Bitcoin Core version 28.0 is now available from:

<https://bitcoincore.org/bin/bitcoin-core-28.0/>

Testnet4/BIP94 support

Support for Testnet4 as specified in [BIP94](https://github.com/bitcoin/bips/blob/master/bip-0094.mediawiki)

has been added. The network can be selected with the `-testnet4` option and

the section header is also named `[testnet4]`.

While the intention is to phase out support for Testnet3 in an upcoming

version, support for it is still available via the known options in this

release. (#29775)

Windows Data Directory

The default data directory on Windows has been moved from `C:\Users\Username\AppData\Roaming\Bitcoin`

to `C:\Users\Username\AppData\Local\Bitcoin`. Bitcoin Core will check the existence

of the old directory first and continue to use that directory for backwards

compatibility if it is present. (#27064)

JSON-RPC 2.0 Support

The JSON-RPC server now recognizes JSON-RPC 2.0 requests and responds with

strict adherence to the [specification](https://www.jsonrpc.org/specification).

See [JSON-RPC-interface.md](https://github.com/bitcoin/bitcoin/blob/master/doc/JSON-RPC-interface.md#json-rpc-11-vs-20) for details. (#27101)

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

P2P and Network Changes

- Previously if Bitcoin Core was listening for P2P connections, either using

default settings or via `bind=addr:port` it would always also bind to

`127.0.0.1:8334` to listen for Tor connections. It was not possible to switch

this off, even if the node didn't use Tor. This has been changed and now

`bind=addr:port` results in binding on `addr:port` only. The default behavior

of binding to `0.0.0.0:8333` and `127.0.0.1:8334` has not been changed.

If you are using a `bind=...` configuration without `bind=...=onion` and rely

on the previous implied behavior to accept incoming Tor connections at

`127.0.0.1:8334`, you need to now make this explicit by using

`bind=... bind=127.0.0.1:8334=onion`. (#22729)

- Bitcoin Core will now fail to start up if any of its P2P binds fail, rather

than the previous behaviour where it would only abort startup if all P2P

binds had failed. (#22729)

- UNIX domain sockets can now be used for proxy connections. Set `-onion` or `-proxy`

to the local socket path with the prefix `unix:` (e.g. `-onion=unix:/home/me/torsocket`).

(#27375)

- UNIX socket paths are now accepted for `-zmqpubrawblock` and `-zmqpubrawtx` with

the format `-zmqpubrawtx=unix:/path/to/file` (#27679)

- Additional "in" and "out" flags have been added to `-whitelist` to control whether

permissions apply to inbound connections and/or manual ones (default: inbound only). (#27114)

- Transactions having a feerate that is too low will be opportunistically paired with

their child transactions and submitted as a package, thus enabling the node to download

1-parent-1-child packages using the existing transaction relay protocol. Combined with

other mempool policies, this change allows limited "package relay" when a parent transaction

is below the mempool minimum feerate. Topologically Restricted Until Confirmation (TRUC)

parents are additionally allowed to be below the minimum relay feerate (i.e., pay 0 fees).

Use the `submitpackage` RPC to submit packages directly to the node. Warning: this P2P

feature is limited (unlike the `submitpackage` interface, a child with multiple unconfirmed

parents is not supported) and not yet reliable under adversarial conditions. (#28970)

Mempool Policy Changes

- Transactions with version number set to 3 are now treated as standard on all networks (#29496),

subject to opt-in Topologically Restricted Until Confirmation (TRUC) transaction policy as

described in [BIP 431](https://github.com/bitcoin/bips/blob/master/bip-0431.mediawiki). The

policy includes limits on spending unconfirmed outputs (#28948), eviction of a previous descendant

if a more incentive-compatible one is submitted (#29306), and a maximum transaction size of 10,000vB

(#29873). 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.

- Pay To Anchor (P2A) is a new standard witness output type for spending,

a newly recognised output template. This allows for key-less anchor

outputs, with compact spending conditions for additional efficiencies on

top of an equivalent `sh(OP_TRUE)` output, in addition to the txid stability

of the spending transaction.

N.B. propagation of this output spending on the network will be limited

until a sufficient number of nodes on the network adopt this upgrade. (#30352)

- 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. (#28984)

- The default value of the `-mempoolfullrbf` configuration option has been changed from 0 to 1,

i.e. `mempoolfullrbf=1`. (#30493)

Updated RPCs

- The `dumptxoutset` RPC now returns the UTXO set dump in a new and

improved format. Correspondingly, the `loadtxoutset` RPC now expects

this new format in the dumps it tries to load. Dumps with the old

format are no longer supported and need to be recreated using the

new format to be usable. (#29612)

- AssumeUTXO mainnet parameters have been added for height 840,000.

This means the `loadtxoutset` RPC can now be used on mainnet with

the matching UTXO set from that height. (#28553)

- The `warnings` field in `getblockchaininfo`, `getmininginfo` and

`getnetworkinfo` now returns all the active node warnings as an array

of strings, instead of a single warning. The current behaviour

can be temporarily restored by running Bitcoin Core with the configuration

option `-deprecatedrpc=warnings`. (#29845)

- Previously when using the `sendrawtransaction` RPC and specifying outputs

that are already in the UTXO set, an RPC error code of `-27` with the

message "Transaction already in block chain" was returned in response.

The error message has been changed to "Transaction outputs already in utxo set"

to more accurately describe the source of the issue. (#30212)

- The default mode for the `estimatesmartfee` RPC has been updated from `conservative` to `economical`,

which is expected to reduce over-estimation for many users, particularly if Replace-by-Fee is an option.

