<p>Bitcoin XT versions 0.11A through 0.11D supported the withdrawn BIP101, which set version = 0x20000007 as a best-guess nod toward the developing versionbits standard, while trying to maximize backward compatibility with the ways nodes might check for compatible versions.</p>

<p>Bitcoin XT version 0.11E supports BIP109, identical to Bitcoin Classic.</p>

CC BY-SA 3.0
2016-04-14T16:49:30.560Z
"best-guess nod toward the developing versionbits standard" -- that's what I'm curious about. What were they thinking?
pinhead
CC BY-SA 3.0
2016-04-14T16:42:01.843Z
2016-04-14T16:42:01.843Z
Tom Harding
<p>I understand the BIP9 version bits base is <code>0x20000000</code> because the BIP specifies that the first three bits must be <code>001</code></p>

<p>Bitcoin Classic adds one more "on" bit <code>0011...</code> to make <code>0x30000000</code></p>

<p>Why did BitcoinXT add THREE bits to the end to make <code>0x20000007</code> instead of just flagging-on one single bit like classic? Or simply use <code>0x20000001</code>?</p>

CC BY-SA 3.0
2016-04-14T16:46:07.723Z
A correction is needed to the question.  BIP9 specifies the first three bits are ``001``, so the hex version will be at least ``0x20000000``.  BIP109 uses the fourth bit to signal support, so the first four bits are ``0011`` with the rest zero, so the version is ``0x30000000`.
Tom Harding
CC BY-SA 3.0
2016-04-14T16:49:04.653Z
@TomHarding thanks for catching that, edited
pinhead
<bitcoin-xt><bitcoin-classic><bip9-version-bits>
Version bits: Why did BitcoinXT choose to set THREE bits to 1 (0x20000007) to flag BIP101?
pinhead
# Version bits: Why did BitcoinXT choose to set THREE bits to 1 (0x20000007) to flag BIP101?

(Asked by: username_0 on 2016-04-13)

I understand the BIP9 version bits base is `0x20000000` because the BIP specifies that the first three bits must be `001`

Bitcoin Classic adds one more "on" bit `0011...` to make `0x30000000`

Why did BitcoinXT add THREE bits to the end to make `0x20000007` instead of just flagging-on one single bit like classic? Or simply use `0x20000001`?

**Tags:** bitcoin-xt, bitcoin-classic, bip9-version-bits

> **Comments:**
> **username_1**: A correction is needed to the question.  BIP9 specifies the first three bits are ``001``, so the hex version will be at least ``0x20000000``.  BIP109 uses the fourth bit to signal support, so the first four bits are ``0011`` with the rest zero, so the version is ``0x30000000`.  
> **username_0**: @username_1 thanks for catching that, edited  

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## 1 answers

### Answer by username_1 on 2016-04-14. Score: 2

Bitcoin XT versions 0.11A through 0.11D supported the withdrawn BIP101, which set version = 0x20000007 as a best-guess nod toward the developing versionbits standard, while trying to maximize backward compatibility with the ways nodes might check for compatible versions.

Bitcoin XT version 0.11E supports BIP109, identical to Bitcoin Classic.

> **Comments:**
> **username_0**: "best-guess nod toward the developing versionbits standard" -- that's what I'm curious about. What were they thinking?  

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