Wiki / Events / UASF (BIP-148)

UASF (BIP-148)

From the Bitcoin Takeover Wiki · ✓ 6 sources · 2 podcast anchors · built 2026-11-13

The 2017 user-activated soft fork that threatened to reject non-SegWit-signalling blocks from 1 August 2017.

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The wiki's angle: the UASF was the small-block side's chain-split threat, the mirror image of the big-block side's hard-fork threats. Whether it forced SegWit or merely coincided with BIP-91 is still argued; this wiki records both mechanisms and the dates.[4][1][3]

Contents

  1. The rule
  2. Advocacy
  3. BIP-91 and the outcome
  4. Heard on Bitcoin Takeover
  5. References

The rule

BIP-148 specified a flag-day soft fork: between midnight 1 August 2017 (median time past 1501545600) and midnight 15 November 2017, every block must signal the existing SegWit deployment bit, and blocks that did not would be rejected[1]. It would only take effect if SegWit was not already locked in by 1 August, and would cease once SegWit locked in[1]. The BIP's author is Shaolin Fry[1].

Advocacy

Fork Wars links Luke Dashjr's guide “How you can help ensure BIP148 is a success” as his stance for this phase[2].

BIP-91 and the outcome

BIP-91, from James Hilliard, let miners lock in mandatory SegWit signalling with 269 of 336 blocks signalling bit 4, the bit named in the New York Agreement[3]. Bitcoin Takeover's soft-fork table records SegWit as “pushed over the line by BIP91 and BIP148”, locking in from block 479,808 and activating at 481,824[4]. The same table classes BIP-148 as an activation tactic rather than a new feature[4].

Heard on Bitcoin Takeover

On S15 E50 (August 2024), Murch said: “The UASF code was never run in the sense that it enforced anything. The miners saw the UASF and they activated SegWit before the date that the UASF would have activated.”[5]

Pete Rizzo framed it more broadly on S15 E39 (May 2024): “it's the economic majority that determines forks”.[6]

References

  1. primaryBIP-148 (Mandatory activation of segwit deployment), Shaolin Fry [archived]
  2. btkFork Wars: the block size war timeline (Bitcoin Takeover) [archived]
  3. primaryBIP-91 (Reduced threshold Segwit MASF) [archived]
  4. btkBitcoin: All the Hard Forks and Soft Forks (BTCTKVR: Forks!) [archived]
  5. episodeS15 E50: Murch on what the UASF did▶ listen at 1:36:12timestamp transcript-derived, pending a listen [archived]
  6. episodeS15 E39: Pete Rizzo on the economic majority▶ listen at 55:49timestamp transcript-derived, pending a listen [archived]

Related

Segregated Witness
The 2017 soft fork that moved signatures out of the legacy block, fixed malleability and became the centre of
New York Agreement
The May 2017 industry deal to activate SegWit at 80% and hard fork to 2 MB within six months, which became Seg
Luke Dashjr
Bitcoin Knots maintainer; central figure of BIP-110 and the 2026 BLAKE2b fork.
Hard fork vs soft fork
The two ways to change Bitcoin's rules: soft forks tighten them and stay backward-compatible; hard forks loose
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