diff --git a/libs/common/src/enums/feature-flag.enum.ts b/libs/common/src/enums/feature-flag.enum.ts
index 05fded6bcaf..71b95ec6057 100644
--- a/libs/common/src/enums/feature-flag.enum.ts
+++ b/libs/common/src/enums/feature-flag.enum.ts
@@ -19,6 +19,7 @@ export enum FeatureFlag {
   PM23801_PrefetchPasswordPrelogin = "pm-23801-prefetch-password-prelogin",
   PM27086_UpdateAuthenticationApisForInputPassword = "pm-27086-update-authentication-apis-for-input-password",
   SafariAccountSwitching = "pm-5594-safari-account-switching",
+  PM31088_MasterPasswordServiceEmitSalt = "pm-31088-master-password-service-emit-salt",
 
   /* Autofill */
   UseUndeterminedCipherScenarioTriggeringLogic = "undetermined-cipher-scenario-logic",
@@ -143,6 +144,7 @@ export const DefaultFeatureFlagValue = {
   [FeatureFlag.PM23801_PrefetchPasswordPrelogin]: FALSE,
   [FeatureFlag.PM27086_UpdateAuthenticationApisForInputPassword]: FALSE,
   [FeatureFlag.SafariAccountSwitching]: FALSE,
+  [FeatureFlag.PM31088_MasterPasswordServiceEmitSalt]: FALSE,
 
   /* Billing */
   [FeatureFlag.TrialPaymentOptional]: FALSE,
diff --git a/libs/common/src/key-management/master-password/services/master-password.service.spec.ts b/libs/common/src/key-management/master-password/services/master-password.service.spec.ts
index f72ae0e7c5e..4a96dedf024 100644
--- a/libs/common/src/key-management/master-password/services/master-password.service.spec.ts
+++ b/libs/common/src/key-management/master-password/services/master-password.service.spec.ts
@@ -17,8 +17,11 @@ import {
   mockAccountServiceWith,
 } from "../../../../spec";
 import { ForceSetPasswordReason } from "../../../auth/models/domain/force-set-password-reason";
+import { FeatureFlag } from "../../../enums/feature-flag.enum";
+import { ServerConfig } from "../../../platform/abstractions/config/server-config";
 import { LogService } from "../../../platform/abstractions/log.service";
 import { SymmetricCryptoKey } from "../../../platform/models/domain/symmetric-crypto-key";
+import { USER_SERVER_CONFIG } from "../../../platform/services/config/default-config.service";
 import { UserId } from "../../../types/guid";
 import { MasterKey, UserKey } from "../../../types/key";
 import { KeyGenerationService } from "../../crypto";
@@ -92,14 +95,52 @@ describe("MasterPasswordService", () => {
         sut.saltForUser$(null as unknown as UserId);
       }).toThrow("userId is null or undefined.");
     });
+    // Removable with unwinding of PM31088_MasterPasswordServiceEmitSalt
     it("throws when userid present but not in account service", async () => {
       await expect(
         firstValueFrom(sut.saltForUser$("00000000-0000-0000-0000-000000000001" as UserId)),
       ).rejects.toThrow("Cannot read properties of undefined (reading 'email')");
     });
-    it("returns salt", async () => {
-      const salt = await firstValueFrom(sut.saltForUser$(userId));
-      expect(salt).toBeDefined();
+    // Removable with unwinding of PM31088_MasterPasswordServiceEmitSalt
+    it("returns email-derived salt for legacy path", async () => {
+      const result = await firstValueFrom(sut.saltForUser$(userId));
+      // mockAccountServiceWith defaults email to "email"
+      expect(result).toBe("email" as MasterPasswordSalt);
+    });
+
+    describe("saltForUser$ master password unlock data migration path", () => {
+      // Flagged with  PM31088_MasterPasswordServiceEmitSalt PM-31088
+      beforeEach(() => {
+        stateProvider.singleUser.getFake(userId, USER_SERVER_CONFIG).nextState({
+          featureStates: {
+            [FeatureFlag.PM31088_MasterPasswordServiceEmitSalt]: true,
+          },
+        } as unknown as ServerConfig);
+      });
+
+      // Unwinding should promote these tests as part of saltForUser suite.
+      it("returns salt from master password unlock data", async () => {
+        const expectedSalt = "custom-salt" as MasterPasswordSalt;
+        const unlockData = new MasterPasswordUnlockData(
+          expectedSalt,
+          new PBKDF2KdfConfig(600_000),
+          makeEncString().toSdk() as MasterKeyWrappedUserKey,
+        );
+        stateProvider.singleUser
+          .getFake(userId, MASTER_PASSWORD_UNLOCK_KEY)
+          .nextState(unlockData.toJSON());
+
+        const result = await firstValueFrom(sut.saltForUser$(userId));
+        expect(result).toBe(expectedSalt);
+      });
+
+      it("throws when master password unlock data is null", async () => {
+        stateProvider.singleUser.getFake(userId, MASTER_PASSWORD_UNLOCK_KEY).nextState(null);
+
+        await expect(firstValueFrom(sut.saltForUser$(userId))).rejects.toThrow(
+          "Master password unlock data not found for user.",
+        );
+      });
     });
   });
 
