diff --git a/.github/configs/feature.yaml b/.github/configs/feature.yaml
index 95af954290a..c75ee01bf5b 100644
--- a/.github/configs/feature.yaml
+++ b/.github/configs/feature.yaml
@@ -12,11 +12,11 @@ monad:
   # --suppress-no-test-exit-code works around a problem where multi-phase fill
   # (triggered by tarball output) fails to proceed on no tests processed
   # in 1st phase (exit code 5)
-  fill-params: --suppress-no-test-exit-code -m blockchain_test --from=MONAD_EIGHT --until=MONAD_NEXT --chain-id=143 -k "not eip4844 and not eip7002 and not eip7251 and not eip7685 and not eip6110 and not eip7594 and not eip7918 and not eip7610 and not eip7934 and not invalid_header"
+  fill-params: --suppress-no-test-exit-code -m blockchain_test --from=MONAD_EIGHT --until=MONAD_NINE --chain-id=143 -k "not eip4844 and not eip7002 and not eip7251 and not eip7685 and not eip6110 and not eip7594 and not eip7918 and not eip7610 and not eip7934 and not invalid_header"
 
 mip3:
   evm-type: develop
   # --suppress-no-test-exit-code works around a problem where multi-phase fill
   # (triggered by tarball output) fails to proceed on no tests processed
   # in 1st phase (exit code 5)
-  fill-params: --suppress-no-test-exit-code -m blockchain_test --from=MONAD_EIGHT --until=MONAD_NEXT --chain-id=143 -k "not eip4844 and not eip7002 and not eip7251 and not eip7685 and not eip6110 and not eip7594 and not eip7918 and not eip7610 and not eip7934 and not invalid_header"
+  fill-params: --suppress-no-test-exit-code -m blockchain_test --from=MONAD_EIGHT --until=MONAD_NINE --chain-id=143 -k "not eip4844 and not eip7002 and not eip7251 and not eip7685 and not eip6110 and not eip7594 and not eip7918 and not eip7610 and not eip7934 and not invalid_header"
diff --git a/README.md b/README.md
index 59133e80145..c49db010af3 100644
--- a/README.md
+++ b/README.md
@@ -29,7 +29,7 @@ uv sync --all-extras
 3. Fill all monadized spec tests as of writing this (see below for explanation of flags):
 
 ```bash
-uv run fill --clean -m "blockchain_test or transaction_test" --from MONAD_EIGHT --until MONAD_NEXT --chain-id 143 -n auto tests
+uv run fill --clean -m "blockchain_test or transaction_test" --from MONAD_EIGHT --until MONAD_NINE --chain-id 143 -n auto tests
 ```
 
 4. The test fixtures to be found in `fixtures/` directory under repo root.
@@ -45,7 +45,7 @@ Filling tests is the process of running Python generators of spec tests [like on
 - **`-m blockchain_test or transaction_test`**: causes these two flavors of fixtures to be generated
   - `blockchain_test` is the currently supported by `monad` flavor of a spec test checking correctness of the state transition. Note this includes `blockchain_test_from_state_test`, meaning that all `state_test(...)` fillers are included
   - `transaction_test` is also supported, tests only correctness of static transaction checks
-- **`--from MONAD_EIGHT --until MONAD_NEXT`**: hardforks for which to generate fixtures. Must match with those defined in `monad`, inclusive
+- **`--from MONAD_EIGHT --until MONAD_NINE`**: hardforks for which to generate fixtures. Must match with those defined in `monad`, inclusive
 - **`--chain-id 143`**: must be specified for signatures and EIP-7702 to work correctly
 - **`-n auto`**: from `pytest`, parallel execution of tests
 - **`tests`**: root directory to traverse to discover tests
diff --git a/packages/testing/src/execution_testing/forks/__init__.py b/packages/testing/src/execution_testing/forks/__init__.py
index b635b656b24..891b4c057da 100644
--- a/packages/testing/src/execution_testing/forks/__init__.py
+++ b/packages/testing/src/execution_testing/forks/__init__.py
@@ -8,7 +8,7 @@
     BPO4,
     BPO5,
     MONAD_EIGHT,
-    MONAD_NEXT,
+    MONAD_NINE,
     Amsterdam,
     ArrowGlacier,
     Berlin,
@@ -36,7 +36,7 @@
     BPO2ToBPO3AtTime15k,
     BPO3ToBPO4AtTime15k,
     CancunToPragueAtTime15k,
-    MONAD_EIGHTToMONAD_NEXTAtTime15k,
+    MONAD_EIGHTToMONAD_NINEAtTime15k,
     OsakaToBPO1AtTime15k,
     ParisToShanghaiAtTime15k,
     PragueToMONAD_EIGHTAtTime15k,
@@ -118,10 +118,10 @@
     "PragueToOsakaAtTime15k",
     "Osaka",
     "OsakaToBPO1AtTime15k",
-    "MONAD_EIGHT",
     "PragueToMONAD_EIGHTAtTime15k",
-    "MONAD_NEXT",
-    "MONAD_EIGHTToMONAD_NEXTAtTime15k",
+    "MONAD_EIGHT",
+    "MONAD_EIGHTToMONAD_NINEAtTime15k",
+    "MONAD_NINE",
     "BPO1",
     "BPO1ToBPO2AtTime15k",
     "BPO2",
diff --git a/packages/testing/src/execution_testing/forks/forks/forks.py b/packages/testing/src/execution_testing/forks/forks/forks.py
index b8e74405468..8c3bec9a0fd 100644
--- a/packages/testing/src/execution_testing/forks/forks/forks.py
+++ b/packages/testing/src/execution_testing/forks/forks/forks.py
@@ -3352,8 +3352,8 @@ def transaction_gas_limit_cap(
         return 30_000_000
 
