gui: Use PSBT v0 #36539

davidgumberg commented at 8:18 AM on October 15, 2026: contributor

This fixes: #36518

There is no test added here for the bump fee PSBT's being v0, since there aren't any existing tests for watch only wallet feebumping in the GUI. If reviewers insist on this I can add it, but I wanted to keep the diff minimal. I have tested this manually.

AFAIU for the external signer stuff it shouldn't matter much whether it's v0 or v2, since users are very unlikely to be using HWI software that doesn't speak v0, but out of caution I've set the external signer PSBT to v0 for the GUI.

This PR originally took the approach of adding a checkbox, (davidgumberg/gui/2026-10-15-psbt-gui), but this was dropped to simplify backporting past string freeze.

LLM Disclosure: The previous approach was drafted using an LLM, but this branch was written by me. I used an LLM to explore adding a fee bump watchonly GUI test, and decided against it.

DrahtBot added the label GUI on Oct 15, 2026

DrahtBot commented at 8:18 AM on October 15, 2026: contributor

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

External sites

Code coverage & benchmarks: https://corecheck.dev/bitcoin/bitcoin/pulls/36539
Ralph review <img src=https://review.fish.foo/assets/bitcoin/bitcoin/36539.png alt="Ralph review status"> https://git.fish.foo/bitcoin/bitcoin/pulls/36539#author-ralph

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fanquake added this to the milestone 32.0 on Oct 15, 2026

davidgumberg commented at 12:53 AM on October 16, 2026: contributor

@achow101 @polespinasa

achow101 commented at 1:12 AM on October 16, 2026: member

I don't think we should be adding any GUI elements for a PR targeting a backport, particularly as it adds strings for translation. We can do v0 only in the GUI I guess.

fanquake commented at 4:45 AM on October 16, 2026: member

cc @hebasto

Sjors commented at 8:13 AM on October 17, 2026: member

We can do v0 only in the GUI I guess.

That seems fine for now if it's easier. There could be a (release) note to use the RPC for v2 when needed.

davidgumberg force-pushed on Oct 18, 2026

davidgumberg renamed this:
~~gui: Make PSBT version toggleable: v0 by default~~
gui: Use PSBT v0
on Oct 18, 2026

davidgumberg commented at 11:11 PM on October 18, 2026: contributor

I've pushed so that the GUI just returns v0 PSBT's.

Sjors commented at 2:41 AM on October 20, 2026: member

Code review f0777e68550cc100ab0341515c5c34bac45fc7a4.

AFAIU for the external signer stuff it shouldn't matter much whether it's v0 or v2, since users are very unlikely to be using HWI software that doesn't speak v0, but out of caution I've set the external signer PSBT to v0 for the GUI.

I think it's better to consistently use v2 for external signers, both from the GUI and RPC.

in src/wallet/feebumper.cpp:345 in f0777e6855 outdated

 339 | @@ -340,8 +340,9 @@ bool SignTransaction(CWallet& wallet, CMutableTransaction& mtx) {
 340 |      LOCK(wallet.cs_wallet);
 341 |  
 342 |      if (wallet.IsWalletFlagSet(WALLET_FLAG_EXTERNAL_SIGNER)) {
 343 | -        // Make a blank psbt
 344 | -        PartiallySignedTransaction psbtx(mtx);
 345 | +        // Make a blank PSBT, this means that users will need to have an
 346 | +        // external signer software that supports BIP-0370.
 347 | +        PartiallySignedTransaction psbtx(mtx, /*version=*/2);

Sjors commented at 2:43 AM on October 20, 2026:

You can use the same comment in the regular send path, if you take my suggestion above.

davidgumberg commented at 4:27 PM on October 26, 2026:

Taken, thanks

w0xlt commented at 5:15 PM on October 20, 2026: contributor

The GUI fee bump with an external signer still uses v2 (WalletModel::bumpFee -> signBumpTransaction -> feebumper::SignTransaction, pinned to v2 and shared with RPC bumpfee).

