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2.4 KiB

(note: this is a temporary file, to be added-to by anybody, and moved to release-notes at release time)

New RPC methods

Fee/Priority estimation

estimatefee nblocks : Returns approximate fee-per-1,000-bytes needed for a transaction to be confirmed within nblocks. Returns -1 if not enough transactions have been observed to compute a good estimate.

estimatepriority nblocks : Returns approximate priority needed for a zero-fee transaction to confirm within nblocks. Returns -1 if not enough free transactions have been observed to compute a good estimate.

Statistics used to estimate fees and priorities are saved in the data directory in the 'fee_estimates.dat' file just before program shutdown, and are read in at startup.

Double-Spend Relay and Alerts

VERY IMPORTANT: It has never been safe, and remains unsafe, to rely on unconfirmed transactions.


When an attempt is seen on the network to spend the same unspent funds more than once, it is no longer ignored. Instead, it is broadcast, to serve as an alert. This broadcast is subject to protections against denial-of-service attacks.

Wallets and other bitcoin services should alert their users to double-spends that affect them. Merchants and other users may have enough time to withhold goods or services when payment becomes uncertain, until confirmation.

Bitcoin Core Wallet Alerts

The Bitcoin Core wallet now makes respend attempts visible in several ways.

If you are online, and a respend affecting one of your wallet transactions is seen, a notification is immediately issued to the command registered with -respendnotify=<cmd>. Additionally, if using the GUI:

  • An alert box is immediately displayed.
  • The affected wallet transaction is highlighted in red until it is confirmed (and it may never be confirmed).

A respendsobserved array is added to gettransaction, listtransactions, and listsinceblock RPC results.


If you rely on an unconfirmed transaction, these change do VERY LITTLE to protect you from a malicious double-spend, because:

  • You may learn about the respend too late to avoid doing whatever you were being paid for
  • Using other relay rules, a double-spender can craft his crime to resist broadcast
  • Miners can choose which conflicting spend to confirm, and some miners may not confirmg the first acceptable spend they see