diff --git a/packages/testing/src/execution_testing/client_clis/clis/execution_specs.py b/packages/testing/src/execution_testing/client_clis/clis/execution_specs.py
index 7d007cca02..cb6acfb75e 100644
--- a/packages/testing/src/execution_testing/client_clis/clis/execution_specs.py
+++ b/packages/testing/src/execution_testing/client_clis/clis/execution_specs.py
@@ -197,6 +197,7 @@ class ExecutionSpecsExceptionMapper(ExceptionMapper):
     """
 
     mapping_substring: ClassVar[Dict[ExceptionBase, str]] = {
+        TransactionException.TYPE_NOT_SUPPORTED: "TransactionTypeError",
         TransactionException.TYPE_4_EMPTY_AUTHORIZATION_LIST: (
             "EmptyAuthorizationListError"
         ),
diff --git a/src/ethereum/forks/monad_eight/transactions.py b/src/ethereum/forks/monad_eight/transactions.py
index 24bb4880a7..2073ae50a1 100644
--- a/src/ethereum/forks/monad_eight/transactions.py
+++ b/src/ethereum/forks/monad_eight/transactions.py
@@ -495,15 +495,14 @@ def decode_transaction(tx: LegacyTransaction | Bytes) -> Transaction:
     Needed because non-legacy transactions aren't RLP.
 
     Legacy transactions are returned as-is, while other transaction types
-    are decoded based on their type identifier prefix.
+    are decoded based on their type identifier prefix. Blob transactions
+    are not accepted, so their type byte is unknown here.
     """
     if isinstance(tx, Bytes):
         if tx[0] == 1:
             return rlp.decode_to(AccessListTransaction, tx[1:])
         elif tx[0] == 2:
             return rlp.decode_to(FeeMarketTransaction, tx[1:])
-        elif tx[0] == 3:
-            return rlp.decode_to(BlobTransaction, tx[1:])
         elif tx[0] == 4:
             return rlp.decode_to(SetCodeTransaction, tx[1:])
         else:
@@ -541,6 +540,9 @@ def validate_transaction(tx: Transaction) -> Tuple[Uint, Uint]:
     [EIP-2681]: https://eips.ethereum.org/EIPS/eip-2681
     [EIP-7623]: https://eips.ethereum.org/EIPS/eip-7623
     """
+    if isinstance(tx, BlobTransaction):
+        raise TransactionTypeError(3)
+
     from .vm.interpreter import MAX_INIT_CODE_SIZE
 
     intrinsic_gas, calldata_floor_gas_cost = calculate_intrinsic_cost(tx)
diff --git a/src/ethereum/forks/monad_next/transactions.py b/src/ethereum/forks/monad_next/transactions.py
index 24bb4880a7..2073ae50a1 100644
--- a/src/ethereum/forks/monad_next/transactions.py
+++ b/src/ethereum/forks/monad_next/transactions.py
@@ -495,15 +495,14 @@ def decode_transaction(tx: LegacyTransaction | Bytes) -> Transaction:
     Needed because non-legacy transactions aren't RLP.
 
     Legacy transactions are returned as-is, while other transaction types
-    are decoded based on their type identifier prefix.
+    are decoded based on their type identifier prefix. Blob transactions
+    are not accepted, so their type byte is unknown here.
     """
     if isinstance(tx, Bytes):
         if tx[0] == 1:
             return rlp.decode_to(AccessListTransaction, tx[1:])
         elif tx[0] == 2:
             return rlp.decode_to(FeeMarketTransaction, tx[1:])
-        elif tx[0] == 3:
-            return rlp.decode_to(BlobTransaction, tx[1:])
         elif tx[0] == 4:
             return rlp.decode_to(SetCodeTransaction, tx[1:])
         else:
@@ -541,6 +540,9 @@ def validate_transaction(tx: Transaction) -> Tuple[Uint, Uint]:
     [EIP-2681]: https://eips.ethereum.org/EIPS/eip-2681
     [EIP-7623]: https://eips.ethereum.org/EIPS/eip-7623
     """
+    if isinstance(tx, BlobTransaction):
+        raise TransactionTypeError(3)
+
     from .vm.interpreter import MAX_INIT_CODE_SIZE
 
     intrinsic_gas, calldata_floor_gas_cost = calculate_intrinsic_cost(tx)
diff --git a/src/ethereum/forks/monad_nine/transactions.py b/src/ethereum/forks/monad_nine/transactions.py
index 24bb4880a7..2073ae50a1 100644
--- a/src/ethereum/forks/monad_nine/transactions.py
+++ b/src/ethereum/forks/monad_nine/transactions.py
@@ -495,15 +495,14 @@ def decode_transaction(tx: LegacyTransaction | Bytes) -> Transaction:
     Needed because non-legacy transactions aren't RLP.
 