Suggestion: a psbt_version param can be added to feebumper::SignTransaction/signBumpTransaction, with the GUI passing 0 and RPC keeping 2.

diff --git a/src/interfaces/wallet.h b/src/interfaces/wallet.h
index 8862f94fab..da140f721e 100644
--- a/src/interfaces/wallet.h
+++ b/src/interfaces/wallet.h
@@ -175,7 +175,7 @@ public:
         CMutableTransaction& mtx) = 0;
 
     //! Sign bump transaction.
-    virtual bool signBumpTransaction(CMutableTransaction& mtx) = 0;
+    virtual bool signBumpTransaction(CMutableTransaction& mtx, uint32_t psbt_version) = 0;
 
     //! Commit bump transaction.
     virtual bool commitBumpTransaction(const Txid& txid,
diff --git a/src/qt/walletmodel.cpp b/src/qt/walletmodel.cpp
index 2422b88579..95454e2265 100644
--- a/src/qt/walletmodel.cpp
+++ b/src/qt/walletmodel.cpp
@@ -524,7 +524,7 @@ bool WalletModel::bumpFee(Txid hash, Txid& new_hash)
     assert(!m_wallet->privateKeysDisabled() || wallet().hasExternalSigner());
 
     // sign bumped transaction
-    if (!m_wallet->signBumpTransaction(mtx)) {
+    if (!m_wallet->signBumpTransaction(mtx, /*psbt_version=*/0)) {
         QMessageBox::critical(nullptr, tr("Fee bump error"), tr("Can't sign transaction."));
         return false;
     }
diff --git a/src/wallet/feebumper.cpp b/src/wallet/feebumper.cpp
index ab64fd8cda..1c7288aedd 100644
--- a/src/wallet/feebumper.cpp
+++ b/src/wallet/feebumper.cpp
@@ -336,13 +336,12 @@ Result CreateRateBumpTransaction(CWallet& wallet, const Txid& txid, const CCoinC
     return Result::OK;
 }
 
-bool SignTransaction(CWallet& wallet, CMutableTransaction& mtx) {
+bool SignTransaction(CWallet& wallet, CMutableTransaction& mtx, uint32_t psbt_version) {
     LOCK(wallet.cs_wallet);
 
     if (wallet.IsWalletFlagSet(WALLET_FLAG_EXTERNAL_SIGNER)) {
-        // Make a blank PSBT, this means that users will need to have an
-        // external signer software that supports BIP-0370.
-        PartiallySignedTransaction psbtx(mtx, /*version=*/2);
+        // Make a blank psbt
+        PartiallySignedTransaction psbtx(mtx, psbt_version);
 
         // First fill transaction with our data without signing,
         // so external signers are not asked to sign more than once.
diff --git a/src/wallet/feebumper.h b/src/wallet/feebumper.h
index 4e0befe412..62faea52af 100644
--- a/src/wallet/feebumper.h
+++ b/src/wallet/feebumper.h
@@ -58,9 +58,10 @@ Result CreateRateBumpTransaction(CWallet& wallet,
     std::optional<uint32_t> original_change_index = std::nullopt);
 
 //! Sign the new transaction,
+//! [@param](/github-metadata-backup-bitcoin-bitcoin/contributor/param/) psbt_version PSBT version passed to an external signer, if the wallet uses one
 //! [@return](/github-metadata-backup-bitcoin-bitcoin/contributor/return/) false if the tx couldn't be found or if it was
 //! impossible to create the signature(s)
-bool SignTransaction(CWallet& wallet, CMutableTransaction& mtx);
+bool SignTransaction(CWallet& wallet, CMutableTransaction& mtx, uint32_t psbt_version);
 
