Assume Valid

Assume valid is a performance option in Bitcoin Core that skips signature verification for blocks buried beneath a specific block hash hardcoded into each software release. During initial sync, a new node still downloads, structurally checks, and applies every block since 2009, but does not re-verify old signatures below that checkpoint.

Why it matters

Signature checking is the most computationally expensive part of validating the blockchain's hundreds of gigabytes of history. Assume valid cuts initial sync time substantially, lowering the cost of running a full node, which supports decentralization. The security trade-off is deliberately narrow: the assumption is only that signatures in deeply buried blocks, already accepted by the entire network for years, are valid.

How it works

Each Bitcoin Core release ships with the hash of a recent block that developers and reviewers have fully validated. If the chain a syncing node downloads contains that exact block, signatures below it are assumed correct, while every other rule, including supply limits, proof of work, and transaction structure, is still enforced on every block. Users who prefer zero assumptions can disable the feature with a single setting and verify every signature back to the genesis block. Because the hash is public in the open-source code, the checkpoint is itself auditable, keeping the trust added by the shortcut close to zero.