     Legacy transactions are returned as-is, while other transaction types
-    are decoded based on their type identifier prefix.
+    are decoded based on their type identifier prefix. Blob transactions
+    are not accepted, so their type byte is unknown here.
     """
     if isinstance(tx, Bytes):
         if tx[0] == 1:
             return rlp.decode_to(AccessListTransaction, tx[1:])
         elif tx[0] == 2:
             return rlp.decode_to(FeeMarketTransaction, tx[1:])
-        elif tx[0] == 3:
-            return rlp.decode_to(BlobTransaction, tx[1:])
         elif tx[0] == 4:
             return rlp.decode_to(SetCodeTransaction, tx[1:])
         else:
@@ -541,6 +540,9 @@ def validate_transaction(tx: Transaction) -> Tuple[Uint, Uint]:
     [EIP-2681]: https://eips.ethereum.org/EIPS/eip-2681
     [EIP-7623]: https://eips.ethereum.org/EIPS/eip-7623
     """
+    if isinstance(tx, BlobTransaction):
+        raise TransactionTypeError(3)
+
     from .vm.interpreter import MAX_INIT_CODE_SIZE
 
     intrinsic_gas, calldata_floor_gas_cost = calculate_intrinsic_cost(tx)
diff --git a/src/ethereum/forks/monad_ten/transactions.py b/src/ethereum/forks/monad_ten/transactions.py
index 24bb4880a7..2073ae50a1 100644
--- a/src/ethereum/forks/monad_ten/transactions.py
+++ b/src/ethereum/forks/monad_ten/transactions.py
@@ -495,15 +495,14 @@ def decode_transaction(tx: LegacyTransaction | Bytes) -> Transaction:
     Needed because non-legacy transactions aren't RLP.
 
     Legacy transactions are returned as-is, while other transaction types
-    are decoded based on their type identifier prefix.
+    are decoded based on their type identifier prefix. Blob transactions
+    are not accepted, so their type byte is unknown here.
     """
     if isinstance(tx, Bytes):
         if tx[0] == 1:
             return rlp.decode_to(AccessListTransaction, tx[1:])
         elif tx[0] == 2:
             return rlp.decode_to(FeeMarketTransaction, tx[1:])
-        elif tx[0] == 3:
-            return rlp.decode_to(BlobTransaction, tx[1:])
         elif tx[0] == 4:
             return rlp.decode_to(SetCodeTransaction, tx[1:])
         else:
@@ -541,6 +540,9 @@ def validate_transaction(tx: Transaction) -> Tuple[Uint, Uint]:
     [EIP-2681]: https://eips.ethereum.org/EIPS/eip-2681
     [EIP-7623]: https://eips.ethereum.org/EIPS/eip-7623
     """
+    if isinstance(tx, BlobTransaction):
+        raise TransactionTypeError(3)
+
     from .vm.interpreter import MAX_INIT_CODE_SIZE
 
     intrinsic_gas, calldata_floor_gas_cost = calculate_intrinsic_cost(tx)
diff --git a/tests/amsterdam/eip7981_increase_access_list_cost/test_transaction_validity.py b/tests/amsterdam/eip7981_increase_access_list_cost/test_transaction_validity.py
index 440e844c86..fffbc62d27 100644
--- a/tests/amsterdam/eip7981_increase_access_list_cost/test_transaction_validity.py
+++ b/tests/amsterdam/eip7981_increase_access_list_cost/test_transaction_validity.py
@@ -258,6 +258,9 @@ def test_mixed_zero_nonzero_bytes_floor_cost(
             3,
             [],
             id="type_3_empty_access_list",
+            marks=pytest.mark.not_valid_for(
+                "MONAD_EIGHT", subsequent_forks=True
+            ),
         ),
         pytest.param(
             4,
diff --git a/tests/istanbul/eip1344_chainid/test_chainid.py b/tests/istanbul/eip1344_chainid/test_chainid.py
index 8379b55cc9..78d48d2153 100644
--- a/tests/istanbul/eip1344_chainid/test_chainid.py
+++ b/tests/istanbul/eip1344_chainid/test_chainid.py
@@ -17,8 +17,8 @@
 
