A zero-value transaction from your wallet to itself, carrying The Library's Merkle root as calldata. Once mined, every one of the 676 archive files hashed into it has a timestamp nobody — including us — can forge. No funds move; the only cost is gas (typically under a cent on Base).
0x086a929795c5f9a74ada8850d7b74785c94bbc843f30a9edf6dfbf5156d149ddVerification, for anyone: take an item from the public manifest at /api/record/library-anchors, recompute its SHA-256, recompute the Merkle root from the manifest's hashes, and confirm the root matches the calldata of the anchoring transaction on Base. If it matches, that item existed in exactly that form when the block was mined. Nothing to take on faith.