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TERM_DEF // TRANSACTION / EPHEMERAL_ANCHORS
EPHEMERAL
ANCHORS
Ephemeral Anchors. Zero-value anyone-can-spend outputs paired with v3 packages to allow CPFP without UTXO bloat.

This page sits in the Transaction section — How money moves: inputs, outputs, fees, signatures, sighash flags, and the formats that wrap them. Read on for what it is, why it exists, how it works under the hood, and what to watch out for.
WHAT_EPHEMERAL_ANCHORS_IS
Ephemeral Anchors — at a glance
TRANSACTION
Ephemeral Anchors is part of the LIGHTNING ANCHORS sub-family of transaction-level concepts. A new output type for Lightning commitment transactions that can be CPFP-bumped without itself requiring a signature. Zero-value anyone-can-spend outputs paired with v3 packages to allow CPFP without UTXO bloat.
Why it exists
DESIGN
Old anchor outputs required each channel party to sign their anchor, complicating wallet UX and adding 1-of-1 multisig overhead. Ephemeral anchors are zero-value SegWit-v1 outputs anyone can spend with empty witness — turning fee-bumping into a single transaction.
HOW_IT_WORKS
Mechanism
HOW IT WORKS
The commitment tx includes an ephemeral anchor output (script: OP_TRUE) worth 0 sats but immediately CPFP-bumpable. To fee-bump, the channel owner constructs a child tx that spends the anchor and provides extra fee. Ephemeral anchors require package relay to propagate.
1. Wallet selects UTXOs whose total value covers the spend amount + estimated fee (coin selection). 2. Wallet builds the transaction body: version, inputs (each with prev txid + vout + sequence), outputs (each with value + scriptPubKey), locktime. 3. Wallet computes the sighash for each input (which parts of the tx the signature commits to — controlled by the SIGHASH flag). 4. Wallet signs each input with the right private key. Witness/scriptSig is populated with the resulting signatures + pubkeys. 5. Tx is broadcast to peers. Mempool propagation: tens of seconds globally. 6. A miner includes it in a block. Confirmation count grows by 1 per block; after ~6 the tx is effectively final.
WORKED_EXAMPLE
Ephemeral Anchors — LIGHTNING ANCHORS
EXAMPLE
Old anchor output: 1-of-1 multisig (channel party's anchor key) 330 sats locked up Each party must store their anchor key separately Ephemeral anchor: script: OP_TRUE (anyone-can-spend) value : 0 sats spendable in the SAME block as the commitment tx requires BIP-431 package relay to propagate Result: simpler wallet code, no extra key management, free anchors
KEY_PROPERTIES
PACKAGE-DEPENDENT
Requires BIP-331 package relay because the anchor is 0-fee and can only propagate together with its CPFP child.
ATOMIC
A transaction is either fully accepted into a block or fully rejected. There is no partial spend.
IMMUTABLE INPUTS
A UTXO can only ever be spent once. After that, it is permanently consumed.
NO BALANCES
Bitcoin tracks UTXOs, not balances. Your wallet computes a balance by summing the UTXOs it controls.
COMMON_PITFALLS
Things that catch people out
PITFALLS
  • address-reuse/">Address reuse degrades privacy — every reuse links more of your UTXOs together publicly. Modern wallets generate a fresh address per receive.
  • Fee estimation matters: under-pay and your tx sits in the mempool for hours; over-pay and you tip the miner more than necessary. Use a fee estimator.
  • "Change outputs" must go back to a fresh address you control. A missing change output sends the difference to the miner as fee — a known footgun.
  • RBF (Replace-By-Fee) lets you re-broadcast a tx with a higher fee. Useful for stuck txs but means a 0-confirmation tx is never truly final.
RELATED_CONCEPTS
Other terms from Transaction — click any to read its page:
Transaction (Tx) Raw Transaction Transaction ID (TXID) wTXID (Witness TXID) Input Output UTXO (Unspent Transaction Output) UTXO Set
TERMINOLOGY_INDEX
TERMINOLOGY
Ephemeral Anchors
Zero-value anyone-can-spend outputs paired with v3 packages to allow CPFP without UTXO bloat.
Transaction (Tx)
A signed payload spending one or more UTXOs and creating new ones; every state change in Bitcoin is a tx.
Raw Transaction
The hex-serialized bytes of a transaction, ready to broadcast or analyze.
Transaction ID (TXID)
HASH256 of a transaction's pre-witness serialization; used to reference outputs by (txid, vout).
wTXID (Witness TXID)
HASH256 of the full transaction including witness data; commits to signatures and used in the witness commitment.
Input
A reference to a previous output being spent, plus the data (scriptSig/witness) authorizing the spend.
Output
An (amount, scriptPubKey) pair created by a transaction; spendable later by a tx whose input references it.
UTXO (Unspent Transaction Output)
An output that hasn't been spent yet; your "balance" is the sum of UTXOs you can sign for.