diff --git a/crates/mega-evm/tests/rex4/deployment.rs b/crates/mega-evm/tests/rex4/deployment.rs
new file mode 100644
index 0000000..2c2a043
--- /dev/null
+++ b/crates/mega-evm/tests/rex4/deployment.rs
@@ -0,0 +1,192 @@
+//! Tests for Rex4 system contract deployment wiring.
+
+use alloy_evm::{block::BlockExecutor, Database, Evm, EvmEnv, EvmFactory};
+use alloy_hardforks::ForkCondition;
+use alloy_op_evm::block::receipt_builder::OpAlloyReceiptBuilder;
+use alloy_primitives::{Address, B256, Bytes};
+use mega_evm::{
+    test_utils::MemoryDatabase, BlockLimits, MegaBlockExecutionCtx, MegaBlockExecutor,
+    MegaEvmFactory, MegaHardfork, MegaHardforkConfig, MegaSpecId, ACCESS_CONTROL_ADDRESS,
+    ACCESS_CONTROL_CODE, ACCESS_CONTROL_CODE_HASH, LIMIT_CONTROL_ADDRESS, LIMIT_CONTROL_CODE,
+    LIMIT_CONTROL_CODE_HASH,
+};
+use revm::{context::BlockEnv, database::State, primitives::U256};
+
+fn rex4_chain_spec() -> MegaHardforkConfig {
+    MegaHardforkConfig::default().with(MegaHardfork::Rex4, ForkCondition::Timestamp(0))
+}
+
+fn rex3_chain_spec() -> MegaHardforkConfig {
+    MegaHardforkConfig::default().with(MegaHardfork::Rex3, ForkCondition::Timestamp(0))
+}
+
+fn make_block_env(timestamp: u64) -> BlockEnv {
+    BlockEnv {
+        number: U256::from(1_u64),
+        timestamp: U256::from(timestamp),
+        gas_limit: 30_000_000,
+        ..Default::default()
+    }
+}
+
+fn assert_contract_deployed<DB: Database>(
+    db: &mut State<DB>,
+    address: Address,
+    expected_code_hash: B256,
+    expected_code: Bytes,
+    name: &str,
+) {
+    let cache_acc = db.load_cache_account(address).expect("should load cache account");
+    let acc_info = cache_acc.account_info().expect("system contract account should exist");
+
+    assert_eq!(
+        acc_info.code_hash, expected_code_hash,
+        "{name} code hash should match expected bytecode"
+    );
+    assert!(acc_info.code.is_some(), "{name} code should be set");
+    let deployed_code = acc_info.code.as_ref().expect("code should be present");
+    assert_eq!(
+        deployed_code.original_bytes(),
+        expected_code,
+        "{name} bytecode should match the embedded system contract code"
+    );
+}
+
+fn assert_contract_not_deployed<DB: Database>(
+    db: &mut State<DB>,
+    address: Address,
+    name: &str,
+) {
+    let cache_acc = db.load_cache_account(address).expect("should load cache account");
+    assert!(
+        cache_acc.account_info().is_none(),
+        "{name} should not be deployed for this spec boundary"
+    );
+}
+
+#[test]
+fn test_rex4_system_contracts_deployed_on_activation() {
+    let mut db = MemoryDatabase::default();
+    let mut state = State::builder().with_database(&mut db).build();
+
+    let mut cfg_env = revm::context::CfgEnv::default();
+    cfg_env.spec = MegaSpecId::REX4;
+    let evm_env = EvmEnv::new(cfg_env, make_block_env(0));
+
+    let evm_factory = MegaEvmFactory::new();
+    let evm = evm_factory.create_evm(&mut state, evm_env);
+    let block_ctx = MegaBlockExecutionCtx::new(
+        B256::ZERO,
+        Some(B256::ZERO),
+        Default::default(),
+        BlockLimits::no_limits(),
+    );
+    let receipt_builder = OpAlloyReceiptBuilder::default();
+    let mut executor = MegaBlockExecutor::new(evm, block_ctx, rex4_chain_spec(), receipt_builder);
+
+    executor.apply_pre_execution_changes().expect("pre-execution changes should succeed");
+
+    let db_ref = executor.evm_mut().db_mut();
+    assert_contract_deployed(
+        db_ref,
+        ACCESS_CONTROL_ADDRESS,
+        ACCESS_CONTROL_CODE_HASH,
+        ACCESS_CONTROL_CODE,
