diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
index b10c17e..536ef92 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
@@ -99,7 +99,6 @@
   getVotingRange,
   StandardLabels,
 } from '../../../utils/label-util';
-import {CommentThread} from '../../../utils/comment-util';
 import {ShowAlertEventDetail} from '../../../types/events';
 import {
   ActionPriority,
@@ -448,9 +447,6 @@
   @property({type: String})
   _actionLoadingMessage = '';
 
-  @property({type: Array})
-  commentThreads: CommentThread[] = [];
-
   @property({
     type: Array,
     computed:
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_html.ts b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_html.ts
index d21c29f..17ca7cf 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_html.ts
@@ -213,11 +213,9 @@
     <gr-confirm-submit-dialog
       id="confirmSubmitDialog"
       class="confirmDialog"
-      change="[[change]]"
       action="[[_revisionSubmitAction]]"
       on-cancel="_handleConfirmDialogCancel"
       on-confirm="_handleSubmitConfirm"
-      comment-threads="[[commentThreads]]"
       hidden=""
     ></gr-confirm-submit-dialog>
     <gr-dialog
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 e4b466b..c4ccb7d 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
@@ -15,7 +15,7 @@
  * limitations under the License.
  */
 import {LitElement, css, html} from 'lit';
-import {customElement, property} from 'lit/decorators';
+import {customElement, property, state} from 'lit/decorators';
 import {subscribe} from '../../lit/subscription-controller';
 import {sharedStyles} from '../../../styles/shared-styles';
 import {appContext} from '../../../services/app-context';
@@ -65,6 +65,11 @@
 import {modifierPressed} from '../../../utils/dom-util';
 import {DropdownLink} from '../../shared/gr-dropdown/gr-dropdown';
 import {fontStyles} from '../../../styles/gr-font-styles';
+import {account$} from '../../../services/user/user-model';
+import {
+  changeComments$,
+  threads$,
+} from '../../../services/comments/comments-model';
 
 export enum SummaryChipStyles {
   INFO = 'info',
@@ -378,31 +383,31 @@
 
 @customElement('gr-change-summary')
 export class GrChangeSummary extends LitElement {
-  @property({type: Object})
+  @state()
   changeComments?: ChangeComments;
 
-  @property({type: Array})
+  @state()
   commentThreads?: CommentThread[];
 
-  @property({type: Object})
+  @state()
   selfAccount?: AccountInfo;
 
-  @property()
+  @state()
   runs: CheckRun[] = [];
 
-  @property()
+  @state()
   showChecksSummary = false;
 
-  @property()
+  @state()
   someProvidersAreLoading = false;
 
-  @property()
+  @state()
   errorMessages: ErrorMessages = {};
 
-  @property()
+  @state()
   loginCallback?: () => void;
 
-  @property()
+  @state()
   actions: Action[] = [];
 
   private showAllChips = new Map<RunStatus | Category, boolean>();
@@ -421,6 +426,9 @@
     subscribe(this, errorMessagesLatest$, x => (this.errorMessages = x));
     subscribe(this, loginCallbackLatest$, x => (this.loginCallback = x));
     subscribe(this, topLevelActionsLatest$, x => (this.actions = x));
+    subscribe(this, changeComments$, x => (this.changeComments = x));
+    subscribe(this, threads$, x => (this.commentThreads = x));
+    subscribe(this, account$, x => (this.selfAccount = x));
   }
 
