diff --git a/src/consensus/params.h b/src/consensus/params.h
index 628fb858c2f6..fee284014ed4 100644
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -35,6 +35,7 @@ enum DeploymentPos : uint16_t {
     DEPLOYMENT_CHECKTEMPLATEVERIFY, // Deployment of CTV (BIP 119)
     DEPLOYMENT_ANYPREVOUT,
     DEPLOYMENT_OP_CAT,
+    DEPLOYMENT_INTERNALKEY,
     // NOTE: Also add new deployments to VersionBitsDeploymentInfo in deploymentinfo.cpp
     MAX_VERSION_BITS_DEPLOYMENTS
 };
diff --git a/src/deploymentinfo.cpp b/src/deploymentinfo.cpp
index 8b5736f17b18..bc7d0e7987f3 100644
--- a/src/deploymentinfo.cpp
+++ b/src/deploymentinfo.cpp
@@ -27,6 +27,10 @@ const struct VBDeploymentInfo VersionBitsDeploymentInfo[Consensus::MAX_VERSION_B
         /*.name =*/ "opcat",
         /*.gbt_force =*/ true,
     },
+    {
+        /*.name =*/ "internalkey",
+        /*.gbt_force =*/ true,
+    },
 };
 
 std::string DeploymentName(Consensus::BuriedDeployment dep)
@@ -91,6 +95,8 @@ const std::map<std::string, uint32_t> g_verify_flag_names{
     FLAG_NAME(DEFAULT_CHECK_TEMPLATE_VERIFY_HASH),
     FLAG_NAME(DISCOURAGE_UPGRADABLE_CHECK_TEMPLATE_VERIFY_HASH),
     FLAG_NAME(DISCOURAGE_CHECK_TEMPLATE_VERIFY_HASH),
+    FLAG_NAME(DISCOURAGE_INTERNALKEY),
+    FLAG_NAME(INTERNALKEY),
     FLAG_NAME(ANYPREVOUT),
     FLAG_NAME(DISCOURAGE_ANYPREVOUT),
     FLAG_NAME(OP_CAT),
diff --git a/src/kernel/chainparams.cpp b/src/kernel/chainparams.cpp
index 71dcbe30db6d..caf49cd564ce 100644
--- a/src/kernel/chainparams.cpp
+++ b/src/kernel/chainparams.cpp
@@ -145,6 +145,7 @@ class CMainParams : public CChainParams {
         consensus.vDeployments[Consensus::DEPLOYMENT_CHECKTEMPLATEVERIFY] = SetupDeployment{.activate = 0x60007700, .abandon = 0x40007700, .never = true};
         consensus.vDeployments[Consensus::DEPLOYMENT_ANYPREVOUT] = SetupDeployment{.activate = 0x60007600, .abandon = 0x40007600, .never = true};
         consensus.vDeployments[Consensus::DEPLOYMENT_OP_CAT] = SetupDeployment{.activate = 0x62000100, .abandon = 0x42000100, .never = true};
+        consensus.vDeployments[Consensus::DEPLOYMENT_INTERNALKEY] = SetupDeployment{.activate = 0x62000100, .abandon = 0x42000100, .never = true};
 
         consensus.nMinimumChainWork = uint256{"000000000000000000000000000000000000000088e186b70e0862c193ec44d6"};
         consensus.defaultAssumeValid = uint256{"000000000000000000011c5890365bdbe5d25b97ce0057589acaef4f1a57263f"}; // 856760
@@ -264,6 +265,7 @@ class CTestNetParams : public CChainParams {
         consensus.vDeployments[Consensus::DEPLOYMENT_CHECKTEMPLATEVERIFY] = SetupDeployment{.activate = 0x60007700, .abandon = 0x40007700, .never = true};
         consensus.vDeployments[Consensus::DEPLOYMENT_ANYPREVOUT] = SetupDeployment{.activate = 0x60007600, .abandon = 0x40007600, .never = true};
         consensus.vDeployments[Consensus::DEPLOYMENT_OP_CAT] = SetupDeployment{.activate = 0x62000100, .abandon = 0x42000100, .never = true};
+consensus.vDeployments[Consensus::DEPLOYMENT_INTERNALKEY] = SetupDeployment{.activate = 0x62000100, .abandon = 0x42000100, .never = true};
 
