release-notes.md

After branching off for a major version release of Bitcoin Core, use this template to create the initial release notes draft.

The release notes draft is a temporary file that can be added to by anyone. See /doc/developer-notes.md#release-notes for the process.

Create the draft, named "version Release Notes Draft" (e.g. "0.20.0 Release Notes Draft"), as a collaborative wiki in:

https://github.com/bitcoin-core/bitcoin-devwiki/wiki/

Before the final release, move the notes back to this git repository.

version Release Notes Draft

Bitcoin Core version version is now available from:

https://bitcoincore.org/bin/bitcoin-core-*version*/

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 Mac) 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.

Compatibility

During this release cycle, work has been done to ensure that the codebase is fully compatible with C++17. The intention is to begin using C++17 features starting with the 0.22.0 release. This means that a compiler that supports C++17 will be required to compile 0.22.0.

Bitcoin Core is supported and extensively tested on operating systems using the Linux kernel, macOS 10.12+, 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.

From Bitcoin Core 0.20.0 onwards, macOS versions earlier than 10.12 are no longer supported. Additionally, Bitcoin Core does not yet change appearance when macOS "dark mode" is activated.

The node's known peers are persisted to disk in a file called peers.dat. The format of this file has been changed in a backwards-incompatible way in order to accommodate the storage of Tor v3 and other BIP155 addresses. This means that if the file is modified by 0.21.0 or newer then older versions will not be able to read it. Those old versions, in the event of a downgrade, will log an error message "Incorrect keysize in addrman deserialization" and will continue normal operation as if the file was missing, creating a new empty one. (#19954)

Notable changes

P2P and network changes

• The mempool now tracks whether transactions submitted via the wallet or RPCs have been successfully broadcast. Every 10-15 minutes, the node will try to announce unbroadcast transactions until a peer requests it via a getdata message or the transaction is removed from the mempool for other reasons. The node will not track the broadcast status of transactions submitted to the node using P2P relay. This version reduces the initial broadcast guarantees for wallet transactions submitted via P2P to a node running the wallet. (#18038)

• The size of the set of transactions that peers have announced and we consider for requests has been reduced from 100000 to 5000 (per peer), and further announcements will be ignored when that limit is reached. If you need to dump (very) large batches of transactions, exceptions can be made for trusted peers using the "relay" network permission. For localhost for example it can be enabled using the command line option -whitelist=relay@127.0.0.1. (#19988)

• The Tor onion service that is automatically created by setting the -listenonion configuration parameter will now be created as a Tor v3 service instead of Tor v2. The private key that was used for Tor v2 (if any) will be left untouched in the onion_private_key file in the data directory (see -datadir) and can be removed if not needed. Bitcoin Core will no longer attempt to read it. The private key for the Tor v3 service will be saved in a file named onion_v3_private_key. To use the deprecated Tor v2 service (not recommended), then onion_private_key can be copied over onion_v3_private_key, e.g. cp -f onion_private_key onion_v3_private_key. (#19954)

Updated RPCs

• The getpeerinfo RPC now has additional last_block and last_transaction fields that return the UNIX epoch time of the last block and the last valid transaction received from each peer. (#19731)

• getnetworkinfo now returns two new fields, connections_in and connections_out, that provide the number of inbound and outbound peer connections. These new fields are in addition to the existing connections field, which returns the total number of peer connections. (#19405)

• Exposed transaction version numbers are now treated as unsigned 32-bit integers instead of signed 32-bit integers. This matches their treatment in consensus logic. Versions greater than 2 continue to be non-standard (matching previous behavior of smaller than 1 or greater than 2 being non-standard). Note that this includes the joinpsbt command, which combines partially-signed transactions by selecting the highest version number. (#16525)

• getmempoolinfo now returns an additional unbroadcastcount field. The mempool tracks locally submitted transactions until their initial broadcast is acknowledged by a peer. This field returns the count of transactions waiting for acknowledgement.

• Mempool RPCs such as getmempoolentry and getrawmempool with verbose=true now return an additional unbroadcast field. This indicates whether initial broadcast of the transaction has been acknowledged by a peer. getmempoolancestors and getmempooldescendants are also updated.