   static override get styles() {
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
index 8d64bc0..8a28cb1 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
@@ -18,7 +18,6 @@
 import '../../../styles/gr-a11y-styles';
 import '../../../styles/gr-paper-styles';
 import '../../../styles/shared-styles';
-import '../../diff/gr-comment-api/gr-comment-api';
 import '../../plugins/gr-endpoint-decorator/gr-endpoint-decorator';
 import '../../plugins/gr-endpoint-param/gr-endpoint-param';
 import '../../shared/gr-account-link/gr-account-link';
@@ -129,10 +128,7 @@
 import {GrIncludedInDialog} from '../gr-included-in-dialog/gr-included-in-dialog';
 import {GrDownloadDialog} from '../gr-download-dialog/gr-download-dialog';
 import {GrChangeMetadata} from '../gr-change-metadata/gr-change-metadata';
-import {
-  ChangeComments,
-  GrCommentApi,
-} from '../../diff/gr-comment-api/gr-comment-api';
+import {ChangeComments} from '../../diff/gr-comment-api/gr-comment-api';
 import {
   assertIsDefined,
   hasOwnProperty,
@@ -230,7 +226,6 @@
 
 export interface GrChangeView {
   $: {
-    commentAPI: GrCommentApi;
     applyFixDialog: GrApplyFixDialog;
     fileList: GrFileList & Element;
     fileListHeader: GrFileListHeader;
@@ -2026,23 +2021,6 @@
       });
   }
 
-  /**
-   * Fetches a new changeComment object, and data for all types of comments
-   * (comments, robot comments, draft comments) is requested.
-   */
-  _reloadComments() {
-    // We are resetting all comment related properties, because we want to avoid
-    // a new change being loaded and then paired with outdated comments.
-    this._changeComments = undefined;
-    this._commentThreads = undefined;
-    this._draftCommentThreads = undefined;
-    this._robotCommentThreads = undefined;
-    if (!this._changeNum)
-      throw new Error('missing required changeNum property');
-
-    this.commentsService.loadAll(this._changeNum, this._patchRange?.patchNum);
-  }
-
   @observe('_changeComments')
   changeCommentsChanged(comments?: ChangeComments) {
     if (!comments) return;
@@ -2124,8 +2102,6 @@
     });
     allDataPromises.push(projectConfigLoaded);
 
-    this._reloadComments();
-
     let coreDataPromise;
 
     // If the patch number is specified
@@ -2230,13 +2206,20 @@
     assertIsDefined(this._changeNum, '_changeNum');
     if (!this._patchRange?.patchNum) throw new Error('missing patchNum');
     const promises = [this._getCommitInfo(), this.$.fileList.reload()];
-    if (patchNumChanged)
+    if (patchNumChanged) {
       promises.push(
-        this.$.commentAPI.reloadPortedComments(
+        this.commentsService.reloadPortedComments(
           this._changeNum,
           this._patchRange?.patchNum
         )
       );
+      promises.push(
+        this.commentsService.reloadPortedDrafts(
+          this._changeNum,
+          this._patchRange?.patchNum
+        )
+      );
+    }
     return Promise.all(promises);
   }
 
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts
index 9341b18..9181ca0 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts
@@ -381,7 +381,6 @@
             on-stop-edit-tap="_handleStopEditTap"
             on-download-tap="_handleOpenDownloadDialog"
             on-included-tap="_handleOpenIncludedInDialog"
-            comment-threads="[[_commentThreads]]"
           ></gr-change-actions>
         </div>
         <!-- end commit actions -->
@@ -439,12 +438,7 @@
                 </gr-editable-content>
               </div>
               <h3 class="assistive-tech-only">Comments and Checks Summary</h3>
-              <gr-change-summary
-                change-comments="[[_changeComments]]"
-                comment-threads="[[_commentThreads]]"
-                self-account="[[_account]]"
-              >
-              </gr-change-summary>
+              <gr-change-summary></gr-change-summary>
               <gr-endpoint-decorator name="commit-container">
                 <gr-endpoint-param name="change" value="[[_change]]">
                 </gr-endpoint-param>
@@ -528,7 +522,6 @@
           change="[[_change]]"
           change-num="[[_changeNum]]"
           revision-info="[[_revisionInfo]]"
-          change-comments="[[_changeComments]]"
           commit-info="[[_commitInfo]]"
           change-url="[[_computeChangeUrl(_change)]]"
           edit-mode="[[_editMode]]"
@@ -720,5 +713,4 @@
       </gr-reply-dialog>
     </template>
   </gr-overlay>
-  <gr-comment-api id="commentAPI"></gr-comment-api>
 `;
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts
index ab17f47..72cd91e 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts
@@ -40,6 +40,7 @@
 import {
   mockPromise,
   queryAndAssert,
+  stubComments,
   stubRestApi,
   stubUsers,
   waitQueryAndAssert,
@@ -1346,10 +1347,8 @@
     sinon.stub(element, '_getCommitInfo');
     sinon.stub(element.$.fileList, 'reload');
     flush();
-    const reloadPortedCommentsStub = sinon.stub(
-      element.$.commentAPI,
-      'reloadPortedComments'
-    );
+    const reloadPortedCommentsStub = stubComments('reloadPortedComments');
+    const reloadPortedDraftsStub = stubComments('reloadPortedDrafts');
     sinon.stub(element.$.fileList, 'collapseAllDiffs');
 
