diff --git a/proto/utxorpc/v1beta/cardano/cardano.proto b/proto/utxorpc/v1beta/cardano/cardano.proto
index ff22309..88a4d44 100644
--- a/proto/utxorpc/v1beta/cardano/cardano.proto
+++ b/proto/utxorpc/v1beta/cardano/cardano.proto
@@ -27,7 +27,7 @@ message TxInput {
   bytes tx_hash = 1; // Hash of the previous transaction.
   uint32 output_index = 2; // Index of the output in the previous transaction.
   TxOutput as_output = 3; // Content of the input represented as output of the related transaction
-  Redeemer redeemer = 4; // Redeemer for the Plutus script.
+  optional Redeemer redeemer = 4; // Redeemer for the Plutus script.
 }
 
 // Represents a transaction output in the Cardano blockchain.
@@ -35,14 +35,14 @@ message TxOutput {
   bytes address = 1; // Address receiving the output.
   BigInt coin = 2; // Amount of ADA in the output.
   repeated Multiasset assets = 3; // Additional native (non-ADA) assets in the output.
-  Datum datum = 4; // Plutus data associated with the output.
-  Script script = 5; // Script associated with the output.
+  optional Datum datum = 4; // Plutus data associated with the output.
+  optional Script script = 5; // Script associated with the output.
 }
 
 message Datum {
   bytes hash = 1; // Hash of this datum as seen on-chain
-  PlutusData payload = 2; // Parsed Plutus data payload
-  bytes original_cbor = 3; // Original cbor-encoded data as seen on-chain
+  optional PlutusData payload = 2; // Parsed Plutus data payload
+  optional bytes original_cbor = 3; // Original cbor-encoded data as seen on-chain
 }
 
 // Represents a custom asset in the Cardano blockchain.
@@ -152,7 +152,7 @@ message HardForkInitiationAction {
 }
 
 message TreasuryWithdrawalsAction {
-  repeated WithdrawalAmount withdrawals = 1; // A map of the withdrawals to make
+  repeated WithdrawalAmount withdrawals = 1; // A list of the withdrawals to make
   bytes policy_hash = 2;
 }
 
@@ -245,11 +245,13 @@ message Constr {
 }
 
 // Represents a big integer for Plutus data in Cardano.
+// The representation here follows CBOR specification for bignums:
+// https://www.rfc-editor.org/rfc/rfc8949.html#name-bignums section 3.4.3.
 message BigInt {
   oneof big_int {
-    int64 int = 1;
-    bytes big_u_int = 2;
-    bytes big_n_int = 3;
+    int64 int = 1; // Stores value fitting within int64 range
+    bytes big_u_int = 2; // Stores unsigned value exceeding int64 range
+    bytes big_n_int = 3; // Stores negative value `n` exceeding int64 range as `-1 - n`
   }
 }
 
@@ -287,6 +289,7 @@ message Script {
     bytes plutus_v1 = 2; // Plutus V1 script.
     bytes plutus_v2 = 3; // Plutus V2 script.
     bytes plutus_v3 = 4; // Plutus V3 script.
+    bytes plutus_v4 = 5; // Plutus V4 script.
   }
 }
 
@@ -592,6 +595,7 @@ message CostModels {
   CostModel plutus_v1 = 1;
   CostModel plutus_v2 = 2;
   CostModel plutus_v3 = 3;
+  CostModel plutus_v4 = 4;
 }
 
 message VotingThresholds {
@@ -759,6 +763,7 @@ message CostModelMap {
   CostModel plutus_v1 = 1;
   CostModel plutus_v2 = 2;
   CostModel plutus_v3 = 3;
+  CostModel plutus_v4 = 4;
 }
 
 // Unified Genesis configuration containing all parameters from all eras