• The bumpfee, fundrawtransaction, sendmany, sendtoaddress, and walletcreatefundedpsbt RPC commands have been updated to include two new fee estimation methods "BTC/kB" and "sat/B". The target is the fee expressed explicitly in the given form. Note that use of this feature will trigger BIP 125 (replace-by-fee) opt-in. (#11413)

• In addition, the estimate_mode parameter is now case insensitive for all of the above RPC commands. (#11413)

• The bumpfee command now uses conf_target rather than confTarget in the options. (#11413)

• The getpeerinfo RPC no longer returns the banscore field unless the configuration option -deprecatedrpc=banscore is used. The banscore field will be fully removed in the next major release. (#19469)

• The testmempoolaccept RPC returns vsize and a fees object with the base fee if the transaction would pass validation. (#19940)

• The getpeerinfo RPC now returns a connection_type field. This indicates the type of connection established with the peer. It will return one of six options. For more information, see the getpeerinfo help documentation. (#19725)

• The getpeerinfo RPC no longer returns the addnode field by default. This field will be fully removed in the next major release. It can be accessed with the configuration option -deprecatedrpc=getpeerinfo_addnode. However, it is recommended to instead use the connection_type field (it will return manual when addnode is true). (#19725)

• The walletcreatefundedpsbt RPC call will now fail with Insufficient funds when inputs are manually selected but are not enough to cover the outputs and fee. Additional inputs can automatically be added through the new add_inputs option. (#16377)

• The fundrawtransaction RPC now supports add_inputs option that when false prevents adding more inputs if necessary and consequently the RPC fails.

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

New RPCs

• The getindexinfo RPC returns the actively running indices of the node, including their current sync status and height. It also accepts an index_name to specify returning only the status of that index. (#19550)

Build System

Updated settings

• The same ZeroMQ notification (e.g. -zmqpubhashtx=address) can now be specified multiple times to publish the same notification to different ZeroMQ sockets. (#18309)

• The -banscore configuration option, which modified the default threshold for disconnecting and discouraging misbehaving peers, has been removed as part of changes in 0.20.1 and in this release to the handling of misbehaving peers. Refer to "Changes regarding misbehaving peers" in the 0.20.1 release notes for details. (#19464)

• The -debug=db logging category, which was deprecated in 0.20 and replaced by -debug=walletdb to distinguish it from coindb, has been removed. (#19202)

• A download permission has been extracted from the noban permission. For compatibility, noban implies the download permission, but this may change in future releases. Refer to the help of the affected settings -whitebind and -whitelist for more details. (#19191)

• Netmasks that contain 1-bits after 0-bits (the 1-bits are not contiguous on the left side, e.g. 255.0.255.255) are no longer accepted. They are invalid according to RFC 4632. Netmasks are used in the -rpcallowip and -whitelist configuration options and in the setban RPC. (#19628)

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

Tools and Utilities

• The connections field of bitcoin-cli -getinfo is expanded to return a JSON object with in, out and total numbers of peer connections. It previously returned a single integer value for the total number of peer connections. (#19405)

• A new bitcoin-cli -generate command, equivalent to RPC generatenewaddress followed by generatetoaddress, can generate blocks for command line testing purposes. This is a client-side version of the former generate RPC. See the help for details. (#19133)

• The bitcoin-cli -getinfo command now displays the wallet name and balance for each of the loaded wallets when more than one is loaded (e.g. in multiwallet mode) and a wallet is not specified with -rpcwallet. (#18594)

New settings

• The startupnotify option is used to specify a command to execute when Bitcoin Core has finished with its startup sequence. (#15367)

Wallet

• Backwards compatibility has been dropped for two getaddressinfo RPC deprecations, as notified in the 0.20 release notes. The deprecated label field has been removed as well as the deprecated labels behavior of returning a JSON object containing name and purpose key-value pairs. Since 0.20, the labels field returns a JSON array of label names. (#19200)

• To improve wallet privacy, the frequency of wallet rebroadcast attempts is reduced from approximately once every 15 minutes to once every 12-36 hours. To maintain a similar level of guarantee for initial broadcast of wallet transactions, the mempool tracks these transactions as a part of the newly introduced unbroadcast set. See the "P2P and network changes" section for more information on the unbroadcast set. (#18038)

• The sendtoaddress and sendmany RPCs accept an optional verbose=True argument to also return the fee reason about the sent tx. (#19501)

• The wallet can create a transaction without change even when the keypool is empty. Previously it failed. (#17219)

• The -salvagewallet startup option has been removed. A new salvage command has been added to the bitcoin-wallet tool which performs the salvage operations that -salvagewallet did. (#18918)

• A new configuration flag -maxapsfee has been added, which sets the max allowed avoid partial spends (APS) fee. It defaults to 0 (i.e. fee is the same with and without APS). Setting it to -1 will disable APS, unless -avoidpartialspends is set. (#14582)

• The wallet will now avoid partial spends (APS) by default, if this does not result in a difference in fees compared to the non-APS variant. The allowed fee threshold can be adjusted using the new -maxapsfee configuration option. (#14582)

