diff --git a/doc/release-notes-28354.md b/doc/release-notes-28354.md
new file mode 100644
index 00000000000..03d421eb426
--- /dev/null
+++ b/doc/release-notes-28354.md
@@ -0,0 +1,6 @@
+Tests
+-----
+
+- Non-standard transactions are now disabled by default on testnet
+  for relay and mempool acceptance. The previous behaviour can be
+  re-enabled by setting `-acceptnonstdtxn=1`. (#28354)
diff --git a/src/init.cpp b/src/init.cpp
index 616883c3a14..47cffdd335e 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -585,7 +585,7 @@ void SetupServerArgs(ArgsManager& argsman)
 
     SetupChainParamsBaseOptions(argsman);
 
-    argsman.AddArg("-acceptnonstdtxn", strprintf("Relay and mine \"non-standard\" transactions (%sdefault: %u)", "testnet/regtest only; ", !testnetChainParams->RequireStandard()), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::NODE_RELAY);
+    argsman.AddArg("-acceptnonstdtxn", strprintf("Relay and mine \"non-standard\" transactions (test networks only; default: %u)", DEFAULT_ACCEPT_NON_STD_TXN), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::NODE_RELAY);
     argsman.AddArg("-incrementalrelayfee=<amt>", strprintf("Fee rate (in %s/kvB) used to define cost of relay, used for mempool limiting and replacement policy. (default: %s)", CURRENCY_UNIT, FormatMoney(DEFAULT_INCREMENTAL_RELAY_FEE)), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::NODE_RELAY);
     argsman.AddArg("-dustrelayfee=<amt>", strprintf("Fee rate (in %s/kvB) used to define dust, the value of an output such that it will cost more than its value in fees at this fee rate to spend it. (default: %s)", CURRENCY_UNIT, FormatMoney(DUST_RELAY_TX_FEE)), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::NODE_RELAY);
     argsman.AddArg("-acceptstalefeeestimates", strprintf("Read fee estimates even if they are stale (%sdefault: %u) fee estimates are considered stale if they are %s hours old", "regtest only; ", DEFAULT_ACCEPT_STALE_FEE_ESTIMATES, Ticks<std::chrono::hours>(MAX_FILE_AGE)), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
diff --git a/src/kernel/chainparams.cpp b/src/kernel/chainparams.cpp
index d9ed1547b36..733a3339b38 100644
--- a/src/kernel/chainparams.cpp
+++ b/src/kernel/chainparams.cpp
@@ -151,7 +151,6 @@ public:
         vFixedSeeds = std::vector<uint8_t>(std::begin(chainparams_seed_main), std::end(chainparams_seed_main));
 
         fDefaultConsistencyChecks = false;
-        fRequireStandard = true;
         m_is_test_chain = false;
         m_is_mockable_chain = false;
 
@@ -259,7 +258,6 @@ public:
         vFixedSeeds = std::vector<uint8_t>(std::begin(chainparams_seed_test), std::end(chainparams_seed_test));
 
         fDefaultConsistencyChecks = false;
-        fRequireStandard = false;
         m_is_test_chain = true;
         m_is_mockable_chain = false;
 
@@ -382,7 +380,6 @@ public:
         bech32_hrp = "tb";
 
         fDefaultConsistencyChecks = false;
-        fRequireStandard = true;
         m_is_test_chain = true;
         m_is_mockable_chain = false;
     }
@@ -474,7 +471,6 @@ public:
         vSeeds.emplace_back("dummySeed.invalid.");
 
         fDefaultConsistencyChecks = true;
-        fRequireStandard = true;
         m_is_test_chain = true;
         m_is_mockable_chain = true;
 
diff --git a/src/kernel/chainparams.h b/src/kernel/chainparams.h
index ad0b49a885d..2d38af609c9 100644
--- a/src/kernel/chainparams.h
+++ b/src/kernel/chainparams.h
@@ -102,8 +102,6 @@ public:
     const CBlock& GenesisBlock() const { return genesis; }
     /** Default value for -checkmempool and -checkblockindex argument */
     bool DefaultConsistencyChecks() const { return fDefaultConsistencyChecks; }
-    /** Policy: Filter transactions that do not match well-defined patterns */
-    bool RequireStandard() const { return fRequireStandard; }
     /** If this chain is exclusively used for testing */
     bool IsTestChain() const { return m_is_test_chain; }
     /** If this chain allows time to be mocked */
@@ -179,7 +177,6 @@ protected:
     CBlock genesis;
     std::vector<uint8_t> vFixedSeeds;
     bool fDefaultConsistencyChecks;
-    bool fRequireStandard;
     bool m_is_test_chain;
     bool m_is_mockable_chain;
     CCheckpointData checkpointData;
diff --git a/src/kernel/mempool_options.h b/src/kernel/mempool_options.h
index 58bb3debbf0..757be41b3c6 100644
--- a/src/kernel/mempool_options.h
+++ b/src/kernel/mempool_options.h
@@ -23,6 +23,8 @@ static constexpr unsigned int DEFAULT_BLOCKSONLY_MAX_MEMPOOL_SIZE_MB{5};
 static constexpr unsigned int DEFAULT_MEMPOOL_EXPIRY_HOURS{336};
 /** Default for -mempoolfullrbf, if the transaction replaceability signaling is ignored */
 static constexpr bool DEFAULT_MEMPOOL_FULL_RBF{false};
+/** Default for -acceptnonstdtxn */
+static constexpr bool DEFAULT_ACCEPT_NON_STD_TXN{false};
 
 namespace kernel {
 /**
diff --git a/src/node/mempool_args.cpp b/src/node/mempool_args.cpp
index 7d8244980d1..f63d9875fc0 100644
--- a/src/node/mempool_args.cpp
+++ b/src/node/mempool_args.cpp
@@ -86,7 +86,7 @@ util::Result<void> ApplyArgsManOptions(const ArgsManager& argsman, const CChainP
         mempool_opts.max_datacarrier_bytes = std::nullopt;
     }
 
-    mempool_opts.require_standard = !argsman.GetBoolArg("-acceptnonstdtxn", !chainparams.RequireStandard());
+    mempool_opts.require_standard = !argsman.GetBoolArg("-acceptnonstdtxn", DEFAULT_ACCEPT_NON_STD_TXN);
     if (!chainparams.IsTestChain() && !mempool_opts.require_standard) {
         return util::Error{strprintf(Untranslated("acceptnonstdtxn is not currently supported for %s chain"), chainparams.GetChainTypeString())};
     }