 
 @pytest.mark.with_all_typed_transactions(
-    marks=lambda tx_type: pytest.mark.skip(
-        reason="type 3 transactions aren't supported in Monad"
+    marks=lambda tx_type: pytest.mark.not_valid_for(
+        "MONAD_EIGHT", subsequent_forks=True
     )
     if tx_type == 3
     else None
diff --git a/tests/monad_eight/typed_transactions/__init__.py b/tests/monad_eight/typed_transactions/__init__.py
new file mode 100644
index 0000000000..d21a75bb78
--- /dev/null
+++ b/tests/monad_eight/typed_transactions/__init__.py
@@ -0,0 +1 @@
+"""Tests for the transaction types Monad forks accept."""
diff --git a/tests/monad_eight/typed_transactions/test_blob_transaction.py b/tests/monad_eight/typed_transactions/test_blob_transaction.py
new file mode 100644
index 0000000000..93b5b4ebb5
--- /dev/null
+++ b/tests/monad_eight/typed_transactions/test_blob_transaction.py
@@ -0,0 +1,65 @@
+"""
+Tests that Monad forks reject blob transactions.
+
+Monad advertises no blob schedule and carries the blob header fields
+fixed at zero, so the type byte EIP-4844 assigns is unknown to the fork
+and a transaction carrying it is invalid rather than merely unused.
+"""
+
+import pytest
+from execution_testing import (
+    Account,
+    Alloc,
+    Block,
+    BlockchainTestFiller,
+    Hash,
+    Transaction,
+    TransactionException,
+    add_kzg_version,
+)
+from execution_testing.forks.helpers import Fork
+
+BLOB_COMMITMENT_VERSION_KZG = 1
+
+pytestmark = [
+    pytest.mark.valid_from("MONAD_EIGHT"),
+    pytest.mark.exception_test,
+]
+
+
+@pytest.mark.parametrize(
+    "gas_limit",
+    [
+        pytest.param(100_000, id="sufficient_gas"),
+        # Below the intrinsic cost, so the transaction would fail generic
+        # validation too; the unknown type is reported ahead of it.
+        pytest.param(1_000, id="below_intrinsic_gas"),
+    ],
+)
+def test_blob_transaction_is_rejected(
+    blockchain_test: BlockchainTestFiller,
+    pre: Alloc,
+    fork: Fork,
+    gas_limit: int,
+) -> None:
+    """A blob transaction is not a transaction type the fork knows."""
+    assert 3 not in fork.tx_types()
+
+    sender = pre.fund_eoa()
+    tx = Transaction(
+        ty=3,
+        to=pre.fund_eoa(amount=0),
+        gas_limit=gas_limit,
+        max_fee_per_blob_gas=1,
+        blob_versioned_hashes=add_kzg_version(
+            [Hash(1)], BLOB_COMMITMENT_VERSION_KZG
+        ),
+        sender=sender,
+        error=TransactionException.TYPE_NOT_SUPPORTED,
+    )
+
+    blockchain_test(
+        pre=pre,
+        post={sender: Account(nonce=0)},
+        blocks=[Block(txs=[tx], exception=tx.error)],
+    )
diff --git a/tests/prague/eip7623_increase_calldata_cost/test_execution_gas.py b/tests/prague/eip7623_increase_calldata_cost/test_execution_gas.py
index e0722edae4..4a6f5de540 100644
--- a/tests/prague/eip7623_increase_calldata_cost/test_execution_gas.py
+++ b/tests/prague/eip7623_increase_calldata_cost/test_execution_gas.py
@@ -69,7 +69,9 @@ def to(
                 True,
                 None,
                 id="type_3",
-                marks=pytest.mark.skip(reason="Not supported in Monad"),
+                marks=pytest.mark.not_valid_for(
+                    "MONAD_EIGHT", subsequent_forks=True
+                ),
             ),
             pytest.param(4, True, [Address(1)], id="type_4"),
         ],
@@ -153,7 +155,9 @@ def to(
                 True,
                 None,
                 id="type_3",
-                marks=pytest.mark.skip(reason="Not supported in Monad"),
+                marks=pytest.mark.not_valid_for(
+                    "MONAD_EIGHT", subsequent_forks=True
+                ),
             ),
             pytest.param(4, True, [Address(1)], id="type_4"),
         ],
diff --git a/tests/prague/eip7623_increase_calldata_cost/test_transaction_validity.py b/tests/prague/eip7623_increase_calldata_cost/test_transaction_validity.py
index 792c8e8fc9..d20f3bb8a0 100644
--- a/tests/prague/eip7623_increase_calldata_cost/test_transaction_validity.py
+++ b/tests/prague/eip7623_increase_calldata_cost/test_transaction_validity.py
@@ -179,7 +179,7 @@ def test_transaction_validity_type_1_type_2(
     )
 
 
-@pytest.mark.skip(reason="Not supported in Monad")
+@pytest.mark.not_valid_for("MONAD_EIGHT", subsequent_forks=True)
 @pytest.mark.parametrize(
     "access_list",
     [