         consensus.nMinimumChainWork = uint256{"000000000000000000000000000000000000000000000f209695166be8b61fa9"};
         consensus.defaultAssumeValid = uint256{"000000000000000465b1a66c9f386308e8c75acef9201f3f577811da09fc90ad"}; // 2873500
@@ -508,6 +510,7 @@ class SigNetParams : public CChainParams {
             .activate = 0x62000100,
             .abandon = 0x42000100,
         };
+        consensus.vDeployments[Consensus::DEPLOYMENT_INTERNALKEY] = SetupDeployment{.activate = 0x62000100, .abandon = 0x42000100, .never = true};
 
         RenounceDeployments(options.renounce, consensus.vDeployments);
 
@@ -584,6 +587,7 @@ class CRegTestParams : public CChainParams
         consensus.vDeployments[Consensus::DEPLOYMENT_CHECKTEMPLATEVERIFY] = SetupDeployment{.activate = 0x60007700, .abandon = 0x40007700, .always = true};
         consensus.vDeployments[Consensus::DEPLOYMENT_ANYPREVOUT] = SetupDeployment{.activate = 0x60007600, .abandon = 0x40007600, .always = true};
         consensus.vDeployments[Consensus::DEPLOYMENT_OP_CAT] = SetupDeployment{.activate = 0x62000100, .abandon = 0x42000100, .always = true};
+consensus.vDeployments[Consensus::DEPLOYMENT_INTERNALKEY] = SetupDeployment{.activate = 0x62000100, .abandon = 0x42000100, .always = true};
         consensus.nMinimumChainWork = uint256{};
         consensus.defaultAssumeValid = uint256{};
 
diff --git a/src/policy/policy.h b/src/policy/policy.h
index ee93555f8e1d..4ff4643e1b9c 100644
--- a/src/policy/policy.h
+++ b/src/policy/policy.h
@@ -121,6 +121,7 @@ static constexpr unsigned int STANDARD_SCRIPT_VERIFY_FLAGS{MANDATORY_SCRIPT_VERI
                                                              SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_CHECK_TEMPLATE_VERIFY_HASH |
                                                              SCRIPT_VERIFY_DEFAULT_CHECK_TEMPLATE_VERIFY_HASH |
                                                              SCRIPT_VERIFY_ANYPREVOUT |
+                                                             SCRIPT_VERIFY_INTERNALKEY |
                                                              SCRIPT_VERIFY_OP_CAT
                                                             };
 
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index ef05d4c3d2d2..a2e2a1fd765b 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -1396,6 +1396,7 @@ UniValue DeploymentInfo(const CBlockIndex* blockindex, const ChainstateManager&
     SoftForkDescPushBack(blockindex, softforks, chainman, Consensus::DEPLOYMENT_CHECKTEMPLATEVERIFY);
     SoftForkDescPushBack(blockindex, softforks, chainman, Consensus::DEPLOYMENT_ANYPREVOUT);
     SoftForkDescPushBack(blockindex, softforks, chainman, Consensus::DEPLOYMENT_OP_CAT);
+    SoftForkDescPushBack(blockindex, softforks, chainman, Consensus::DEPLOYMENT_INTERNALKEY);
     return softforks;
 }
 } // anon namespace
diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index b113efb54d55..fab6b219b0b6 100644
--- a/src/script/interpreter.cpp
+++ b/src/script/interpreter.cpp
@@ -1283,6 +1283,17 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
                 }
                 break;
 
