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,
testnet4 is similarly creating havoc. [2]
The goal of testnet is
to mimic the Bitcoin mainnet. This is why it is useful to have in
addition to a more control testing environment such as Signet.
The
given rationale for a difficulty reset was to let developers
occasionally mine blocks on their laptop. But you cannot have your cake
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
on both count: it neither mimics mainnet nor allows developers to mine
active blocks on their laptop.
I propose to fix this by removing
the difficulty reset rule from testnet4 through a flag day hard fork on
2026-01-01. I picked a date well in the future to minimize disruption.
This leaves enough time for a patch to be reviewed, merged, included in
the next major Bitcoin Core release, backported to previous releases and
adopted by the infrastructure running on testnet4. That should be
enough for a test network.