+        "MegaAccessControl",
+    );
+    assert_contract_deployed(
+        db_ref,
+        LIMIT_CONTROL_ADDRESS,
+        LIMIT_CONTROL_CODE_HASH,
+        LIMIT_CONTROL_CODE,
+        "MegaLimitControl",
+    );
+}
+
+#[test]
+fn test_rex4_system_contract_deployment_is_idempotent() {
+    let mut db = MemoryDatabase::default();
+    let mut state = State::builder().with_database(&mut db).build();
+
+    let mut cfg_env = revm::context::CfgEnv::default();
+    cfg_env.spec = MegaSpecId::REX4;
+    let evm_env = EvmEnv::new(cfg_env, make_block_env(0));
+
+    let evm_factory = MegaEvmFactory::new();
+    let evm = evm_factory.create_evm(&mut state, evm_env);
+    let block_ctx = MegaBlockExecutionCtx::new(
+        B256::ZERO,
+        Some(B256::ZERO),
+        Default::default(),
+        BlockLimits::no_limits(),
+    );
+    let receipt_builder = OpAlloyReceiptBuilder::default();
+    let mut executor = MegaBlockExecutor::new(evm, block_ctx, rex4_chain_spec(), receipt_builder);
+
+    executor.apply_pre_execution_changes().expect("first pre-execution changes should succeed");
+
+    {
+        let db_ref = executor.evm_mut().db_mut();
+        assert_contract_deployed(
+            db_ref,
+            ACCESS_CONTROL_ADDRESS,
+            ACCESS_CONTROL_CODE_HASH,
+            ACCESS_CONTROL_CODE,
+            "MegaAccessControl",
+        );
+        assert_contract_deployed(
+            db_ref,
+            LIMIT_CONTROL_ADDRESS,
+            LIMIT_CONTROL_CODE_HASH,
+            LIMIT_CONTROL_CODE,
+            "MegaLimitControl",
+        );
+    }
+
+    executor
+        .apply_pre_execution_changes()
+        .expect("second pre-execution changes should also succeed");
+
+    let db_ref = executor.evm_mut().db_mut();
+    assert_contract_deployed(
+        db_ref,
+        ACCESS_CONTROL_ADDRESS,
+        ACCESS_CONTROL_CODE_HASH,
+        ACCESS_CONTROL_CODE,
+        "MegaAccessControl after second apply",
+    );
+    assert_contract_deployed(
+        db_ref,
+        LIMIT_CONTROL_ADDRESS,
+        LIMIT_CONTROL_CODE_HASH,
+        LIMIT_CONTROL_CODE,
+        "MegaLimitControl after second apply",
+    );
+}
+
+#[test]
+fn test_rex3_boundary_does_not_deploy_rex4_system_contracts() {
+    let mut db = MemoryDatabase::default();
+    let mut state = State::builder().with_database(&mut db).build();
+
+    let mut cfg_env = revm::context::CfgEnv::default();
+    cfg_env.spec = MegaSpecId::REX3;
+    let evm_env = EvmEnv::new(cfg_env, make_block_env(0));
+
+    let evm_factory = MegaEvmFactory::new();
+    let evm = evm_factory.create_evm(&mut state, evm_env);
+    let block_ctx = MegaBlockExecutionCtx::new(
+        B256::ZERO,
+        Some(B256::ZERO),
+        Default::default(),
+        BlockLimits::no_limits(),
+    );
+    let receipt_builder = OpAlloyReceiptBuilder::default();
+    let mut executor = MegaBlockExecutor::new(evm, block_ctx, rex3_chain_spec(), receipt_builder);
+
+    executor.apply_pre_execution_changes().expect("pre-execution changes should succeed");
+
+    let db_ref = executor.evm_mut().db_mut();
+    assert_contract_not_deployed(db_ref, ACCESS_CONTROL_ADDRESS, "MegaAccessControl");
+    assert_contract_not_deployed(db_ref, LIMIT_CONTROL_ADDRESS, "MegaLimitControl");
+}
diff --git a/crates/mega-evm/tests/rex4/main.rs b/crates/mega-evm/tests/rex4/main.rs
index 703ccad..2513a5c 100644
--- a/crates/mega-evm/tests/rex4/main.rs
+++ b/crates/mega-evm/tests/rex4/main.rs
@@ -1,6 +1,7 @@
 //! Tests for `Rex4` hardfork features.
 
 mod access_control;
+mod deployment;
 mod frame_limits;
 mod frame_state_growth;
 mod gas_detention;