diff --git a/src/lib/__snapshots__/create-config.test.ts.snap b/src/lib/__snapshots__/create-config.test.ts.snap
index 601e7287fa..638a9a3ed8 100644
--- a/src/lib/__snapshots__/create-config.test.ts.snap
+++ b/src/lib/__snapshots__/create-config.test.ts.snap
@@ -72,6 +72,7 @@ exports[`should create default config 1`] = `
       "anonymiseEventLog": false,
       "batchMetrics": false,
       "changeRequests": false,
+      "clientFeaturesMemoizedEtags": false,
       "embedProxy": true,
       "embedProxyFrontend": true,
       "favorites": false,
@@ -89,6 +90,7 @@ exports[`should create default config 1`] = `
       "anonymiseEventLog": false,
       "batchMetrics": false,
       "changeRequests": false,
+      "clientFeaturesMemoizedEtags": false,
       "embedProxy": true,
       "embedProxyFrontend": true,
       "favorites": false,
diff --git a/src/lib/routes/client-api/feature.test.ts b/src/lib/routes/client-api/feature.test.ts
index 9519226207..21ceb9ac5f 100644
--- a/src/lib/routes/client-api/feature.test.ts
+++ b/src/lib/routes/client-api/feature.test.ts
@@ -7,6 +7,7 @@ import FeatureController from './feature';
 import { createTestConfig } from '../../../test/config/test-config';
 import { secondsToMilliseconds } from 'date-fns';
 import { ClientSpecService } from '../../services/client-spec-service';
+import etag from 'etag';
 
 async function getSetup() {
     const base = `/random${Math.round(Math.random() * 1000)}`;
@@ -101,6 +102,74 @@ test('if caching is enabled should memoize', async () => {
     expect(getClientFeatures).toHaveBeenCalledTimes(1);
 });
 
+test('if caching and etags are enabled should add etag for query to list', async () => {
+    const getClientFeatures = jest.fn().mockReturnValue([]);
+    const getActive = jest.fn().mockReturnValue([]);
+    const respondWithValidation = jest.fn().mockReturnValue({});
+    const validPath = jest.fn().mockReturnValue(jest.fn());
+    const responseStatus = jest.fn();
+    const responseEnd = jest.fn();
+    const responseJson = jest.fn();
+    const clientSpecService = new ClientSpecService({ getLogger });
+    const openApiService = { respondWithValidation, validPath };
+    const featureToggleServiceV2 = { getClientFeatures };
+    const segmentService = { getActive };
+    const controller = new FeatureController(
+        {
+            clientSpecService,
+            // @ts-expect-error
+            openApiService,
+            // @ts-expect-error
+            featureToggleServiceV2,
+            // @ts-expect-error
+            segmentService,
+        },
+        {
+            getLogger,
+            clientFeatureCaching: {
+                enabled: true,
+                maxAge: secondsToMilliseconds(10),
+            },
+            flagResolver: {
+                isEnabled: () => true,
+            },
+        },
+    );
+    const response = {
+        json: responseJson,
+        status: responseStatus,
+        end: responseEnd,
+    };
+    await controller.getAllCached(
+        // @ts-expect-error
+        { query: {}, header: () => undefined },
+        response,
+    );
+    await controller.getAllCached(
+        // @ts-expect-error
+        {
+            query: {},
+            header: (name: string) => {
+                if ('If-None-Match' === name) {
+                    return etag(
+                        JSON.stringify({
+                            version: 2,
+                            features: [],
+                            query: { inlineSegmentConstraints: true },
+                            segments: [],
+                        }),
+                    );
+                } else {
+                    return undefined;
+                }
+            },
+        },
+        response,
+    );
+    expect(responseStatus).toHaveBeenCalledWith(304);
+    expect(responseEnd).toHaveBeenCalledTimes(1);
+});
+
 test('if caching is not enabled all calls goes to service', async () => {
     const getClientFeatures = jest.fn().mockReturnValue([]);
     const getActive = jest.fn().mockReturnValue([]);
diff --git a/src/lib/routes/client-api/feature.ts b/src/lib/routes/client-api/feature.ts
index e3306dc83f..d41a073c09 100644
--- a/src/lib/routes/client-api/feature.ts
+++ b/src/lib/routes/client-api/feature.ts
@@ -120,7 +120,10 @@ export default class FeatureController extends Controller {
                 },
             );
             this.logger.info('Cached features was enabled');
-            if (flagResolver.isEnabled(FEATURE_TOGGLE_MEMOIZED_ETAGS)) {
+            if (
+                flagResolver &&
+                flagResolver.isEnabled(FEATURE_TOGGLE_MEMOIZED_ETAGS)
+            ) {
                 this.logger.info('Memoized etags was enabled');
                 this.route({
                     method: 'get',
@@ -151,18 +154,20 @@ export default class FeatureController extends Controller {
             this.featureToggleServiceV2.getClientFeatures(query),
             this.segmentService.getActive(),
         ]).then((data) => {
-            if (flagResolver?.isEnabled(FEATURE_TOGGLE_MEMOIZED_ETAGS)) {
-                this.seenEtags.set(
-                    JSON.stringify(query),
-                    etag(
-                        JSON.stringify({
-                            version,
-                            features: data[0],
-                            query: { ...query },
-                            segments: data[1],
-                        }),
-                    ),
-                );
+            if (
+                flagResolver &&
+                flagResolver.isEnabled(FEATURE_TOGGLE_MEMOIZED_ETAGS)
+            ) {
+                const key = JSON.stringify(query);
+                const value = {
+                    version,
+                    features: data[0],
+                    query: { ...query },
+                    segments: data[1],
+                };
+                const stringValue = JSON.stringify(value);
+                const hash = etag(stringValue);
+                this.seenEtags.set(key, hash);
             }
             return data;
         });
@@ -241,15 +246,17 @@ export default class FeatureController extends Controller {
     ): Promise<void> {
         const query = await this.resolveQuery(req);
         const [features, segments] = await this.cachedFeatures(query);
-        const modifiedSince = req.header('If-None-Match').substring(2);
-        this.logger.debug(`ETag header from Client: ${modifiedSince}`);
-        const cached = this.seenEtags.get(JSON.stringify(query));
-        this.logger.debug(`ETag header from memoizee ${cached}`);
-        if (modifiedSince !== undefined && modifiedSince === cached) {
-            // We have a match. Return 304
-            res.status(304);
-            res.end();
-            return;
+        const modifiedSince = req.header('If-None-Match');
+        if (modifiedSince && modifiedSince.length > 0) {
+            this.logger.debug(`ETag header from Client: ${modifiedSince}`);
+            const cached = this.seenEtags.get(JSON.stringify(query));
+            this.logger.debug(`ETag header from memoizee ${cached}`);
+            if (modifiedSince.replace('W/', '') === cached) {
+                // We have a match. Return 304
+                res.status(304);
+                res.end();
+                return;
+            }
         }
         if (this.clientSpecService.requestSupportsSpec(req, 'segments')) {
             this.openApiService.respondWithValidation(