# BlockHeader A Bitcoin block header — exactly 80 bytes holding the six fields that make up the proof-of-work commitment: `version (4) | prev hash (32) | merkle root (32) | time (4) | nBits (4) | nonce (4)`. ``` final class BlockHeader ``` ## Overview Headers are what miners iterate (changing the `nonce` until the resulting hash is ≤ the target implied by `bits`) and what the P2P network gossips before blocks. Use for header-first IBD and for lightweight chain-presence checks that don’t need full transaction data. Wraps the opaque `btck_BlockHeader` type; `deinit` calls `btck_block_header_destroy` when the last Swift reference drops.