashtag trended on crypto Twitter.
  
  Luke Dashjr and other Bitcoin Core contributors supported the approach. UASF hats became a symbol of the movement.
  
• 2017 (May 23): The New York Agreement (NYA) was signed, an industry agreement supporting SegWit followed by a block size increase.
  
  BIP-91 was the technical implementation created to fulfill the first half of that agreement.
  
• 2017 (July 23): BIP-91 locked in (SegWit signaling via a lower 80% threshold), effectively making BIP-148’s August 1 deadline moot.
  
• 2017 (August 1): SegWit was in the process of activating. Bitcoin Cash (BCH) forked off Bitcoin on this date, partly as a response to the SegWit/UASF controversy.
  
• 2017 (August 24): SegWit officially activated on Bitcoin at block 481,824.
  

In Simple Terms

1. SegWit was ready, but miners wouldn’t activate it — they needed 95% to signal support, but only ~30% did.
   
2. Users got frustrated and proposed BIP-148: Starting August 1, our nodes will reject any block that doesn’t support SegWit.
   
3. This was a power move — if enough users, exchanges, and businesses ran BIP-148 nodes, miners who didn’t signal SegWit would be mining on a worthless chain.
   
4. The threat worked — miners agreed to signal SegWit (via a compromise called BIP-91) before the August 1 deadline, and SegWit activated without a chain split.
   

Important: BIP-148 established a fundamental governance precedent in Bitcoin: users — not miners — are the ultimate authority over protocol rules.

While miners provide hash power, the economic majority (exchanges, businesses, users) decides which chain has value.

This principle, sometimes called “economic node governance,” remains central to Bitcoin’s political philosophy.

Real-World Examples

Example 1: The UASF Movement

• Scenario: SegWit activation had been stalled for over a year, with miners seemingly blocking a widely supported upgrade.
  
• Implementation: Developers, users, and businesses rallied behind BIP-148. The movement organized via social media, with #UASF trending globally. UASF hats (parodying “MAGA” hats with the Bitcoin logo) became iconic.
  
• Outcome: The grassroots movement demonstrated that users could coordinate to override miner obstruction, fundamentally changing the perceived power dynamics in Bitcoin governance.
  

Example 2: The BIP-91 Compromise

• Scenario: Facing the BIP-148 deadline, miners needed a face-saving way to signal SegWit without appearing to capitulate to user pressure.
  
• Implementation: Following the political New York Agreement, the technical proposal BIP-91 was created to allow SegWit activation with a lower 80% threshold, intended to satisfy the agreement’s terms while avoiding a BIP-148 chain split.
  
• Outcome: BIP-91 locked in on July 23, and SegWit activated in August. The promised block size increase (SegWit2x) was later abandoned due to lack of community support — meaning users got SegWit without the compromise.
  

Example 3: Bitcoin Cash Fork

• Scenario: Miners and developers who opposed SegWit and supported larger blocks saw BIP-148 as an aggressive user action.
  
• Implementation: On August 1, 2017 (the same date as BIP-148’s activation), Bitcoin Cash forked off from Bitcoin with 8 MB blocks and no SegWit.
  
• Outcome: Bitcoin Cash became a separate cryptocurrency, while Bitcoin continued with SegWit. The fork illustrated the ultimate consequence of irreconcilable governance disagreements.
  

Advantages

Disadvantages & Risks

Frequently Asked Questions