     const value: AppElementChangeViewParams = {
@@ -1374,6 +1373,7 @@
     element.params = {...value};
     await flush();
     assert.isTrue(reloadPortedCommentsStub.calledOnce);
+    assert.isTrue(reloadPortedDraftsStub.calledOnce);
   });
 
   test('do not reload entire page when patchRange doesnt change', async () => {
diff --git a/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog.ts b/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog.ts
index 9d371d3..a9b7b81 100644
--- a/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog.ts
+++ b/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog.ts
@@ -20,14 +20,18 @@
 import '../../plugins/gr-endpoint-decorator/gr-endpoint-decorator';
 import '../../plugins/gr-endpoint-param/gr-endpoint-param';
 import '../gr-thread-list/gr-thread-list';
-import {ChangeInfo, ActionInfo} from '../../../types/common';
+import {ActionInfo} from '../../../types/common';
 import {GrDialog} from '../../shared/gr-dialog/gr-dialog';
 import {pluralize} from '../../../utils/string-util';
 import {CommentThread, isUnresolved} from '../../../utils/comment-util';
 import {sharedStyles} from '../../../styles/shared-styles';
 import {LitElement, css, html} from 'lit';
-import {customElement, property, query} from 'lit/decorators';
+import {customElement, property, query, state} from 'lit/decorators';
 import {fontStyles} from '../../../styles/gr-font-styles';
+import {subscribe} from '../../lit/subscription-controller';
+import {change$} from '../../../services/change/change-model';
+import {threads$} from '../../../services/comments/comments-model';
+import {ParsedChangeInfo} from '../../../types/types';
 
 @customElement('gr-confirm-submit-dialog')
 export class GrConfirmSubmitDialog extends LitElement {
@@ -47,16 +51,16 @@
    */
 
   @property({type: Object})
-  change?: ChangeInfo;
-
-  @property({type: Object})
   action?: ActionInfo;
 
-  @property({type: Array})
-  commentThreads?: CommentThread[] = [];
+  @state()
+  change?: ParsedChangeInfo;
 
-  @property({type: Boolean})
-  _initialised = false;
+  @state()
+  unresolvedThreads: CommentThread[] = [];
+
+  @state()
+  initialised = false;
 
   static override get styles() {
     return [
@@ -84,6 +88,16 @@
     ];
   }
 
+  constructor() {
+    super();
+    subscribe(this, change$, x => (this.change = x));
+    subscribe(
+      this,
+      threads$,
+      x => (this.unresolvedThreads = x.filter(isUnresolved))
+    );
+  }
+
   private renderPrivate() {
     if (!this.change?.is_private) return '';
     return html`
@@ -106,11 +120,11 @@
           icon="gr-icons:warning"
           class="warningBeforeSubmit"
         ></iron-icon>
-        ${this._computeUnresolvedCommentsWarning(this.change)}
+        ${this.computeUnresolvedCommentsWarning()}
       </p>
       <gr-thread-list
         id="commentList"
-        .threads="${this._computeUnresolvedThreads(this.commentThreads)}"
+        .threads="${this.unresolvedThreads}"
         .change="${this.change}"
         .changeNum="${this.change?._number}"
         logged-in
@@ -121,7 +135,7 @@
   }
 