 
-class MONAD_NEXT(MONAD_EIGHT, Osaka, solc_name="cancun"):  # noqa: N801
-    """MONAD_NEXT fork."""
+class MONAD_NINE(MONAD_EIGHT, Osaka, solc_name="cancun"):  # noqa: N801
+    """MONAD_NINE fork."""
 
     @classmethod
     def valid_opcodes(
diff --git a/packages/testing/src/execution_testing/forks/forks/transition.py b/packages/testing/src/execution_testing/forks/forks/transition.py
index 1b0f9e0f5e2..b3667e56a42 100644
--- a/packages/testing/src/execution_testing/forks/forks/transition.py
+++ b/packages/testing/src/execution_testing/forks/forks/transition.py
@@ -7,7 +7,7 @@
     BPO3,
     BPO4,
     MONAD_EIGHT,
-    MONAD_NEXT,
+    MONAD_NINE,
     Amsterdam,
     Berlin,
     Cancun,
@@ -62,9 +62,9 @@ class PragueToMONAD_EIGHTAtTime15k(Prague):  # noqa: N801
     pass
 
 
-@transition_fork(to_fork=MONAD_NEXT, at_timestamp=15_000)
-class MONAD_EIGHTToMONAD_NEXTAtTime15k(MONAD_EIGHT):  # noqa: N801
-    """Prague to MONAD_NEXT transition at Timestamp 15k."""
+@transition_fork(to_fork=MONAD_NINE, at_timestamp=15_000)
+class MONAD_EIGHTToMONAD_NINEAtTime15k(MONAD_EIGHT):  # noqa: N801
+    """MONAD_EIGHT to MONAD_NINE transition at Timestamp 15k."""
 
     pass
 
diff --git a/src/ethereum/forks/monad_next/__init__.py b/src/ethereum/forks/monad_nine/__init__.py
similarity index 75%
rename from src/ethereum/forks/monad_next/__init__.py
rename to src/ethereum/forks/monad_nine/__init__.py
index a04059da2b7..6ef692ad94a 100644
--- a/src/ethereum/forks/monad_next/__init__.py
+++ b/src/ethereum/forks/monad_nine/__init__.py
@@ -1,5 +1,5 @@
 """
-MONAD_NEXT fork introduces Monad specific changes to the Ethereum protocol.
+MONAD_NINE fork introduces Monad specific changes to the Ethereum protocol.
 """
 
 from ethereum.fork_criteria import ByTimestamp, ForkCriteria
diff --git a/src/ethereum/forks/monad_next/blocks.py b/src/ethereum/forks/monad_nine/blocks.py
similarity index 91%
rename from src/ethereum/forks/monad_next/blocks.py
rename to src/ethereum/forks/monad_nine/blocks.py
index bd638633406..945b50b12ae 100644
--- a/src/ethereum/forks/monad_next/blocks.py
+++ b/src/ethereum/forks/monad_nine/blocks.py
@@ -38,7 +38,7 @@ class Withdrawal:
     chain) to the execution layer, as validated by the consensus layer. Each
     withdrawal is listed in the block's list of withdrawals. See [`block`].
 