For users that require high confidence in their fee estimates at the cost of potentially over-estimating,

the `conservative` mode remains available. (#30275)

- RPC `scantxoutset` now returns 2 new fields in the "unspents" JSON array: `blockhash` and `confirmations`.

See the scantxoutset help for details. (#30515)

- RPC `submitpackage` now allows 2 new arguments to be passed: `maxfeerate` and `maxburnamount`. See the

subtmitpackage help for details. (#28950)

Changes to wallet-related RPCs can be found in the Wallet section below.

Updated REST APIs

- Parameter validation for `/rest/getutxos` has been improved by rejecting

truncated or overly large txids and malformed outpoint indices via raising

an HTTP_BAD_REQUEST "Parse error". These requests were previously handled

silently. (#30482, #30444)

Build System

- GCC 11.1 or later, or Clang 16.0 or later,

are now required to compile Bitcoin Core. (#29091, #30263)

- 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. (#29987)

- `--enable-lcov-branch-coverage` has been removed, given

incompatibilities between lcov version 1 & 2. `LCOV_OPTS`

should be used to set any options instead. (#30192)

Updated Settings

- When running with `-alertnotify`, an alert can now be raised multiple

times instead of just once. Previously, it was only raised when unknown

new consensus rules were activated. Its scope has now been increased to

include all kernel warnings. Specifically, alerts will now also be raised

when an invalid chain with a large amount of work has been detected.

Additional warnings may be added in the future. (#30058)

Changes to GUI or wallet related settings can be found in the GUI or Wallet section below.

Wallet

- The wallet now detects when wallet transactions conflict with the mempool. Mempool-conflicting

transactions can be seen in the `"mempoolconflicts"` field of `gettransaction`. The inputs

of mempool-conflicted transactions can now be respent without manually abandoning the

transactions when the parent transaction is dropped from the mempool, which can cause wallet

balances to appear higher. (#27307)

- A new `max_tx_weight` option has been added to the RPCs `fundrawtransaction`, `walletcreatefundedpsbt`, and `send`.

It specifies the maximum transaction weight. If the limit is exceeded during funding, the transaction will not be built.

The default value is 4,000,000 WU. (#29523)

- 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. (#29130)

- A new RPC `gethdkeys` lists all of the BIP32 HD keys in use by all of the descriptors in the wallet.

These keys can be used in conjunction with `createwalletdescriptor` to create and add single key

descriptors to the wallet for a particular key that the wallet already knows. (#29130)

- The `sendall` RPC can now spend unconfirmed change and will include additional fees as necessary

for the resulting transaction to bump the unconfirmed transactions' feerates to the specified feerate. (#28979)

- In RPC `bumpfee`, if a `fee_rate` is specified, the feerate is no longer restricted

to following the wallet's incremental feerate of 5 sat/vb. The feerate must still be

at least the sum of the original fee and the mempool's incremental feerate. (#27969)

GUI Changes

- The "Migrate Wallet" menu allows users to migrate any legacy wallet in their wallet

directory, regardless of the wallets loaded. (gui#824)

- The "Information" window now displays the maximum mempool size along with the

mempool usage. (gui#825)

Low-level Changes

Tests

- The BIP94 timewarp attack mitigation is now active on the `regtest` network. (#30681)

- A new `-testdatadir` option has been added to `test_bitcoin` to allow specifying the

location of unit test data directories. (#26564)

Blockstorage

- Block files are now XOR'd by default with a key stored in the blocksdir.

Previous releases of Bitcoin Core or previous external software will not be able to read the blocksdir with a non-zero XOR-key.

Refer to the `-blocksxor` help for more details. (#28052)

Chainstate

- The chainstate database flushes that occur when blocks are pruned will no longer

empty the database cache. The cache will remain populated longer, which significantly

reduces the time for initial block download to complete. (#28280)

Dependencies

- The dependency on Boost.Process has been replaced with cpp-subprocess, which is contained in source.

Builders will no longer need Boost.Process to build with external signer support. (#28981)

Thanks to everyone who directly contributed to this release:

- 0xb10c

- Alfonso Roman Zubeldia

- Andrew Toth

- AngusP

- Anthony Towns

- Antoine Poinsot

- Anton A

- Ava Chow

- Ayush Singh

- Ben Westgate

- Brandon Odiwuor

- brunoerg

- bstin

- Charlie

- Christopher Bergqvist

- Cory Fields

- crazeteam

- Daniela Brozzoni

- David Gumberg

- dergoegge

- Edil Medeiros

- Epic Curious

- Fabian Jahr

- furszy

- glozow

- Greg Sanders

- hanmz

- Hennadii Stepanov

- Hernan Marino

- Hodlinator

- ishaanam

- ismaelsadeeq

- Jadi

- Jon Atack

- josibake

- jrakibi

- kevkevin

- kevkevinpal

- Konstantin Akimov

- Larry Ruane

- Lőrinc

- Luis Schwab

- Luke Dashjr

- marcofleon

- Marnix

- Martin Saposnic

- Matt Corallo

- Matthew Zipkin

- Matt Whitlock

- Max Edwards

- Michael Dietz

- Murch

- nanlour

- pablomartin4btc

- Peter Todd

- Pieter Wuille

- @RandyMcMillan

- RoboSchmied

- Roman Zeyde

- Ryan Ofsky

- Sergi Delgado Segura

- Sjors Provoost

- spicyzboss

- StevenMia

- stickies-v

- stratospher

- Suhas Daftuar

- sunerok

- tdb3

- TheCharlatan

- umiumi

- Vasil Dimov

- virtu

- willcl-ark