A mainnet is the point at which a blockchain project stops being a work in progress and becomes a live, self-sustaining network with its own consensus rules, validators or miners, and native asset. Everything recorded there, from a simple transfer to a smart contract deployment, carries real economic weight and is treated as final once confirmed.

Reaching mainnet is usually the last step of a longer development cycle. Teams first build and iterate on a testnet, a disposable copy of the network that uses worthless tokens so bugs, consensus issues, and smart contract logic can be stress-tested without risking user funds. Once the code has been audited and proven stable, developers publish a genesis block, the first block of the new chain, and open the network to the public. From that moment the chain runs independently, with its own history, its own validator set, and, for a Layer 1 network, its own base layer security rather than relying on another chain.

Some projects launch a mainnet from scratch, while others perform a "mainnet swap," migrating holders of a placeholder token, often an ERC-20 issued during a fundraising round, onto native coins once the chain goes live. Ethereum's own mainnet, launched in 2015, is the best known example: it turned a tested prototype into the production network millions of dApps now run on. Because mainnet activity is permanent and value bearing, most teams keep a parallel testnet running even after launch, so future upgrades can still be trialed safely before reaching production.