+                case OP_INTERNALKEY: {
+                    // OP_INTERNALKEY is only available in Tapscript
+                    if (sigversion == SigVersion::BASE || sigversion == SigVersion::WITNESS_V0) {
+                        return set_error(serror, SCRIPT_ERR_BAD_OPCODE);
+                    }
+                    // Always present in Tapscript
+                    assert(execdata.m_internal_key);
+                    stack.emplace_back(execdata.m_internal_key->begin(), execdata.m_internal_key->end());
+                    break;
+                }
+
                 default:
                     return set_error(serror, SCRIPT_ERR_BAD_OPCODE);
             }
@@ -1988,6 +1999,12 @@ std::optional<bool> CheckTapscriptOpSuccess(const CScript& exec_script, unsigned
                     } else if (!(flags & SCRIPT_VERIFY_OP_CAT)) {
                         return set_success(serror);
                     }
+                } else if (opcode == OP_INTERNALKEY) {
+                    if (flags & SCRIPT_VERIFY_DISCOURAGE_INTERNALKEY) {
+                        return set_error(serror, SCRIPT_ERR_DISCOURAGE_OP_SUCCESS);
+                    } else if (!(flags & SCRIPT_VERIFY_INTERNALKEY)) {
+                        return set_success(serror);
+                    }
                 } else {
                     // OP_SUCCESS behaviour
                     if (flags & SCRIPT_VERIFY_DISCOURAGE_OP_SUCCESS) {
diff --git a/src/script/interpreter.h b/src/script/interpreter.h
index ff041ca611ee..4e31354392d2 100644
--- a/src/script/interpreter.h
+++ b/src/script/interpreter.h
@@ -163,6 +163,12 @@ enum : uint32_t {
     SCRIPT_VERIFY_OP_CAT = (1U << 26),
     SCRIPT_VERIFY_DISCOURAGE_OP_CAT = (1U << 27),
 
+    // Executing OP_INTERNALKEY
+    SCRIPT_VERIFY_INTERNALKEY = (1U << 30),
+
+    // Making OP_INTERNALKEY non-standard
+    SCRIPT_VERIFY_DISCOURAGE_INTERNALKEY = (1U << 31),
+
     // Constants to point to the highest flag in use. Add new flags above this line.
     //
     SCRIPT_VERIFY_END_MARKER
diff --git a/src/script/script.cpp b/src/script/script.cpp
index fc77d70a9e9e..fb63ff45fa42 100644
--- a/src/script/script.cpp
+++ b/src/script/script.cpp
@@ -149,6 +149,9 @@ std::string GetOpName(opcodetype opcode)
     // Opcode added by BIP 342 (Tapscript)
     case OP_CHECKSIGADD            : return "OP_CHECKSIGADD";
 
+    // Opcode added by BIP 349
+    case OP_INTERNALKEY            : return "OP_INTERNALKEY";
+
     case OP_INVALIDOPCODE          : return "OP_INVALIDOPCODE";
 
     default:
diff --git a/src/script/script.h b/src/script/script.h
index 1bd615c6e816..ce6db09292a0 100644
--- a/src/script/script.h
+++ b/src/script/script.h
@@ -209,6 +209,9 @@ enum opcodetype
     // Opcode added by BIP 342 (Tapscript)
     OP_CHECKSIGADD = 0xba,
 
+    // Opcode added by BIP 349
+    OP_INTERNALKEY = 0xcb,
+
     OP_INVALIDOPCODE = 0xff,
 };
 
diff --git a/src/test/data/tx_valid.json b/src/test/data/tx_valid.json
index e087557925c9..f4bb33133ebc 100644
--- a/src/test/data/tx_valid.json
+++ b/src/test/data/tx_valid.json
@@ -672,5 +672,13 @@
 "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",
  "CLEANSTACK,DISCOURAGE_CHECK_TEMPLATE_VERIFY_HASH"],
 
