doc: archive release notes for v31.0

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+v31.0 Release Notes
+===================
+
+Bitcoin Core version 31.0 is now available from:
+
+  <https://bitcoincore.org/bin/bitcoin-core-31.0/>
+
+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.
+
+Compatibility
+==============
+
+Bitcoin Core is supported and tested on the following operating systems or
+newer: Linux Kernel 3.17, macOS 14, and Windows 10 (version 1903). 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
+===============
+
+The default `-dbcache` value has been increased to 1024 MiB from 450 MiB on
+systems where at least 4096 MiB of RAM is detected. This improves performance
+but increases memory usage. On some systems (for example when running in
+containers), the detected RAM may exceed the memory actually available, which
+can lead to out-of-memory conditions. To maintain the previous behavior, set
+`-dbcache=450`. See
+[reduce-memory.md](https://github.com/bitcoin/bitcoin/blob/master/doc/reduce-memory.md)
+for further guidance on low-memory systems. (#34692)
+
+Mempool
+-------
+
+The mempool has been reimplemented with a new design ("cluster mempool"), to
+facilitate better decision-making when constructing block templates, evicting
+transactions, relaying transactions, and validating replacement transactions
+(RBF). Most changes should be transparent to users, but some behavior changes
+are noted:
+
+- The mempool no longer enforces ancestor or descendant size/count limits.
+Instead, two new default policy limits are introduced governing connected
+components, or clusters, in the mempool, limiting clusters to 64 transactions
+and up to 101 kB in virtual size.  Transactions are considered to be in the same
+cluster if they are connected to each other via any combination of parent/child
+relationships in the mempool. These limits can be overridden using command-line
+arguments; see the extended help (`-help-debug`) for more information.
+
+- Within the mempool, transactions are ordered based on the feerate at which
+they are expected to be mined, which takes into account the full set, or
+"chunk", of transactions that would be included together (e.g., a parent and its
+child, or more complicated subsets of transactions). This ordering is utilized
+by the algorithms that implement transaction selection for constructing block
+templates; eviction from the mempool when it is full; and transaction relay
+announcements to peers.
+
+- The replace-by-fee validation logic has been updated so that transaction
+replacements are only accepted if the resulting mempool's feerate diagram is
+strictly better than before the replacement. This eliminates all known cases of
+replacements occurring that make the mempool worse off, which was possible under
+previous RBF rules. For singleton transactions (that are in clusters by
+themselves) it's sufficient for a replacement to have a higher fee and feerate
+than the original. See [delvingbitcoin.org
+post](https://delvingbitcoin.org/t/an-overview-of-the-cluster-mempool-proposal/393#rbf-can-now-be-made-incentive-compatible-for-miners-11)
+for more information.
+
+- Two new RPCs have been added: `getmempoolcluster` will provide the set of
+transactions in the same cluster as the given transaction, along with the
+ordering of those transactions and grouping into chunks; and
+`getmempoolfeeratediagram` will return the feerate diagram of the entire
+mempool.
+
+- Chunk size and chunk fees are now also included in the output of
+`getmempoolentry`.
+
+- The "CPFP Carveout" has been removed from the mempool logic. The CPFP carveout
+allowed one additional child transaction to be added to a package that's already
+at its descendant limit, but only if that child has exactly one ancestor (the
+package's root) and is small (no larger than 10kvB). Nothing is allowed to
+bypass the cluster count limit. It is expected that smart contracting use-cases
+requiring similar functionality employ TRUC transactions and sibling eviction
+instead going forward.
+
+- Some additional discussion can be found at
+[doc/policy/mempool-terminology.md](https://github.com/bitcoin/bitcoin/blob/master/doc/policy/mempool-terminology.md)
+and
+[doc/policy/mempool-replacements.md](https://github.com/bitcoin/bitcoin/blob/master/doc/policy/mempool-replacements.md).
+
+P2P and network changes
+-----------------------
+
+- Normally local transactions are broadcast to all connected peers with which we
+do transaction relay. Now, for the `sendrawtransaction` RPC this behavior can be
+changed to only do the broadcast via the Tor or I2P networks. A new boolean
+option `-privatebroadcast` has been added to enable this behavior. This improves
+the privacy of the transaction originator in two aspects:
+  1. Their IP address (and thus geolocation) is never known to the recipients.
