Bitcoin Unlimited v0.12 "X-Relay" -:- First Official BU Release


Staff member
Aug 22, 2015
Announcing BitcoinUnlimited v0.12.0

Official BU Client Release focused on main-chain scaling, and introducing Extreme Thin Block technology "X-Relay" to Bitcoin, reducing the bandwidth required for nodes to transmit newly mined blocks by an average of 90%. For example 1 MB blocks require only 100KB being transferred.

BitcoinUnlimited v0.12.0 Highlights are:

Core v0.12.0 code-base plus:


Effective block limit via emergent network consensus
  • BUIP001 Fixed block limit made obsolete
  • BU follows the blockchain with most PoW as per the original Nakamoto Consensus
  • Separation of the mining block size (default 1MB) from the non-mining block acceptance size (default 16MB)
  • Block size limits and acceptance depth individually configurable
  • Classic block version for mining
Public notification of individual settings
  • BUIP005 User agent subversion text contains full node settings
  • Miner settings are published in coinbase transaction text
Xtreme Thinblocks
  • BUIP010 Reduces real-time block propagation sizes by an average of 90% returning the network overhead for newly mined blocks to the state it was in mid-2012.
    A 98% reduction is possible where a large mempool is available and miners are selecting recent txns.
Xpress Validation
  • BUIP010 Superfast block validation leverages the earlier validation of transactions which are in the mempool so that only previously unseen transactions in a block need full validation.
  • BUIP001 Users can easily configure how much bandwidth should be used for Bitcoin, allowing the BU client to run unobtrusively in a home network.


Replace-by-Fee [commented out]
  • BUIP004 Community vote determines that there is no consensus for a feature which undermines the 0-confirmation use-case
Alert Key [commented out]
  • BUIP013 Community vote determines that there is no consensus for privileged access to remain with a few individuals for the sending of unsolicited free-text messages to all BU full nodes.

Acknowledgements with special thanks for coding and testing:
Andrew Stone
Peter Tschipper

Download location:
Source code:
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Active Member
Nov 16, 2015
Bitcoin Unlimited is the best Bitcoin client presently available. Ahead of its time I still think, which is why Classic stands the greater chance of reaching consensus, fortunately Bitcoin Unlimited is completly compatible with all of the changes within Bitcoin Classic, it is a beautiful thing. :)


Active Member
Mar 14, 2016
Good work guys.
Do you plan to submit xtream thin blocks and xpress validation enhancements to core?
Even only to know (and document) their reaction to the pull request.


New Member
Sep 18, 2015
I compiled BU 0.12 from source a few weeks ago (March 2). Do I need to upgrade? Or is this all pretty much the same code?

edit: nm, I see I'm behind 49 commits from git, I'll pull and recompile just to be sure
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Active Member
Aug 28, 2015
@Christoph Bergmann @pinhead

source = git cloned BU repo?

to be on the safe side:

- clone BU git hub repo,
- git checkout 0.12bu (it should be the default)
- compile the source