Mainnet

Every other Bitcoin network exists to rehearse for this one. Mainnet is identified by four magic bytes, f9beb4d9, at the front of every message its nodes exchange, and by default port 8333, so software tuned to a test network cannot even read its traffic. When an exchange, a spot ETF, or your hardware wallet says bitcoin, it means a mainnet coin and nothing else.

How it works

Mainnet is defined by three things: a fixed starting point, a set of consensus rules, and a network identity.

The starting point is the genesis block, whose timestamp of 1231006505 corresponds to January 3, 2009. Its hash is compiled into every implementation, so a node that disagrees about it is not on bitcoin at all. The rules are the ones people usually mean by bitcoin: a ceiling of 21 million coins, a subsidy that halves every 210,000 blocks and last dropped to 3.125 BTC at block 840,000 on April 20, 2024, and a difficulty retarget that keeps blocks arriving roughly every ten minutes.

The network identity is what stops the chains mixing. Each network prefixes its peer-to-peer messages with its own four byte start string and listens on its own default port, so a mainnet node and a test node simply cannot hold a conversation. Address encodings differ too: mainnet uses 1, 3, bc1q and bc1p, while the test networks use m, n, 2, tb1 and bcrt1. Derivation paths carry the same split, because SLIP-0044 assigns coin type 0 to mainnet and coin type 1 to every test network, which means one recovery phrase produces completely different addresses depending on which network your wallet believes it is on.

Where you see it

The word mainnet appears in software that also offers something else.

Bitcoin Core, Electrum, and Sparrow all have a network selector, and a block explorer usually has a chain switch near the search box. If a wallet you installed to hold real coins is showing addresses beginning tb1 or bcrt1, it is not on mainnet and anything it displays as a balance is play money.

The costly confusion is not with test networks, though. It is with other chains that borrow the bitcoin name. Exchange withdrawal screens ask you to choose a network before you enter an address, and the menu can include wrapped bitcoin on Ethereum, a BEP20 version on BNB Chain, and Lightning alongside the plain on-chain option. Only the entry labelled Bitcoin or BTC sends a real mainnet coin to a real bitcoin address. Pick a wrapped variant and the exchange will happily send a token on somebody else's ledger to an address your bitcoin wallet has no keys for, and there is no undo. Check the network field on every withdrawal before the amount field, and use the withdrawal fee figures in our exchange reviews to sanity check what you are being charged for the correct one.

Mainnet vs testnet

Mainnet coins are scarce and priced by markets; testnet coins are handed out free by faucets and have no market to speak of. The protocol keeps them apart at the encoding level, so a mainnet wallet will reject a testnet address outright rather than send to it, which is one of the few footguns bitcoin genuinely removes for you. The real risk runs the other way: treating a transaction you made on a test network as evidence that a payment worked. It proves the software ran, nothing more.