diff --git a/java/com/google/gerrit/server/experiments/ExperimentFeaturesConstants.java b/java/com/google/gerrit/server/experiments/ExperimentFeaturesConstants.java
index 5a4580c..32ec401 100644
--- a/java/com/google/gerrit/server/experiments/ExperimentFeaturesConstants.java
+++ b/java/com/google/gerrit/server/experiments/ExperimentFeaturesConstants.java
@@ -20,14 +20,9 @@
 public class ExperimentFeaturesConstants {
 
   /** Features that are known experiments and can be referenced in the code. */
-  public static String UI_FEATURE_PATCHSET_COMMENTS = "UiFeature__patchset_comments";
-
-  public static String UI_FEATURE_SUBMIT_REQUIREMENTS_UI = "UiFeature__submit_requirements_ui";
-
   public static String GERRIT_BACKEND_FEATURE_ATTACH_NONCE_TO_DOCUMENTATION =
       "GerritBackendFeature__attach_nonce_to_documentation";
 
   /** Features, enabled by default in the current release. */
-  public static final ImmutableSet<String> DEFAULT_ENABLED_FEATURES =
-      ImmutableSet.of(UI_FEATURE_PATCHSET_COMMENTS, UI_FEATURE_SUBMIT_REQUIREMENTS_UI);
+  public static final ImmutableSet<String> DEFAULT_ENABLED_FEATURES = ImmutableSet.of();
 }
diff --git a/javatests/com/google/gerrit/acceptance/server/experiments/ExperimentFeaturesIT.java b/javatests/com/google/gerrit/acceptance/server/experiments/ExperimentFeaturesIT.java
index b2a0ded..e011ffc 100644
--- a/javatests/com/google/gerrit/acceptance/server/experiments/ExperimentFeaturesIT.java
+++ b/javatests/com/google/gerrit/acceptance/server/experiments/ExperimentFeaturesIT.java
@@ -68,10 +68,7 @@
       values = {"UiFeature__patchset_comments", "UiFeature__submit_requirements_ui"})
   public void configOverride_defaultFeatureDisabled() {
     assertThat(experimentFeatures.isFeatureEnabled("enabledFeature")).isTrue();
-    assertThat(
-            experimentFeatures.isFeatureEnabled(
-                ExperimentFeaturesConstants.UI_FEATURE_PATCHSET_COMMENTS))
-        .isFalse();
+    assertThat(experimentFeatures.isFeatureEnabled("UiFeature__patchset_comments")).isFalse();
     assertThat(experimentFeatures.getEnabledExperimentFeatures()).containsExactly("enabledFeature");
   }
 }
diff --git a/javatests/com/google/gerrit/httpd/raw/IndexServletTest.java b/javatests/com/google/gerrit/httpd/raw/IndexServletTest.java
index f65e823..06ea8b6 100644
--- a/javatests/com/google/gerrit/httpd/raw/IndexServletTest.java
+++ b/javatests/com/google/gerrit/httpd/raw/IndexServletTest.java
@@ -60,15 +60,13 @@
     String testCdnPath = "bar-cdn";
     String testFaviconURL = "zaz-url";
 
-    // Pick any known experiment enabled by default;
-    String disabledDefault = ExperimentFeaturesConstants.UI_FEATURE_PATCHSET_COMMENTS;
-    assertThat(ExperimentFeaturesConstants.DEFAULT_ENABLED_FEATURES).contains(disabledDefault);
+    assertThat(ExperimentFeaturesConstants.DEFAULT_ENABLED_FEATURES).isEmpty();
 
     org.eclipse.jgit.lib.Config serverConfig = new org.eclipse.jgit.lib.Config();
     serverConfig.setStringList(
         "experiments", null, "enabled", ImmutableList.of("NewFeature", "DisabledFeature"));
     serverConfig.setStringList(
-        "experiments", null, "disabled", ImmutableList.of("DisabledFeature", disabledDefault));
+        "experiments", null, "disabled", ImmutableList.of("DisabledFeature"));
     ExperimentFeatures experimentFeatures = new ConfigExperimentFeatures(serverConfig);
     IndexServlet servlet =
         new IndexServlet(
@@ -97,7 +95,6 @@
                 + "\\x5b\\x5d\\x7d');");
     ImmutableSet<String> enabledDefaults =
         ExperimentFeaturesConstants.DEFAULT_ENABLED_FEATURES.stream()
-            .filter(e -> !e.equals(disabledDefault))
             .collect(ImmutableSet.toImmutableSet());
     List<String> expectedEnabled = new ArrayList<>();
     expectedEnabled.add("NewFeature");
diff --git a/polygerrit-ui/app/elements/change/gr-change-summary/gr-change-summary.ts b/polygerrit-ui/app/elements/change/gr-change-summary/gr-change-summary.ts
index 84bdffb..b726292 100644
--- a/polygerrit-ui/app/elements/change/gr-change-summary/gr-change-summary.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-summary/gr-change-summary.ts
@@ -55,7 +55,6 @@
 