+ ["Test OP_INTERNALKEY"],
+ [[["e2f2baee9c59389b34e39742ce05debf64aaa7a00fbdab88614f4d3c133186d5",
+  0,
+  "1 0x20 0xa9e62de0f9782710f702214fc81c0f0f90fb3537987b3685caad6d52db305447",
+  155000]],
+"02000000000101d58631133c4d4f6188abbd0fa0a7aa64bfde05ce4297e3349b38599ceebaf2e20000000000ffffffff01f0490200000000002251202ca3bc76489a54904ad2507005789afc1e6b362b451be89f69de39ddf9ba8abf0223cb2050929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac08721c050929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac000000000",
+ "DISCOURAGE_INTERNALKEY"],
+
 ["Make diffs cleaner by leaving a comment here without comma at the end"]
 ]
diff --git a/src/test/script_tests.cpp b/src/test/script_tests.cpp
index 40b4830c2f94..bcbad4756176 100644
--- a/src/test/script_tests.cpp
+++ b/src/test/script_tests.cpp
@@ -1747,7 +1747,7 @@ BOOST_AUTO_TEST_CASE(formatscriptflags)
 {
     // quick check that FormatScriptFlags reports any unknown/unexpected bits
     BOOST_CHECK_EQUAL(FormatScriptFlags(SCRIPT_VERIFY_P2SH), "P2SH");
-    BOOST_CHECK_EQUAL(FormatScriptFlags(SCRIPT_VERIFY_P2SH | (1u<<31)), "P2SH,0x80000000");
+    BOOST_CHECK_EQUAL(FormatScriptFlags(SCRIPT_VERIFY_P2SH | (1u<<29)), "P2SH,0x20000000");
     BOOST_CHECK_EQUAL(FormatScriptFlags(SCRIPT_VERIFY_TAPROOT | (1u<<28)), "TAPROOT,0x10000000");
     BOOST_CHECK_EQUAL(FormatScriptFlags(1u<<28), "0x10000000");
 }
diff --git a/src/test/txvalidationcache_tests.cpp b/src/test/txvalidationcache_tests.cpp
index af36a9569315..06717fc044f9 100644
--- a/src/test/txvalidationcache_tests.cpp
+++ b/src/test/txvalidationcache_tests.cpp
@@ -130,7 +130,7 @@ static void ValidateCheckInputsForAllFlags(const CTransaction &tx, uint32_t fail
         TxValidationState state;
 
         // Randomly selects flag combinations
-        uint32_t test_flags = (uint32_t) insecure_rand.randrange((SCRIPT_VERIFY_END_MARKER - 1) << 1);
+        uint32_t test_flags = (uint32_t) insecure_rand.randrange((uint64_t)(SCRIPT_VERIFY_END_MARKER - 1) << 1);
 
         // Filter out incompatible flag choices
         if ((test_flags & SCRIPT_VERIFY_CLEANSTACK)) {
diff --git a/src/validation.cpp b/src/validation.cpp
index 261549219d35..eb5138bc0cd0 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1255,6 +1255,7 @@ bool MemPoolAccept::PolicyScriptChecks(const ATMPArgs& args, Workspace& ws)
              { Consensus::DEPLOYMENT_CHECKTEMPLATEVERIFY, SCRIPT_VERIFY_DISCOURAGE_CHECK_TEMPLATE_VERIFY_HASH },
              { Consensus::DEPLOYMENT_ANYPREVOUT, SCRIPT_VERIFY_DISCOURAGE_ANYPREVOUT },
              { Consensus::DEPLOYMENT_OP_CAT, SCRIPT_VERIFY_DISCOURAGE_OP_CAT },
+             { Consensus::DEPLOYMENT_INTERNALKEY, SCRIPT_VERIFY_DISCOURAGE_INTERNALKEY },
     });
 
     // Check input scripts and signatures.
@@ -2429,6 +2430,11 @@ unsigned int GetBlockScriptFlags(const CBlockIndex& block_index, const Chainstat
         flags |= SCRIPT_VERIFY_OP_CAT;
     }
 
+    // Enforce OP_INTERNALKEY (BIP349)
+    if (DeploymentActiveAt(block_index, chainman, Consensus::DEPLOYMENT_INTERNALKEY)) {
+        flags |= SCRIPT_VERIFY_INTERNALKEY;
+    }
+
     return flags;
 }
 
diff --git a/test/functional/feature_taproot.py b/test/functional/feature_taproot.py
index f45a11dd6c59..bcbc600765cd 100755
--- a/test/functional/feature_taproot.py
+++ b/test/functional/feature_taproot.py
@@ -65,6 +65,7 @@
     OP_EQUAL,
     OP_EQUALVERIFY,
     OP_IF,
+    OP_INTERNALKEY,
     OP_NOP,
     OP_NOT,
     OP_NOTIF,
@@ -660,6 +661,22 @@ def byte_popper(expr):
 