+  2. If the originator sends two otherwise unrelated transactions, they will not
+  be linkable. This is because a separate connection is used for broadcasting
+  each transaction. (#29415)
+
+- New RPCs have been added to introspect and control private broadcast:
+`getprivatebroadcastinfo` reports transactions currently being privately
+broadcast, and `abortprivatebroadcast` removes matching transactions from the
+private broadcast queue. (#34329)
+
+- Transactions participating in one-parent-one-child package relay can now have
+the parent with a feerate lower than the `-minrelaytxfee` feerate, even 0 fee.
+This expands the change from 28.0 to also cover packages of non-TRUC
+transactions. Note that in general the package child can have additional
+unconfirmed parents, but they must already be in-mempool for the new package to
+be relayed. (#33892)
+
+- The release has asmap data embedded for the first time, allowing the asmap
+feature to be used without any externally sourced file. The embedded map [was
+created on 2026-03-05](https://github.com/bitcoin/bitcoin/pull/34696). Despite
+the data being available, the option remains off-by-default. Users still need to
+set `-asmap` or `-asmap=1` explicitly to make it possible to use a peer's ASN
+(ISP/hoster identifier) in netgroup bucketing in order to ensure a higher
+diversity in their peer set.
+
+Updated RPCs
+------------
+
+- `gettxspendingprevout` has 2 new optional arguments: `mempool_only` and
+`return_spending_tx`. If `mempool_only` is true it will limit scans to the
+mempool even if `txospenderindex` is available. If `return_spending_tx` is true,
+the full spending tx will be returned. In addition if `txospenderindex` is
+available and a confirmed spending transaction is found, its block hash will be
+returned. (#24539)
+
+- The `getpeerinfo` RPC no longer returns the `startingheight` field unless the
+configuration option `-deprecatedrpc=startingheight` is used. The
+`startingheight` field will be fully removed in the next major release. (#34197)
+
+- The `getblock` RPC now returns a `coinbase_tx` object at verbosity levels 1,
+2, and 3. It contains `version`, `locktime`, `sequence`, `coinbase` and
+`witness`. This allows for efficiently querying coinbase transaction properties
+without fetching the full transaction data at verbosity 2+. (#34512)
+
+REST API
+--------
+
+- A new REST API endpoint
+(`/rest/blockpart/<BLOCK-HASH>.<bin|hex>?offset=<OFFSET>&size=<SIZE>`) has been
+introduced for efficiently fetching a range of bytes from block `<BLOCK-HASH>`.
+(#33657)
+
+Build System
+------------
+
+- The minimum supported Clang compiler version has been raised to 17.0 (#33555).
+- The minimum supported GCC compiler version has been raised to 12.1 (#33842).
+
+Updated settings
+----------------
+
+- The `-paytxfee` startup option and the `settxfee` RPC are now deleted after
+being deprecated in Bitcoin Core 30.0. They used to allow the user to set a
+static fee rate for wallet transactions, which could potentially lead to
+overpaying or underpaying. Users should instead rely on fee estimation or
+specify a fee rate per transaction using the `fee_rate` argument in RPCs such as
+`fundrawtransaction`, `sendtoaddress`, `send`, `sendall`, and `sendmany`.
+(#32138)
+
+- Specifying `-asmap` or `-asmap=1` will load the embedded asmap data instead of
+an external file. In previous releases, if `-asmap` was specified without a
+filename, this would try to load an `ip_asn.map` data file. Now loading an
+external asmap file always requires an explicit filename like
+`-asmap=ip_asn.map`.
+
+- The `-maxorphantx` startup option has been removed. It was previously
+deprecated and has no effect anymore since v30.0. (#33872)
+
+- `tor` has been removed as a network specification. It was deprecated in favour
+of `onion` in v0.17.0. (#34031)
+
+- When `-logsourcelocations` is enabled, the log output now contains just the
+function name instead of the entire function signature. (#34088)
+
+- The default `-dbcache` value has been increased to `1024` MiB from `450` MiB
+on systems where at least `4096` MiB of RAM is detected. This is a performance
+increase, but will use more memory. To maintain the previous behaviour, set
+`-dbcache=450`. (#34692)
+
+- `-privatebroadcast` is added to enable private broadcast behavior for
+`sendrawtransaction`.
+
+New settings
+------------
+
+- `-txospenderindex` enables the creation of a transaction output spender index
+that, if present, will be scanned by `gettxspendingprevout` if a spending
+transaction was not found in the mempool. (#24539)
+
+GUI changes
+-----------
+
+- The GUI has been updated to Qt 6.8. (#34650)
+
+- The `createwallet`, `createwalletdescriptor` and `migratewallet` commands are
+filtered from the console history to improve security and privacy. (gui#901)
+
+- The Restore Wallet dialog shows an error message if the restored wallet name
+is empty. (gui#924)
+
+Fee Estimation
+--------------
+
+The Bitcoin Core fee estimator minimum fee rate bucket was updated from **1
+sat/vB** to **0.1 sat/vB**, which matches the node’s default `minrelaytxfee`. This
+means that for a given confirmation target, if a sub-1 sat/vB fee rate bucket is
+the minimum tracked with sufficient data, its average value will be returned as
+the fee rate estimate.
+
+Restarting a node with this change invalidates previously saved
+estimates in `fee_estimates.dat`, the fee estimator will start tracking fresh
+stats.
+
+IPC Interface
+-------------
+
+- The IPC mining interface now requires mining clients to use the latest
+`mining.capnp` schema. Clients built against older schemas will fail when
+calling `Init.makeMining` and receive an RPC error indicating the old mining
+interface is no longer supported. Mining clients must update to the latest
+schema and regenerate bindings to continue working. (#34568)
+- `Mining.createNewBlock` now has a `cooldown` behavior (enabled by default)
+that waits for IBD to finish and for the tip to catch up. This usually prevents
+a flood of templates during startup, but is not guaranteed. (#34184)
+- `Mining.interrupt()` can be used to interrupt `Mining.waitTipChanged` and
+`Mining.createNewBlock`. (#34184)
+- `Mining.createNewBlock` and `Mining.checkBlock` now require a `context`
+parameter.
+- `Mining.waitTipChanged` now has a default `timeout` (effectively infinite /
+`maxDouble`) if the client omits it.
+- `BlockTemplate.getCoinbaseTx()` now returns a structured `CoinbaseTx` instead
+of raw bytes.
+- Removed `BlockTemplate.getCoinbaseCommitment()` and
+`BlockTemplate.getWitnessCommitmentIndex()`.
+- Cap’n Proto default values were updated to match the corresponding C++
+defaults for mining-related option structs (e.g. `BlockCreateOptions`,
+`BlockWaitOptions`, `BlockCheckOptions`).
+
+Credits
+=======
+
+Thanks to everyone who directly contributed to this release:
+
+- 0xb10c
+- Alexander Wiederin
+- Alfonso Roman Zubeldia
+- amisha
+- ANAVHEOBA
+- Andrew Toth
+- Anthony Towns
+- Antoine Poinsot
+- ANtutov
+- Anurag chavan
+- Ava Chow
+- bensig
+- Ben Westgate
+- billymcbip
+- b-l-u-e
+- Brandon Odiwuor
+- brunoerg
+- Bruno Garcia
+- Calin Culianu
+- Carl Dong
+- Chandra Pratap
+- Chris Stewart
+- Coder
+- Cory Fields
+- da1sychain
+- Daniela Brozzoni
+- Daniel Pfeifer
+- David Gumberg
+- dergoegge
+- Dmitry Goncharov
+- Enoch Azariah
+- Eugene Siegel
+- Fabian Jahr
+- fanquake
+- Fibonacci747
+- flack
+- frankomosh
+- furszy
+- glozow
+- Greg Sanders
+- Hao Xu
+- Hennadii Stepanov
+- Henry Romp
+- Hodlinator
+- ismaelsadeeq
+- janb84
+- jayvaliya
+- joaonevess
+- John Moffett
+- Josh Doman
+- kevkevinpal
+- l0rinc
+- Luke Dashjr
+- Mara van der Laan
+- MarcoFalke
+- marcofleon
+- Martin Zumsande
+- Matthew Zipkin
+- Max Edwards
+- Murch
+- Musa Haruna
+- naiyoma
+- nervana21
+- Novo
+- optout
+- pablomartin4btc
+- Padraic Slattery
+- Pieter Wuille
+- Pol Espinasa
+- pythcoiner
+- rkrux
+- Robin David
+- Roman Zeyde
+- rustaceanrob
+- Ryan Ofsky
+- SatsAndSports
+- scgbckbone
+- Sebastian Falbesoner
+- sedited
+- seduless
+- Sergi Delgado Segura
+- Sjors Provoost
+- SomberNight
+- sstone
+- stickies-v
+- stratospher
+- stringintech
+- Suhas Daftuar
+- tboy1337
+- TheCharlatan
+- Tim Ruffing
+- Vasil Dimov
+- w0xlt
+- WakeTrainDev
+- Weixie Cui
+- willcl-ark
+- Woolfgm
+- yancy
+- Yash Bhutwala
+- yuvicc
+- zaidmstrr
+
+As well as to everyone that helped with translations on
+[Transifex](https://explore.transifex.com/bitcoin/bitcoin/).