• The createwallet, loadwallet, and unloadwallet RPCs now accept load_on_startup options to modify the settings list. Unless these options are explicitly set to true or false, the list is not modified, so the RPC methods remain backwards compatible. (#15937)

• A new send RPC with similar syntax to walletcreatefundedpsbt, including support for coin selection and a custom fee rate. The send RPC is experimental and may change in subsequent releases. Using it is encouraged once it's no longer experimental: sendmany and sendtoaddress may be deprecated in a future release. (#16378)

• fundrawtransaction and walletcreatefundedpsbt when used with the lockUnspents argument now lock manually selected coins, in addition to automatically selected coins. Note that locked coins are never used in automatic coin selection, but can still be manually selected. (#18244)

• The -zapwallettxes startup option has been removed and its functionality removed from the wallet. This option was originally intended to allow for the fee bumping of transactions that did not signal RBF. This functionality has been superseded with the abandon transaction feature. (#19671)

• The error code when no wallet is loaded, but a wallet RPC is called, has been changed from -32601 (method not found) to -18 (wallet not found). (#20101)

Automatic wallet creation removed

Bitcoin Core will no longer automatically create new wallets on startup. It will load existing wallets specified by -wallet options on the command line or in bitcoin.conf or settings.json files. And by default it will also load a top-level unnamed ("") wallet. However, if specified wallets don't exist, Bitcoin Core will now just log warnings instead of creating new wallets with new keys and addresses like previous releases did.

New wallets can be created through the GUI (which has a more prominent create wallet option), through the bitcoin-cli createwallet or bitcoin-wallet create commands, or the createwallet RPC. (#15454)

Experimental Descriptor Wallets

Please note that Descriptor Wallets are still experimental and not all expected functionality is available. Additionally there may be some bugs and current functions may change in the future. Bugs and missing functionality can be reported to the issue tracker.

0.21 introduces a new type of wallet - Descriptor Wallets. Descriptor Wallets store scriptPubKey information using descriptors. This is in contrast to the Legacy Wallet structure where keys are used to generate scriptPubKeys and addresses. Because of this shift to being script based instead of key based, many of the confusing things that Legacy Wallets do are not possible with Descriptor Wallets. Descriptor Wallets use a definition of "mine" for scripts which is simpler and more intuitive than that used by Legacy Wallets. Descriptor Wallets also uses different semantics for watch-only things and imports.

As Descriptor Wallets are a new type of wallet, their introduction does not affect existing wallets. Users who already have a Bitcoin Core wallet can continue to use it as they did before without any change in behavior. Newly created Legacy Wallets (which is the default type of wallet) will behave as they did in previous versions of Bitcoin Core.

The differences between Descriptor Wallets and Legacy Wallets are largely limited to non user facing things. They are intended to behave similarly except for the import/export and watchonly functionality as described below.

Creating Descriptor Wallets

Descriptor Wallets are not created by default. They must be explicitly created using the createwallet RPC or via the GUI. A descriptors option has been added to createwallet. Setting descriptors to true will create a Descriptor Wallet instead of a Legacy Wallet.

In the GUI, a checkbox has been added to the Create Wallet Dialog to indicate that a Descriptor Wallet should be created.

Without those options being set, a Legacy Wallet will be created instead. Additionally the Default Wallet created upon first startup of Bitcoin Core will be a Legacy Wallet.

IsMine Semantics

IsMine refers to the function used to determine whether a script belongs to the wallet. This is used to determine whether an output belongs to the wallet. IsMine in Legacy Wallets returns true if the wallet would be able to sign an input that spends an output with that script. Since keys can be involved in a variety of different scripts, this definition for IsMine can lead to many unexpected scripts being considered part of the wallet.

With Descriptor Wallets, descriptors explicitly specify the set of scripts that are owned by the wallet. Since descriptors are deterministic and easily enumerable, users will know exactly what scripts the wallet will consider to belong to it. Additionally the implementation of IsMine in Descriptor Wallets is far simpler than for Legacy Wallets. Notably, in Legacy Wallets, IsMine allowed for users to take one type of address (e.g. P2PKH), mutate it into another address type (e.g. P2WPKH), and the wallet would still detect outputs sending to the new address type even without that address being requested from the wallet. Descriptor Wallets does not allow for this and will only watch for the addresses that were explicitly requested from the wallet.

These changes to IsMine will make it easier to reason about what scripts the wallet will actually be watching for in outputs. However for the vast majority of users, this change is largely transparent and will not have noticeable effect.

