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Release Notes for Bitcoin Cash Node version 27.0.0

Bitcoin Cash Node version 27.0.0 is now available from:


This is a major release of Bitcoin Cash Node (BCHN) that implements the May 15, 2024 Network Upgrade.

This release implements the following consensus CHIPs:

This version contains various additional minor corrections and improvements.

Users who are running any of our previous releases (25.0.0 or v26.x.0) are urged to upgrade to v27.0.0 ahead of 15 May 2024.

Usage recommendations

The update to Bitcoin Cash Node 27.0.0 is required for the May 15, 2024 Bitcoin Cash network upgrade.

Network changes

This major release implements the Adaptive Blocksize Limit Algorithm for Bitcoin Cash, which is a change to consensus rules that allows the maximum block size to gradually increase and decrease based on how full blocks are.

Added functionality

  • Added configuration option -percentblockmaxsize which is an alternative to -blockmaxsize. -percentmaxblocksize can be used to configure the node's maximum mined block size as a percentage of the maximum block size for the network. So for instance the default on mainnet is -percentblockmaxsize=50.0 (16 MB). Can be any value from 0.0 to 100.0.

Deprecated functionality

  • While 32-bit builds are still supported in this release, they are deprecated and planned to be removed from BCHN after the May 2024 upgrade.

Modified functionality

  • The -excessiveblocksize configuration value has modified semantics pre-upgrade vs post-upgrade. After ABLA activates, it acts as a floor value as the base "minimum" max block size.
  • Added an additional returned data item to the getmininginfo RPC: "miningblocksizelimit", which is the block size limit used for mining as configured for the node by e.g.: -blockmaxsize.
  • The Qt GUI RPC console now is fixed to match the HTTP RPC with respect to stateful "config related" commands. Commands such as getmininginfo and getexcessiveblock now match the actual node config (and the HTTP RPC).
  • The default size cap for mining blocks has been set to 50% of the capacity on networks where it has previously been set to 25%. This effectively increases the soft (mining) blocksize default from 8MB to 16MB. Mining pools that wish to generate bigger or smaller blocks can still adjust the configuration option as usual.

Removed functionality


New RPC methods

A 'fillmempool' RPC method has been added for regtest.

User interface changes

  • The new configuration option -percentblockmaxsize has been added. It is described in more detail in the "Added functionality" section above.


Bitcoin Cash Node 27.0.0 does not introduce any known regressions as compared to 26.1.0.


The following are limitations in this release of which users should be aware:

  1. CashToken support is low-level at this stage. The wallet application does not yet keep track of the user's tokens. Tokens are only manageable via RPC commands currently. They only persist through the UTXO database and block database at this point. There are existing RPC commands to list and filter for tokens in the UTXO set. RPC raw transaction handling commands have been extended to allow creation (and sending) of token transactions. Interested users are advised to consult the functional test in test/functional/ for examples on token transaction construction and listing. Future releases will aim to extend the RPC API with more convenient ways to create and spend tokens, as well as upgrading the wallet storage and indexing subsystems to persistently store data about tokens of interest to the user. Later we expect to add GUI wallet management of Cash Tokens.

  2. Transactions with SIGHASH_UTXO are not covered by DSProofs at present.

  3. P2SH-32 is not used by default in the wallet (regular P2SH-20 remains the default wherever P2SH is treated).

  4. The markup of Double Spend Proof events in the wallet does not survive a restart of the wallet, as the information is not persisted to the wallet.

  5. The ABLA algorithm for BCH is currently temporarily set to cap the max block size at 2GB. This is due to limitations in the p2p protocol (as well as the block data file format in BCHN).

Known Issues

Some issues could not be closed in time for release, but we are tracking all of them on our GitLab repository.

  • The minimum macOS version is 10.14 (Mojave). Earlier macOS versions are no longer supported.

  • Windows users are recommended not to run multiple instances of bitcoin-qt or bitcoind on the same machine if the wallet feature is enabled. There is risk of data corruption if instances are configured to use the same wallet folder.

  • Some users have encountered unit tests failures when running in WSL environments (e.g. WSL/Ubuntu). At this time, WSL is not considered a supported environment for the software. This may change in future. It has been reported that using WSL2 improves the issue.

  • doc/ needs revision (Issue #65).

  • For users running from sources built with BerkeleyDB releases newer than the 5.3 which is used in this release, please take into consideration the database format compatibility issues described in Issue #34. When building from source it is recommended to use BerkeleyDB 5.3 as this avoids wallet database incompatibility issues with the official release.