 import {SummaryChipStyles} from './gr-summary-chip';
 import {when} from 'lit/directives/when.js';
-import {KnownExperimentId} from '../../../services/flags/flags';
 import {combineLatest} from 'rxjs';
 import {userModelToken} from '../../../models/user/user-model';
 
@@ -120,8 +119,6 @@
 
   private readonly reporting = getAppContext().reportingService;
 
-  private readonly flagsService = getAppContext().flagsService;
-
   constructor() {
     super();
     subscribe(
@@ -174,24 +171,22 @@
       () => this.getUserModel().account$,
       x => (this.selfAccount = x)
     );
-    if (this.flagsService.isEnabled(KnownExperimentId.MENTION_USERS)) {
-      subscribe(
-        this,
-        () =>
-          combineLatest([
-            this.getUserModel().account$,
-            this.getCommentsModel().threads$,
-          ]),
-        ([selfAccount, threads]) => {
-          if (!selfAccount || !selfAccount.email) return;
-          const unresolvedThreadsMentioningSelf = getMentionedThreads(
-            threads,
-            selfAccount
-          ).filter(isUnresolved);
-          this.mentionCount = unresolvedThreadsMentioningSelf.length;
-        }
-      );
-    }
+    subscribe(
+      this,
+      () =>
+        combineLatest([
+          this.getUserModel().account$,
+          this.getCommentsModel().threads$,
+        ]),
+      ([selfAccount, threads]) => {
+        if (!selfAccount || !selfAccount.email) return;
+        const unresolvedThreadsMentioningSelf = getMentionedThreads(
+          threads,
+          selfAccount
+        ).filter(isUnresolved);
+        this.mentionCount = unresolvedThreadsMentioningSelf.length;
+      }
+    );
   }
 
   static override get styles() {
@@ -575,8 +570,6 @@
   }
 
   private renderMentionChip() {
-    if (!this.flagsService.isEnabled(KnownExperimentId.MENTION_USERS))
-      return nothing;
     if (!this.mentionCount) return nothing;
     return html` <gr-summary-chip
       class="mentionSummary"
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts
index d4cff78..218594b 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts
@@ -121,7 +121,6 @@
 import {subscribe} from '../../lit/subscription-controller';
 import {configModelToken} from '../../../models/config/config-model';
 import {hasHumanReviewer, isOwner} from '../../../utils/change-util';
-import {KnownExperimentId} from '../../../services/flags/flags';
 import {commentsModelToken} from '../../../models/comments/comments-model';
 import {
   CommentEditingChangedDetail,
@@ -384,8 +383,6 @@
   private readonly restApiService: RestApiService =
     getAppContext().restApiService;
 
-  private readonly flagsService = getAppContext().flagsService;
-
   private readonly getPluginLoader = resolve(this, pluginLoaderToken);
 
   private readonly getConfigModel = resolve(this, configModelToken);
@@ -671,9 +668,6 @@
       this,
       () => this.getCommentsModel().mentionedUsersInUnresolvedDrafts$,
       x => {
-        if (!this.flagsService.isEnabled(KnownExperimentId.MENTION_USERS)) {
-          return;
-        }
         this.mentionedUsersInUnresolvedDrafts = x.filter(
           v => !this.isAlreadyReviewerOrCC(v)
         );
@@ -1441,18 +1435,13 @@
     ).filter(isDefined);
 
     for (const user of newAttentionSetUsers) {
-      let reason;
-      if (this.flagsService.isEnabled(KnownExperimentId.MENTION_USERS)) {
-        reason =
-          getMentionedReason(
-            this.draftCommentThreads,
-            this.account,
-            user,
-            this.serverConfig
-          ) ?? '';
-      } else {
-        reason = getReplyByReason(this.account, this.serverConfig);
-      }
+      const reason =
+        getMentionedReason(
+          this.draftCommentThreads,
+          this.account,
+          user,
+          this.serverConfig
+        ) ?? '';
       reviewInput.add_to_attention_set.push({user: getUserId(user), reason});
     }
     reviewInput.remove_from_attention_set = [];
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.ts b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.ts
index 12b1c40..f7b3aec 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.ts
@@ -13,7 +13,6 @@
   query,
   queryAll,
   queryAndAssert,
-  stubFlags,
   stubRestApi,
   waitUntilVisible,
 } from '../../../test/test-utils';
@@ -59,7 +58,6 @@
 import {accountKey} from '../../../utils/account-util';
 import {GrButton} from '../../shared/gr-button/gr-button';
 import {GrAccountLabel} from '../../shared/gr-account-label/gr-account-label';
-import {KnownExperimentId} from '../../../services/flags/flags';
 import {Key, Modifier} from '../../../utils/dom-util';
 import {GrComment} from '../../shared/gr-comment/gr-comment';
 import {testResolver} from '../../../test/common-test-setup';
@@ -2527,9 +2525,6 @@
 