-    [`block`]: ref:ethereum.forks.monad_next.blocks.Block.withdrawals
+    [`block`]: ref:ethereum.forks.monad_nine.blocks.Block.withdrawals
     """
 
     index: U64
@@ -87,7 +87,7 @@ class Header:
 
     [`keccak256`]: ref:ethereum.crypto.hash.keccak256
     [RLP]: https://ethereum.github.io/ethereum-rlp/src/ethereum_rlp/rlp.py.html
-    [`EMPTY_OMMER_HASH`]: ref:ethereum.forks.monad_next.fork.EMPTY_OMMER_HASH
+    [`EMPTY_OMMER_HASH`]: ref:ethereum.forks.monad_nine.fork.EMPTY_OMMER_HASH
     """
 
     coinbase: Address
@@ -110,8 +110,8 @@ class Header:
     of the Merkle-Patricia [Trie] representing the Ethereum world state.
 
     [`keccak256`]: ref:ethereum.crypto.hash.keccak256
-    [`state_root()`]: ref:ethereum.forks.monad_next.state.state_root
-    [Trie]: ref:ethereum.forks.monad_next.trie.Trie
+    [`state_root()`]: ref:ethereum.forks.monad_nine.state.state_root
+    [Trie]: ref:ethereum.forks.monad_nine.trie.Trie
     """
 
     transactions_root: Root
@@ -122,8 +122,8 @@ class Header:
     transactions as the parameter.
 
     [`keccak256`]: ref:ethereum.crypto.hash.keccak256
-    [`root()`]: ref:ethereum.forks.monad_next.trie.root
-    [Trie]: ref:ethereum.forks.monad_next.trie.Trie
+    [`root()`]: ref:ethereum.forks.monad_nine.trie.root
+    [Trie]: ref:ethereum.forks.monad_nine.trie.Trie
     """
 
     receipt_root: Root
@@ -133,8 +133,8 @@ class Header:
     function over the Merkle-Patricia [trie] constructed from the receipts.
 
     [`keccak256`]: ref:ethereum.crypto.hash.keccak256
-    [`root()`]: ref:ethereum.forks.monad_next.trie.root
-    [Trie]: ref:ethereum.forks.monad_next.trie.Trie
+    [`root()`]: ref:ethereum.forks.monad_nine.trie.root
+    [Trie]: ref:ethereum.forks.monad_nine.trie.Trie
     """
 
     bloom: Bloom
@@ -142,7 +142,7 @@ class Header:
     Bloom filter for logs generated by transactions in this block.
     Constructed from all logs in the block using the [logs bloom] mechanism.
 
-    [logs bloom]: ref:ethereum.forks.monad_next.bloom.logs_bloom
+    [logs bloom]: ref:ethereum.forks.monad_nine.bloom.logs_bloom
     """
 
     difficulty: Uint
@@ -238,7 +238,7 @@ class Header:
     [EIP-7685]. See [`compute_requests_hash`][crh] for more details.
 
     [EIP-7685]: https://eips.ethereum.org/EIPS/eip-7685
-    [crh]: ref:ethereum.forks.monad_next.requests.compute_requests_hash
+    [crh]: ref:ethereum.forks.monad_nine.requests.compute_requests_hash
     [SHA2-256]: https://en.wikipedia.org/wiki/SHA-2
     """
 
@@ -265,8 +265,8 @@ class Block:
     Withdrawals represent ETH transfers from validators to their recipients,
     introduced by the consensus layer. Ommers remain deprecated and empty.
 
-    [`header`]: ref:ethereum.forks.monad_next.blocks.Header
-    [withdrawals]: ref:ethereum.forks.monad_next.blocks.Withdrawal
+    [`header`]: ref:ethereum.forks.monad_nine.blocks.Header
+    [withdrawals]: ref:ethereum.forks.monad_nine.blocks.Withdrawal
     """
 
     header: Header
@@ -274,7 +274,7 @@ class Block:
     The block header containing metadata and cryptographic commitments. Refer
     to [headers] for more details on the fields included in the header.
 
-    [headers]: ref:ethereum.forks.monad_next.blocks.Header
+    [headers]: ref:ethereum.forks.monad_nine.blocks.Header
     """
 
     transactions: Tuple[Bytes | LegacyTransaction, ...]
@@ -305,11 +305,11 @@ class Log:
     [`LOG1`], [`LOG2`], [`LOG3`] and [`LOG4`]), which can be efficiently
     searched using the bloom filter in the block header.
 
