Bitcoin Testing Signet

signet

A test network where blocks are signed by a fixed key (or set of keys) rather than mined competitively. Replaces testnet for many purposes.

Default signet

Bitcoin Core ships with a default signet (-signet). Block challenge is signetchallenge=... provided in config.

bitcoind -signet -daemon

10-minute block target, similar to mainnet.

Custom signet

You can run your own signet with custom challenge:

[signet]
signetchallenge=<output_script>
addnode=<your-seed-node>:38333

Block-signing key holders produce blocks; everyone else validates.

Mutinynet

A custom signet by MutinyWallet team:

• 30-second block target (vs default's 10 min).
• Useful for fast Lightning testing.
• Fast feedback loop for protocol experimentation.

[signet]
signetchallenge=512102f7561d208dd9ae99bf497273e16f389bdbd6c4742ddb8e6b216e64fa2928ad8f51ae
addnode=45.79.52.207:38333

(Example — check current Mutinynet docs for current challenge.)

Use cases

• Lightning protocol testing with realistic block delays.
• Multi-party experiments without mainnet fees.
• Wallet integration testing more public-like than regtest.
• Mutinynet specifically for fast LN iteration.

Testnet3 vs testnet4

The "testnet" that signet is usually compared against has two incarnations. Testnet3 (genesis February 2011) was deprecated in Core 28.0 (Oct 2024), which is the release that shipped testnet4. As of Bitcoin Core 31.1 (July 2026) testnet3 is still there, but -testnet is documented as "Support for testnet3 is deprecated and will be removed in an upcoming release" and the node logs the same warning at startup. Two removal PRs (#31974, #35779) were opened and closed unmerged; the "when to drop testnet3" tracking issue (#31975) is still open as of September 2026. Assume testnet3 works today and plan to migrate.

Testnet4 is specified in BIP94 (Fabian Jahr; status "Deployed" as of September 2026) and selected with -testnet4 / a [testnet4] config section. It keeps mainnet consensus rules — every soft fork through taproot enforced from block 1 — plus three testnet-specific rules:

1. The 20-minute minimum-difficulty exception is preserved, but the first block of each difficulty period must use the real difficulty.
2. Retargeting takes its base difficulty from the first block of the previous period, not the last. This is the block-storm fix: on testnet3 a min-difficulty last block pinned the next period's difficulty to 1-4, so years of blocks could be mined in weeks.
3. Time-warp prevention: the first block of a period must have nTime >= previous block's nTime - 600.

Network parameters: message start 0x1c163f28, p2p port 48333, RPC port 48332, datadir subdirectory testnet4, genesis timestamped 03/May/2024 ... hashing to 00000000da84f2bafbbc53dee25a72ae507ff4914b867c565be350b0da8bf043. The bech32 HRP is tb, shared with testnet3 and signet — addresses are indistinguishable across the three, coins are not interchangeable. Tip height was about 152,500 in September 2026.

bitcoind -testnet4 -daemon

Compared

Faucets

• Default signet: signet.bublina.eu.org/faucet, others.
• Mutinynet: faucet.mutinynet.com.
• Testnet3: cycling faucets, often empty.
• Testnet4: coinfaucet.eu/en/btc-testnet4/ (live September 2026).

See also

• regtest/SKILL.md
• testnet/SKILL.md
• polar/SKILL.md
• ../core/operations/SKILL.md