Inside Bitcoin

251
252Build System
253------------
254
255- The next major release is planned to drop support for building Bitcoin Core on
256  Windows with MSVC, once clang-cl support is ready. See
257  [#36153](https://github.com/bitcoin/bitcoin/issues/36153).
258- The undocumented `BITCOIN_GENBUILD_NO_GIT` environment variable is no longer
259  required and has been removed. The build system now automatically detects when
260  it is being built from a source archive or as a subproject of a git-aware
261  parent project and skips git metadata fetching. Users who need to disable git
262  execution explicitly can still do so by configuring with
263  `-DCMAKE_DISABLE_FIND_PACKAGE_Git=ON`. (#32220)
264
265Updated settings
266----------------
267
268- The `bip125-replaceable` key in the wallet transaction RPCs such as
269  `listtransactions`, `listsinceblock`, and `gettransaction` is marked as
270  deprecated. Users still have the option to retrieve this key by passing the
271  `-deprecatedrpc=bip125` startup option. Also, the `-walletrbf` startup option
272  has been marked as deprecated and will be fully removed in the next release.
273  Using this option emits a warning in the logs. (#34917)
274- The `libevent` logging category has been removed. Configurations like
275  `-debug=libevent` or `-debugexclude=libevent` will log a deprecation warning
276  and be ignored. These configurations will result in an error in a future
277  release.
278- A new configuration option `-rpcmaxconnections` (default `16`) limits the
279  number of simultaneously connected HTTP clients to the server. The application
280  will now attempt to reserve file descriptors for the HTTP server sockets. If
281  your system has limited resources, consider using a lower setting.
282- A new `mining` logging category has been added, enabled with `-debug=mining`.
283  The `CreateNewBlock(): block weight: ...` line, previously logged on every
284  block template build regardless of logging configuration, is now logged only
285  when this category is enabled. `getblocktemplate` and Mining IPC users are
286  encouraged to enable it to see this log and future mining log.
287
288Changes to GUI or wallet related settings can be found in the GUI or Wallet section below.
289
290New settings
291------------
292
293- Block validation can now prefetch input prevouts from the chainstate database
294  in parallel while connecting blocks, speeding up validation when prevouts need
295  to be read from disk. A new `-prevoutfetchthreads=<n>` option controls the
296  number of prefetch worker threads. The default is 8 threads, up to a maximum
297  of 16; set it to 0 to disable parallel prefetching. (#35295)
298
299Tools and Utilities
300-------------------
301
302- CLI -addrinfo now returns the full set of known addresses. In previous
303  versions (v22.0 - v30.0) the set of returned addresses was filtered for
304  quality and recency. This was changed since it does not match the logic for
305  selecting peers to connect to, which does not filter. Note: CLI -addrinfo now
306  requires bitcoind v26.0 or later, as it uses the getaddrmaninfo RPC
307  internally. Users querying older, unmaintained node versions would need to use
308  an older bitcoin-cli version. (#26988)
309- A new `bitcoin-util getchainparams` command returns hardcoded details about
310  the selected chain. (#35610)
311
312Wallet
313------
314
315- A new RPC `addhdkey` is added which allows a BIP 32 extended key to be added
316  to the wallet without needing to import it as part of a separate descriptor.
317  This key will not be used to produce any output scripts unless it is
318  explicitly imported as part of a separate descriptor independent of the
319  `addhdkey` RPC. (#29136)
320- A new `exportwatchonlywallet` RPC creates a watchonly wallet file from an
321  existing descriptor wallet. The exported file contains the wallet's public
322  descriptors (with derived key caches where needed), transactions, and address
323  book data, but no private keys. It can be imported on another node using the
324  existing `restorewallet` RPC. (#32489)
325- The [Offline Signing Tutorial](/doc/offline-signing-tutorial.md) has been
326  updated to use `exportwatchonlywallet` for setting up the online watch-only
327  wallet, replacing the previous manual descriptor import workflow. (#32489)
328- A new `derivehdkey` RPC is available to obtain an xpub or xprv for a
329  derivation path with at least one hardened step from an HD key known to the
330  wallet. This can be used to coordinate a multisig setup, where each signer
331  shares an xpub using a different derivation path than the default
332  single-signature descriptors. The example in `doc/multisig-tutorial.md` is
333  updated to use this RPC. (#32784)
334- The `fee_reason` field returned by wallet transaction creation RPCs now
335  reports the reason the wallet selected the fee rate ("Fee Rate Estimator",
336  "Mempool Min Fee", "User Specified Fee", "Fallback fee" or
337  "Minimum Required Fee") instead of the block policy fee rate estimator's
338  internal threshold details. Those details remain available in the block
339  policy fee rate estimator debug log. (#34075)
340- Wallet names that are relative paths including `..` and `.` elements, and
341  wallets named `/` are no longer allowed. Any users that depended on this
342  behavior can instead use absolute paths to their wallet or move their wallet
343  to a safer path. (#34544)
344- The `send` and `sendall` RPCs are no longer marked as experimental. (#35601)
345- The `fundrawtransaction` RPC no longer accepts a boolean as the second
346  positional argument. This silent no-op fallback was removed and the argument
347  is now fully type checked. Passing a boolean will raise an error. (#35836)
348- On non-Windows systems, an authenticated RPC caller allowed to create wallets
349  could execute arbitrary commands as the node process account when