-    [`LOG0`]: ref:ethereum.forks.monad_next.vm.instructions.log.log0
-    [`LOG1`]: ref:ethereum.forks.monad_next.vm.instructions.log.log1
-    [`LOG2`]: ref:ethereum.forks.monad_next.vm.instructions.log.log2
-    [`LOG3`]: ref:ethereum.forks.monad_next.vm.instructions.log.log3
-    [`LOG4`]: ref:ethereum.forks.monad_next.vm.instructions.log.log4
+    [`LOG0`]: ref:ethereum.forks.monad_nine.vm.instructions.log.log0
+    [`LOG1`]: ref:ethereum.forks.monad_nine.vm.instructions.log.log1
+    [`LOG2`]: ref:ethereum.forks.monad_nine.vm.instructions.log.log2
+    [`LOG3`]: ref:ethereum.forks.monad_nine.vm.instructions.log.log3
+    [`LOG4`]: ref:ethereum.forks.monad_nine.vm.instructions.log.log4
     """
 
     address: Address
diff --git a/src/ethereum/forks/monad_next/bloom.py b/src/ethereum/forks/monad_nine/bloom.py
similarity index 100%
rename from src/ethereum/forks/monad_next/bloom.py
rename to src/ethereum/forks/monad_nine/bloom.py
diff --git a/src/ethereum/forks/monad_next/exceptions.py b/src/ethereum/forks/monad_nine/exceptions.py
similarity index 100%
rename from src/ethereum/forks/monad_next/exceptions.py
rename to src/ethereum/forks/monad_nine/exceptions.py
diff --git a/src/ethereum/forks/monad_next/fork.py b/src/ethereum/forks/monad_nine/fork.py
similarity index 100%
rename from src/ethereum/forks/monad_next/fork.py
rename to src/ethereum/forks/monad_nine/fork.py
diff --git a/src/ethereum/forks/monad_next/fork_types.py b/src/ethereum/forks/monad_nine/fork_types.py
similarity index 100%
rename from src/ethereum/forks/monad_next/fork_types.py
rename to src/ethereum/forks/monad_nine/fork_types.py
diff --git a/src/ethereum/forks/monad_next/requests.py b/src/ethereum/forks/monad_nine/requests.py
similarity index 100%
rename from src/ethereum/forks/monad_next/requests.py
rename to src/ethereum/forks/monad_nine/requests.py
diff --git a/src/ethereum/forks/monad_next/state.py b/src/ethereum/forks/monad_nine/state.py
similarity index 100%
rename from src/ethereum/forks/monad_next/state.py
rename to src/ethereum/forks/monad_nine/state.py
diff --git a/src/ethereum/forks/monad_next/transactions.py b/src/ethereum/forks/monad_nine/transactions.py
similarity index 100%
rename from src/ethereum/forks/monad_next/transactions.py
rename to src/ethereum/forks/monad_nine/transactions.py
diff --git a/src/ethereum/forks/monad_next/trie.py b/src/ethereum/forks/monad_nine/trie.py
similarity index 100%
rename from src/ethereum/forks/monad_next/trie.py
rename to src/ethereum/forks/monad_nine/trie.py
diff --git a/src/ethereum/forks/monad_next/utils/__init__.py b/src/ethereum/forks/monad_nine/utils/__init__.py
similarity index 100%
rename from src/ethereum/forks/monad_next/utils/__init__.py
rename to src/ethereum/forks/monad_nine/utils/__init__.py
diff --git a/src/ethereum/forks/monad_next/utils/address.py b/src/ethereum/forks/monad_nine/utils/address.py
similarity index 94%
rename from src/ethereum/forks/monad_next/utils/address.py
rename to src/ethereum/forks/monad_nine/utils/address.py
index 13e61313b87..cd5b3602bc1 100644
--- a/src/ethereum/forks/monad_next/utils/address.py
+++ b/src/ethereum/forks/monad_nine/utils/address.py
@@ -8,7 +8,7 @@
 Introduction
 ------------
 
-Address specific functions used in this MONAD_NEXT version of
+Address specific functions used in this MONAD_NINE version of
 specification.
 """
 
@@ -82,7 +82,7 @@ def compute_create2_contract_address(
 
     Returns
     -------
-    address: `ethereum.forks.monad_next.fork_types.Address`
+    address: `ethereum.forks.monad_nine.fork_types.Address`
         The computed address of the new account.
 
