diff --git a/packages/sentinel-api-service/CHANGELOG.md b/packages/sentinel-api-service/CHANGELOG.md
index f7ea8b2377b..11991fa8afd 100644
--- a/packages/sentinel-api-service/CHANGELOG.md
+++ b/packages/sentinel-api-service/CHANGELOG.md
@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- **BREAKING:** `SentinelSimulationResponseTransaction.gasCost` is now typed `string` instead of `number`, matching the value the Sentinel API actually returns on the wire (a quoted decimal string, not a JSON number) ([#10050](https://github.com/MetaMask/core/pull/10050))
+  - Consumers reading `gasCost` and treating it as a `number` (e.g. doing arithmetic directly on it) must parse it first, e.g. via `new BN(gasCost)` or `BigInt(gasCost)`.
+
 ## [1.0.1]
 
 ### Changed
diff --git a/packages/sentinel-api-service/src/types.ts b/packages/sentinel-api-service/src/types.ts
index 63658e6e4b8..13aef1c9697 100644
--- a/packages/sentinel-api-service/src/types.ts
+++ b/packages/sentinel-api-service/src/types.ts
@@ -449,10 +449,10 @@ export type SentinelSimulationResponseTransaction = {
   fees?: SentinelSimulationFeeLevel[];
 
   /**
-   * Estimated total gas cost of the transaction, in wei as a decimal number.
+   * Estimated total gas cost of the transaction, in wei as a decimal string.
    * Included in the `stateDiff` when `withGas` is true.
    */
-  gasCost?: number;
+  gasCost?: string;
 
   /** Required `gasLimit` for the transaction. */
   gasLimit?: Hex;
diff --git a/packages/transaction-controller/src/api/simulation-api.ts b/packages/transaction-controller/src/api/simulation-api.ts
index 4d080a3055e..cfc1494d0bc 100644
--- a/packages/transaction-controller/src/api/simulation-api.ts
+++ b/packages/transaction-controller/src/api/simulation-api.ts
@@ -225,10 +225,10 @@ export type SimulationResponseTransaction = {
   }[];
 
   /**
-   * Estimated total gas cost of the transaction.
+   * Estimated total gas cost of the transaction, in wei as a decimal string.
    * Included in the stateDiff if `withGas` is true.
    */
-  gasCost?: number;
+  gasCost?: string;
 
   /** Required `gasLimit` for the transaction. */
   gasLimit?: Hex;
diff --git a/packages/transaction-controller/src/utils/balance-changes.test.ts b/packages/transaction-controller/src/utils/balance-changes.test.ts
index 91948e6eadf..69a19c0627f 100644
--- a/packages/transaction-controller/src/utils/balance-changes.test.ts
+++ b/packages/transaction-controller/src/utils/balance-changes.test.ts
@@ -198,7 +198,7 @@ function createEventResponseMock(
 function createNativeBalanceResponse(
   previousBalance: string,
   newBalance: string,
-  gasCost: number = 0,
+  gasCost: string = '0',
 ): SimulationResponse {
   return {
     transactions: [
@@ -343,7 +343,7 @@ describe('Balance Change Utils', () => {
 
       it('ignoring gas cost', async () => {
         simulateTransactionsMock.mockResolvedValueOnce(
-          createNativeBalanceResponse('0x3', '0x8', 2),
+          createNativeBalanceResponse('0x3', '0x8', '2'),
         );
 
         const result = await getBalanceChanges(REQUEST_MOCK);
@@ -363,6 +363,33 @@ describe('Balance Change Utils', () => {
           simulationRevert: undefined,
         });
       });
+
+      it('supports a gas cost above Number.MAX_SAFE_INTEGER', async () => {
+        // A wei-scale gas cost this large is realistic on chains such as
+        // Polygon, and would previously throw when the wire value was
+        // mistakenly parsed as a JS `number` via `new BN(offset)`.
+        const largeGasCost = '10500000000000000'; // 2^53 (9007199254740992) < this
+        simulateTransactionsMock.mockResolvedValueOnce(
+          createNativeBalanceResponse('0x0', '0x0', largeGasCost),
+        );
+
+        const result = await getBalanceChanges(REQUEST_MOCK);
+
+        expect(result).toStrictEqual({
+          simulationData: {
+            callTraceErrors: [],
+            nativeBalanceChange: {
+              difference: '0x254db1c2244000',
+              isDecrease: false,
+              newBalance: '0x254db1c2244000',
+              previousBalance: '0x0',
+            },
+            tokenBalanceChanges: [],
+          },
+          gasUsed: undefined,
+          simulationRevert: undefined,
+        });
+      });
     });
 
     describe('returns token balance changes', () => {
diff --git a/packages/transaction-controller/src/utils/balance-changes.ts b/packages/transaction-controller/src/utils/balance-changes.ts
index b366a75ba53..ca30759a1c6 100644
--- a/packages/transaction-controller/src/utils/balance-changes.ts
+++ b/packages/transaction-controller/src/utils/balance-changes.ts
@@ -699,7 +699,7 @@ function extractRootRevert(
 function getSimulationBalanceChange(
   previousBalance: Hex,
   newBalance: Hex,
-  offset: number = 0,
+  offset: string = '0',
 ): SimulationBalanceChange | undefined {
   const newBalanceBN = hexToBN(newBalance).add(new BN(offset));
   const previousBalanceBN = hexToBN(previousBalance);