Imports and Exports

In Legacy Wallets, raw scripts and keys could be imported to the wallet. Those imported scripts and keys are treated separately from the keys generated by the wallet. This complicates the IsMine logic as it has to distinguish between spendable and watchonly.

Descriptor Wallets handle importing scripts and keys differently. Only complete descriptors can be imported. These descriptors are then added to the wallet as if it were a descriptor generated by the wallet itself. This simplifies the IsMine logic so that it no longer has to distinguish between spendable and watchonly. As such, the watchonly model for Descriptor Wallets is also different and described in more detail in the next section.

To import into a Descriptor Wallet, a new importdescriptors RPC has been added that uses a syntax similar to that of importmulti.

As Legacy Wallets and Descriptor Wallets use different mechanisms for storing and importing scripts and keys the existing import RPCs have been disabled for descriptor wallets. New export RPCs for Descriptor Wallets have not yet been added.

The following RPCs are disabled for Descriptor Wallets:

• importprivkey
• importpubkey
• importaddress
• importwallet
• dumpprivkey
• dumpwallet
• importmulti
• addmultisigaddress
• sethdseed

Watchonly Wallets

A Legacy Wallet contains both private keys and scripts that were being watched. Those watched scripts would not contribute to your normal balance. In order to see the watchonly balance and to use watchonly things in transactions, an include_watchonly option was added to many RPCs that would allow users to do that. However it is easy to forget to include this option.

Descriptor Wallets move to a per-wallet watchonly model. Instead an entire wallet is considered to be watchonly depending on whether it was created with private keys disabled. This eliminates the need to distinguish between things that are watchonly and things that are not within a wallet itself.

This change does have a caveat. If a Descriptor Wallet with private keys enabled has a multiple key descriptor without all of the private keys (e.g. multi(...) with only one private key), then the wallet will fail to sign and broadcast transactions. Such wallets would need to use the PSBT workflow but the typical GUI Send, sendtoaddress, etc. workflows would still be available, just non-functional.

This issue is worsened if the wallet contains both single key (e.g. wpkh(...)) descriptors and such multiple key descriptors as some transactions could be signed and broadast and others not. This is due to some transactions containing only single key inputs, while others would contain both single key and multiple key inputs, depending on which are available and how the coin selection algorithm selects inputs. However this is not considered to be a supported use case; multisigs should be in their own wallets which do not already have descriptors. Although users cannot export descriptors with private keys for now as explained earlier.

BIP 44/49/84 Support

The change to using descriptors changes the default derivation paths used by Bitcoin Core to adhere to BIP 44/49/84. Descriptors with different derivation paths can be imported without issue.

Wallet RPC changes

• The upgradewallet RPC replaces the -upgradewallet command line option. (#15761)
• The settxfee RPC will fail if the fee was set higher than the -maxtxfee command line setting. The wallet will already fail to create transactions with fees higher than -maxtxfee. (#18467)

GUI changes

• Wallets created or loaded in the GUI will now be automatically loaded on startup, so they don't need to be manually reloaded next time Bitcoin Core is started. The list of wallets to load on startup is stored in \<datadir\>/settings.json and augments any command line or bitcoin.conf -wallet= settings that specify more wallets to load. Wallets that are unloaded in the GUI get removed from the settings list so they won't load again automatically next startup. (#19754)

• The GUI Peers window no longer displays a "Ban Score" field. This is part of changes in 0.20.1 and in this release to the handling of misbehaving peers. Refer to "Changes regarding misbehaving peers" in the 0.20.1 release notes for details. (#19512)

Low-level changes

RPC

• To make RPC sendtoaddress more consistent with sendmany the following error sendtoaddress codes were changed from -4 to -6:

  • Insufficient funds
  • Fee estimation failed
  • Transaction has too long of a mempool chain

• The sendrawtransaction error code for exceeding maxfeerate has been changed from -26 to -25. The error string has been changed from "absurdly-high-fee" to "Fee exceeds maximum configured by user (e.g. -maxtxfee, maxfeerate)." The testmempoolaccept RPC returns max-fee-exceeded rather than absurdly-high-fee as the reject-reason. (#19339)

• To make wallet and rawtransaction RPCs more consistent, the error message for exceeding maximum feerate has been changed to "Fee exceeds maximum configured by user (e.g. -maxtxfee, maxfeerate)." (#19339)

Tests

• The BIP 325 default signet can be enabled by the -chain=signet or -signet setting. The settings -signetchallenge and -signetseednode allow enabling a custom signet.

Credits

Thanks to everyone who directly contributed to this release:

As well as to everyone that helped with translations on Transifex.