diff --git a/crates/optimism/chainspec/src/lib.rs b/crates/optimism/chainspec/src/lib.rs
index a2b9124935..e923d55f04 100644
--- a/crates/optimism/chainspec/src/lib.rs
+++ b/crates/optimism/chainspec/src/lib.rs
@@ -810,6 +810,7 @@ mod tests {
         "fjordTime": 50,
         "graniteTime": 51,
         "holoceneTime": 52,
+        "isthmusTime": 53,
         "optimism": {
           "eip1559Elasticity": 60,
           "eip1559Denominator": 70
@@ -833,6 +834,8 @@ mod tests {
         assert_eq!(actual_granite_timestamp, Some(serde_json::Value::from(51)).as_ref());
         let actual_holocene_timestamp = genesis.config.extra_fields.get("holoceneTime");
         assert_eq!(actual_holocene_timestamp, Some(serde_json::Value::from(52)).as_ref());
+        let actual_isthmus_timestamp = genesis.config.extra_fields.get("isthmusTime");
+        assert_eq!(actual_isthmus_timestamp, Some(serde_json::Value::from(53)).as_ref());
 
         let optimism_object = genesis.config.extra_fields.get("optimism").unwrap();
         assert_eq!(
@@ -879,6 +882,7 @@ mod tests {
         "fjordTime": 50,
         "graniteTime": 51,
         "holoceneTime": 52,
+        "isthmusTime": 53,
         "optimism": {
           "eip1559Elasticity": 60,
           "eip1559Denominator": 70,
@@ -903,6 +907,8 @@ mod tests {
         assert_eq!(actual_granite_timestamp, Some(serde_json::Value::from(51)).as_ref());
         let actual_holocene_timestamp = genesis.config.extra_fields.get("holoceneTime");
         assert_eq!(actual_holocene_timestamp, Some(serde_json::Value::from(52)).as_ref());
+        let actual_isthmus_timestamp = genesis.config.extra_fields.get("isthmusTime");
+        assert_eq!(actual_isthmus_timestamp, Some(serde_json::Value::from(53)).as_ref());
 
         let optimism_object = genesis.config.extra_fields.get("optimism").unwrap();
         assert_eq!(
diff --git a/crates/optimism/chainspec/src/superchain/chain_metadata.rs b/crates/optimism/chainspec/src/superchain/chain_metadata.rs
index 90330817b7..c44efb6571 100644
--- a/crates/optimism/chainspec/src/superchain/chain_metadata.rs
+++ b/crates/optimism/chainspec/src/superchain/chain_metadata.rs
@@ -158,7 +158,8 @@ mod tests {
         "ecotone_time": 1710374401,
         "fjord_time": 1720627201,
         "granite_time": 1726070401,
-        "holocene_time": 1736445601
+        "holocene_time": 1736445601,
+        "isthmus_time": 1746806401
       },
       "optimism": {
         "eip1559_elasticity": 6,
@@ -179,6 +180,7 @@ mod tests {
         assert_eq!(config.hardforks.fjord_time, Some(1720627201));
         assert_eq!(config.hardforks.granite_time, Some(1726070401));
         assert_eq!(config.hardforks.holocene_time, Some(1736445601));
+        assert_eq!(config.hardforks.isthmus_time, Some(1746806401));
         // optimism
         assert_eq!(config.optimism.as_ref().unwrap().eip1559_elasticity, 6);
         assert_eq!(config.optimism.as_ref().unwrap().eip1559_denominator, 50);
@@ -196,7 +198,7 @@ mod tests {
             fjord_time: Some(1720627201),
             granite_time: Some(1726070401),
             holocene_time: Some(1736445601),
-            isthmus_time: None,
+            isthmus_time: Some(1746806401),
             optimism: Option::from(ChainConfigExtraFieldsOptimism {
                 eip1559_elasticity: 6,
                 eip1559_denominator: 50,
@@ -212,7 +214,7 @@ mod tests {
         assert_eq!(value.get("fjordTime").unwrap(), 1720627201);
         assert_eq!(value.get("graniteTime").unwrap(), 1726070401);
         assert_eq!(value.get("holoceneTime").unwrap(), 1736445601);
-        assert_eq!(value.get("isthmusTime"), None);
+        assert_eq!(value.get("isthmusTime").unwrap(), 1746806401);
         let optimism = value.get("optimism").unwrap();
         assert_eq!(optimism.get("eip1559Elasticity").unwrap(), 6);
         assert_eq!(optimism.get("eip1559Denominator").unwrap(), 50);
@@ -242,7 +244,7 @@ mod tests {
         assert_eq!(chain_config.merge_netsplit_block, Some(0));
         assert_eq!(chain_config.shanghai_time, Some(1704992401));
         assert_eq!(chain_config.cancun_time, Some(1710374401));
-        assert_eq!(chain_config.prague_time, None);
+        assert_eq!(chain_config.prague_time, Some(1746806401));
         assert_eq!(chain_config.osaka_time, None);
         assert_eq!(chain_config.terminal_total_difficulty, Some(U256::ZERO));
         assert!(chain_config.terminal_total_difficulty_passed);
@@ -256,7 +258,7 @@ mod tests {
         assert_eq!(chain_config.extra_fields.get("fjordTime").unwrap(), 1720627201);
         assert_eq!(chain_config.extra_fields.get("graniteTime").unwrap(), 1726070401);
         assert_eq!(chain_config.extra_fields.get("holoceneTime").unwrap(), 1736445601);
-        assert_eq!(chain_config.extra_fields.get("isthmusTime"), None);
+        assert_eq!(chain_config.extra_fields.get("isthmusTime").unwrap(), 1746806401);
         let optimism = chain_config.extra_fields.get("optimism").unwrap();
         assert_eq!(optimism.get("eip1559Elasticity").unwrap(), 6);
         assert_eq!(optimism.get("eip1559Denominator").unwrap(), 50);
@@ -274,7 +276,8 @@ mod tests {
             "ecotone_time": 1710374401,
             "fjord_time": 1720627201,
             "granite_time": 1726070401,
-            "holocene_time": 1736445601
+            "holocene_time": 1736445601,
+            "isthmus_time": 1746806401
           },
           "optimism": {
             "eip1559_elasticity": 6,
@@ -289,7 +292,7 @@ mod tests {
         assert_eq!(chain_config.chain_id, 10);
         assert_eq!(chain_config.shanghai_time, Some(1704992401));
         assert_eq!(chain_config.cancun_time, Some(1710374401));
-        assert_eq!(chain_config.prague_time, None);
+        assert_eq!(chain_config.prague_time, Some(1746806401));
         assert_eq!(chain_config.berlin_block, Some(3950000));
         assert_eq!(chain_config.london_block, Some(105235063));
         assert_eq!(chain_config.arrow_glacier_block, Some(105235063));
@@ -303,7 +306,7 @@ mod tests {
         assert_eq!(chain_config.extra_fields.get("fjordTime").unwrap(), 1720627201);
         assert_eq!(chain_config.extra_fields.get("graniteTime").unwrap(), 1726070401);
         assert_eq!(chain_config.extra_fields.get("holoceneTime").unwrap(), 1736445601);
-        assert_eq!(chain_config.extra_fields.get("isthmusTime"), None);
+        assert_eq!(chain_config.extra_fields.get("isthmusTime").unwrap(), 1746806401);
         let optimism = chain_config.extra_fields.get("optimism").unwrap();
         assert_eq!(optimism.get("eip1559Elasticity").unwrap(), 6);
         assert_eq!(optimism.get("eip1559Denominator").unwrap(), 50);