Definition
Ephemeral anchors are a Bitcoin relay-policy refinement that creates a clean, contention-free way to fee-bump multi-party transactions such as Lightning commitment transactions. They build on the TRUC / version-3 transaction relay rules (BIP-431) and on package relay, requiring no consensus change.
How they work
An ephemeral anchor is a tiny zero-value output whose entire script is anyone-can-spend (for example, a bare OP_TRUE). A parent transaction can carry such an output and pay little or even zero fee on its own; under the policy it is only relayed when accompanied in a package by a child that pays enough fee for both. Because the anchor is anyone-can-spend, any participant — not just the parties who receive the parent's other outputs — can attach that fee-paying child.
Why it is an improvement
Earlier anchor-output designs gave each counterparty its own anchor and required deducting real value to fund it, enlarging the transaction and complicating fee management. A zero-value, shared anchor removes the need to pre-allocate funds, shrinks the on-chain footprint, and provides a single agreed point for adding fees — which also reduces "pinning" attacks that exploit ambiguous fee-bumping paths. The output is ephemeral: it must be spent in the same package, so no dust lingers in the UTXO set.
Ephemeral anchors work hand in hand with package relay and the rebindable-signature channels enabled by AnyPrevOut. D-Central documents these mempool-policy tools as part of an educational Bitcoin reference.
In Simple Terms
Ephemeral anchors are a Bitcoin relay-policy refinement that creates a clean, contention-free way to fee-bump multi-party transactions such as Lightning commitment transactions. They build on…