diff --git a/beacon_chain/libnimbus_lc/libnimbus_lc.nim b/beacon_chain/libnimbus_lc/libnimbus_lc.nim
index a77de39dbd..20ad5baca2 100644
--- a/beacon_chain/libnimbus_lc/libnimbus_lc.nim
+++ b/beacon_chain/libnimbus_lc/libnimbus_lc.nim
@@ -1421,7 +1421,7 @@ type
     storageKeys: seq[Eth2Digest]
 
   ETHAuthorization = object
-    chainId: uint64
+    chainId: UInt256
     address: ExecutionAddress
     nonce: uint64
     authority: ExecutionAddress
@@ -1429,7 +1429,7 @@ type
 
   ETHTransaction = object
     hash: Eth2Digest
-    chainId: uint64
+    chainId: UInt256
     `from`: ExecutionAddress
     nonce: uint64
     maxPriorityFeePerGas: uint64
@@ -1539,8 +1539,8 @@ proc ETHTransactionsCreateFromJson(
 
     # Construct transaction
     static:
-      doAssert sizeof(uint64) == sizeof(ChainId)
-      doAssert sizeof(uint64) == sizeof(data.chainId.get)
+      doAssert sizeof(UInt256) == sizeof(ChainId)
+      doAssert sizeof(UInt256) == sizeof(data.chainId.get)
       doAssert sizeof(uint64) == sizeof(data.gas)
       doAssert sizeof(uint64) == sizeof(data.gasPrice)
       doAssert sizeof(uint64) == sizeof(data.maxPriorityFeePerGas.get)
@@ -1556,13 +1556,13 @@ proc ETHTransactionsCreateFromJson(
         return nil
     if data.authorizationList.isSome:
       for authorization in data.authorizationList.get:
-        static: doAssert sizeof(uint64) == sizeof(authorization.chainId)
+        static: doAssert sizeof(UInt256) == sizeof(authorization.chainId)
         if authorization.v > uint8.high:
           return nil
     let
       tx = eth_types.EthTransaction(
         txType: txType,
-        chainId: data.chainId.get(0.Quantity).ChainId,
+        chainId: data.chainId.get(0.u256),
         nonce: distinctBase(data.nonce),
         gasPrice: data.gasPrice.GasInt,
         maxPriorityFeePerGas:
@@ -1663,7 +1663,7 @@ proc ETHTransactionsCreateFromJson(
         authority = recoverSignerAddress(sig, auth.rlpHashForSigning).valueOr:
           return nil
       authorizationList.add ETHAuthorization(
-        chainId: distinctBase(auth.chainId),
+        chainId: auth.chainId,
         address: ExecutionAddress(data: auth.address.data),
         nonce: auth.nonce,
         authority: ExecutionAddress(data: authority),
@@ -1671,7 +1671,7 @@ proc ETHTransactionsCreateFromJson(
 
     txs.add ETHTransaction(
       hash: keccak256(rlpBytes),
-      chainId: distinctBase(tx.chainId),
+      chainId: tx.chainId,
       `from`: ExecutionAddress(data: fromAddress),
       nonce: tx.nonce,
       maxPriorityFeePerGas: tx.maxPriorityFeePerGas.uint64,
@@ -1755,7 +1755,7 @@ func ETHTransactionGetHash(
   addr transaction[].hash
 
 func ETHTransactionGetChainId(
-    transaction: ptr ETHTransaction): ptr uint64 {.exported.} =
+    transaction: ptr ETHTransaction): ptr UInt256 {.exported.} =
   ## Obtains the chain ID of a transaction.
   ##
   ## * The returned value is allocated in the given transaction.
@@ -2115,7 +2115,7 @@ func ETHAuthorizationListGet(
   addr authorizationList[][authorizationIndex.int]
 
 func ETHAuthorizationGetChainId(
-    authorization: ptr ETHAuthorization): ptr uint64 {.exported.} =
+    authorization: ptr ETHAuthorization): ptr UInt256 {.exported.} =
   ## Obtains the chain ID of an authorization tuple.
   ##
   ## * The returned value is allocated in the given authorization tuple.
diff --git a/research/fakeee.nim b/research/fakeee.nim
index ab2cddab3a..eed1764746 100644
--- a/research/fakeee.nim
+++ b/research/fakeee.nim
@@ -1,5 +1,5 @@
 # beacon_chain
-# Copyright (c) 2022-2024 Status Research & Development GmbH
+# Copyright (c) 2022-2025 Status Research & Development GmbH
 # Licensed and distributed under either of
 #   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
@@ -45,15 +45,6 @@ proc setupEngineAPI*(server: RpcServer) =
       msg: "Unknown payload"
     )
 
-  # https://github.com/ethereum/execution-apis/blob/v1.0.0-beta.3/src/engine/paris.md#engine_exchangetransitionconfigurationv1
-  server.rpc("engine_exchangeTransitionConfigurationV1") do(conf: TransitionConfigurationV1) -> TransitionConfigurationV1:
-    info "engine_exchangeTransitionConfigurationV1",
-      ttd = conf.terminalTotalDifficulty,
-      number = uint64(conf.terminalBlockNumber),
-      blockHash = conf.terminalBlockHash
-
-    return conf
-
   # https://github.com/ethereum/execution-apis/blob/v1.0.0-beta.3/src/engine/paris.md#engine_forkchoiceupdatedv1
   server.rpc("engine_forkchoiceUpdatedV1") do(
       update: ForkchoiceStateV1,
diff --git a/vendor/nim-eth b/vendor/nim-eth
index ac1be3135a..57fa21263a 160000
--- a/vendor/nim-eth
+++ b/vendor/nim-eth
@@ -1 +1 @@
-Subproject commit ac1be3135a7f41d2822544a7c0b7b498c5b824da
+Subproject commit 57fa21263a50a325e80636280f976e8077f6627c
diff --git a/vendor/nim-web3 b/vendor/nim-web3
index a3bc5ad48e..d20c21e90b 160000
--- a/vendor/nim-web3
+++ b/vendor/nim-web3
@@ -1 +1 @@
-Subproject commit a3bc5ad48e2b05fa253ba68bbd5b84e4ea234f50
+Subproject commit d20c21e90b74d4b74cd98deaac080d8757f37bbd