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From: Sjors Provoost <sjors@sprovoost.nl>
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Subject: [bitcoindev] Does anyone still need testnet3?
Message-Id: <9FAA7EEC-BD22-491E-B21B-732AEA15F556@sprovoost.nl>
Date: Fri, 14 Mar 2025 09:52:10 +0100
To: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
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Dear list,

Testnet 4 was proposed last year in BIP94 [0] and is supported by Bitcoin C=
ore since v28.

To make Bitcoin Core easier to maintain we would like to drop support for T=
estnet3 in a future release. This will happen no earlier than v30 this fall=
. The upcoming v29 release still supports it, and will throughout its maint=
enance period [1].

The network itself can't be deleted, so anyone willing to maintain node sof=
tware themselves can keep using testnet3 until the end of time.

One of the motivations for introducing testnet4 was that testnet3 became in=
creasing impractical to use due to block storms. So perhaps everyone alread=
y moved on to using testnet4 or a signet.

As an aside, it's possible to create a pure proof-of-work permissionless si=
gnet without any signatures, by setting the challenge to OP_TRUE. [2]

However, if anyone is still using testnet3 and needs more time to move away=
 from it, please let us know. E.g. as a reply to the list or a comment on t=
he Github issue [3]. This could include libraries, staging environments, te=
stnet wallets, etc.

Although the v29 maintenance window will last for a few years, it's also im=
portant to know if dropping testnet3 would prevent you from upgrading to th=
e next major node version. In other words, if migrating away from testnet3 =
would take you longer than all of 2025.

Although "I don't feel like it" isn't a great technical argument, it's stil=
l useful to know what to expect and perhaps others can help.

- Sjors

[0] https://github.com/bitcoin/bips/blob/master/bip-0094.mediawiki
[1] https://bitcoincore.org/en/lifecycle/#maintenance-period
[2] https://github.com/bitcoin/bips/blob/master/bip-0325.mediawiki#specific=
ation
[3] https://github.com/bitcoin/bitcoin/issues/31975

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