By EZ in Releases — Oct 10, 2024

Bitcoin Core v28.0: Testnet4, Full RBF by Default & More

Bitcoin Core 28.0 is the latest major release of predominant Bitcoin full node implementation.

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Bitcoin Core v28 supports testnet4 and introduces a variety of P2P/mempool policy changes, including opportunistic 1-parent-1-child (1p1c) package relay, default relay of opt-in TRUC and pay-to-anchor transactions, limited package RBF relay, and full-RBF is now on by default.
It also adds default parameters for assumeUTXO, enabling the loadtxoutset RPC to use a UTXO set downloaded outside the Bitcoin network (etc. via torrents).
The update also packages many other new features, updated RPCs, fixes, stability and performance improvements, as well as updated translations.

NOTE: LND users need to set -deprecatedrpc=warnings flag before updating. Electrs users need to update it to the latest version, too.

What's new

Some of more notable changes introduced in Bitcoin Core v28 include:

Testnet4/BIP94 Support. Support for Testnet4 as specified in BIP94 has been added. Testnet3 will be phased out in an upcoming version.
- The BIP94 timewarp attack mitigation is now active on the regtest network.
Opportunistic one-parent-one-child (1p1c) package relay. Transactions with low fee rates can be paired with their child transactions and submitted as a package, allowing nodes to download 1-parent-1-child packages via the transaction relay protocol.
Default relay of opt-in topologically restricted until confirmation (TRUC) transactions. The new policy includes limits on spending unconfirmed outputs, eviction of a previous descendant if a more incentive-compatible one is submitted, and a maximum transaction size of 10,000vB.
- "These restrictions simplify the assessment of incentive compatibility of accepting or replacing TRUC transactions, thus ensuring any replacements are more profitable for the node and making fee-bumping more reliable."
Default relay of pay-to-anchor (P2A) transactions. Pay To Anchor is a new standard witness output type for spending, a newly recognized output template.
Limited package RBF relay. Limited package RBF is now enabled, where the proposed conflicting package would result in a connected component, aka cluster, of size 2 in the mempool. All clusters being conflicted against must be of size 2 or lower.
Full RBF by default. The default value of the -mempoolfullrbf configuration option has been changed from 0 to 1, i.e. mempoolfullrbf=1.
AssumeUTXO available on mainnet. AssumeUTXO mainnet parameters have been added for height 840,000. The loadtxoutset RPC can now be used on mainnet with the matching UTXO set from that height.
New Windows Data Directory. The default Windows data directory has been moved to C:\Users\Username\AppData\Local\Bitcoin. If old directory is present, the client will continue to use it for backwards compatibility.
JSON-RPC 2.0 Support. The JSON-RPC server now recognizes JSON-RPC 2.0 requests and responds with strict adherence to the specification.
- "JSON-RPC clients may need to be updated to be compatible with the JSON-RPC server. Please open an issue on GitHub if any compatibility issues are found."
libbitcoinconsensus Removal. The libbitcoin-consensus library was deprecated in 27.0 and is now completely removed.
Easier to migrate legacy wallets to descriptor wallet format.
- The "Migrate Wallet" menu allows users to migrate any legacy wallet in their wallet directory, regardless of the wallets loaded.
- A new createwalletdescriptor RPC allows users to add new automatically generated descriptors to their wallet. This can be used to upgrade wallets created prior to the introduction of a new standard descriptor, such as taproot.
Blockstorage improvements. Block files are now XOR'd by default with a key stored in the blocksdir.
Maximum mempool size along with the mempool usage are now displayed in the "Information" window.
UNIX domain sockets can now be used for proxy connections.
GCC 11.1 or later, or Clang 16.0 or later, are now required to compile Bitcoin Core.
The minimum required glibc to run Bitcoin Core is now 2.31. This means that RHEL 8 and Ubuntu 18.04 (Bionic) are no-longer supported.