Repository: bitcoin/bitcoin
File: src/kernel/chainparams.cpp (C++)

Code before:
        consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].bit = 2;
        consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nStartTime = Consensus::BIP9Deployment::ALWAYS_ACTIVE;
        consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nTimeout = Consensus::BIP9Deployment::NO_TIMEOUT;
        consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].min_activation_height = 0; // No activation delay

        consensus.nMinimumChainWork = uint256{};
        consensus.defaultAssumeValid = uint256{};

        pchMessageStart[0] = 0x1c;
        pchMessageStart[1] = 0x16;
        pchMessageStart[2] = 0x3f;
        pchMessageStart[3] = 0x28;
        nDefaultPort = 48333;
        nPruneAfterHeight = 1000;
        m_assumed_blockchain_size = 0;
        m_assumed_chain_state_size = 0;

        genesis = CreateGenesisBlock(1711910298, 2215745201, 0x1d00ffff, 1, 50 * COIN);
        consensus.hashGenesisBlock = genesis.GetHash();
        assert(consensus.hashGenesisBlock == uint256S("0x000000008d6faa98083fa55742aa82d4ed249bd1bfc3239c706e0a61ef9e3931"));
        assert(genesis.hashMerkleRoot == uint256S("0x4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b"));

        vFixedSeeds.clear();
        vSeeds.clear();
        // nodes with support for servicebits filtering should be at the top
        // TODO: Add Testnet4 seeds

        base58Prefixes[PUBKEY_ADDRESS] = std::vector<unsigned char>(1,111);
        base58Prefixes[SCRIPT_ADDRESS] = std::vector<unsigned char>(1,196);
        base58Prefixes[SECRET_KEY] =     std::vector<unsigned char>(1,239);
        base58Prefixes[EXT_PUBLIC_KEY] = {0x04, 0x35, 0x87, 0xCF};
        base58Prefixes[EXT_SECRET_KEY] = {0x04, 0x35, 0x83, 0x94};

        bech32_hrp = "tb";

        vFixedSeeds = std::vector<uint8_t>(std::begin(chainparams_seed_test), std::end(chainparams_seed_test));

        fDefaultConsistencyChecks = false;
        m_is_mockable_chain = false;

        checkpointData = {
            {
                {},
            }
        };

        m_assumeutxo_data = {
            {}
        };

        chainTxData = ChainTxData{

Review comment (suggestion):
4e8b29ae234a05181ff9fd64ab3a74ba997e2eac: you can add `seed.testnet4.bitcoin.sprovoost.nl` here. I'll update it if the magic bytes change.

Code after:
        consensus.MinBIP9WarningHeight = 0;
        consensus.powLimit = uint256S("00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
        consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks
        consensus.nPowTargetSpacing = 10 * 60;
        consensus.fPowAllowMinDifficultyBlocks = true;
        consensus.enforce_BIP94 = true;
        consensus.fPowNoRetargeting = false;
        consensus.nRuleChangeActivationThreshold = 1512; // 75% for testchains
        consensus.nMinerConfirmationWindow = 2016; // nPowTargetTimespan / nPowTargetSpacing
        consensus.vDeployments[Consensus::DEPLOYMENT_TESTDUMMY].bit = 28;
        consensus.vDeployments[Consensus::DEPLOYMENT_TESTDUMMY].nStartTime = Consensus::BIP9Deployment::NEVER_ACTIVE;
        consensus.vDeployments[Consensus::DEPLOYMENT_TESTDUMMY].nTimeout = Consensus::BIP9Deployment::NO_TIMEOUT;
        consensus.vDeployments[Consensus::DEPLOYMENT_TESTDUMMY].min_activation_height = 0; // No activation delay

        // Deployment of Taproot (BIPs 340-342)
        consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].bit = 2;
        consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nStartTime = Consensus::BIP9Deployment::ALWAYS_ACTIVE;
        consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nTimeout = Consensus::BIP9Deployment::NO_TIMEOUT;
        consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].min_activation_height = 0; // No activation delay

        consensus.nMinimumChainWork = uint256{};
        consensus.defaultAssumeValid = uint256{};

        pchMessageStart[0] = 0x1c;
        pchMessageStart[1] = 0x16;
        pchMessageStart[2] = 0x3f;
        pchMessageStart[3] = 0x28;
        nDefaultPort = 48333;
        nPruneAfterHeight = 1000;
        m_assumed_blockchain_size = 0;
        m_assumed_chain_state_size = 0;

        const char* testnet4_genesis_msg = "03/May/2024 000000000000000000001ebd58c244970b3aa9d783bb001011fbe8ea8e98e00e";
        const CScript testnet4_genesis_script = CScript() << ParseHex("000000000000000000000000000000000000000000000000000000000000000000") << OP_CHECKSIG;
        genesis = CreateGenesisBlock(testnet4_genesis_msg,
                testnet4_genesis_script,
                1714777860,
                393743547,
                0x1d00ffff,
                1,
                50 * COIN);
        consensus.hashGenesisBlock = genesis.GetHash();
        assert(consensus.hashGenesisBlock == uint256S("0x00000000da84f2bafbbc53dee25a72ae507ff4914b867c565be350b0da8bf043"));
        assert(genesis.hashMerkleRoot == uint256S("0x7aa0a7ae1e223414cb807e40cd57e667b718e42aaf9306db9102fe28912b7b4e"));

        vFixedSeeds.clear();
        vSeeds.clear();
        // nodes with support for servicebits filtering should be at the top
        vSeeds.emplace_back("seed.testnet4.bitcoin.sprovoost.nl."); // Sjors Provoost
        vSeeds.emplace_back("seed.testnet4.wiz.biz."); // Jason Maurice