350  `-walletnotify` was configured, by crafting a wallet name with regex
351  replacement characters. Wallet notification placeholder replacement now treats
352  wallet names literally. (#36048)
353- The `removeprunedfunds` RPC has been deprecated and will be removed in the
354  next major release. In order to continue using it, `bitcoind` must be started
355  with the `-deprecatedrpc=removeprunedfunds` option. (#35605)
356
357GUI changes
358-----------
359
360- A menu action has been added to allow creating a watchonly wallet file from an
361  existing descriptor wallet. This option mirrors the `exportwatchonlywallet`
362  RPC - the exported file can be imported to another node using the Restore
363  Wallet menu action. (gui#872)
364- The "Enable Replace-By-Fee" checkbox has been removed from the Send tab, and
365  the send confirmation dialog no longer states whether a transaction signals
366  BIP 125 replaceability. Transactions created in the GUI now follow the wallet's
367  `-walletrbf` setting, which defaults to signalling replaceability and is
368  deprecated in this release (see Updated settings). (gui#936)
369- The migrate wallet option now allows to disable wallet loading after
370  migrating. It is useful in case the node is pruned and the wallet was created
371  before the pruned height. (gui#953)
372- The GUI is now built with Qt 6.8.4. (#35709)
373
374Mining
375------
376
377- The IPC mining interface now rejects out-of-range block template options
378  instead of silently clamping them, such as oversized reserved block weight or
379  coinbase sigops limits. (#33966)
380- The `-blockmaxweight` startup option is now rejected when it is lower than
381  `-blockreservedweight`, instead of being silently clamped. (#33966)
382
383
384IPC Interface
385-------------
386
387- `BlockTemplate.submitSolution` now returns `reason` and `debug` rejection
388  details in addition to the boolean result. Clients must regenerate IPC
389  bindings from the updated `mining.capnp` schema to use the new method. The
390  previous `@7` method now returns an error directing clients to update.
391  (#34672)
392- `BlockTemplate.submitSolution` now reports duplicate blocks as failures with
393  `reason="duplicate"`, matching `Mining.submitBlock`, instead of returning
394  success for duplicate submissions. (#34672)
395
396Logging
397-------
398
399- BIP 9 bits 5 to 28 inclusive are now ignored for soft fork signaling, as per
400  BIP 323. We won't warn about unknown deployments when receiving blocks that
401  set any of those bits in their version. (#34779)
402
403REST API
404--------
405
406- REST responses now include `Cache-Control` headers to guide intermediary
407  caches. Immutable responses such as block binary and hex data, block parts,
408  block filters, spent transaction outputs, and block-specific deployment info
409  are marked cacheable for one day. Responses that can change with active chain
410  or node state, as well as errors, are marked `no-store`. (#34794)
411
412Low-level changes
413=================
414
415Indexes
416-------
417
418- The transaction index (`-txindex`) now stores less data on disk; a fully
419  rebuilt index takes less than half the space. The index is backwards
420  compatible, so existing users will not see the space saving unless the index
421  is recreated. To do so, stop the node, delete the `<datadir>/indexes/txindex`
422  directory, and restart; rebuilding can take up to a few hours depending on
423  hardware. Progress can be monitored using the `getindexinfo` RPC. Once
424  rebuilt, the index can no longer be read by previous releases, so downgrading
425  will rebuild it again in the old format. When downgrading permanently, delete
426  the `<datadir>/indexes/txindex` directory first, since previous releases do
427  not reclaim the space used by entries in the new format. (#35531)
428- The transaction output spender index (`-txospenderindex`) now uses less disk
429  space. Existing indexes remain compatible and no action is required. To
430  reclaim the space for data indexed before upgrading, stop the node, delete the
431  `<datadir>/indexes/txospenderindex/` directory, and restart with
432  `-txospenderindex` enabled to rebuild it. (#35634, #35568)
433
434RPC
435---
436
437- Libevent has been replaced with a custom HTTP server (#35182). Certain HTTP
438  edge cases will observe different behavior to be more RFC-compliant:
439  - Stricter enforcement of maximum headers size (8192 bytes)
440  - Reject requests with whitespace in header field-names
441  - "Line Folding" is rejected (whitespace at start of a header line)
442  - Tolerate `%` at the end of requested URLs
443  - Multiple "Content-Length" headers with different values are rejected
444- Clients attempting to connect from addresses not allowed by the `-rpcallowip`
445  option (or its default, `localhost`) will now be immediately disconnected
446  instead of receiving a `403 Forbidden`. (#35592)
447
448Credits
449=======
450
451Thanks to everyone who directly contributed to this release:
452
453- 0xb10c
454- Adam Andrews
455- Alexander Wiederin
456- Alfonso Roman Zubeldia
457- ameen-alam
458- amisha
459- Amiti Uttarwar
460- Andreas Kouloumos
461- Andrew Toth
462- Anthony Towns
463- Anthropic Security
464- Antoine Poinsot
465- ArvinFarrelP
466- Ava Chow
467- azuchi
468- benthecarman
469- Ben Woosley
470- Bicaru20
471- b-l-u-e
472- Bortlesboat
473- Brandon Odiwuor
474- Bruno Garcia
475- CaesarCoder
476- Chandra Pratap
477- codeabysss
478- Cory Fields
479- Craig Raw
480- crStiv
481- csjones
482- cyb3ralbert
483- Daniela Brozzoni
484- Daniel Pfeifer
485- Danny van Heumen
486- David Gumberg
487- deadmanoz
488- dergoegge
489- ekzyis
490- Enoch Azariah
491- Eugene Siegel
492- Evan Sultanik
493- Fabian Jahr
494- fanquake
495- frankomosh
496- Gloria Zhao
497- Greg Sanders
498- Guillermo Fernandes
499- GuTS805
500- Hao Xu