diff --git a/libs/common/src/key-management/master-password/services/master-password.service.ts b/libs/common/src/key-management/master-password/services/master-password.service.ts
index 28d4f58d7dc..f1a074ff14c 100644
--- a/libs/common/src/key-management/master-password/services/master-password.service.ts
+++ b/libs/common/src/key-management/master-password/services/master-password.service.ts
@@ -1,6 +1,6 @@
 // FIXME: Update this file to be type safe and remove this and next line
 // @ts-strict-ignore
-import { firstValueFrom, map, Observable } from "rxjs";
+import { firstValueFrom, iif, map, Observable, switchMap } from "rxjs";
 
 import { AccountService } from "@bitwarden/common/auth/abstractions/account.service";
 import { assertNonNullish } from "@bitwarden/common/auth/utils";
@@ -12,8 +12,10 @@ import { KdfConfig } from "@bitwarden/key-management";
 import { PureCrypto } from "@bitwarden/sdk-internal";
 
 import { ForceSetPasswordReason } from "../../../auth/models/domain/force-set-password-reason";
+import { FeatureFlag, getFeatureFlagValue } from "../../../enums/feature-flag.enum";
 import { LogService } from "../../../platform/abstractions/log.service";
 import { SymmetricCryptoKey } from "../../../platform/models/domain/symmetric-crypto-key";
+import { USER_SERVER_CONFIG } from "../../../platform/services/config/default-config.service";
 import {
   MASTER_PASSWORD_DISK,
   MASTER_PASSWORD_MEMORY,
@@ -102,9 +104,29 @@ export class MasterPasswordService implements InternalMasterPasswordServiceAbstr
 
   saltForUser$(userId: UserId): Observable<MasterPasswordSalt> {
     assertNonNullish(userId, "userId");
-    return this.accountService.accounts$.pipe(
-      map((accounts) => accounts[userId].email),
-      map((email) => this.emailToSalt(email)),
+
+    // Note: We can't use the config service as an abstraction here because it creates a circular dependency: ConfigService -> ConfigApiService -> ApiService -> VaultTimeoutSettingsService -> KeyService -> MP service.
+    return this.stateProvider.getUser(userId, USER_SERVER_CONFIG).state$.pipe(
+      map((serverConfig) =>
+        getFeatureFlagValue(serverConfig, FeatureFlag.PM31088_MasterPasswordServiceEmitSalt),
+      ),
+      switchMap((enabled) =>
+        iif(
+          () => enabled,
+          this.masterPasswordUnlockData$(userId).pipe(
+            map((unlockData) => {
+              if (unlockData == null) {
+                throw new Error("Master password unlock data not found for user.");
+              }
+              return unlockData.salt;
+            }),
+          ),
+          this.accountService.accounts$.pipe(
+            map((accounts) => accounts[userId].email),
+            map((email) => this.emailToSalt(email)),
+          ),
+        ),
+      ),
     );
   }