diff --git a/clientlibs/js/src/DataService/DataService.spec.ts b/clientlibs/js/src/DataService/DataService.spec.ts
index ff0a1b2a7..c1e4df28b 100644
--- a/clientlibs/js/src/DataService/DataService.spec.ts
+++ b/clientlibs/js/src/DataService/DataService.spec.ts
@@ -118,6 +118,16 @@ describe('DataService', () => {
     });
   });
 
+  describe('#clearFeatureFlags', () => {
+    it('should clear previously set feature flags', () => {
+      dataService.setFeatureFlags(['testFlagKey']);
+
+      dataService.clearFeatureFlags();
+
+      expect(dataService.getFeatureFlags()).toBeNull();
+    });
+  });
+
   describe('#rotateAssignmentList', () => {
     it('should return the rotated assignment list', () => {
       const assignmentList: IExperimentAssignmentv5 = {
diff --git a/clientlibs/js/src/DataService/DataService.ts b/clientlibs/js/src/DataService/DataService.ts
index c1f4266a7..3122afa2f 100644
--- a/clientlibs/js/src/DataService/DataService.ts
+++ b/clientlibs/js/src/DataService/DataService.ts
@@ -42,6 +42,10 @@ export class DataService {
     this.featureFlags = featureFlags;
   }
 
+  clearFeatureFlags() {
+    this.featureFlags = null;
+  }
+
   public rotateAssignmentList(assignment: IExperimentAssignmentv5) {
     if (assignment.assignedCondition.length > 1) {
       assignment.assignedCondition.push(assignment.assignedCondition.shift());
diff --git a/clientlibs/js/src/UpGradeClient/UpgradeClient.spec.ts b/clientlibs/js/src/UpGradeClient/UpgradeClient.spec.ts
index 01ccba789..7afd932a6 100644
--- a/clientlibs/js/src/UpGradeClient/UpgradeClient.spec.ts
+++ b/clientlibs/js/src/UpGradeClient/UpgradeClient.spec.ts
@@ -155,6 +155,58 @@ describe('UpgradeClient', () => {
 
       expect(ApiService.prototype.setFeatureFlagUserGroupsForSession).toHaveBeenCalledWith(undefined, undefined);
     });
+
+    it('should clear the cached feature flags', () => {
+      ApiService.prototype.setFeatureFlagUserGroupsForSession = jest.fn();
+      const clearFeatureFlags = jest.spyOn(DataService.prototype, 'clearFeatureFlags');
+
+      upgradeClient.setFeatureFlagUserGroupsForSession({
+        groupsForSession: { classId: ['classB'] },
+        includeStoredUserGroups: false,
+      });
+
+      expect(clearFeatureFlags).toHaveBeenCalled();
+      clearFeatureFlags.mockRestore();
+    });
+
+    it('should not clear the cached feature flags when the options are invalid', () => {
+      ApiService.prototype.setFeatureFlagUserGroupsForSession = jest.fn();
+      const clearFeatureFlags = jest.spyOn(DataService.prototype, 'clearFeatureFlags');
+
+      expect(() => {
+        upgradeClient.setFeatureFlagUserGroupsForSession({ groupsForSession: null, includeStoredUserGroups: false });
+      }).toThrow();
+
+      expect(clearFeatureFlags).not.toHaveBeenCalled();
+      clearFeatureFlags.mockRestore();
+    });
+
+    it('should cause the next getAllFeatureFlags call to refetch against the new groups', async () => {
+      // the real DataService cache is left unmocked here, since invalidating it is the behavior under test
+      ApiService.prototype.setFeatureFlagUserGroupsForSession = jest.fn();
+      const getAllFeatureFlags = jest
+        .spyOn(ApiService.prototype, 'getAllFeatureFlags')
+        .mockResolvedValue(['classAFlag']);
+
+      // baseline: the first call fetches and caches, the second is served from the cache
+      expect(await upgradeClient.getAllFeatureFlags()).toEqual(['classAFlag']);
+      expect(await upgradeClient.getAllFeatureFlags()).toEqual(['classAFlag']);
+      expect(getAllFeatureFlags).toHaveBeenCalledTimes(1);
+
+      getAllFeatureFlags.mockResolvedValue(['classBFlag']);
+      upgradeClient.setFeatureFlagUserGroupsForSession({
+        groupsForSession: { classId: ['classB'] },
+        includeStoredUserGroups: false,
+      });
+
+      // the cleared cache forces exactly one refetch, whose result becomes the new cached value
+      expect(await upgradeClient.getAllFeatureFlags()).toEqual(['classBFlag']);
+      expect(getAllFeatureFlags).toHaveBeenCalledTimes(2);
+      expect(await upgradeClient.getAllFeatureFlags()).toEqual(['classBFlag']);
+      expect(getAllFeatureFlags).toHaveBeenCalledTimes(2);
+
+      getAllFeatureFlags.mockRestore();
+    });
   });
 
   describe('#getAllExperimentConditions', () => {
diff --git a/clientlibs/js/src/UpGradeClient/UpgradeClient.ts b/clientlibs/js/src/UpGradeClient/UpgradeClient.ts
index 976984edc..27fd63db9 100644
--- a/clientlibs/js/src/UpGradeClient/UpgradeClient.ts
+++ b/clientlibs/js/src/UpGradeClient/UpgradeClient.ts
@@ -176,6 +176,11 @@ export default class UpgradeClient {
    * Note: This is a convenience method, this can also be set directly in the constructor of UpgradeClient.
    * See example usage in the constructor documentation.
    *
+   * Note: Calling this clears any cached feature flags, since those were resolved against the previous
+   * groups. The next `getAllFeatureFlags()`/`hasFeatureFlag()` call will refetch against the new groups.
+   * If you need to retain flags for the previous groups, capture the array returned by
+   * `getAllFeatureFlags()` before switching.
+   *
    * @example
    * ```typescript
    *
@@ -211,6 +216,8 @@ export default class UpgradeClient {
       featureFlagOptions?.groupsForSession,
       featureFlagOptions?.includeStoredUserGroups
     );
+
+    this.dataService.clearFeatureFlags();
   }
 
   /**
@@ -515,7 +522,7 @@ export default class UpgradeClient {
    */
 
   async getAllFeatureFlags(options = { ignoreCache: false }): Promise<string[]> {
-    let response = options.ignoreCache ? null : await this.dataService.getFeatureFlags();
+    let response = options.ignoreCache ? null : this.dataService.getFeatureFlags();
     if (response == null) {
       response = await this.apiService.getAllFeatureFlags();
       if (Array.isArray(response)) {