 //! Commit the bumpfee transaction.
 //! [@return](/github-metadata-backup-bitcoin-bitcoin/contributor/return/) success in case of CWallet::CommitTransaction was successful,
diff --git a/src/wallet/interfaces.cpp b/src/wallet/interfaces.cpp
index a7d24ca0b9..3a70e88c3a 100644
--- a/src/wallet/interfaces.cpp
+++ b/src/wallet/interfaces.cpp
@@ -300,7 +300,7 @@ public:
         std::vector<CTxOut> outputs; // just an empty list of new recipients for now
         return feebumper::CreateRateBumpTransaction(*m_wallet.get(), txid, coin_control, errors, old_fee, new_fee, mtx, /* require_mine= */ true, outputs) == feebumper::Result::OK;
     }
-    bool signBumpTransaction(CMutableTransaction& mtx) override { return feebumper::SignTransaction(*m_wallet.get(), mtx); }
+    bool signBumpTransaction(CMutableTransaction& mtx, uint32_t psbt_version) override { return feebumper::SignTransaction(*m_wallet.get(), mtx, psbt_version); }
     bool commitBumpTransaction(const Txid& txid,
         CMutableTransaction&& mtx,
         std::vector<bilingual_str>& errors,
diff --git a/src/wallet/rpc/spend.cpp b/src/wallet/rpc/spend.cpp
index e228298c0c..9de3464675 100644
--- a/src/wallet/rpc/spend.cpp
+++ b/src/wallet/rpc/spend.cpp
@@ -1138,7 +1138,8 @@ static RPCMethod bumpfee_helper(std::string method_name)
     // For bumpfee, return the new transaction id.
     // For psbtbumpfee, return the base64-encoded unsigned PSBT of the new transaction.
     if (!want_psbt) {
-        if (!feebumper::SignTransaction(*pwallet, mtx)) {
+        // External signers must support BIP-0370 (PSBT v2)
+        if (!feebumper::SignTransaction(*pwallet, mtx, /*psbt_version=*/2)) {
             if (pwallet->IsWalletFlagSet(WALLET_FLAG_EXTERNAL_SIGNER)) {
                 throw JSONRPCError(RPC_WALLET_ERROR, "Transaction incomplete. Try psbtbumpfee instead.");
             }

</details>

fanquake removed this from the milestone 32.0 on Oct 21, 2026

fanquake added this to the milestone 32.1 on Oct 21, 2026

fanquake added the label Needs Backport (32.x) on Oct 21, 2026

fanquake commented at 11:07 AM on October 21, 2026: member

Pushed this to the 32.1 milestone.

fanquake removed this from the milestone 32.1 on Oct 26, 2026

fanquake added this to the milestone 32.2 on Oct 26, 2026

davidgumberg force-pushed on Oct 26, 2026

gui: wallet: Use v0 PSBT

PSBTv2 is not very interesting for current GUI users, and defaulting to
it causes issues for existing users. To make this change minimal and
avoid touching strings, this commit, only changes the default back
instead of making the version configurable.

The external signer PSBT will still be version 2, and I've added an
explicit argument here to show that. This will break users who are using
HWI versions < 2.1.0.
(https://github.com/bitcoin-core/HWI/releases/tag/2.1.0)

23dcb03a2c

refactor: psbt: Don't set a default version for PSBT constructor 3fdc45d1fa

davidgumberg force-pushed on Oct 26, 2026

davidgumberg commented at 4:26 PM on October 26, 2026: contributor

I've modified this so that the external signer PSBT's are v2, this breaks support with external signer software that doesn't know about v2, which is quite reasonable I think, so I've added a release note about that.

DrahtBot added the label CI failed on Oct 26, 2026

Sjors commented at 12:24 PM on October 27, 2026: member

ACK 3fdc45d1fa2a6f32f251aa6f639a52bbfd5245b0

Sadly we missed the 32.1 milestone, time flies.

hebasto commented at 1:57 PM on October 27, 2026: member

I've re-run previously cancelled CI jobs.

DrahtBot removed the label CI failed on Oct 27, 2026

w0xlt commented at 7:59 PM on October 27, 2026: contributor

crACK 3fdc45d1fa2a6f32f251aa6f639a52bbfd5245b0