   suite('mention users', () => {
     setup(async () => {
-      stubFlags('isEnabled')
-        .withArgs(KnownExperimentId.MENTION_USERS)
-        .returns(true);
       element.account = createAccountWithId(1);
       element.requestUpdate();
       await element.updateComplete;
diff --git a/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list.ts b/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list.ts
index 80a1a9a..c09d2a2 100644
--- a/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list.ts
+++ b/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list.ts
@@ -42,7 +42,6 @@
 import {resolve} from '../../../models/dependency';
 import {changeModelToken} from '../../../models/change/change-model';
 import {Interaction} from '../../../constants/reporting';
-import {KnownExperimentId} from '../../../services/flags/flags';
 import {HtmlPatched} from '../../../utils/lit-util';
 import {userModelToken} from '../../../models/user/user-model';
 import {specialFilePathCompare} from '../../../utils/path-list-util';
@@ -205,8 +204,6 @@
 
   private readonly reporting = getAppContext().reportingService;
 
-  private readonly flagsService = getAppContext().flagsService;
-
   private readonly getUserModel = resolve(this, userModelToken);
 
   private readonly patched = new HtmlPatched(key => {
@@ -495,14 +492,10 @@
       value: CommentTabState.UNRESOLVED,
     });
     if (this.account) {
-      if (this.flagsService.isEnabled(KnownExperimentId.MENTION_USERS)) {
-        items.push({
-          text: `Mentions (${
-            getMentionedThreads(threads, this.account).length
-          })`,
-          value: CommentTabState.MENTIONS,
-        });
-      }
+      items.push({
+        text: `Mentions (${getMentionedThreads(threads, this.account).length})`,
+        value: CommentTabState.MENTIONS,
+      });
       items.push({
         text: `Drafts (${threads.filter(isDraftThread).length})`,
         value: CommentTabState.DRAFTS,
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
index 66beaf1..c1cc863 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
@@ -275,9 +275,7 @@
         this.save();
       });
     }
-    if (this.flagsService.isEnabled(KnownExperimentId.MENTION_USERS)) {
-      this.messagePlaceholder = 'Mention others with @';
-    }
+    this.messagePlaceholder = 'Mention others with @';
     subscribe(
       this,
       () => this.getUserModel().account$,
diff --git a/polygerrit-ui/app/elements/shared/gr-formatted-text/gr-formatted-text.ts b/polygerrit-ui/app/elements/shared/gr-formatted-text/gr-formatted-text.ts
index 627ea27..45eca40 100644
--- a/polygerrit-ui/app/elements/shared/gr-formatted-text/gr-formatted-text.ts
+++ b/polygerrit-ui/app/elements/shared/gr-formatted-text/gr-formatted-text.ts
@@ -18,8 +18,6 @@
 import {CommentLinks, EmailAddress} from '../../../api/rest-api';
 import {linkifyUrlsAndApplyRewrite} from '../../../utils/link-util';
 import '../gr-account-chip/gr-account-chip';
-import {KnownExperimentId} from '../../../services/flags/flags';
-import {getAppContext} from '../../../services/app-context';
 
 /**
  * This element optionally renders markdown and also applies some regex
@@ -36,8 +34,6 @@
   @state()
   private repoCommentLinks: CommentLinks = {};
 
-  private readonly flagsService = getAppContext().flagsService;
-
   private readonly getConfigModel = resolve(this, configModelToken);
 