     """
diff --git a/src/ethereum/forks/monad_next/utils/hexadecimal.py b/src/ethereum/forks/monad_nine/utils/hexadecimal.py
similarity index 100%
rename from src/ethereum/forks/monad_next/utils/hexadecimal.py
rename to src/ethereum/forks/monad_nine/utils/hexadecimal.py
diff --git a/src/ethereum/forks/monad_next/utils/message.py b/src/ethereum/forks/monad_nine/utils/message.py
similarity index 95%
rename from src/ethereum/forks/monad_next/utils/message.py
rename to src/ethereum/forks/monad_nine/utils/message.py
index 265468cdc13..abdea2652a2 100644
--- a/src/ethereum/forks/monad_next/utils/message.py
+++ b/src/ethereum/forks/monad_nine/utils/message.py
@@ -8,7 +8,7 @@
 Introduction
 ------------
 
-Message specific functions used in this MONAD_NEXT version of
+Message specific functions used in this MONAD_NINE version of
 specification.
 """
 
@@ -42,7 +42,7 @@ def prepare_message(
 
     Returns
     -------
-    message: `ethereum.forks.monad_next.vm.Message`
+    message: `ethereum.forks.monad_nine.vm.Message`
         Items containing contract creation or message call specific data.
 
     """
diff --git a/src/ethereum/forks/monad_next/vm/__init__.py b/src/ethereum/forks/monad_nine/vm/__init__.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/__init__.py
rename to src/ethereum/forks/monad_nine/vm/__init__.py
diff --git a/src/ethereum/forks/monad_next/vm/eoa_delegation.py b/src/ethereum/forks/monad_nine/vm/eoa_delegation.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/eoa_delegation.py
rename to src/ethereum/forks/monad_nine/vm/eoa_delegation.py
diff --git a/src/ethereum/forks/monad_next/vm/exceptions.py b/src/ethereum/forks/monad_nine/vm/exceptions.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/exceptions.py
rename to src/ethereum/forks/monad_nine/vm/exceptions.py
diff --git a/src/ethereum/forks/monad_next/vm/gas.py b/src/ethereum/forks/monad_nine/vm/gas.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/gas.py
rename to src/ethereum/forks/monad_nine/vm/gas.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/__init__.py b/src/ethereum/forks/monad_nine/vm/instructions/__init__.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/__init__.py
rename to src/ethereum/forks/monad_nine/vm/instructions/__init__.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/arithmetic.py b/src/ethereum/forks/monad_nine/vm/instructions/arithmetic.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/arithmetic.py
rename to src/ethereum/forks/monad_nine/vm/instructions/arithmetic.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/bitwise.py b/src/ethereum/forks/monad_nine/vm/instructions/bitwise.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/bitwise.py
rename to src/ethereum/forks/monad_nine/vm/instructions/bitwise.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/block.py b/src/ethereum/forks/monad_nine/vm/instructions/block.py
similarity index 85%
rename from src/ethereum/forks/monad_next/vm/instructions/block.py
rename to src/ethereum/forks/monad_nine/vm/instructions/block.py
index 107944113b0..a8d9d8fa769 100644
--- a/src/ethereum/forks/monad_next/vm/instructions/block.py
+++ b/src/ethereum/forks/monad_nine/vm/instructions/block.py
@@ -30,9 +30,9 @@ def block_hash(evm: Evm) -> None:
 
     Raises
     ------
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.StackUnderflowError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.StackUnderflowError`
         If `len(stack)` is less than `1`.
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.OutOfGasError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.OutOfGasError`
         If `evm.gas_left` is less than `20`.
 
     """
@@ -79,9 +79,9 @@ def coinbase(evm: Evm) -> None:
 
     Raises
     ------
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.StackOverflowError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.StackOverflowError`
         If `len(stack)` is equal to `1024`.
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.OutOfGasError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.OutOfGasError`
         If `evm.gas_left` is less than `2`.
 
     """
@@ -113,9 +113,9 @@ def timestamp(evm: Evm) -> None:
 
     Raises
     ------
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.StackOverflowError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.StackOverflowError`
         If `len(stack)` is equal to `1024`.
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.OutOfGasError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.OutOfGasError`
         If `evm.gas_left` is less than `2`.
 
     """
@@ -146,9 +146,9 @@ def number(evm: Evm) -> None:
 
     Raises
     ------
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.StackOverflowError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.StackOverflowError`
         If `len(stack)` is equal to `1024`.
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.OutOfGasError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.OutOfGasError`
         If `evm.gas_left` is less than `2`.
 
     """
@@ -179,9 +179,9 @@ def prev_randao(evm: Evm) -> None:
 
     Raises
     ------
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.StackOverflowError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.StackOverflowError`
         If `len(stack)` is equal to `1024`.
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.OutOfGasError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.OutOfGasError`
         If `evm.gas_left` is less than `2`.
 
     """
@@ -212,9 +212,9 @@ def gas_limit(evm: Evm) -> None:
 
     Raises
     ------
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.StackOverflowError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.StackOverflowError`
         If `len(stack)` is equal to `1024`.
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.OutOfGasError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.OutOfGasError`
         If `evm.gas_left` is less than `2`.
 
