diff --git a/lib/core/optimizely_config/index.ts b/lib/core/optimizely_config/index.ts
index 4b435b830..8fd66246e 100644
--- a/lib/core/optimizely_config/index.ts
+++ b/lib/core/optimizely_config/index.ts
@@ -62,7 +62,6 @@ export class OptimizelyConfig {
   public events: OptimizelyEvent[];
   private datafile: string;
 
-
   constructor(configObj: ProjectConfig, datafile: string, logger?: LoggerFacade) {
     this.sdkKey = configObj.sdkKey ?? '';
     this.environmentKey = configObj.environmentKey ?? '';
diff --git a/lib/core/project_config/index.tests.js b/lib/core/project_config/index.tests.js
index 24134e3cd..d920ed7a3 100644
--- a/lib/core/project_config/index.tests.js
+++ b/lib/core/project_config/index.tests.js
@@ -31,6 +31,15 @@ var logger = getLogger();
 
 describe('lib/core/project_config', function() {
   describe('createProjectConfig method', function() {
+    // Copy experimentIds to experimentsIds in each event to fix typo in property name
+    // https://github.com/optimizely/javascript-sdk/issues/991
+    const copyEventExperimentIds = (event) => {
+      return {
+        ...event,
+        experimentsIds: event.experimentIds,
+      }
+    };
+
     it('should set properties correctly when createProjectConfig is called', function() {
       var testData = testDatafile.getTestProjectConfig();
       var configObj = projectConfig.createProjectConfig(testData);
@@ -42,7 +51,7 @@ describe('lib/core/project_config', function() {
       assert.strictEqual(configObj.accountId, testData.accountId);
       assert.strictEqual(configObj.projectId, testData.projectId);
       assert.strictEqual(configObj.revision, testData.revision);
-      assert.deepEqual(configObj.events, testData.events);
+      assert.deepEqual(configObj.events, testData.events.map((e) => copyEventExperimentIds(e)));
       assert.deepEqual(configObj.audiences, testData.audiences);
       testData.groups.forEach(function(group) {
         group.experiments.forEach(function(experiment) {
@@ -99,13 +108,13 @@ describe('lib/core/project_config', function() {
       assert.deepEqual(configObj.experimentKeyMap, expectedExperimentKeyMap);
 
       var expectedEventKeyMap = {
-        testEvent: testData.events[0],
-        'Total Revenue': testData.events[1],
-        testEventWithAudiences: testData.events[2],
-        testEventWithoutExperiments: testData.events[3],
-        testEventWithExperimentNotRunning: testData.events[4],
-        testEventWithMultipleExperiments: testData.events[5],
-        testEventLaunched: testData.events[6],
+        testEvent: copyEventExperimentIds(testData.events[0]),
+        'Total Revenue': copyEventExperimentIds(testData.events[1]),
+        testEventWithAudiences: copyEventExperimentIds(testData.events[2]),
+        testEventWithoutExperiments: copyEventExperimentIds(testData.events[3]),
+        testEventWithExperimentNotRunning: copyEventExperimentIds(testData.events[4]),
+        testEventWithMultipleExperiments: copyEventExperimentIds(testData.events[5]),
+        testEventLaunched: copyEventExperimentIds(testData.events[6]),
       };
 
       assert.deepEqual(configObj.eventKeyMap, expectedEventKeyMap);
diff --git a/lib/core/project_config/index.ts b/lib/core/project_config/index.ts
index a52b46efa..9f0258fac 100644
--- a/lib/core/project_config/index.ts
+++ b/lib/core/project_config/index.ts
@@ -1,5 +1,5 @@
 /**
- * Copyright 2016-2024, Optimizely
+ * Copyright 2016-2025, Optimizely
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,6 +50,10 @@ interface Event {
   key: string;
   id: string;
   experimentsIds: string[];
+
+  // the field is named experimentIds in the datafile, but this type previously defined it as experimentsIds.
+  // keeping both to avoid breaking changes, removed experimentsIds in v6.
+  experimentIds: string[]; // fix typo in property name (https://github.com/optimizely/javascript-sdk/issues/991)
 }
 
 interface VariableUsageMap {
@@ -101,6 +105,16 @@ const MODULE_NAME = 'PROJECT_CONFIG';
 // eslint-disable-next-line  @typescript-eslint/no-explicit-any
 function createMutationSafeDatafileCopy(datafile: any): ProjectConfig {
   const datafileCopy = assign({}, datafile);
+
+  datafileCopy.events = (datafile.events || []).map((event: Event) => {
+    const eventCopy: Event = assign({}, event);
+
+    // Copy experimentIds to experimentsIds in each event to fix typo in property name
+    // https://github.com/optimizely/javascript-sdk/issues/991
+    eventCopy.experimentsIds = event.experimentIds;
+    return eventCopy;
+  });
+
   datafileCopy.audiences = (datafile.audiences || []).map((audience: Audience) => {
     return assign({}, audience);
   });
diff --git a/lib/shared_types.ts b/lib/shared_types.ts
index 75885b83e..9e52c8a69 100644
--- a/lib/shared_types.ts
+++ b/lib/shared_types.ts
@@ -1,5 +1,5 @@
 /**
- * Copyright 2020-2024, Optimizely
+ * Copyright 2020-2025, Optimizely
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -469,6 +469,10 @@ export type OptimizelyEvent = {
   id: string;
   key: string;
   experimentsIds: string[];
+
+  // the field is named experimentIds in the datafile, but this type previously defined it as experimentsIds.
+  // keeping both to avoid breaking changes, removed experimentsIds in v6.
+  experimentIds: string[]; // fix typo in property name (https://github.com/optimizely/javascript-sdk/issues/991)
 };
 
 export interface OptimizelyFeature {