  • The test_bitcoin-qt test executable fails on Linux Mint 20 (see Issue #144). This does not otherwise appear to impact the functioning of the BCHN software on that platform.

  • With a certain combination of build flags that included disabling the QR code library, a build failure was observed where an erroneous linking against the QR code library (not present) was attempted (Issue #138).

  • Possible out-of-memory error when starting bitcoind with high excessiveblocksize value (Issue #156)

  • A problem was observed on scalenet where nodes would sometimes hang for around 10 minutes, accepting RPC connections but not responding to them (see #210).

  • Startup and shutdown time of nodes on scalenet can be long (see Issue #313).

  • Race condition in one of the tests (see Issue #409).

  • Occasional failure in (see Issue #403).

  • test failure when run as part of suite on certain many-core platforms (see Issue #380).

  • Spurious 'insufficient funds' failure during benchmark (see Issue #377).

  • If compiling from source, secp256k1 now no longer works with latest openssl3.x series. There are workarounds (see Issue #364).

  • Spurious AssertionError: Mempool sync timed out in several tests (see Issue #357).

  • For some platforms, there may be a need to install additional libraries in order to build from source (see Issue #431 and discussion in MR 1523).

  • More TorV3 static seeds may be needed to get -onlynet=onion working (see Issue #429).

  • Memory usage can be very high if repeatedly doing RPC getblock with verbose=2 on a hash of known big blocks (see Issue #466).

  • A GUI crash failure was observed when attempting to encrypt a large imported wallet (see Issue #490).

  • Nodes on 32-bit platforms could fail if blocks reach a size over 1GiB (per ABLA this would take multiple years, and by then 32-bit platforms will no longer be supported in any case). Technically, this is because blocks may take 2x-3x as much memory when unserialized into memory as they do when serialized, and 32-bit machines often cannot address more than 2GiB in a userspace process, and can never address more than 4GiB.

  • The 'wallet_multiwallet' functional test fails on latest Arch Linux due to a change in semantics in a dependency (see Issue #505). This is not expected to impact functionality otherwise, only a particular edge case of the test.

  • The 'p2p_extversion' functional test is sensitive to timing issues when run at high load (see Issue #501).

Changes since Bitcoin Cash Node 26.1.0

New documents


Removed documents


Notable commits grouped by functionality

Security or consensus relevant fixes

  • 286ca4e9ce4a3a127b89f0711b6b8bc0f3819762 Implement CHIP-2023-04 Adaptive Blocksize Limit Algorithm

Interfaces / RPC

  • 37f9f474c5a1f396bc4fed20e5fb3d3fc8e94513 Bump node expiry to May 15, 2025, introduce tentative "upgrade11"
  • a7b52f819182b4693c21bc520b17405f3252df14 Add the RPC fillmempool (regtest only)
  • b110d07a901543f522c3797dd421a023c18a6e5b Added new CLI arg -percentblockmaxsize as an alternative to -blockmaxsize
  • e4bc71dfb9caaf1c5dc917309db7c228e1488634 Add the ability to see the configured -blockmaxsize from the RPC

Features in internal development: support for UTXO commitments


Data directory changes


Performance optimizations

  • 40e3d6ce6c2880a8af982b2b13970ad706370af7 Update the codebase to do a height-based check for upgrade 9
  • 6877945346bc2a7ce6b2be1033d7b7e4b9a91843 Increase the default mining block sizes
  • a130eb09b48d39a5794f8af7a0e68545a7bebec7 Add ReadBlockSizeFromDisk() function to blockstorage.cpp
  • bedee413c700b2ca2cd7599e28e9ccf325712f06 [qa] Update chainparams assumevalid and minimumchainwork for 27.0.0
  • e635da2b4f91319ffc1d648d7385324ff2c4bb40 [qa] Update network checkpoints


  • 24bd12154e6bb527ce69510a75cbbf45b5984839 Alternative fix for Qt GUI RPC Console using an "ephemeral" config object