   private renderChangeEdit() {
-    if (!this._computeHasChangeEdit(this.change)) return '';
+    if (!this.computeHasChangeEdit()) return '';
     return html`
       <iron-icon
         icon="gr-icons:warning"
@@ -133,7 +147,7 @@
   }
 
   private renderInitialised() {
-    if (!this._initialised) return '';
+    if (!this.initialised) return '';
     return html`
       <div class="header" slot="header">${this.action?.label}</div>
       <div class="main" slot="main">
@@ -159,48 +173,43 @@
       id="dialog"
       confirm-label="Continue"
       confirm-on-enter=""
-      @cancel=${this._handleCancelTap}
-      @confirm=${this._handleConfirmTap}
+      @cancel=${this.handleCancelTap}
+      @confirm=${this.handleConfirmTap}
     >
       ${this.renderInitialised()}
     </gr-dialog>`;
   }
 
   init() {
-    this._initialised = true;
+    this.initialised = true;
   }
 
   resetFocus() {
     this.dialog?.resetFocus();
   }
 
-  _computeHasChangeEdit(change?: ChangeInfo) {
-    return (
-      !!change &&
-      !!change.revisions &&
-      Object.values(change.revisions).some(rev => rev._number === 'edit')
+  // Private method, but visible for testing.
+  computeHasChangeEdit() {
+    return Object.values(this.change?.revisions ?? {}).some(
+      rev => rev._number === 'edit'
     );
   }
 
-  _computeUnresolvedThreads(commentThreads?: CommentThread[]) {
-    if (!commentThreads) return [];
-    return commentThreads.filter(thread => isUnresolved(thread));
-  }
-
-  _computeUnresolvedCommentsWarning(change?: ChangeInfo) {
-    if (!change) return '';
-    const unresolvedCount = change.unresolved_comment_count;
+  // Private method, but visible for testing.
+  computeUnresolvedCommentsWarning() {
+    if (!this.change) return '';
+    const unresolvedCount = this.change.unresolved_comment_count;
     if (!unresolvedCount) throw new Error('unresolved comments undefined or 0');
     return `Heads Up! ${pluralize(unresolvedCount, 'unresolved comment')}.`;
   }
 
-  _handleConfirmTap(e: Event) {
+  private handleConfirmTap(e: Event) {
     e.preventDefault();
     e.stopPropagation();
     this.dispatchEvent(new CustomEvent('confirm', {bubbles: false}));
   }
 
-  _handleCancelTap(e: Event) {
+  private handleCancelTap(e: Event) {
     e.preventDefault();
     e.stopPropagation();
     this.dispatchEvent(new CustomEvent('cancel', {bubbles: false}));
diff --git a/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog_test.ts b/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog_test.ts
index e1823b1..0426cb6 100644
--- a/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog_test.ts
@@ -16,7 +16,10 @@
  */
 
 import '../../../test/common-test-setup-karma';
-import {createChange, createRevision} from '../../../test/test-data-generators';
+import {
+  createParsedChange,
+  createRevision,
+} from '../../../test/test-data-generators';
 import {queryAndAssert} from '../../../test/test-utils';
 import {PatchSetNum} from '../../../types/common';
 import {GrConfirmSubmitDialog} from './gr-confirm-submit-dialog';
@@ -28,13 +31,13 @@
 
   setup(() => {
     element = basicFixture.instantiate();
-    element._initialised = true;
+    element.initialised = true;
   });
 
   test('display', async () => {
     element.action = {label: 'my-label'};
     element.change = {
-      ...createChange(),
+      ...createParsedChange(),
       subject: 'my-subject',
       revisions: {},
     };
@@ -47,23 +50,23 @@
     assert.notEqual(message.textContent!.indexOf('my-subject'), -1);
   });
 
