What is a testnet?

A testnet is a separate version of a blockchain built for testing. It runs similar software to the real network, but its coins are meant to be worthless, so developers can try out apps, wallets and upgrades without risking money. The real network that holds value is called mainnet.

What is the difference between mainnet and testnet?

Mainnet is the live network where transactions involve real value. When an exchange quotes the price of ETH, it means mainnet ETH. A testnet is a rehearsal space.

The two networks are kept apart. According to ethereum.org, the same account address can exist on both, but balances and history do not carry over. It also advises against reusing the same accounts across mainnet and testnets.

Testnets also tend to be run differently. Many Ethereum testnets use a small, approved group of validators instead of an open set, which keeps them stable for developers.

What is Sepolia?

Sepolia is the default Ethereum testnet for building apps, as of October 2026. Its validators are run by client and testing teams. Hoodi is the testnet for practicing staking and testing protocol upgrades, and it replaced Holesky, which was deprecated in September 2025.

Layer 2 networks have their own testnets too, such as Arbitrum Sepolia, which connect to Ethereum's testnets.

How do you get testnet tokens?

Testnet tokens usually come from a faucet, a site where you enter your address and receive a small amount for free. On Solana, developers use Devnet for building apps and can request test SOL from the command line or from a faucet. Solana's Testnet is mostly used by validators to stress-test new releases, and airdrops are not available on mainnet.

Testnet tokens are not supposed to be bought or sold. If someone offers to sell them to you as an investment, treat it as a warning sign.

Why did Bitcoin create testnet4?

Bitcoin's older testnet3 ran for about 13 years and developed problems. A quirk in its difficulty rules caused "block storms," where huge numbers of blocks were mined in a short burst. In one case, about three years of blocks were produced in a few weeks. Testnet coins were also being traded and used in scam airdrops.

BIP 94 created testnet4 in 2024 to fix the difficulty issue and enforce mainnet rules from the start. Bitcoin Core 28.0, released on October 2, 2024, added support for it while keeping testnet3 for the time being.

To learn more about the networks themselves, see what is a node and how blockchain works.