Code quality

  • 0eaa947c39b874944ce8b208f667f83694a666a0 Code quality nit: Fix a G++ 12 warning in blockstorage.cpp
  • 45ad5a4a2cb34cc05b0830037942727c5a2a1efc Make class CAutoFile move-assignable and move-constructible
  • 4624f046484200b1b8c118b135894d3122c9f6b9 Compiler warning fix: Remove unused variable in policy.cpp
  • 7b781217f8722436d6ed437502d4d889fbb1904a Trivial: Fix two typos in comments in miner_tests.cpp
  • 7f2b83aca1d0819da2d3539616246571e997b9a6 [qa] Bump version to 27.0.0, rotate release notes
  • 94433b8e3972f39418f12566f7fd0323c2f4b164 Add support for generic serialization of std::optional
  • 959d6ed06f4a43f3742214bd375eb3c2dcdaaf22 Add GetNextBlockSizeLimit(), refactor BlockAssembler to use it
  • a395e319eea1cf52a6ed4a07bacd91df9c9a5c79 Fix comparing wrong blocksize parameter variable
  • b7110f8aca0e320f8c716ffaa6c57340eeee6176 [qa] Update blockchain data sizes for mainnet for v27.0.0
  • bf9c3c754c69daa5ee80c3587932defd9b734335 Rename the "excessive block size" concept in the C++ codebase
  • c8bcd188937c9ca6fbb5c7c499a87e4d190056d3 Compiler warning fix: Remove unused variable in txmempool.cpp
  • ca48aa4c644282935c1ff868e24f03aab8ea828a [qa] Update copyrights across the codebase
  • d0f989cb9954d9743430b49215042f18df7695a2 Add Upgrade 10 "Activation" API and unit test
  • fa886d49c7177a4ac5d2e9facc6d99bd9f0da315 Remove const_cast<Config &> from various places in code.

Documentation updates

  • 73e413cdf4a60d389e933a3d140713e5692f8ac9 [doc] Update Clang formatting tools documentation
  • 79c8650d229d191cae2aeb59b4cccefe05589534 [qa] Update test network document to reflect testnet3/4 remain fixed
  • b46cec23212b10682928a20d657eb1025a43d28f [doc] Update header include guard documentation
  • e3181397524c4fabcbafee026dd6fe81621f63cb [doc] Add ABLA CHIP to BCHN's BCH upgrades document

Build / general

  • ebed3da1dc7f60abd5f0e1ca6278b79ad6132b66 Added HAVE_INT128 test and variable to bitcoin-config.h

Build / Linux

  • 2adefbfc7f6a0225f32fb7f8823d257c4a8a51c4 build: Support building inside of a git worktree

Build / Windows

  • 9a767b3c9db219c772d53292a65e2cd8f2d52211 [build] Remove unnecessary _Event_WINDOWS_LIBRARIES

Build / MacOSX


Tests / test framework

  • 67ca3f406f42d155adacaa5d247456ef79649542 [tests] fix PEP 484 implicit optional error
  • 88300e6d2d34e1e820ad15fff36f644eb5f9e62a Add a unit test for the Config class's "percent max blocksize" setter/getter
  • f4a906bd05da68aac0a99b622764dd8354c277d8 test framework: Pass down the rpc_timeout to wait_until on node restart



Seeds / seeder software

  • 0521923f432cf4abc978510785e94e775ea1c1f8 Update regex'es in ahead of May 2024 upgrade
  • 2c08e4c74f10a10f873feaa2ca44e46936655f78 [qa] Update static seeds for some test networks
  • 43a1620e306d0567b6b937ac05e58ac1941234ed [qa] Update mainnet static seeds for v27.0.0 release
  • 55f5916401fb474c44d15b2d962928bd34856b88 [qa] Update static seeds for chipnet test network

Maintainer tools





  • 66442fd03829c0ce9667533b03546134095324b9 [qa] Update freetrader public key (expiry extension to 2025-06-07)

Continuous Integration (GitLab CI)

  • 64fd5f891fe1a02875b0e16f088862b6312423a9 [ci] Pin the pymdown-extensions dependency to v10.2.1
  • 9300b882e022085272e3090bb0349110fdbbe8e7 CI: Save more sanitizer-undefined artifacts on failure


  • 1ae5ca204e1104a0f2f6b46ae93eedb307196379 [backport] refactor: Drop owns_lock() call
  • 34301c7128f505fef08712527e3ab522a9eeb906 [backport] build: libevent 2.1.12-stable
  • 8e889ee9c9e2830cf77a3d2f59cf652b4e4e9b3b [backport] refactor: Do not discard try_lock() return value
  • b9a103d2f0a8b17952e4829af570b29013a91bdc [backport] [cmake] Use the protobuf supplied cmake file instead of the cmake supplied one
  • c97419daeb7907dcad3958a9dcbe0939a10fd587 [backport] build: suppress array-bounds errors in libxkbcommon
  • fc9c13e97036c5a8619cdfa310371cc765684052 [backport] bump libevent to 2.1.11 in depends