-  test('_computeUnresolvedCommentsWarning', () => {
-    const change = {...createChange(), unresolved_comment_count: 1};
+  test('computeUnresolvedCommentsWarning', () => {
+    element.change = {...createParsedChange(), unresolved_comment_count: 1};
     assert.equal(
-      element._computeUnresolvedCommentsWarning(change),
+      element.computeUnresolvedCommentsWarning(),
       'Heads Up! 1 unresolved comment.'
     );
 
-    const change2 = {...createChange(), unresolved_comment_count: 2};
+    element.change = {...createParsedChange(), unresolved_comment_count: 2};
     assert.equal(
-      element._computeUnresolvedCommentsWarning(change2),
+      element.computeUnresolvedCommentsWarning(),
       'Heads Up! 2 unresolved comments.'
     );
   });
 
-  test('_computeHasChangeEdit', () => {
-    const change = {
-      ...createChange(),
+  test('computeHasChangeEdit', () => {
+    element.change = {
+      ...createParsedChange(),
       revisions: {
         d442ff05d6c4f2a3af0eeca1f67374b39f9dc3d8: {
           ...createRevision(),
@@ -73,10 +76,10 @@
       unresolved_comment_count: 0,
     };
 
-    assert.isTrue(element._computeHasChangeEdit(change));
+    assert.isTrue(element.computeHasChangeEdit());
 
-    const change2 = {
-      ...createChange(),
+    element.change = {
+      ...createParsedChange(),
       revisions: {
         d442ff05d6c4f2a3af0eeca1f67374b39f9dc3d8: {
           ...createRevision(),
@@ -84,6 +87,6 @@
         },
       },
     };
-    assert.isFalse(element._computeHasChangeEdit(change2));
+    assert.isFalse(element.computeHasChangeEdit());
   });
 });
diff --git a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.ts b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.ts
index 1b44e35..920844b 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.ts
+++ b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.ts
@@ -39,7 +39,6 @@
   BasePatchSetNum,
 } from '../../../types/common';
 import {DiffPreferencesInfo} from '../../../types/diff';
-import {ChangeComments} from '../../diff/gr-comment-api/gr-comment-api';
 import {GrDiffModeSelector} from '../../diff/gr-diff-mode-selector/gr-diff-mode-selector';
 import {GrButton} from '../../shared/gr-button/gr-button';
 import {fireEvent} from '../../../utils/event-util';
@@ -101,9 +100,6 @@
   changeUrl?: string;
 
   @property({type: Object})
-  changeComments?: ChangeComments;
-
-  @property({type: Object})
   commitInfo?: CommitInfo;
 
   @property({type: Boolean})
diff --git a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_html.ts b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_html.ts
index 5a85531..fbba2fc 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_html.ts
@@ -132,7 +132,6 @@
       <div class="patchInfoContent">
         <gr-patch-range-select
           id="rangeSelect"
-          change-comments="[[changeComments]]"
           change-num="[[changeNum]]"
           patch-num="[[patchNum]]"
           base-patch-num="[[basePatchNum]]"
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts
index 95984b8..d02f09b 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts
@@ -18,7 +18,6 @@
 import '../../../styles/shared-styles';
 import '../../diff/gr-diff-cursor/gr-diff-cursor';
 import '../../diff/gr-diff-host/gr-diff-host';
-import '../../diff/gr-comment-api/gr-comment-api';
 import '../../diff/gr-diff-preferences-dialog/gr-diff-preferences-dialog';
 import '../../edit/gr-edit-file-controls/gr-edit-file-controls';
 import '../../shared/gr-button/gr-button';
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.js b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.js
index 0db7690..ee65837 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.js
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.js
@@ -16,7 +16,6 @@
  */
 
