Testnet

Nobody buys these coins, because faucets give them away. The network has run since 2011 and has already been replaced once: BIP94 defined testnet4, which shipped in Bitcoin Core 28.0 in October 2024 after the older chain drifted into a state nobody could rely on. For anyone buying bitcoin, the one thing worth remembering is that a testnet transaction proves nothing about a real payment.

How it works

Status: testnet3, the version most tutorials still describe, has been superseded by testnet4, specified in BIP94 and shipped in Bitcoin Core 28.0 in October 2024. New integration work should target testnet4 or signet.

Testnet runs bitcoin's ordinary consensus rules with one large exception bolted on. If twenty minutes pass without a block, the next block may be mined at the minimum possible difficulty, so a single laptop can keep the chain moving when nobody serious is pointing hardware at it. That rule is what makes a free test network survivable, and it is also what wrecked the third version of it.

The failure mode is easy to describe. Someone with real mining hardware waits for the difficulty to fall to its floor, mines a burst of thousands of trivial blocks, and the chain lurches forward with reorganizations hundreds of blocks deep. Combined with a timewarp weakness in the retargeting arithmetic, this let miners drag testnet3's difficulty down and burn through its remaining coin issuance far faster than anyone intended, which left faucets empty and confirmation times meaningless.

Testnet4 keeps the twenty minute escape hatch but forbids it from applying to the first block of a difficulty period, and it anchors each retarget to the start of its own epoch so the timewarp trick no longer works. It also began from a fresh genesis block, so its history is short. The two versions run side by side for now on different ports, 18333 for testnet3 and 48333 for testnet4, and both use the same address prefixes: m, n, 2 and tb1.

Where you see it

Testnet is where the software you rely on gets exercised before it reaches you.

Exchange engineering teams wire up deposit and withdrawal handling here, hardware wallet firmware is tested here, and anyone building a payment integration runs their first hundred attempts here rather than on money. Faucet sites hand out coins to whoever asks, which is the clearest possible signal of what they are worth.

You are most likely to meet testnet through a scam. A convincing screenshot of a confirmed transaction means nothing if the explorer behind it was switched to a test network, and fake support agents have used exactly that trick to claim a refund was already sent. Two checks settle it: the address in a real payment to you begins with 1, 3 or bc1, and the explorer URL should not contain the word testnet. If someone offers to sell you testnet coins, there is nothing to buy.

Testnet vs signet

Testnet is mined by whoever shows up, so its block schedule is chaotic; signet blocks are only valid if a named operator signs them, so its schedule is not. That single difference is why signet has largely taken over serious testing. Testnet still answers one question signet cannot, which is how software behaves when mining itself misbehaves, but if you want a test network that resembles mainnet on an ordinary day, signet is the closer match.