diff --git a/doc/release-notes-extended-coinbase-maturity.md b/doc/release-notes-extended-coinbase-maturity.md
new file mode 100644
index 000000000000..411f1b1c7fbb
--- /dev/null
+++ b/doc/release-notes-extended-coinbase-maturity.md
@@ -0,0 +1,48 @@
+### Extended coinbase maturity (temporary softfork)
+
+Coinbase outputs created while this deployment is active can only be spent
+once the spending block's parent has a median-time-past at least 45 days
+(3,888,000 seconds) past the coinbase block's median-time-past,
+on top of the usual 100 confirmations. Measuring the delay in median-time-past
+rather than blocks keeps it 45 days of real time however fast or slow
+blocks come, and a miner cannot shorten it: block times cannot run more than
+about two hours ahead of real time, so neither can the median.
+
+The rule applies to every block from the first one whose parent's
+median-time-past reaches the deployment's start time, and expires together
+with RDTS: from the first block whose parent's median-time-past reaches the
+RDTS expiry (2027-09-01 00:00 UTC on mainnet) every coinbase output is again
+spendable after 100 confirmations, including those created during the window
+that had not yet served their 45 days.
+
+Only outputs created inside the window are affected. A coinbase output created
+before activation keeps the 100-block rule throughout, so activating the
+deployment cannot lock an output that was already spendable. The 100-block
+rule continues to apply to every coinbase output at all times.
+
+The start time is not yet scheduled on mainnet or testnet4 in this release
+(see `src/kernel/chainparams.cpp`); the deployment does nothing until it is.
+
+Miners: block rewards mined inside the window cannot be spent for 45 days
+(or until the RDTS expiry, whichever comes first). Pools that pay their miners
+directly from coinbase outputs pass this delay through to those miners. A
+non-upgraded miner that spends its own reward at 100 confirmations produces a
+block that upgraded nodes reject.
+
+Wallet: rewards subject to the rule are reported as immature (in
+`getbalances` `immature`, `listtransactions` category `immature` and the
+GUI) until they can be spent, and are not selected for spending before then,
+so the wallet never creates a transaction the network would reject. The
+"blocks to maturity" the wallet reports for such a reward is an estimate,
+the remaining time at the target block spacing.
+
+`getdeploymentinfo` reports the deployment as `extended_coinbase_maturity`, a
+`flagday` entry with `start_time`, `expiry_time` (the RDTS expiry), `active`
+(for the next block) and, once the queried chain's median-time-past has reached
+the start time, `height`, the activation height on that chain. It is omitted
+on chains where the deployment is not scheduled. `getblocktemplate` lists
+`extended_coinbase_maturity` in `rules` while the deployment is active; no
+client-side support is required.
+
+On regtest the deployment is scheduled with `-extendedcoinbasematurity=<time>`,
+which requires `-rdtsexpiry` and must precede it.
diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index 54ab526e2b7c..08a5d23f587c 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -93,6 +93,20 @@ void ReadRegTestArgs(const ArgsManager& args, CChainParams::RegTestOptions& opti
         options.rdts_expiry_time = expiry;
     }
 
+    if (const auto arg{args.GetArg("-extendedcoinbasematurity", "")}; !arg.empty()) {
+        // The rule expires with RDTS: without an RDTS expiry, or with a start
+        // at or after it, it could never apply, which is indistinguishable
+        // from not scheduling it at all.
+        if (!options.rdts_expiry_time) {
+            throw std::runtime_error("-extendedcoinbasematurity requires -rdtsexpiry=<time> (the rule expires with RDTS).");
+        }
+        int64_t start;
+        if (!ParseInt64(arg, &start) || start >= *options.rdts_expiry_time) {
+            throw std::runtime_error(strprintf("Invalid start (%s) for -extendedcoinbasematurity=<time>: must precede the RDTS expiry (%d).", arg, *options.rdts_expiry_time));
+        }
+        options.extended_coinbase_maturity_start_time = start;
+    }
+
     if (const auto arg{args.GetArg("-blake2b_headline")}; arg) {
         if (!options.activation_heights.contains(Consensus::BuriedDeployment::DEPLOYMENT_BLAKE2B)) {
             throw std::runtime_error("-blake2b_headline requires -testactivationheight=blake2b@<height>");
diff --git a/src/chainparamsbase.cpp b/src/chainparamsbase.cpp
index e2ff25346d0c..05bd3142ad56 100644
--- a/src/chainparamsbase.cpp
+++ b/src/chainparamsbase.cpp
@@ -6,6 +6,7 @@
 #include <chainparamsbase.h>
 
 #include <common/args.h>
+#include <consensus/consensus.h>
 #include <tinyformat.h>
 #include <util/chaintype.h>
 
@@ -18,6 +19,7 @@ void SetupChainParamsBaseOptions(ArgsManager& argsman)
                  "This is intended for regression testing tools and app development. Equivalent to -chain=regtest.", ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::CHAINPARAMS);
     argsman.AddArg("-testactivationheight=name@height.", "Set the activation height of 'name' (segwit, bip34, dersig, cltv, csv, blake2b). (regtest-only)", ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-rdtsexpiry=<time>", "Schedule the RDTS expiry: RDTS rules apply to blocks from the blake2b activation height until the parent block's median-time-past reaches <time>. Requires -testactivationheight=blake2b@<height>. (regtest-only)", ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
+    argsman.AddArg("-extendedcoinbasematurity=<time>", strprintf("Schedule the extended coinbase maturity soft fork: coinbase outputs created from the first block whose parent's median-time-past reaches <time> cannot be spent until the median-time-past has advanced %d seconds past their block's, until the RDTS expiry. Requires -rdtsexpiry, which <time> must precede. (regtest-only)", EXTENDED_COINBASE_MATURITY_TIME), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-blake2b_headline=<headline>", "Specify consensus-critical proof-of-time news headline. Requires -testactivationheight=blake2b@<height>. (regtest-only)", ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-testnet", "Use the testnet3 chain. Equivalent to -chain=test. Support for testnet3 is deprecated and will be removed in an upcoming release. Consider moving to testnet4 now by using -testnet4.", ArgsManager::ALLOW_ANY, OptionsCategory::CHAINPARAMS);
     argsman.AddArg("-testnet4", "Use the testnet4 chain. Equivalent to -chain=testnet4.", ArgsManager::ALLOW_ANY, OptionsCategory::CHAINPARAMS);
diff --git a/src/consensus/consensus.h b/src/consensus/consensus.h
index 69dd2b605950..e4553fe2a10c 100644
--- a/src/consensus/consensus.h
+++ b/src/consensus/consensus.h
@@ -19,6 +19,11 @@ static const unsigned int REDUCED_DATA_MAX_BLOCK_WEIGHT = 800000;
 static const int64_t MAX_BLOCK_SIGOPS_COST = 80000;
 /** Coinbase transaction outputs can only be spent after this number of new blocks (network rule) */
 static const int COINBASE_MATURITY = 100;
+/** Extended coinbase maturity, applied by the temporary soft fork to coinbase outputs created while it is
+ *  active: the spending block's parent must have a median-time-past at least this many seconds past the
+ *  coinbase block's median-time-past (45 days, the time 6480 ten-minute blocks would take;
+ *  see Consensus::Params::ExtendedCoinbaseMaturityActiveAt) */
+static const int64_t EXTENDED_COINBASE_MATURITY_TIME = 3888000;
 
