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Date: Tue, 18 Mar 2025 14:29:35 +0000
To: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
From: "'Antoine Poinsot' via Bitcoin Development Mailing List" <bitcoindev@googlegroups.com>
Subject: [bitcoindev] Unbreaking testnet4
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Hi,

Testnet4 was rolled out a year ago to address the shortcomings of testnet3.=
 One of those shortcomings was the difficulty reset creating havoc. [0] In =
spite of this a similar rule was adopted for testnet4. [1] As a result, tes=
tnet4 is similarly creating havoc. [2]

The goal of testnet is to mimic the Bitcoin mainnet. This is why it is usef=
ul to have in addition to a more control testing environment such as Signet=
.

The given rationale for a difficulty reset was to let developers occasional=
ly mine blocks on their laptop. But you cannot have your cake and eat it to=
o: either the network is permissionless (PoW) or you assign identities and =
privileges to some (Signet). By trying to do both at the same time testnet4=
 created a loophole for abuse. As a result it failed on both count: it neit=
her mimics mainnet nor allows developers to mine active blocks on their lap=
top.

I propose to fix this by removing the difficulty reset rule from testnet4 t=
hrough a flag day hard fork on 2026-01-01. I picked a date well in the futu=
re to minimize disruption. This leaves enough time for a patch to be review=
ed, merged, included in the next major Bitcoin Core release, backported to =
previous releases and adopted by the infrastructure running on testnet4. Th=
at should be enough for a test network.

Let me know what you think,
Antoine

[0] https://gnusha.org/pi/bitcoindev/CADL_X_eXjbRFROuJU0b336vPVy5Q2RJvhcx64=
NSNPH-3fDCUfw@mail.gmail.com
[1] https://github.com/bitcoin/bips/blob/master/bip-0094.mediawiki#rule-spe=
cification
[2] [https://fork.observer](https://fork.observer/) - pick the network on t=
he top right corner

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<div style=3D"font-family: Arial, sans-serif; font-size: 14px;"><div style=
=3D"font-family: Arial, sans-serif; font-size: 14px;"><div>Hi,<br><br>Testn=
et4
 was  rolled out a year ago to address the shortcomings of testnet3. One
 of those shortcomings was the difficulty reset creating havoc. [0] In=20
spite of this a similar rule was adopted for testnet4. [1] As a result,=20
testnet4 is similarly creating havoc. [2]<br><br>The goal of testnet is=20
to mimic the Bitcoin mainnet. This is why it is useful to have in=20
addition to a more control testing environment such as Signet.<br><br>The
 given rationale for a difficulty reset was to let developers=20
occasionally mine blocks on their laptop. But you cannot have your cake=20
and eat it too: either the network is permissionless (PoW) or you assign
 identities and privileges to some (Signet). By trying to do both at the
 same time testnet4 created a loophole for abuse. As a result it failed=20
on both count: it neither mimics mainnet nor allows developers to mine=20
active blocks on their laptop.<br><br>I propose to fix this by removing=20
the difficulty reset rule from testnet4 through a flag day hard fork on=20
2026-01-01. I picked a date well in the future to minimize disruption.=20
This leaves enough time for a patch to be reviewed, merged, included in=20
the next major Bitcoin Core release, backported to previous releases and
 adopted by the infrastructure running on testnet4. That should be=20
enough for a test network.<br></div><div><br>Let me know what you think,<br=
>Antoine<br><br>[0] <span><a href=3D"https://gnusha.org/pi/bitcoindev/CADL_=
X_eXjbRFROuJU0b336vPVy5Q2RJvhcx64NSNPH-3fDCUfw@mail.gmail.com" rel=3D"noref=
errer nofollow noopener" target=3D"_blank">https://gnusha.org/pi/bitcoindev=
/CADL_X_eXjbRFROuJU0b336vPVy5Q2RJvhcx64NSNPH-3fDCUfw@mail.gmail.com</a></sp=
an><br>[1] <span><a href=3D"https://github.com/bitcoin/bips/blob/master/bip=
-0094.mediawiki#rule-specification" rel=3D"noreferrer nofollow noopener" ta=
rget=3D"_blank">https://github.com/bitcoin/bips/blob/master/bip-0094.mediaw=
iki#rule-specification</a></span><br>[2] <span><a href=3D"https://fork.obse=
rver/" rel=3D"noreferrer nofollow noopener" target=3D"_blank">https://fork.=
observer</a> - pick the network on the top right corner</span></div></div>
<div class=3D"protonmail_signature_block protonmail_signature_block-empty" =
style=3D"font-family: Arial, sans-serif; font-size: 14px;">
    <div class=3D"protonmail_signature_block-user protonmail_signature_bloc=
k-empty">
       =20
            </div>
   =20
            <div class=3D"protonmail_signature_block-proton protonmail_sign=
ature_block-empty">
       =20
            </div>
</div>
</div>

<p></p>

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