Testnet 4

The five-minute read

One action, walked through

1. Open BIP 94 and read the status line before the examples.
2. Write down the rule in one sentence. A fair version of that sentence is: A new test network with the goal to replace Testnet 3.
3. Name the object that changes: CPU, TBTC.
4. Ask what an old client, an old contract, or an offline counterparty does. If the document is silent, the silence is part of the design.

The argument, unpacked

What has to be true

• You are implementing BIP 94 at the status the text itself states: Deployed.
• The object that has to change is CPU, TBTC. A neighbouring document with a similar name is not this one.
• Parameter choices in one release are not the proof.

What happened after the paper

The source marks this deployed. That is a statement about the text, not a promise that every wallet or node has shipped it. Later documents can narrow, replace, or ignore this one. Cite the number you mean.

What to check before you use the idea

• What does Testnet 4 treat as decided, and what can still be reorged?
• What share of stake or hash power does the argument need?
• Which objects are defined: CPU, TBTC?

Terms

BIP 94

The public text titled Testnet 4.

Deployed

The document's own label for how finished the text is. It is not a market fact.

The problem the paper names

A consensus change that is only described in a client does not tell an outside verifier what must be true.

What the design proposes

• A new test network with the goal to replace Testnet 3.
• This network comes with small but important improvements of the consensus rules, that should make it impractical to attack the network using only CPU mining.
• Quoting the original mailing list post from Jameson Lopp https://gnusha.org/pi/bitcoindev/CADL_X_eXjbRFROuJU0b336vPVy5Q2RJvhcx64NSNPH-3fDCUfw@mail.gmail.com/ : Testnet3 has been running for 13 years.

How the mechanism is specified

• Taken from the specification, the next constraint is: This network comes with small but important improvements of the consensus rules, that should make it impractical to attack the network using only CPU mining.
• Locate CPU, TBTC in BIP 94 and apply it to one transaction or call.
• Then check the failure the class of rule always has: a node that did not upgrade, a reverted call, a replayed signature, or a peer that does not speak the message.

What this page does not treat as proven

• Final in the EIP process is not finality of a checkpoint.
• Parameter choices in one release are not the proof.
• The source marks this deployed. That is a statement about the text, not a promise that every wallet or node has shipped it.

Why a venture studio still reads it

Use BIP 94 when a pitch says 'Testnet 4' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.