     """
@@ -242,9 +242,9 @@ def chain_id(evm: Evm) -> None:
 
     Raises
     ------
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.StackOverflowError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.StackOverflowError`
         If `len(stack)` is equal to `1024`.
-    :py:class:`~ethereum.forks.monad_next.vm.exceptions.OutOfGasError`
+    :py:class:`~ethereum.forks.monad_nine.vm.exceptions.OutOfGasError`
         If `evm.gas_left` is less than `2`.
 
     """
diff --git a/src/ethereum/forks/monad_next/vm/instructions/comparison.py b/src/ethereum/forks/monad_nine/vm/instructions/comparison.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/comparison.py
rename to src/ethereum/forks/monad_nine/vm/instructions/comparison.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/control_flow.py b/src/ethereum/forks/monad_nine/vm/instructions/control_flow.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/control_flow.py
rename to src/ethereum/forks/monad_nine/vm/instructions/control_flow.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/environment.py b/src/ethereum/forks/monad_nine/vm/instructions/environment.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/environment.py
rename to src/ethereum/forks/monad_nine/vm/instructions/environment.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/keccak.py b/src/ethereum/forks/monad_nine/vm/instructions/keccak.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/keccak.py
rename to src/ethereum/forks/monad_nine/vm/instructions/keccak.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/log.py b/src/ethereum/forks/monad_nine/vm/instructions/log.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/log.py
rename to src/ethereum/forks/monad_nine/vm/instructions/log.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/memory.py b/src/ethereum/forks/monad_nine/vm/instructions/memory.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/memory.py
rename to src/ethereum/forks/monad_nine/vm/instructions/memory.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/stack.py b/src/ethereum/forks/monad_nine/vm/instructions/stack.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/stack.py
rename to src/ethereum/forks/monad_nine/vm/instructions/stack.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/storage.py b/src/ethereum/forks/monad_nine/vm/instructions/storage.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/storage.py
rename to src/ethereum/forks/monad_nine/vm/instructions/storage.py
diff --git a/src/ethereum/forks/monad_next/vm/instructions/system.py b/src/ethereum/forks/monad_nine/vm/instructions/system.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/instructions/system.py
rename to src/ethereum/forks/monad_nine/vm/instructions/system.py
diff --git a/src/ethereum/forks/monad_next/vm/interpreter.py b/src/ethereum/forks/monad_nine/vm/interpreter.py
similarity index 99%
rename from src/ethereum/forks/monad_next/vm/interpreter.py
rename to src/ethereum/forks/monad_nine/vm/interpreter.py
index 0eb2369253c..73c43e2e213 100644
--- a/src/ethereum/forks/monad_next/vm/interpreter.py
+++ b/src/ethereum/forks/monad_nine/vm/interpreter.py
@@ -180,7 +180,7 @@ def process_create_message(message: Message) -> Evm:
 
     Returns
     -------
-    evm: :py:class:`~ethereum.forks.monad_next.vm.Evm`
+    evm: :py:class:`~ethereum.forks.monad_nine.vm.Evm`
         Items containing execution specific objects.
 
     """
@@ -240,7 +240,7 @@ def process_message(message: Message) -> Evm:
 
     Returns
     -------
-    evm: :py:class:`~ethereum.forks.monad_next.vm.Evm`
+    evm: :py:class:`~ethereum.forks.monad_nine.vm.Evm`
         Items containing execution specific objects
 