   // Private const but used in tests.
@@ -214,9 +210,7 @@
 
   override updated() {
     // Look for @mentions and replace them with an account-label chip.
-    if (this.flagsService.isEnabled(KnownExperimentId.MENTION_USERS)) {
-      this.convertEmailsToAccountChips();
-    }
+    this.convertEmailsToAccountChips();
   }
 
   private convertEmailsToAccountChips() {
diff --git a/polygerrit-ui/app/elements/shared/gr-formatted-text/gr-formatted-text_test.ts b/polygerrit-ui/app/elements/shared/gr-formatted-text/gr-formatted-text_test.ts
index 3881c62..3187ada 100644
--- a/polygerrit-ui/app/elements/shared/gr-formatted-text/gr-formatted-text_test.ts
+++ b/polygerrit-ui/app/elements/shared/gr-formatted-text/gr-formatted-text_test.ts
@@ -15,14 +15,9 @@
 import './gr-formatted-text';
 import {GrFormattedText} from './gr-formatted-text';
 import {createConfig} from '../../../test/test-data-generators';
-import {
-  queryAndAssert,
-  stubFlags,
-  waitUntilObserved,
-} from '../../../test/test-utils';
+import {queryAndAssert, waitUntilObserved} from '../../../test/test-utils';
 import {CommentLinks, EmailAddress} from '../../../api/rest-api';
 import {testResolver} from '../../../test/common-test-setup';
-import {KnownExperimentId} from '../../../services/flags/flags';
 import {GrAccountChip} from '../gr-account-chip/gr-account-chip';
 
 suite('gr-formatted-text tests', () => {
@@ -412,38 +407,7 @@
       );
     });
 
-    test('does not handle @mentions if not enabled', async () => {
-      stubFlags('isEnabled')
-        .withArgs(KnownExperimentId.MENTION_USERS)
-        .returns(false);
-      element.content = '@someone@google.com';
-      await element.updateComplete;
-
-      assert.shadowDom.equal(
-        element,
-        /* HTML */ `
-          <marked-element>
-            <div slot="markdown-html" class="markdown-html">
-              <p>
-                @
-                <a
-                  href="mailto:someone@google.com"
-                  rel="noopener"
-                  target="_blank"
-                >
-                  someone@google.com
-                </a>
-              </p>
-            </div>
-          </marked-element>
-        `
-      );
-    });
-
-    test('handles @mentions if enabled', async () => {
-      stubFlags('isEnabled')
-        .withArgs(KnownExperimentId.MENTION_USERS)
-        .returns(true);
+    test('handles @mentions', async () => {
       element.content = '@someone@google.com';
       await element.updateComplete;
 
@@ -470,9 +434,6 @@
     });
 
     test('does not handle @mentions that is part of a code block', async () => {
-      stubFlags('isEnabled')
-        .withArgs(KnownExperimentId.MENTION_USERS)
-        .returns(true);
       element.content = '`@`someone@google.com';
       await element.updateComplete;
 
diff --git a/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.ts b/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.ts
index a1a1e84..e1e4ca5 100644
--- a/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.ts
+++ b/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.ts
@@ -17,12 +17,11 @@
 import {Key} from '../../../utils/dom-util';
 import {ValueChangedEvent} from '../../../types/events';
 import {fire} from '../../../utils/event-util';
-import {LitElement, css, html, nothing} from 'lit';
+import {LitElement, css, html} from 'lit';
 import {customElement, property, query, state} from 'lit/decorators.js';
 import {sharedStyles} from '../../../styles/shared-styles';
 import {PropertyValues} from 'lit';
 import {classMap} from 'lit/directives/class-map.js';
-import {KnownExperimentId} from '../../../services/flags/flags';
 import {NumericChangeId, ServerInfo} from '../../../api/rest-api';
 import {subscribe} from '../../lit/subscription-controller';
 import {resolve} from '../../../models/dependency';
@@ -115,8 +114,6 @@
 
   private readonly getChangeModel = resolve(this, changeModelToken);
 
-  private readonly flagsService = getAppContext().flagsService;
-
   private readonly restApiService = getAppContext().restApiService;
 
   private readonly getConfigModel = resolve(this, configModelToken);
@@ -265,8 +262,6 @@
   }
 
   private renderMentionsDropdown() {
-    if (!this.flagsService.isEnabled(KnownExperimentId.MENTION_USERS))
-      return nothing;
     return html` <gr-autocomplete-dropdown
       id="mentionsSuggestions"
       .suggestions=${this.suggestions}
@@ -524,8 +519,6 @@
   }
 
   private isMentionsDropdownActive() {
-    if (!this.flagsService.isEnabled(KnownExperimentId.MENTION_USERS))
-      return false;
     return (
       this.specialCharIndex !== -1 && this.text[this.specialCharIndex] === '@'
     );
@@ -540,10 +533,8 @@
   private computeSpecialCharIndex() {
     const charAtCursor = this.text[this.textarea!.selectionStart - 1];
 
