I just read about Bitcoin Core and Bitcoin-XT, and I want to know what is the difference between Bitcoin Core and Bitcoin-XT?

And which is better Bitcoin Core or Bitcoin-XT?

2 Answers 2


The two pieces of software, Bitcoin Core and Bitcoin-XT, are very similar. Bitcoin-XT is actually just a fork of Bitcoin Core with some features added that Bitcoin Core developers didn't deem appropriate, such as a larger block size (BIP 101) and relaying of double spends.

Bitcoin Core is more up-to-date with all of the work that the community doing. Additionally, Bitcoin-XT now has a different consensus protocol regarding the maximum size of blocks. There has been much debate within the bitcoin community about if/how/when to increase the artificially imposed block size limit (of 1 MB), and one attempt to resolve this debate is being done through Bitcoin-XT.

The Bitcoin-XT README.md has these notes on how it is different than Bitcoin Core:

  1. Support for larger blocks. XT has support for BIP 101 by Gavin Andresen, which schedules an increase from the one megabyte limit Bitcoin is now hitting.

  2. Relaying of double spends. Bitcoin Core will simply drop unconfirmed transactions that double spend other unconfirmed transactions, forcing merchants who want to know about them to connect to thousands of nodes in the hope of spotting them. This is unreliable, wastes resources and isn't feasible on mobile devices. Bitcoin XT incorporates work by Tom Harding and Gavin Andresen that relays the first observed double spend of a transaction. Additionally, it will highlight it in red in the user interface. Other wallets also have the opportunity to use the new information to alert the user that there is a fraud attempt against them.

  3. Support for querying the UTXO set given an outpoint. This is useful for apps that use partial transactions, such as the Lighthouse crowdfunding app. The feature allows a client to check that a partial SIGHASH_ANYONECANPAY transaction is correctly signed and by querying multiple nodes, build up some confidence that the output is not already spent.

  4. DNS seed changes: bitseed.xf2.org is removed as it no longer works, and seeds from Addy Yeow and Mike Hearn are (re)added to increase seed diversity and redundancy.

So, if you support these changes and/or the possible future changes on the consensus-block-size-limit, run Bitcoin-XT. The releases are available here: https://github.com/bitcoinxt/bitcoinxt/releases

  • 1
    Seems that Satoshi Nakamoto - or someone claiming to be Satoshi - is in deeply disagreement with the XT fork lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-August/…
    – Gui Ambros
    Aug 15, 2015 at 20:56
  • 8
    I highly doubt that email is from the real Satoshi Nakamoto. No PGP signature, and it honestly doesn't sound much like his other writings. Sounds more like a dump of the arguments others have already made. I think if Satoshi did give a response, it would include something more original.
    – morsecoder
    Aug 16, 2015 at 3:29
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    Down-voters of a perfectly unbiased answer like this are users who would rather information like this be censored away from the public. To that down-voter, you are not fully grasping the most fundamental principle that Bitcoin is built upon: decentralization.
    – morsecoder
    Aug 17, 2015 at 19:38
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    in my opinion Bitcoin is a protocol. if you create a protocol with different rules (such that it accepts different block sizes) then you're using a slightly different version of the protocol and therefore are not really using Bitcoin. it's like saying, "if you want to see my website correctly you have to download this slightly different web-browser that renders JSON instead of HTML". sure you can do that, but you're not really using the web then. you're using another web that renders JSON instead of HTML. Aug 17, 2015 at 21:37
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    @LucaMatteis, it's fine to take that point of view, but it's all besides the point, with respect to my previous comment. Just because you personally don't support a 'Bitcoin' that has larger block sizes doesn't mean this information shouldn't be available to those that do.
    – morsecoder
    Aug 17, 2015 at 22:06

Core. Bram Cohen has a good writeup on medium

The upcoming ‘crisis’ which is being used as a justification for a hard fork is something which it’s easy to convince people who aren’t very familiar with the technology will be a disaster. There’s a hard limit on the rate which transactions can happen, about five per second, and the transaction rate in bitcoin has been approaching that over time. We’re going to hit a wall! The sky is falling!

So what happens when that limit is reached?

Transaction fees go up.

Literally, that’s all that happens. That’s the big ‘crisis’. What’s being claimed is: Transaction fees might go above two cents! The sky is falling! I am not exaggerating.


Raising the block size limit is the idea of Gavin Andresen, former Bitcoin lead developer, who initially went around to core developers and players in the Bitcoin ecosystem trying to convince them that it should be done. The core developers had reactions ranging from neutral to vitriolically against it. Rather than accept this strongly negative reaction as a sign that his idea is a bad one, or attempting to work on some kind of compromise proposal, Gavin’s now blaming the arguing on a lack of benevolent dictator or clear voting process. There are several obvious problems with this. In projects which have a real Benevolent Dictator For Life, that person was the one who created the project. Gavin didn’t invent Bitcoin. He isn’t even a Bitcoin developer any more. He resigned his position as lead developer a year ago, and has been largely inactive since. Using a voting process, or even a system of rough consensus among core developers would cause his proposal to be quickly rejected. It’s only the exertion of outside political force which has forced it to be taken seriously.

  • 6
    This is a political statement which doesn't answer the question.
    – morsecoder
    Jun 22, 2015 at 17:08
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    But I'll bite. What's more central to the value proposition of bitcoin? An artificial consensus limit of 1 MB that pretty much everyone agrees will need to be removed eventually, or bitcoin as a low-cost payment rails? Fees will go up, sure, but the fact that that happens means that other transactions with lower fees are being pushed out. This means that if we leave the 1 MB limit in place, then for many users, bitcoin simply won't work, or will be too expensive. Such a scenario is not good for bitcoin adoption.
    – morsecoder
    Jun 22, 2015 at 20:37
  • @StephenM347 I disagree - this is kind of a "vi or emacs" question where neither is objectively better. I agree with the other points.
    – Nick ODell
    Jun 23, 2015 at 2:41
  • Gavin is not a problem, miner's greed is a real problem. If XT will erase miners ability to ask more comissions and keep block size limit enough then I will support XT
    – qpaycm
    Jun 25, 2015 at 14:42
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    @user568021 Not necessarily. If everyone sends transactions at the same rate as before, even if the cost goes up a little bit, the cost will have to go way up. The fee will have to go up enough that enough people quit sending transactions to keep the block size at 1MB.
    – BenjiWiebe
    Aug 30, 2015 at 1:59

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