 import '../../../test/common-test-setup-karma.js';
-import '../../diff/gr-comment-api/gr-comment-api.js';
 import '../../shared/gr-date-formatter/gr-date-formatter.js';
 import {getMockDiffResponse} from '../../../test/mocks/diff-response.js';
 import './gr-file-list.js';
@@ -49,7 +48,6 @@
     'gr-file-list-comment-api-mock', html`
     <gr-file-list id="fileList"
         change-comments="[[_changeComments]]"></gr-file-list>
-    <gr-comment-api id="commentAPI"></gr-comment-api>
 `);
 
 const basicFixture = fixtureFromElement(commentApiMock.is);
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.js b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.js
index 0939daa..a3b8873 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.js
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.js
@@ -16,7 +16,6 @@
  */
 
 import '../../../test/common-test-setup-karma.js';
-import '../../diff/gr-comment-api/gr-comment-api.js';
 import './gr-messages-list.js';
 import {createCommentApiMockWithTemplateElement} from '../../../test/mocks/comment-api.js';
 import {TEST_ONLY} from './gr-messages-list.js';
@@ -30,7 +29,6 @@
      <gr-messages-list
          id="messagesList"
          change-comments="[[_changeComments]]"></gr-messages-list>
-     <gr-comment-api id="commentAPI"></gr-comment-api>
 `);
 
 const basicFixture = fixtureFromTemplate(html`
diff --git a/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts b/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts
index 7e7e507..32c732e 100644
--- a/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts
+++ b/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts
@@ -14,16 +14,12 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import {PolymerElement} from '@polymer/polymer/polymer-element';
-import {htmlTemplate} from './gr-comment-api_html';
-import {customElement, property} from '@polymer/decorators';
 import {
   CommentBasics,
   PatchRange,
   PatchSetNum,
   RobotCommentInfo,
   UrlEncodedCommentId,
-  NumericChangeId,
   PathToCommentsInfoMap,
   FileInfo,
   ParentPatchSetNum,
@@ -45,7 +41,6 @@
   addPath,
 } from '../../../utils/comment-util';
 import {PatchSetFile, PatchNumOnly, isPatchSetFile} from '../../../types/types';
-import {appContext} from '../../../services/app-context';
 import {CommentSide, Side} from '../../../constants/constants';
 import {pluralize} from '../../../utils/string-util';
 import {NormalizedFileInfo} from '../../change/gr-file-list/gr-file-list';
@@ -611,38 +606,3 @@
     return createCommentThreads(comments);
   }
 }
-
-@customElement('gr-comment-api')
-export class GrCommentApi extends PolymerElement {
-  static get template() {
-    return htmlTemplate;
-  }
-
-  @property({type: Object})
-  _changeComments?: ChangeComments;
-
-  private readonly restApiService = appContext.restApiService;
-
-  private readonly commentsService = appContext.commentsService;
-
-  reloadPortedComments(changeNum: NumericChangeId, patchNum: PatchSetNum) {
-    if (!this._changeComments) {
-      this.commentsService.loadAll(changeNum);
-      return Promise.resolve();
-    }
-    return Promise.all([
-      this.restApiService.getPortedComments(changeNum, patchNum),
-      this.restApiService.getPortedDrafts(changeNum, patchNum),
-    ]).then(res => {
-      if (!this._changeComments) return;
-      this._changeComments =
-        this._changeComments.cloneWithUpdatedPortedComments(res[0], res[1]);
-    });
-  }
-}
-
-declare global {
-  interface HTMLElementTagNameMap {
-    'gr-comment-api': GrCommentApi;
-  }
-}
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
index 6facdca..8d75230 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
@@ -20,7 +20,6 @@
 
 import {dom} from '@polymer/polymer/lib/legacy/polymer.dom.js';
 import {createDefaultDiffPrefs, Side} from '../../../constants/constants.js';
-import {_testOnly_resetState} from '../../../services/comments/comments-model.js';
 import {createChange, createComment, createCommentThread} from '../../../test/test-data-generators.js';
 import {addListenerForTest, mockPromise, stubRestApi} from '../../../test/test-utils.js';
 import {EditPatchSetNum, ParentPatchSetNum} from '../../../types/common.js';
@@ -43,7 +42,6 @@
     element.path = 'some/path';
     sinon.stub(element.reporting, 'time');
     sinon.stub(element.reporting, 'timeEnd');
-    _testOnly_resetState();
     await flush();
   });
 