-    if (this.flagsService.isEnabled(KnownExperimentId.MENTION_USERS)) {
-      if (charAtCursor === '@' && this.specialCharIndex === -1) {
-        this.specialCharIndex = this.getSpecialCharIndex(this.text);
-      }
+    if (charAtCursor === '@' && this.specialCharIndex === -1) {
+      this.specialCharIndex = this.getSpecialCharIndex(this.text);
     }
     if (charAtCursor === ':' && this.specialCharIndex === -1) {
       this.specialCharIndex = this.getSpecialCharIndex(this.text);
diff --git a/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea_test.ts b/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea_test.ts
index f8ae38c..0400e85 100644
--- a/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea_test.ts
+++ b/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea_test.ts
@@ -7,12 +7,7 @@
 import './gr-textarea';
 import {GrTextarea} from './gr-textarea';
 import {ItemSelectedEvent} from '../gr-autocomplete-dropdown/gr-autocomplete-dropdown';
-import {
-  pressKey,
-  stubFlags,
-  stubRestApi,
-  waitUntil,
-} from '../../../test/test-utils';
+import {pressKey, stubRestApi, waitUntil} from '../../../test/test-utils';
 import {fixture, html, assert} from '@open-wc/testing';
 import {createAccountWithEmail} from '../../../test/test-data-generators';
 import {Key} from '../../../utils/dom-util';
@@ -31,14 +26,16 @@
       element,
       /* HTML */ `<div id="hiddenText"></div>
         <span id="caratSpan"> </span>
+        <gr-autocomplete-dropdown id="emojiSuggestions" is-hidden="">
+        </gr-autocomplete-dropdown>
         <gr-autocomplete-dropdown
-          id="emojiSuggestions"
+          id="mentionsSuggestions"
           is-hidden=""
-          style="position: fixed; top: 150px; left: 392.5px; box-sizing: border-box; max-height: 300px; max-width: 785px;"
+          role="listbox"
         >
         </gr-autocomplete-dropdown>
         <iron-autogrow-textarea aria-disabled="false" focused="" id="textarea">
-        </iron-autogrow-textarea> `,
+        </iron-autogrow-textarea>`,
       {
         // gr-autocomplete-dropdown sizing seems to vary between local & CI
         ignoreAttributes: [
@@ -49,47 +46,6 @@
   });
 
   suite('mention users', () => {
-    setup(async () => {
-      stubFlags('isEnabled').returns(true);
-      element.requestUpdate();
-      await element.updateComplete;
-    });
-
-    test('renders', () => {
-      assert.shadowDom.equal(
-        element,
-        /* HTML */ `
-          <div id="hiddenText"></div>
-          <span id="caratSpan"> </span>
-          <gr-autocomplete-dropdown
-            id="emojiSuggestions"
-            is-hidden=""
-            style="position: fixed; top: 478px; left: 321px; box-sizing: border-box; max-height: 956px; max-width: 642px;"
-          >
-          </gr-autocomplete-dropdown>
-          <gr-autocomplete-dropdown
-            id="mentionsSuggestions"
-            is-hidden=""
-            role="listbox"
-            style="position: fixed; top: 478px; left: 321px; box-sizing: border-box; max-height: 956px; max-width: 642px;"
-          >
-          </gr-autocomplete-dropdown>
-          <iron-autogrow-textarea
-            focused=""
-            aria-disabled="false"
-            id="textarea"
-          >
-          </iron-autogrow-textarea>
-        `,
-        {
-          // gr-autocomplete-dropdown sizing seems to vary between local & CI
-          ignoreAttributes: [
-            {tags: ['gr-autocomplete-dropdown'], attributes: ['style']},
-          ],
-        }
-      );
-    });
-
     test('mentions selector is open when @ is typed & the textarea has focus', async () => {
       // Needed for Safari tests. selectionStart is not updated when text is
       // updated.
diff --git a/polygerrit-ui/app/services/flags/flags.ts b/polygerrit-ui/app/services/flags/flags.ts
index ad15a62..29e9259 100644
--- a/polygerrit-ui/app/services/flags/flags.ts
+++ b/polygerrit-ui/app/services/flags/flags.ts
@@ -19,7 +19,5 @@
   PUSH_NOTIFICATIONS_DEVELOPER = 'UiFeature__push_notifications_developer',
   PUSH_NOTIFICATIONS = 'UiFeature__push_notifications',
   SUGGEST_EDIT = 'UiFeature__suggest_edit',
-  MENTION_USERS = 'UiFeature__mention_users',
-  RENDER_MARKDOWN = 'UiFeature__render_markdown',
   REBASE_CHAIN = 'UiFeature__rebase_chain',
 }