Since Bitcoin's consensus rules do not restrict non-monetary data on the blockchain (as discussed previously), mempool policies—node-specific filters for transaction relay and acceptance—serve as the primary mechanism to limit such data from propagating widely and entering blocks. For instance, traditional policies capped OP_RETURN outputs (a common way to embed arbitrary data) at 83 bytes and limited them to one per transaction, discouraging spam or bloat by making these transactions harder to relay across the network. Without these policies, valid transactions with excessive non-monetary data could flood mempools more easily, increasing the likelihood of inclusion by miners. However, policies are not absolute barriers: miners can still directly include consensus-valid transactions with such data if they choose, though this is rare due to relay challenges and economic incentives. Recent changes in Bitcoin Core (as of the October 2025 release) have relaxed the default OP_RETURN limit in policies, shifting more reliance toward miner discretion and user fees to manage data growth. In essence, mempool filtering remains essential for practical control over the timechain's composition.