     """
diff --git a/src/ethereum/forks/monad_next/vm/memory.py b/src/ethereum/forks/monad_nine/vm/memory.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/memory.py
rename to src/ethereum/forks/monad_nine/vm/memory.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/__init__.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/__init__.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/__init__.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/__init__.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/alt_bn128.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/alt_bn128.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/alt_bn128.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/alt_bn128.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/blake2f.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/blake2f.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/blake2f.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/blake2f.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/bls12_381/__init__.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/bls12_381/__init__.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/bls12_381/__init__.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/bls12_381/__init__.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/bls12_381/bls12_381_g1.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/bls12_381/bls12_381_g1.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/bls12_381/bls12_381_g1.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/bls12_381/bls12_381_g1.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/bls12_381/bls12_381_g2.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/bls12_381/bls12_381_g2.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/bls12_381/bls12_381_g2.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/bls12_381/bls12_381_g2.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/bls12_381/bls12_381_pairing.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/bls12_381/bls12_381_pairing.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/bls12_381/bls12_381_pairing.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/bls12_381/bls12_381_pairing.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/ecrecover.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/ecrecover.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/ecrecover.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/ecrecover.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/identity.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/identity.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/identity.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/identity.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/mapping.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/mapping.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/mapping.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/mapping.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/modexp.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/modexp.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/modexp.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/modexp.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/p256verify.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/p256verify.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/p256verify.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/p256verify.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/point_evaluation.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/point_evaluation.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/point_evaluation.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/point_evaluation.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/ripemd160.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/ripemd160.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/ripemd160.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/ripemd160.py
diff --git a/src/ethereum/forks/monad_next/vm/precompiled_contracts/sha256.py b/src/ethereum/forks/monad_nine/vm/precompiled_contracts/sha256.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/precompiled_contracts/sha256.py
rename to src/ethereum/forks/monad_nine/vm/precompiled_contracts/sha256.py
diff --git a/src/ethereum/forks/monad_next/vm/runtime.py b/src/ethereum/forks/monad_nine/vm/runtime.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/runtime.py
rename to src/ethereum/forks/monad_nine/vm/runtime.py
diff --git a/src/ethereum/forks/monad_next/vm/stack.py b/src/ethereum/forks/monad_nine/vm/stack.py
similarity index 100%
rename from src/ethereum/forks/monad_next/vm/stack.py
rename to src/ethereum/forks/monad_nine/vm/stack.py
diff --git a/src/ethereum_spec_tools/evm_tools/utils.py b/src/ethereum_spec_tools/evm_tools/utils.py
index a2e633de6bd..0b0855bae73 100644
--- a/src/ethereum_spec_tools/evm_tools/utils.py
+++ b/src/ethereum_spec_tools/evm_tools/utils.py
@@ -27,8 +27,8 @@
 W = TypeVar("W", Uint, U64, U256)
 
 EXCEPTION_MAPS = {
-    "MONAD_NEXT": {
-        "fork_blocks": [("monad_next", 0)],
+    "MONAD_NINE": {
+        "fork_blocks": [("monad_nine", 0)],
     },
     "MONAD_EIGHT": {
         "fork_blocks": [("monad_eight", 0)],
diff --git a/tests/frontier/opcodes/test_data_copy_oog.py b/tests/frontier/opcodes/test_data_copy_oog.py
index f71c5bb50e4..bc83b283ba9 100644
--- a/tests/frontier/opcodes/test_data_copy_oog.py
+++ b/tests/frontier/opcodes/test_data_copy_oog.py
@@ -12,7 +12,7 @@
     Storage,
     Transaction,
 )
-from execution_testing.forks.forks.forks import MONAD_NEXT
+from execution_testing.forks.forks.forks import MONAD_NINE
 from execution_testing.forks.helpers import Fork
 
 REFERENCE_SPEC_GIT_PATH = "EIPS/eip-211.md"
@@ -59,12 +59,12 @@ def test_calldatacopy_word_copy_oog(
     if expect_success:
         subcall_gas = 5000
     else:
-        # MIP-3 (MONAD_NEXT) uses linear memory cost (words // 2) instead of
+        # MIP-3 (MONAD_NINE) uses linear memory cost (words // 2) instead of
         # quadratic (3*words + words²/512), so memory expansion is cheaper.
         # Pre-MIP-3: MSTORE costs 3 + 98 = 101 gas for 32 words
         # MIP-3: MSTORE costs 3 + 16 = 19 gas for 32 words
         # We need enough gas for setup but not for CALLDATACOPY word copy cost.
-        subcall_gas = 68 if fork >= MONAD_NEXT else 150
+        subcall_gas = 68 if fork >= MONAD_NINE else 150
 
     storage = Storage()
     storage_key = storage.store_next(1 if expect_success else 0)
@@ -141,7 +141,7 @@ def test_codecopy_word_copy_oog(
     if expect_success:
         subcall_gas = 5000
     else:
-        subcall_gas = 68 if fork >= MONAD_NEXT else 150
+        subcall_gas = 68 if fork >= MONAD_NINE else 150
 
     storage = Storage()
     storage_key = storage.store_next(1 if expect_success else 0)
diff --git a/tests/monad_nine/mip3_linear_memory/test_gas_cost.py b/tests/monad_nine/mip3_linear_memory/test_gas_cost.py
index 5cfc8fca4a2..d261267c029 100644
--- a/tests/monad_nine/mip3_linear_memory/test_gas_cost.py
+++ b/tests/monad_nine/mip3_linear_memory/test_gas_cost.py
@@ -15,7 +15,7 @@
     Transaction,
     gas_test,
 )
-from execution_testing.forks.forks.forks import MONAD_NEXT
+from execution_testing.forks.forks.forks import MONAD_NINE
 from execution_testing.forks.helpers import Fork
 from execution_testing.vm import Opcode
 