 static const int WITNESS_SCALE_FACTOR = 4;
 
diff --git a/src/consensus/params.h b/src/consensus/params.h
index 0231e63b20a3..9a10951f96fb 100644
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -123,6 +123,23 @@ struct Params {
      * behaviour is unchanged on chains that do not set it.
      */
     int64_t RdtsExpiryTime{std::numeric_limits<int64_t>::min()};
+    /**
+     * Extended coinbase maturity, a temporary soft fork: while it is active,
+     * coinbase outputs created since it activated can only be spent once the
+     * spending block's parent has a median-time-past at least
+     * EXTENDED_COINBASE_MATURITY_TIME past the coinbase block's, on top of
+     * the usual COINBASE_MATURITY blocks. It is active for a block when the
+     * parent's median-time-past has reached this start time and not yet the
+     * RDTS expiry (see ExtendedCoinbaseMaturityActiveAt): it expires with
+     * RDTS, after which every coinbase output is again spendable at
+     * COINBASE_MATURITY. Outputs created before activation are never
+     * affected, so activating cannot lock an output that was already
+     * spendable.
+     *
+     * The default leaves the deployment unscheduled (the start follows every
+     * median-time-past).
+     */
+    int64_t ExtendedCoinbaseMaturityStartTime{std::numeric_limits<int64_t>::max()};
     /** Don't warn about unknown BIP 9 activations below this height.
      * This prevents us from warning about the CSV and segwit activations. */
     int MinBIP9WarningHeight;
@@ -195,6 +212,14 @@ struct Params {
     {
         return IsBlake2bHeight(height) && mtp_prev < RdtsExpiryTime;
     }
+
+    /** Whether the extended coinbase maturity rule applies to a block whose
+     *  parent has the given median-time-past. It expires with RDTS, so it is
+     *  never active on a chain with no RDTS expiry. */
+    bool ExtendedCoinbaseMaturityActiveAt(int64_t mtp_prev) const
+    {
+        return mtp_prev >= ExtendedCoinbaseMaturityStartTime && mtp_prev < RdtsExpiryTime;
+    }
 };
 
 } // namespace Consensus
diff --git a/src/interfaces/chain.h b/src/interfaces/chain.h
index 45dbb98bed15..70d9086db4bb 100644
--- a/src/interfaces/chain.h
+++ b/src/interfaces/chain.h
@@ -144,6 +144,14 @@ class Chain
     //! pruned), and contains transactions.
     virtual bool haveBlockOnDisk(int height) = 0;
 
+    //! Whether the temporary extended coinbase maturity soft fork still
+    //! holds back a coinbase output created at the given height of the
+    //! active chain from being spent in the block after the current tip,
+    //! and if so an estimate of the blocks until it no longer does (at
+    //! least 1). 0 when it does not (the COINBASE_MATURITY depth rule is
+    //! the caller's to apply).
+    virtual int extendedCoinbaseBlocksToMaturity(int coinbase_height) = 0;
+
     virtual bool pruneLockExists(const std::string& name) const = 0;
     virtual bool updatePruneLock(const std::string& name, const node::PruneLockInfo& lock_info, bool sync=false) = 0;
     virtual bool deletePruneLock(const std::string& name) = 0;
diff --git a/src/kernel/chainparams.cpp b/src/kernel/chainparams.cpp
index 8ba49ad591e1..387d96974db8 100644
--- a/src/kernel/chainparams.cpp
+++ b/src/kernel/chainparams.cpp
@@ -131,6 +131,10 @@ class CMainParams : public CChainParams {
         // reaching ACTIVE, and that deployment has been removed.)
         consensus.RdtsExpiryTime = 1819756800; // September 1st, 2027 00:00 UTC
 
+        // Extended coinbase maturity (temporary soft fork, expires with RDTS
+        // above): the start time is set at release cut. Unscheduled until then.
+        // consensus.ExtendedCoinbaseMaturityStartTime = ...;
+
         consensus.nMinimumChainWork = uint256{"00000000000000000000000000000000000000013e00277374c9f9eeadc70200"};
         consensus.defaultAssumeValid = uint256{"0000000000000078ed1e20cac1acf78df6d1060c78059fb6331e17141c881fc8"}; // 964264
 
@@ -403,6 +407,7 @@ class CTestNet4Params : public CChainParams {
 
         consensus.Blake2bHeight = 150308;
         consensus.RdtsExpiryTime = 1791903600; // October 13th, 2026 15:00:00 UTC
+        // Extended coinbase maturity: unscheduled until release cut (see mainnet).
 
         consensus.nMinimumChainWork = uint256{"0000000000000000000000000000000000000000000001d6dce8651b6094e4c1"};
         consensus.defaultAssumeValid = uint256{"0000000000003ed4f08dbdf6f7d6b271a6bcffce25675cb40aa9fa43179a89f3"}; // 72600
@@ -665,6 +670,13 @@ class CRegTestParams : public CChainParams
             consensus.RdtsExpiryTime = *opts.rdts_expiry_time;
         }
 
+        // Optionally schedule the extended coinbase maturity soft fork (see
+        // -extendedcoinbasematurity). It expires with RDTS, so it requires the
+        // RDTS expiry scheduled above.
+        if (opts.extended_coinbase_maturity_start_time) {
+            consensus.ExtendedCoinbaseMaturityStartTime = *opts.extended_coinbase_maturity_start_time;
+        }
+
         for (const auto& [deployment_pos, version_bits_params] : opts.version_bits_parameters) {
             consensus.vDeployments[deployment_pos].nStartTime = version_bits_params.start_time;
             consensus.vDeployments[deployment_pos].nTimeout = version_bits_params.timeout;
diff --git a/src/kernel/chainparams.h b/src/kernel/chainparams.h
index 63ab289be206..51859bd30d0a 100644
--- a/src/kernel/chainparams.h
+++ b/src/kernel/chainparams.h
@@ -170,6 +170,11 @@ class CChainParams
         //! height until the parent block's median-time-past reaches this
         //! value (see -rdtsexpiry). Requires a blake2b activation height.
         std::optional<int64_t> rdts_expiry_time{};
+        //! If set, the extended coinbase maturity rule applies to blocks
+        //! whose parent's median-time-past has reached this value, until the
+        //! RDTS expiry (see -extendedcoinbasematurity). Requires
+        //! rdts_expiry_time, which it must precede.
+        std::optional<int64_t> extended_coinbase_maturity_start_time{};
         std::optional<std::vector<unsigned char>> blake2b_headline{};
     };
 
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index fec8adb20966..852f30642ef0 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -10,6 +10,7 @@
 #include <chainparamsbase.h>
 #include <common/args.h>
 #include <common/pcp.h>
+#include <consensus/consensus.h>
 #include <consensus/merkle.h>
 #include <consensus/validation.h>
 #include <deploymentstatus.h>
@@ -66,6 +67,7 @@
 
 #include <bitcoin-build-config.h> // IWYU pragma: keep
 
+#include <algorithm>
 #include <any>
 #include <memory>
 #include <optional>
@@ -581,6 +583,19 @@ class ChainImpl : public Chain
         const CBlockIndex* block{chainman().ActiveChain()[height]};
         return block && ((block->nStatus & BLOCK_HAVE_DATA) != 0) && block->nTx > 0;
     }
+    int extendedCoinbaseBlocksToMaturity(int coinbase_height) override
+    {
+        LOCK(::cs_main);
+        const Consensus::Params& params{chainman().GetConsensus()};
+        const CBlockIndex* tip{chainman().ActiveChain().Tip()};
+        if (!tip || !params.ExtendedCoinbaseMaturityActiveAt(tip->GetMedianTimePast())) return 0;
+        const CBlockIndex* coinbase_block{chainman().ActiveChain()[coinbase_height]};
+        if (!coinbase_block || !coinbase_block->pprev ||
+            !params.ExtendedCoinbaseMaturityActiveAt(coinbase_block->pprev->GetMedianTimePast())) return 0;
+        const int64_t remaining{coinbase_block->GetMedianTimePast() + EXTENDED_COINBASE_MATURITY_TIME - tip->GetMedianTimePast()};
+        if (remaining <= 0) return 0;
+        return std::max<int64_t>(1, (remaining + params.nPowTargetSpacing - 1) / params.nPowTargetSpacing);
+    }
     bool pruneLockExists(const std::string& name) const override
     {
         LOCK(cs_main);
diff --git a/src/qt/transactiondesc.cpp b/src/qt/transactiondesc.cpp
index 5ceb7621d3da..512c07a503ed 100644
--- a/src/qt/transactiondesc.cpp
+++ b/src/qt/transactiondesc.cpp
@@ -329,7 +329,13 @@ QString TransactionDesc::toHTML(interfaces::Node& node, interfaces::Wallet& wall
 
     if (wtx.is_coinbase)
     {
-        quint32 numBlocksToMaturity = COINBASE_MATURITY +  1;
+        // While still maturing, the wallet's count reflects the maturity that
+        // actually applies (the temporary extended maturity soft fork may
+        // require more than COINBASE_MATURITY, as an estimate); once mature,
+        // show the default.
+        quint32 numBlocksToMaturity = status.blocks_to_maturity > 0 && status.is_in_main_chain
+            ? status.blocks_to_maturity + status.depth_in_main_chain
+            : COINBASE_MATURITY + 1;
         strHTML += "<br>" + tr("Generated coins must mature %1 blocks before they can be spent. When you generated this block, it was broadcast to the network to be added to the block chain. If it fails to get into the chain, its state will change to \"not accepted\" and it won't be spendable. This may occasionally happen if another node generates a block within a few seconds of yours.").arg(QString::number(numBlocksToMaturity)) + "<br>";
     }
 
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 8353366862c7..3e3c6b592778 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -1913,10 +1913,11 @@ RPCHelpMan getblockchaininfo()
 namespace {
 const std::vector<RPCResult> RPCHelpForDeployment{
     {RPCResult::Type::STR, "type", "one of \"buried\", \"bip9\", \"flagday\""},
-    {RPCResult::Type::NUM, "height", /*optional=*/true, "height of the first block which enforces the rules (only for \"buried\" and \"flagday\" types, or \"bip9\" type with \"active\" status; for \"flagday\" this is the BLAKE2b hardfork height)"},
+    {RPCResult::Type::NUM, "height", /*optional=*/true, "height of the first block which enforces the rules (only for \"buried\" and \"flagday\" types, or \"bip9\" type with \"active\" status; for \"reduced_data\" this is the BLAKE2b hardfork height; for \"extended_coinbase_maturity\" it is the activation height on the queried block's chain, present once that chain's median time past has reached start_time)"},
     {RPCResult::Type::NUM, "height_end", /*optional=*/true, "height of the last block which enforces the rules (only for \"bip9\" type with \"active\" status and temporary deployments)"},
     {RPCResult::Type::BOOL, "active", "true if the rules are enforced for the mempool and the next block (the mempool applies the RDTS rules regardless of this flag)"},
-    {RPCResult::Type::NUM_TIME, "expiry_time", /*optional=*/true, "median time past at and after which the rules are no longer enforced (only for \"flagday\" type; a block is past expiry when its parent's median time past has reached this value)"},
+    {RPCResult::Type::NUM_TIME, "start_time", /*optional=*/true, "median time past at and after which the rules are enforced (only for the \"extended_coinbase_maturity\" flag-day deployment; a block enforces the rules when its parent's median time past has reached this value)"},
+    {RPCResult::Type::NUM_TIME, "expiry_time", /*optional=*/true, "median time past at and after which the rules are no longer enforced (only for \"flagday\" type; a block is past expiry when its parent's median time past has reached this value; \"extended_coinbase_maturity\" shares the \"reduced_data\" expiry)"},
     {RPCResult::Type::OBJ, "bip9", /*optional=*/true, "status of bip9 softforks (only for \"bip9\" type)",
     {
         {RPCResult::Type::NUM, "bit", /*optional=*/true, "the bit (0-28) in the block version field used to signal this softfork (only for \"started\" and \"locked_in\" status)"},
@@ -1940,26 +1941,51 @@ const std::vector<RPCResult> RPCHelpForDeployment{
     }},
 };
 
-// RDTS (a flag-day deployment, not a versionbits one): rules apply to every
-// block from the BLAKE2b hardfork height until the parent block's
-// median-time-past reaches RdtsExpiryTime. Reported as-of the queried block,
-// with "active" meaning the next block, like the versionbits entries. Omitted
-// entirely when unscheduled (plain regtest), as NEVER_ACTIVE deployments are.
-void RdtsFlagDayDescPushBack(const CBlockIndex* blockindex, UniValue& softforks, const ChainstateManager& chainman)
+// Flag-day deployments (not versionbits ones): rules apply to every block
+// from an activation point until the parent block's median-time-past reaches
+// an expiry. Reported as-of the queried block, with "active" meaning the next
+// block, like the versionbits entries. Omitted entirely when unscheduled
+// (plain regtest), as NEVER_ACTIVE deployments are.
+void FlagDayDescPushBack(UniValue& softforks, const std::string& name, std::optional<int> height, std::optional<int64_t> start_time, int64_t expiry_time, bool active_next)
 {
-    const Consensus::Params& params{chainman.GetConsensus()};
-    if (params.Blake2bHeight == std::numeric_limits<int>::max() ||
-        params.RdtsExpiryTime == std::numeric_limits<int64_t>::min()) return;
+    if (expiry_time == std::numeric_limits<int64_t>::min()) return;
 
     UniValue rv(UniValue::VOBJ);
     rv.pushKV("type", "flagday");
-    rv.pushKV("height", params.RdtsActivationHeight());
-    rv.pushKV("expiry_time", params.RdtsExpiryTime);
+    if (height) rv.pushKV("height", *height);
+    if (start_time) rv.pushKV("start_time", *start_time);
+    rv.pushKV("expiry_time", expiry_time);
+    rv.pushKV("active", active_next);
+    softforks.pushKV(name, std::move(rv));
+}
+
+// RDTS: from the BLAKE2b hardfork height until RdtsExpiryTime.
+void RdtsFlagDayDescPushBack(const CBlockIndex* blockindex, UniValue& softforks, const ChainstateManager& chainman)
+{
+    const Consensus::Params& params{chainman.GetConsensus()};
+    if (params.Blake2bHeight == std::numeric_limits<int>::max()) return;
     // "active" describes the NEXT block, as the versionbits entries do, so the
     // queried block is that block's parent and its median-time-past is exactly
     // the parent median-time-past RdtsActiveAt expects.
-    rv.pushKV("active", params.RdtsActiveAt(blockindex->nHeight + 1, blockindex->GetMedianTimePast()));
-    softforks.pushKV("reduced_data", std::move(rv));
+    FlagDayDescPushBack(softforks, "reduced_data", params.RdtsActivationHeight(), std::nullopt, params.RdtsExpiryTime,
+                        params.RdtsActiveAt(blockindex->nHeight + 1, blockindex->GetMedianTimePast()));
+}
+
+// Extended coinbase maturity: from the block whose parent's median-time-past
+// reaches ExtendedCoinbaseMaturityStartTime until the RDTS expiry (it expires
+// with RDTS). The activation height depends on the chain, so it is reported
+// once the queried block's chain has determined it.
+void ExtendedCoinbaseMaturityDescPushBack(const CBlockIndex* blockindex, UniValue& softforks, const ChainstateManager& chainman)
+{
+    const Consensus::Params& params{chainman.GetConsensus()};
+    if (params.ExtendedCoinbaseMaturityStartTime == std::numeric_limits<int64_t>::max()) return;
+    const int64_t mtp{blockindex->GetMedianTimePast()};
+    std::optional<int> height;
+    if (mtp >= params.ExtendedCoinbaseMaturityStartTime) {
+        height = MedianTimePastActivationHeight(*blockindex, params.ExtendedCoinbaseMaturityStartTime);
+    }
+    FlagDayDescPushBack(softforks, "extended_coinbase_maturity", height, params.ExtendedCoinbaseMaturityStartTime, params.RdtsExpiryTime,
+                        params.ExtendedCoinbaseMaturityActiveAt(mtp));
 }
 
 UniValue DeploymentInfo(const CBlockIndex* blockindex, const ChainstateManager& chainman)
@@ -1973,6 +1999,7 @@ UniValue DeploymentInfo(const CBlockIndex* blockindex, const ChainstateManager&
     SoftForkDescPushBack(blockindex, softforks, chainman, Consensus::DEPLOYMENT_TESTDUMMY);
     SoftForkDescPushBack(blockindex, softforks, chainman, Consensus::DEPLOYMENT_TAPROOT);
     RdtsFlagDayDescPushBack(blockindex, softforks, chainman);
+    ExtendedCoinbaseMaturityDescPushBack(blockindex, softforks, chainman);
     return softforks;
 }
 } // anon namespace
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index 5c93cf652fee..de42e4844581 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -1082,6 +1082,12 @@ static UniValue TemplateToJSON(const Consensus::Params& consensusParams, const C
     if (rdts_active) {
         aRules.push_back("reduced_data");
     }
+    // Extended coinbase maturity (a flag-day deployment expiring with RDTS).
+    // Enforced during transaction selection; advertised unprefixed like
+    // "reduced_data", as clients need no special support for it.
+    if (pindexPrev != nullptr && consensusParams.ExtendedCoinbaseMaturityActiveAt(pindexPrev->GetMedianTimePast())) {
+        aRules.push_back("extended_coinbase_maturity");
+    }
 
     result.pushKV("version", block_header.GetCompleteVersion());
     result.pushKV("rules", std::move(aRules));
diff --git a/src/test/validation_tests.cpp b/src/test/validation_tests.cpp
index 4806533bc0b6..28ff293cf424 100644
--- a/src/test/validation_tests.cpp
+++ b/src/test/validation_tests.cpp
@@ -4,6 +4,8 @@
 
 #include <chainparams.h>
 #include <consensus/amount.h>
+#include <coins.h>
+#include <consensus/consensus.h>
 #include <consensus/merkle.h>
 #include <core_io.h>
 #include <hash.h>
@@ -13,7 +15,9 @@
 #include <util/chaintype.h>
 #include <validation.h>
 
+#include <limits>
 #include <string>
+#include <vector>
 
 #include <test/util/setup_common.h>
 
@@ -398,4 +402,108 @@ BOOST_AUTO_TEST_CASE(block_malleation)
     }
 }
 
+//! A chain of `length` block indexes with skip pointers, block i stamped `times[i]`.
+static std::vector<CBlockIndex> MakeTimedChain(const std::vector<int64_t>& times)
+{
+    std::vector<CBlockIndex> chain(times.size());
+    for (size_t i = 0; i < times.size(); ++i) {
+        chain[i].nHeight = i;
+        chain[i].nTime = times[i];
+        chain[i].pprev = i == 0 ? nullptr : &chain[i - 1];
+        chain[i].BuildSkip();
+    }
+    return chain;
+}
+
+BOOST_AUTO_TEST_CASE(median_time_past_activation_height)
+{
+    // Consensus keeps median-time-past non-decreasing along a chain (a block's
+    // time must exceed its parent's median); non-decreasing times reproduce
+    // that here, with plateaus to exercise the "first block whose parent
+    // reached it" boundary.
+    std::vector<int64_t> times;
+    int64_t t{1000};
+    for (int i = 0; i < 300; ++i) {
+        times.push_back(t);
+        if (i % 7 == 0) t += 10; // plateaus of equal times, then a jump
+    }
+    const auto chain{MakeTimedChain(times)};
+    const CBlockIndex& tip{chain.back()};
+
+    // Brute force: the first height whose parent's median-time-past is >= start.
+    const auto expected = [&](int64_t start) {
+        for (int h = 1; h <= tip.nHeight; ++h) {
+            if (chain[h - 1].GetMedianTimePast() >= start) return h;
+        }
+        return tip.nHeight + 1;
+    };
+    for (int64_t start = times.front() - 5; start <= tip.GetMedianTimePast(); ++start) {
+        BOOST_CHECK_EQUAL(MedianTimePastActivationHeight(tip, start), expected(start));
+        // The same answer from any ancestor whose median-time-past has reached it.
+        for (int h : {tip.nHeight / 2, tip.nHeight - 1}) {
+            if (chain[h].GetMedianTimePast() >= start) {
+                BOOST_CHECK_EQUAL(MedianTimePastActivationHeight(chain[h], start), expected(start));
+            }
+        }
+    }
+    // A start the genesis block already satisfies activates at height 1.
+    BOOST_CHECK_EQUAL(MedianTimePastActivationHeight(tip, times.front()), 1);
+    BOOST_CHECK_EQUAL(MedianTimePastActivationHeight(chain[0], times.front()), 1);
+}
+
+BOOST_AUTO_TEST_CASE(coinbase_mature_for_extended_rule)
+{
+    // Ten-minute blocks, so median-time-past advances 600 s per block.
+    std::vector<int64_t> times;
+    for (int i = 0; i < 300; ++i) times.push_back(1'000'000 + 600 * i);
+    const auto chain{MakeTimedChain(times)};
+    const auto coinbase_at = [](int height) { return Coin{CTxOut{1, CScript{}}, height, /*fCoinBaseIn=*/true}; };
+    const Coin plain{CTxOut{1, CScript{}}, 60, /*fCoinBaseIn=*/false};
+
+    Consensus::Params params{};
+    // Unscheduled (defaults): every output passes, whatever the times.
+    BOOST_CHECK(CoinbaseMatureForExtendedRule(params, coinbase_at(60), chain[61]));
+    // A start without an RDTS expiry never activates (it expires with RDTS).
+    params.ExtendedCoinbaseMaturityStartTime = chain[50].GetMedianTimePast();
+    BOOST_CHECK(CoinbaseMatureForExtendedRule(params, coinbase_at(60), chain[61]));
+    params.RdtsExpiryTime = chain[250].GetMedianTimePast();
+    // Block 51 is the first whose parent (50) has reached the start; block
+    // 251 the first whose parent has reached the expiry.
+
+    // Non-coinbase outputs are never subject.
+    BOOST_CHECK(CoinbaseMatureForExtendedRule(params, plain, chain[100]));
+    // Outputs created before activation (block 50 and earlier) are never
+    // subject, however young.
+    BOOST_CHECK(CoinbaseMatureForExtendedRule(params, coinbase_at(50), chain[51]));
+    BOOST_CHECK(CoinbaseMatureForExtendedRule(params, coinbase_at(49), chain[200]));
+    // An in-window output waits until the parent's median-time-past is
+    // EXTENDED_COINBASE_MATURITY_TIME past its block's: from block 51's
+    // median-time-past that is 3888000 / 600 = 6480 blocks later, beyond
+    // this chain, so it stays locked throughout the window...
+    BOOST_CHECK(!CoinbaseMatureForExtendedRule(params, coinbase_at(51), chain[52]));
+    BOOST_CHECK(!CoinbaseMatureForExtendedRule(params, coinbase_at(51), chain[151]));
+    BOOST_CHECK(!CoinbaseMatureForExtendedRule(params, coinbase_at(51), chain[249]));
+    // ...and is released by the hard expiry (block 251's parent has reached it).
+    BOOST_CHECK(CoinbaseMatureForExtendedRule(params, coinbase_at(51), chain[250]));
+    BOOST_CHECK(CoinbaseMatureForExtendedRule(params, coinbase_at(51), chain[299]));
+
+    // The exact boundary, with a shorter maturity: build a chain whose
+    // median-time-past jumps by the maturity time between two blocks.
+    const int64_t maturity{EXTENDED_COINBASE_MATURITY_TIME};
+    std::vector<int64_t> jump_times;
+    for (int i = 0; i < 120; ++i) jump_times.push_back(1'000'000 + (i < 80 ? 600 * i : 600 * 80 + maturity + 600 * (i - 80)));
+    const auto jump{MakeTimedChain(jump_times)};
+    Consensus::Params jump_params{};
+    jump_params.ExtendedCoinbaseMaturityStartTime = jump[20].GetMedianTimePast();
+    jump_params.RdtsExpiryTime = std::numeric_limits<int64_t>::max() / 2;
+    const Coin cb{coinbase_at(60)};
+    const int64_t due{jump[60].GetMedianTimePast() + maturity};
+    for (int h = 61; h < 120; ++h) {
+        BOOST_CHECK_EQUAL(CoinbaseMatureForExtendedRule(jump_params, cb, jump[h]), jump[h].GetMedianTimePast() >= due);
+    }
+    // Sanity: the boundary is actually crossed inside this chain.
+    BOOST_CHECK(!CoinbaseMatureForExtendedRule(jump_params, cb, jump[80]));
+    BOOST_CHECK(CoinbaseMatureForExtendedRule(jump_params, cb, jump[119]));
+}
+
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/validation.cpp b/src/validation.cpp
index f19ef0e45901..71cdad97ce5f 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -272,6 +272,45 @@ bool CheckSequenceLocksAtTip(CBlockIndex* tip,
     return EvaluateSequenceLocks(index, {lock_points.height, lock_points.time});
 }
 
+int MedianTimePastActivationHeight(const CBlockIndex& tip, int64_t start_time)
+{
+    assert(tip.GetMedianTimePast() >= start_time);
+    // Binary search over the ancestors for the lowest height whose
+    // median-time-past has reached start_time; the block after it is the first
+    // whose parent's has. Valid because a block's time must exceed its parent's
+    // median-time-past, which keeps median-time-past non-decreasing along a chain.
+    int lo{0};
+    int hi{tip.nHeight};
+    while (lo < hi) {
+        const int mid{lo + (hi - lo) / 2};
+        if (Assert(tip.GetAncestor(mid))->GetMedianTimePast() >= start_time) {
+            hi = mid;
+        } else {
+            lo = mid + 1;
+        }
+    }
+    return lo + 1;
+}
+
+bool CoinbaseMatureForExtendedRule(const Consensus::Params& params, const Coin& coin, const CBlockIndex& block_prev)
+{
+    if (!coin.IsCoinBase()) return true;
+    const int64_t mtp_prev{block_prev.GetMedianTimePast()};
+    if (!params.ExtendedCoinbaseMaturityActiveAt(mtp_prev)) return true;
+    const CBlockIndex* coinbase_block{Assert(block_prev.GetAncestor(coin.nHeight))};
+    // Only outputs created while the rule was active are subject to it
+    // (grandfathering). The spending block is inside the window, so the
+    // creating block, an ancestor, is past the expiry only if it is too.
+    if (coinbase_block->pprev == nullptr ||
+        !params.ExtendedCoinbaseMaturityActiveAt(coinbase_block->pprev->GetMedianTimePast())) {
+        return true;
+    }
+    // Both ends are median-time-past values, which never decrease along a
+    // chain, so the answer for the next block is knowable from the tip and
+    // holds unchanged until the tip changes.
+    return mtp_prev >= coinbase_block->GetMedianTimePast() + EXTENDED_COINBASE_MATURITY_TIME;
+}
+
 // Returns the script flags which should be checked for a given block
 static unsigned int GetBlockScriptFlags(const CBlockIndex& block_index, const ChainstateManager& chainman);
 
@@ -431,7 +470,10 @@ void Chainstate::MaybeUpdateMempoolForReorg(
             }
         }
 
-        // If the transaction spends any coinbase outputs, it must be mature.
+        // If the transaction spends any coinbase outputs, it must be mature,
+        // under the extended rule too: it may apply to the next block again
+        // after a reorg back across its expiry, and the new tip's
+        // median-time-past may be lower (see CoinbaseMatureForExtendedRule).
         if (it->GetSpendsCoinbase()) {
             for (const CTxIn& txin : tx.vin) {
                 if (m_mempool->exists(GenTxid::Txid(txin.prevout.hash))) continue;
@@ -441,6 +483,9 @@ void Chainstate::MaybeUpdateMempoolForReorg(
                 if (coin.IsCoinBase() && mempool_spend_height - coin.nHeight < COINBASE_MATURITY) {
                     return true;
                 }
+                if (!CoinbaseMatureForExtendedRule(m_chainman.GetConsensus(), coin, *m_chain.Tip())) {
+                    return true;
+                }
             }
         }
         // Transaction is still valid and cached LockPoints are updated.
@@ -1019,6 +1064,16 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
         return false; // state filled in by CheckTxInputs
     }
 
+    // The extended coinbase maturity rule (see CoinbaseMatureForExtendedRule)
+    // is likewise evaluated for the next block, whose parent is the tip.
+    for (const CTxIn& txin : tx.vin) {
+        const Coin& coin{m_view.AccessCoin(txin.prevout)};
+        if (!CoinbaseMatureForExtendedRule(m_active_chainstate.m_chainman.GetConsensus(), coin, *m_active_chainstate.m_chain.Tip())) {
+            return state.Invalid(TxValidationResult::TX_PREMATURE_SPEND, "bad-txns-premature-spend-of-coinbase",
+                                 strprintf("coinbase at height %d is not yet mature under the extended maturity rule", coin.nHeight));
+        }
+    }
+
     if (m_pool.m_opts.minrelaymaturity) {
         auto max_coin_height = block_height_next - m_pool.m_opts.minrelaymaturity;
         static_assert(std::is_signed_v<decltype(max_coin_height)>, "Unsigned max_coin_height needs a range check");
@@ -2993,6 +3048,14 @@ bool Chainstate::ConnectBlock(const CBlock& block, BlockValidationState& state,
 
     const CheckTxInputsRules chk_input_rules{reduced_data_active ? CheckTxInputsRules::OutputSizeLimit : CheckTxInputsRules::None};
 
+    // Extended coinbase maturity (see CoinbaseMatureForExtendedRule): a
+    // temporary soft fork that expires with RDTS. While it is active for this
+    // block, coinbase outputs created since its activation on this chain may
+    // only be spent once this block's parent has a median-time-past at least
+    // EXTENDED_COINBASE_MATURITY_TIME past the coinbase block's; the check is
+    // made per input below, alongside the BIP68 height lookup.
+    const bool extended_coinbase_maturity_active{params.GetConsensus().ExtendedCoinbaseMaturityActiveAt(pindex->pprev->GetMedianTimePast())};
+
     // Check generation tx output sizes if REDUCED_DATA is active
     if (chk_input_rules.test(CheckTxInputsRules::OutputSizeLimit)) {
         TxValidationState tx_state;
@@ -3040,12 +3103,19 @@ bool Chainstate::ConnectBlock(const CBlock& block, BlockValidationState& state,
             prevheights.resize(tx.vin.size());
             flags_per_input.clear();
             for (size_t j = 0; j < tx.vin.size(); j++) {
-                prevheights[j] = view.AccessCoin(tx.vin[j].prevout).nHeight;
+                const Coin& coin{view.AccessCoin(tx.vin[j].prevout)};
+                prevheights[j] = coin.nHeight;
                 if (prevheights[j] < reduced_data_start_height) {
                     flags_per_input.resize(tx.vin.size(), flags);
                     flags_per_input[j] = flags & ~REDUCED_DATA_MANDATORY_VERIFY_FLAGS;
                 }
+                if (extended_coinbase_maturity_active && !CoinbaseMatureForExtendedRule(params.GetConsensus(), coin, *pindex->pprev)) {
+                    state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-txns-premature-spend-of-coinbase",
+                                  strprintf("coinbase at height %d is not yet mature under the extended maturity rule, spent in transaction %s", coin.nHeight, tx.GetHash().ToString()));
+                    break;
+                }
             }
+            if (!state.IsValid()) break;
 
             if (!SequenceLocks(tx, nLockTimeFlags, prevheights, *pindex)) {
                 state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-txns-nonfinal",
diff --git a/src/validation.h b/src/validation.h
index e38d63f554d2..2e32cc779c83 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -347,6 +347,29 @@ std::optional<LockPoints> CalculateLockPointsAtTip(
 bool CheckSequenceLocksAtTip(CBlockIndex* tip,
                              const LockPoints& lock_points);
 
+/**
+ * The activation height, on the chain ending at `tip`, of a deployment
+ * scheduled by median-time-past: the height of the first block whose parent's
+ * median-time-past is at least `start_time`. Median-time-past never decreases
+ * along a chain, so the blocks it activates for form a suffix of the chain.
+ * Requires tip.GetMedianTimePast() >= start_time, so that the answer is at most
+ * tip.nHeight + 1 (the block built on `tip`).
+ */
+int MedianTimePastActivationHeight(const CBlockIndex& tip, int64_t start_time);
+
+/**
+ * Extended coinbase maturity (see Consensus::Params::ExtendedCoinbaseMaturityActiveAt):
+ * whether spending `coin` in the block built on `block_prev` satisfies the
+ * rule. True for any non-coinbase output, whenever the rule is not active for
+ * that block, and for a coinbase output created before the rule activated on
+ * that chain; otherwise the parent's median-time-past must be at least
+ * EXTENDED_COINBASE_MATURITY_TIME past the coinbase block's. The COINBASE_MATURITY
+ * depth requirement is separate (Consensus::CheckTxInputs) and always applies.
+ * `coin` must be an unspent output of that chain, so that its creating block is
+ * an ancestor of `block_prev`.
+ */
+bool CoinbaseMatureForExtendedRule(const Consensus::Params& params, const Coin& coin, const CBlockIndex& block_prev);
+
 void LimitMempoolSize(CTxMemPool&, CCoinsViewCache&);
 
 /**
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index c8dbcfd1b790..902ad5e52f48 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -3646,7 +3646,16 @@ int CWallet::GetTxBlocksToMaturity(const CWalletTx& wtx) const
     }
     int chain_depth = GetTxDepthInMainChain(wtx);
     assert(chain_depth >= 0); // coinbase tx should not be conflicted
-    return std::max(0, (COINBASE_MATURITY+1) - chain_depth);
+    int blocks_to_maturity{std::max(0, (COINBASE_MATURITY + 1) - chain_depth)};
+    // A confirmed coinbase may also be held back by the temporary extended
+    // maturity soft fork; the chain knows for how much longer (an estimate,
+    // since that rule is a median-time-past one).
+    if (HaveChain()) {
+        if (auto* conf = wtx.state<TxStateConfirmed>()) {
+            blocks_to_maturity = std::max(blocks_to_maturity, chain().extendedCoinbaseBlocksToMaturity(conf->confirmed_block_height));
+        }
+    }
+    return blocks_to_maturity;
 }
 
 bool CWallet::IsTxImmatureCoinBase(const CWalletTx& wtx) const
diff --git a/test/functional/feature_extended_coinbase_maturity.py b/test/functional/feature_extended_coinbase_maturity.py
new file mode 100755
index 000000000000..df47e56a7a2a
--- /dev/null
+++ b/test/functional/feature_extended_coinbase_maturity.py
@@ -0,0 +1,280 @@
+#!/usr/bin/env python3
+# Copyright (c) 2026 The Bitcoin Knots developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test the extended coinbase maturity temporary soft fork.
+
+While the deployment is active, a coinbase output created since it activated
+can only be spent once the spending block's parent has a median-time-past at
+least EXTENDED_COINBASE_MATURITY_TIME past the coinbase block's (on top of the
+usual COINBASE_MATURITY confirmations). It activates for the first block whose
+parent's median-time-past reaches -extendedcoinbasematurity and expires with
+RDTS (-rdtsexpiry).
+
+Covered:
+- option validation (requires -rdtsexpiry, must precede it)
+- activation height derived from median-time-past; getdeploymentinfo/getblocktemplate
+- grandfathering: a coinbase from the block before activation keeps the 100-block rule
+- an in-window coinbase is rejected at depth >= 100 by the mempool and in a block
+- spendable exactly when the parent's median-time-past reaches the maturity time;
+  the reorg filter evicts the spend once a reorg drops the median below it again
+- hard expiry: a still-locked coinbase becomes spendable once the parent's
+  median-time-past reaches the expiry, and a reorg back across it evicts the spend
+- the wallet reports the reward as immature while locked and trusted afterwards
+- -reindex reproduces the chain and derives the same activation height
+"""
+
+from test_framework.blocktools import (
+    COINBASE_MATURITY,
+    add_witness_commitment,
+    create_block,
+)
+from test_framework.p2p import P2PInterface
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal,
+    assert_greater_than,
+    assert_raises_rpc_error,
+)
+from test_framework.wallet import MiniWallet
+
+EXTENDED_COINBASE_MATURITY_TIME = 3_888_000  # 45 days
+BLAKE2B_HEIGHT = 120
+# Mock clock: pre-activation blocks are stamped from T0, the window opens once
+# the median-time-past reaches START, and RDTS (with it, this rule) expires at
+# EXPIRY, late enough that a coinbase created well into the window is still
+# locked by then. Block times creep by one second per block.
+T0 = 1_600_000_000
+START = T0 + 10_000
+EXPIRY = START + EXTENDED_COINBASE_MATURITY_TIME + 200_000
+REJECT = 'bad-txns-premature-spend-of-coinbase'
+
+
+class ExtendedCoinbaseMaturityTest(BitcoinTestFramework):
+    def add_options(self, parser):
+        self.add_wallet_options(parser)
+
+    def set_test_params(self):
+        self.num_nodes = 1
+        self.setup_clean_chain = True
+        self.base_args = [
+            f'-testactivationheight=blake2b@{BLAKE2B_HEIGHT}',
+            f'-rdtsexpiry={EXPIRY}',
+            f'-extendedcoinbasematurity={START}',
+        ]
+        self.extra_args = [self.base_args]
+
+    def mine(self, count):
+        """Mine count blocks to the MiniWallet, keeping the mock clock within
+        the two-hour future window of the creeping block times."""
+        node = self.nodes[0]
+        while count > 0:
+            chunk = min(count, 1000)
+            self.mocktime = max(self.mocktime, node.getblockheader(node.getbestblockhash())['time']) + chunk
+            node.setmocktime(self.mocktime)
+            self.generate(self.wallet, chunk, sync_fun=self.no_op)
+            count -= chunk
+
+    def mtp(self, height):
+        node = self.nodes[0]
+        return node.getblockheader(node.getblockhash(height))['mediantime']
+
+    def coinbase_utxo(self, height):
+        node = self.nodes[0]
+        txid = node.getblock(node.getblockhash(height))['tx'][0]
+        return self.wallet.get_utxo(txid=txid)
+
+    def assert_spend_rejected(self, tx_hex):
+        node = self.nodes[0]
+        assert_equal(node.testmempoolaccept([tx_hex])[0]['reject-reason'], REJECT)
+        assert_raises_rpc_error(-26, REJECT, node.sendrawtransaction, tx_hex)
+
+    def submit_block_with(self, tx_hex):
+        """Mine a block carrying tx_hex ourselves and return submitblock's verdict."""
+        node = self.nodes[0]
+        tmpl = node.getblocktemplate({'rules': ['segwit', 'blake2b']})
+        block = create_block(tmpl=tmpl, txlist=[tx_hex])
+        add_witness_commitment(block)
+        block.solve()
+        return node.submitblock(block.serialize().hex())
+
+    def assert_deploymentinfo(self, *, active, height=None):
+        info = self.nodes[0].getdeploymentinfo()['deployments']['extended_coinbase_maturity']
+        assert_equal(info['type'], 'flagday')
+        assert_equal(info['start_time'], START)
+        assert_equal(info['expiry_time'], EXPIRY)
+        assert_equal(info['active'], active)
+        assert_equal(info.get('height'), height)
+
+    def assert_gbt_rule(self, *, active):
+        tmpl = self.nodes[0].getblocktemplate({'rules': ['segwit', 'blake2b']})
+        assert_equal('extended_coinbase_maturity' in tmpl['rules'], active)
+
+    def mine_until_mtp(self, time):
+        """Stamp blocks at `time` until the tip's median-time-past reaches it:
+        five leave it short (the median is the sixth of eleven), the sixth
+        reaches it. Returns the hashes of the fifth and sixth blocks."""
+        node = self.nodes[0]
+        self.mocktime = time
+        node.setmocktime(self.mocktime)
+        self.generate(node, 5, sync_fun=self.no_op)
+        assert_greater_than(time, self.mtp(node.getblockcount()))
+        short = node.getbestblockhash()
+        self.generate(node, 1, sync_fun=self.no_op)
+        assert_equal(self.mtp(node.getblockcount()), time)
+        return short, node.getbestblockhash()
+
+    def run_test(self):
+        node = self.nodes[0]
+
+        self.log.info("Option validation")
+        self.stop_node(0)
+        node.assert_start_raises_init_error(
+            extra_args=[f'-testactivationheight=blake2b@{BLAKE2B_HEIGHT}', f'-extendedcoinbasematurity={START}'],
+            expected_msg='Error: -extendedcoinbasematurity requires -rdtsexpiry=<time> (the rule expires with RDTS).')
+        node.assert_start_raises_init_error(
+            extra_args=[f'-testactivationheight=blake2b@{BLAKE2B_HEIGHT}', f'-rdtsexpiry={EXPIRY}', f'-extendedcoinbasematurity={EXPIRY}'],
+            expected_msg=f'Error: Invalid start ({EXPIRY}) for -extendedcoinbasematurity=<time>: must precede the RDTS expiry ({EXPIRY}).')
+        self.start_node(0)
+        node.add_p2p_connection(P2PInterface())  # getblocktemplate needs a peer
+
+        self.wallet = MiniWallet(node)
+        self.mocktime = T0
+        node.setmocktime(self.mocktime)
+
+        self.log.info("Before activation: the 100-block rule applies")
+        self.generate(self.wallet, 200, sync_fun=self.no_op)  # crosses the BLAKE2b fork
+        assert_greater_than(START, self.mtp(200))
+        self.assert_deploymentinfo(active=False)
+        self.assert_gbt_rule(active=False)
+        spend = self.wallet.create_self_transfer(utxo_to_spend=self.coinbase_utxo(201 - COINBASE_MATURITY))
+        node.sendrawtransaction(spend['hex'])
+        self.generate(self.wallet, 1, sync_fun=self.no_op)
+
+        self.log.info("Activation: the first block whose parent's median-time-past reaches the start time")
+        self.mocktime = START
+        node.setmocktime(self.mocktime)
+        while self.mtp(node.getblockcount()) < START:
+            self.assert_deploymentinfo(active=False)
+            self.generate(self.wallet, 1, sync_fun=self.no_op)
+        activation = node.getblockcount() + 1
+        self.log.info(f"  activation height {activation}")
+        self.assert_deploymentinfo(active=True, height=activation)
+        self.assert_gbt_rule(active=True)
+        self.generate(self.wallet, 1, sync_fun=self.no_op)  # block `activation`, the first in the window
+        self.assert_deploymentinfo(active=True, height=activation)
+        grandfathered = self.coinbase_utxo(activation - 1)
+        locked = self.coinbase_utxo(activation)
+        locked_due = self.mtp(activation) + EXTENDED_COINBASE_MATURITY_TIME
+
+        self.log.info("Inside the window: pre-activation coinbases keep the 100-block rule")
+        self.mine(COINBASE_MATURITY)  # tip = activation + 100
+        spend = self.wallet.create_self_transfer(utxo_to_spend=grandfathered)
+        node.sendrawtransaction(spend['hex'])
+        self.generate(node, 1, sync_fun=self.no_op)  # tip = activation + 101
+        assert_equal(node.getrawmempool(), [])
+
+        self.log.info("Inside the window: an in-window coinbase is locked past 100 confirmations")
+        locked_spend = self.wallet.create_self_transfer(utxo_to_spend=locked)
+        self.assert_spend_rejected(locked_spend['hex'])
+        assert_equal(self.submit_block_with(locked_spend['hex']), REJECT)
+        assert_equal(node.getblockcount(), activation + 101)
+
+        if self.is_wallet_compiled():
+            self.log.info("Wallet: an in-window reward stays immature past 100 confirmations")
+            node.createwallet('miner')
+            wallet_rpc = node.get_wallet_rpc('miner')
+            self.mocktime += 1
+            node.setmocktime(self.mocktime)
+            self.generatetoaddress(node, 1, wallet_rpc.getnewaddress(), sync_fun=self.no_op)
+            reward_height = node.getblockcount()
+            self.mine(COINBASE_MATURITY + 10)
+            balances = wallet_rpc.getbalances()['mine']
+            assert_greater_than(balances['immature'], 0)
+            assert_equal(balances['trusted'], 0)
+            assert_equal(wallet_rpc.listunspent(), [])
+            reward = wallet_rpc.listtransactions()[0]
+            assert_equal(reward['category'], 'immature')
+            assert_equal(reward['blockheight'], reward_height)
+            assert_greater_than(reward['confirmations'], COINBASE_MATURITY)
+
+        self.log.info("-reindex reproduces the chain and the activation height")
+        tip = node.getbestblockhash()
+        self.restart_node(0, extra_args=self.base_args + ['-reindex'])
+        node.setmocktime(self.mocktime)
+        node.add_p2p_connection(P2PInterface())
+        self.wait_until(lambda: node.getbestblockhash() == tip)
+        self.assert_deploymentinfo(active=True, height=activation)
+        self.assert_gbt_rule(active=True)
+        self.assert_spend_rejected(locked_spend['hex'])
+
+        self.log.info("Spendable once the parent's median-time-past reaches the coinbase block's plus the maturity time")
+        short_block, boundary_block = self.mine_until_mtp(locked_due)
+        # At the fifth block the median is still one block short
+        node.invalidateblock(boundary_block)
+        assert_equal(node.getbestblockhash(), short_block)
+        self.assert_deploymentinfo(active=True, height=activation)
+        self.assert_spend_rejected(locked_spend['hex'])
+        node.reconsiderblock(boundary_block)
+        assert_equal(node.getbestblockhash(), boundary_block)
+        node.sendrawtransaction(locked_spend['hex'])
+        assert_equal(node.getrawmempool(), [locked_spend['txid']])
+        self.generate(node, 1, sync_fun=self.no_op)
+        mature_block = node.getbestblockhash()
+        assert locked_spend['txid'] in node.getblock(mature_block)['tx']
+
+        self.log.info("A reorg dropping the median below the maturity time evicts the spend from the mempool")
+        node.invalidateblock(mature_block)
+        assert_equal(node.getrawmempool(), [locked_spend['txid']])  # the median still reaches it
+        node.invalidateblock(boundary_block)
+        assert_equal(node.getrawmempool(), [])
+        node.reconsiderblock(boundary_block)
+        assert_equal(node.getbestblockhash(), mature_block)
+        assert_equal(node.getrawmempool(), [])
+
+        self.log.info("Hard expiry: the rule ends once the parent's median-time-past reaches the RDTS expiry")
+        # A coinbase created well into the window, whose maturity time falls
+        # after the expiry, so that the expiry is what releases it.
+        self.mine_until_mtp(locked_due + 100_000)
+        self.generate(self.wallet, 1, sync_fun=self.no_op)
+        late_height = node.getblockcount()
+        assert_greater_than(self.mtp(late_height) + EXTENDED_COINBASE_MATURITY_TIME, EXPIRY)
+        self.mine(COINBASE_MATURITY + 5)
+        late_spend = self.wallet.create_self_transfer(utxo_to_spend=self.coinbase_utxo(late_height))
+        self.assert_spend_rejected(late_spend['hex'])
+        short_block, last_active_tip = self.mine_until_mtp(EXPIRY)
+        node.invalidateblock(last_active_tip)
+        assert_equal(node.getbestblockhash(), short_block)
+        self.assert_deploymentinfo(active=True, height=activation)
+        self.assert_gbt_rule(active=True)
+        self.assert_spend_rejected(late_spend['hex'])
+        node.reconsiderblock(last_active_tip)
+        self.assert_deploymentinfo(active=False, height=activation)
+        self.assert_gbt_rule(active=False)
+        node.sendrawtransaction(late_spend['hex'])
+        self.generate(node, 1, sync_fun=self.no_op)
+        expired_block = node.getbestblockhash()
+        assert late_spend['txid'] in node.getblock(expired_block)['tx']
+
+        self.log.info("A reorg back across the expiry evicts the spend from the mempool")
+        node.invalidateblock(expired_block)
+        assert_equal(node.getrawmempool(), [late_spend['txid']])  # parent MTP still at EXPIRY
+        node.invalidateblock(last_active_tip)
+        self.assert_deploymentinfo(active=True, height=activation)
+        assert_equal(node.getrawmempool(), [])
+        node.reconsiderblock(last_active_tip)
+        assert_equal(node.getbestblockhash(), expired_block)
+        assert_equal(node.getrawmempool(), [])
+
+        if self.is_wallet_compiled():
+            self.log.info("Wallet: the reward is trusted once matured")
+            node.loadwallet('miner')  # not loaded since the restart
+            wallet_rpc = node.get_wallet_rpc('miner')
+            balances = wallet_rpc.getbalances()['mine']
+            assert_equal(balances['immature'], 0)
+            assert_greater_than(balances['trusted'], 0)
+            assert_equal(wallet_rpc.listtransactions()[0]['category'], 'generate')
+
+
+if __name__ == '__main__':
+    ExtendedCoinbaseMaturityTest(__file__).main()
diff --git a/test/functional/test_runner.py b/test/functional/test_runner.py
index e912af0f5cfc..4f2a91b6d67b 100755
--- a/test/functional/test_runner.py
+++ b/test/functional/test_runner.py
@@ -98,6 +98,7 @@
     'rpc_combinerawtransaction_unified.py --descriptors',
     'feature_taproot.py',
     'feature_reduced_data_temporary_deployment.py',
+    'feature_extended_coinbase_maturity.py',
     'feature_bip9_max_activation_height.py',
     'feature_rdts.py',
     'feature_rdts_ignore_rejects.py',