 # === Actual test cases ===
 
+def spenders_internalkey_active():
+
+    secs = [generate_privkey() for _ in range(8)]
+    pubs = [compute_xonly_pubkey(sec)[0] for sec in secs]
+
+    spenders = []
+
+    scripts = [
+        ("ik", CScript([OP_INTERNALKEY, OP_EQUAL])),
+    ]
+
+    tap = taproot_construct(pubs[0], scripts)
+
+    add_spender(spenders, "ik/success", tap=tap, leaf="ik", inputs=[pubs[0]], failure={"inputs": [pubs[1]]})
+
+    return spenders
 
 def spenders_taproot_active():
     """Return a list of Spenders for testing post-Taproot activation behavior."""
@@ -1784,7 +1801,7 @@ def run_test(self):
         self.gen_test_vectors()
 
         self.log.info("Post-activation tests...")
-        self.test_spenders(self.nodes[0], spenders_taproot_active(), input_counts=[1, 2, 2, 2, 2, 3])
+        self.test_spenders(self.nodes[0], spenders_taproot_active() + spenders_internalkey_active(), input_counts=[1, 2, 2, 2, 2, 3])
         # Run each test twice; once in isolation, and once combined with others. Testing in isolation
         # means that the standardness is verified in every test (as combined transactions are only standard
         # when all their inputs are standard).
diff --git a/test/functional/rpc_blockchain.py b/test/functional/rpc_blockchain.py
index f54fd0851b1d..cad8ad6537f9 100755
--- a/test/functional/rpc_blockchain.py
+++ b/test/functional/rpc_blockchain.py
@@ -196,7 +196,7 @@ def check_signalling_deploymentinfo_result(self, gdi_result, height, blockhash):
         assert_equal(gdi_result, {
           "hash": blockhash,
           "height": height,
-          "script_flags": ["ANYPREVOUT","CHECKLOCKTIMEVERIFY","CHECKSEQUENCEVERIFY","DEFAULT_CHECK_TEMPLATE_VERIFY_HASH","DERSIG","NULLDUMMY","OP_CAT","P2SH","TAPROOT","WITNESS"],
+          "script_flags": ["ANYPREVOUT","CHECKLOCKTIMEVERIFY","CHECKSEQUENCEVERIFY","DEFAULT_CHECK_TEMPLATE_VERIFY_HASH","DERSIG", "INTERNALKEY", "NULLDUMMY","OP_CAT","P2SH","TAPROOT","WITNESS"],
           "deployments": {
             'bip34': {'type': 'buried', 'active': True, 'height': 2},
             'bip66': {'type': 'buried', 'active': True, 'height': 3},
@@ -261,7 +261,21 @@ def check_signalling_deploymentinfo_result(self, gdi_result, height, blockhash):
                 'height': 0,
                 'active': True,
             },
-          }
+            "internalkey": {
+                "type": "heretical",
+                "height": 0,
+                "active": True,
+                "heretical": {
+                    "binana-id": "BIN-2024-0001-000",
+                    "start_time": -1,
+                    "timeout": 9223372036854775807,
+                    "period": 144,
+                    "status": "active",
+                    "since": 0,
+                    "status_next": "active"
+                }
+            }
+        }
         })
 
     def _test_getdeploymentinfo(self):
diff --git a/test/functional/test_framework/script.py b/test/functional/test_framework/script.py
index b386c452f77a..5081b6bbf8b1 100644
--- a/test/functional/test_framework/script.py
+++ b/test/functional/test_framework/script.py
@@ -254,6 +254,8 @@ def __new__(cls, n):
 # BIP 342 opcodes (Tapscript)
 OP_CHECKSIGADD = CScriptOp(0xba)
 
+OP_INTERNALKEY = CScriptOp(0xcb)
+
 OP_INVALIDOPCODE = CScriptOp(0xff)
 
 OPCODE_NAMES.update({
@@ -969,4 +971,6 @@ def is_op_success(o):
     # assume OP_CAT is activated in tests
     if o == OP_CAT:
         return False
+    if o == OP_INTERNALKEY:
+        return False
     return o == 0x50 or o == 0x62 or o == 0x89 or o == 0x8a or o == 0x8d or o == 0x8e or (o >= 0x7e and o <= 0x81) or (o >= 0x83 and o <= 0x86) or (o >= 0x95 and o <= 0x99) or (o >= 0xbb and o <= 0xfe)