@@ -61,7 +61,7 @@ def test_cost_non_quadratic(
     )
     storage = (
         {slot_code_worked: value_code_worked}
-        if not fail and fork >= MONAD_NEXT
+        if not fail and fork >= MONAD_NINE
         else {}
     )
 
@@ -140,7 +140,7 @@ def memory_sizes(
     yield pytest.param(0x20, id="single_word")
     yield pytest.param(0x100, id="large_copy")
     yield pytest.param(0x2000, id="above_quadratic_threshold_copy")
-    if fork >= MONAD_NEXT:
+    if fork >= MONAD_NINE:
         yield pytest.param(Spec.MAX_TX_MEMORY_USAGE, id="max")
 
 
@@ -409,7 +409,7 @@ def test_returndatacopy_gas_cost(
         ),
     ],
 )
-@pytest.mark.valid_from("MONAD_NEXT")
+@pytest.mark.valid_from("MONAD_NINE")
 def test_consecutive_expansions(
     state_test: StateTestFiller,
     pre: Alloc,
diff --git a/tests/monad_nine/mip3_linear_memory/test_oom.py b/tests/monad_nine/mip3_linear_memory/test_oom.py
index d35fee627db..9bbb7894505 100644
--- a/tests/monad_nine/mip3_linear_memory/test_oom.py
+++ b/tests/monad_nine/mip3_linear_memory/test_oom.py
@@ -45,7 +45,7 @@
 outer_marker_value = 0xDEADBEEF
 
 pytestmark = [
-    pytest.mark.valid_from("MONAD_NEXT"),
+    pytest.mark.valid_from("MONAD_NINE"),
     pytest.mark.pre_alloc_group(
         "mip3_tests",
         reason="Tests linear memory MIP-3",
diff --git a/tests/monad_nine/mip3_linear_memory/test_oom_deep.py b/tests/monad_nine/mip3_linear_memory/test_oom_deep.py
index f4ee9b6eb33..0dbbfb006ee 100644
--- a/tests/monad_nine/mip3_linear_memory/test_oom_deep.py
+++ b/tests/monad_nine/mip3_linear_memory/test_oom_deep.py
@@ -1,8 +1,8 @@
 """
 Tests deep nested call frames with memory allocation.
 
-Tests that run on both MONAD_EIGHT and MONAD_NEXT to compare behavior:
-- MONAD_NEXT: OOM when cumulative memory exceeds 8MB limit
+Tests that run on both MONAD_EIGHT and MONAD_NINE to compare behavior:
+- MONAD_NINE: OOM when cumulative memory exceeds 8MB limit
 - MONAD_EIGHT: can go above this limit if allocations spread across frames
 """
 
@@ -17,7 +17,7 @@
     Transaction,
 )
 from execution_testing.base_types.base_types import Address
-from execution_testing.forks.forks.forks import MONAD_NEXT
+from execution_testing.forks.forks.forks import MONAD_NINE
 from execution_testing.forks.helpers import Fork
 
 from .spec import Spec, ref_spec_3
@@ -44,7 +44,7 @@ def test_nested_frames_deep(
     """
     Test memory allocation across many nested call frames.
 
-    Uses small chunk sizes to maximize depth. In MONAD_NEXT, reverts when
+    Uses small chunk sizes to maximize depth. In MONAD_NINE, reverts when
     cumulative memory exceeds MAX_TX_MEMORY_USAGE. This test contrasts that
     in MONAD_EIGHT one tx can allocate more memory in total and serves as
     a sanity check.
@@ -53,7 +53,7 @@ def test_nested_frames_deep(
     chunk_size = 128 * 1024  # 128KB per frame
 
     # Calculate expected max depth for each fork
-    # MONAD_NEXT: limited by 8MB cumulative memory = 64 frames
+    # MONAD_NINE: limited by 8MB cumulative memory = 64 frames
     # MONAD_EIGHT: limited by gas (quadratic cost + 63/64 forwarding)
     #   ~150 frames
     max_depth = (
@@ -87,7 +87,7 @@ def test_nested_frames_deep(
     )
 
     # Calculate expected successful depth based on fork
-    if fork >= MONAD_NEXT:
+    if fork >= MONAD_NINE:
         # OOM at cumulative memory > 8MB
         expected_max_success_depth = Spec.MAX_TX_MEMORY_USAGE // chunk_size
     else: