bitcoin/doc/release-notes/release-notes-28.0.md

Bitcoin Core version 28.0 is now available from:

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

This release includes new features, various bug fixes and performance
improvements, as well as updated translations.

Please report bugs using the issue tracker at GitHub:

  <https://github.com/bitcoin/bitcoin/issues>

To receive security and update notifications, please subscribe to:

  <https://bitcoincore.org/en/list/announcements/join/>

How to Upgrade
==============

If you are running an older version, shut it down. Wait until it has completely
shut down (which might take a few minutes in some cases), then run the
installer (on Windows) or just copy over `/Applications/Bitcoin-Qt` (on macOS)
or `bitcoind`/`bitcoin-qt` (on Linux).

Upgrading directly from a version of Bitcoin Core that has reached its EOL is
possible, but it might take some time if the data directory needs to be migrated. Old
wallet versions of Bitcoin Core are generally supported.

Running Bitcoin Core binaries on macOS requires self signing.
```
cd /path/to/bitcoin-28.0/bin
xattr -d com.apple.quarantine bitcoin-cli bitcoin-qt bitcoin-tx bitcoin-util bitcoin-wallet bitcoind test_bitcoin
codesign -s - bitcoin-cli bitcoin-qt bitcoin-tx bitcoin-util bitcoin-wallet bitcoind test_bitcoin
```

Compatibility
==============

Bitcoin Core is supported and extensively tested on operating systems
using the Linux Kernel 3.17+, macOS 11.0+, and Windows 7 and newer. Bitcoin
Core should also work on most other UNIX-like systems but is not as
frequently tested on them. It is not recommended to use Bitcoin Core on
unsupported systems.

Notable changes
===============

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
---------------------------

The libbitcoin-consensus library was deprecated in 27.0 and is now completely removed. (#29648)

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)

Credits
=======

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
- fanquake
- furszy
- glozow
- Greg Sanders
- hanmz
- Hennadii Stepanov
- Hernan Marino
- Hodlinator
- ishaanam
- ismaelsadeeq
- Jadi
- Jon Atack
- josibake
- jrakibi
- kevkevin
- kevkevinpal
- Konstantin Akimov
- laanwj
- Larry Ruane
- Lőrinc
- Luis Schwab
- Luke Dashjr
- MarcoFalke
- marcofleon
- Marnix
- Martin Saposnic
- Martin Zumsande
- Matt Corallo
- Matthew Zipkin
- Matt Whitlock
- Max Edwards
- Michael Dietz
- Murch
- nanlour
- pablomartin4btc
- Peter Todd
- Pieter Wuille
- @RandyMcMillan
- RoboSchmied
- Roman Zeyde
- Ryan Ofsky
- Sebastian Falbesoner
- Sergi Delgado Segura
- Sjors Provoost
- spicyzboss
- StevenMia
- stickies-v
- stratospher
- Suhas Daftuar
- sunerok
- tdb3
- TheCharlatan
- umiumi
- Vasil Dimov
- virtu
- willcl-ark

As well as to everyone that helped with translations on
[Transifex](https://www.transifex.com/bitcoin/bitcoin/).