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
index 0ffe61f..64186f4 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
@@ -65,7 +65,7 @@
   GrDropdownList,
 } from '../../shared/gr-dropdown-list/gr-dropdown-list';
 import {GrOverlay} from '../../shared/gr-overlay/gr-overlay';
-import {ChangeComments, GrCommentApi} from '../gr-comment-api/gr-comment-api';
+import {ChangeComments} from '../gr-comment-api/gr-comment-api';
 import {GrDiffModeSelector} from '../gr-diff-mode-selector/gr-diff-mode-selector';
 import {
   BasePatchSetNum,
@@ -134,7 +134,6 @@
 
 export interface GrDiffView {
   $: {
-    commentAPI: GrCommentApi;
     diffHost: GrDiffHost;
     reviewed: HTMLInputElement;
     dropdown: GrDropdownList;
@@ -348,8 +347,6 @@
 
   private readonly userService = appContext.userService;
 
-  private readonly commentsService = appContext.commentsService;
-
   private readonly shortcuts = appContext.shortcutsService;
 
   _throttledToggleFileReviewed?: (e: KeyboardEvent) => void;
@@ -1074,8 +1071,6 @@
 
     if (!this._change) promises.push(this._getChangeDetail(this._changeNum));
 
-    if (!this._changeComments) this._loadComments(value.patchNum);
-
     promises.push(this._getChangeEdit());
 
     this.$.diffHost.cancel();
@@ -1464,11 +1459,6 @@
     return url;
   }
 
-  _loadComments(patchSet?: PatchSetNum) {
-    assertIsDefined(this._changeNum, '_changeNum');
-    return this.commentsService.loadAll(this._changeNum, patchSet);
-  }
-
   @observe(
     '_changeComments',
     '_files.changeFilesByPath',
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_html.ts b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_html.ts
index 16adb45..d87d192 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_html.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_html.ts
@@ -426,5 +426,4 @@
     on-reload-diff-preference="_handleReloadingDiffPreference"
   >
   </gr-diff-preferences-dialog>
-  <gr-comment-api id="commentAPI"></gr-comment-api>
 `;
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.js b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.js
index 46ec5d0..5c04ab0 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.js
@@ -30,7 +30,7 @@
 import {EditPatchSetNum} from '../../../types/common.js';
 import {CursorMoveResult} from '../../../api/core.js';
 import {EventType} from '../../../types/events.js';
-import {_testOnly_resetState, _testOnly_setState} from '../../../services/browser/browser-model.js';
+import {_testOnly_setState} from '../../../services/browser/browser-model.js';
 
 const basicFixture = fixtureFromElement('gr-diff-view');
 
@@ -69,8 +69,6 @@
       stubRestApi('getDiffDrafts').returns(Promise.resolve({}));
       stubRestApi('getPortedComments').returns(Promise.resolve({}));
 
-      _testOnly_resetState();
-
       element = basicFixture.instantiate();
       element._changeNum = '42';
       element._path = 'some/path.txt';
@@ -2040,7 +2038,6 @@
           Promise.resolve([]));
       element = basicFixture.instantiate();
       element._changeNum = '42';
-      return element._loadComments();
     });
 
     test('_getFiles add files with comments without changes', () => {
diff --git a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select.ts b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select.ts
index 501f688..5d4405f 100644
--- a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select.ts
+++ b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select.ts
@@ -50,10 +50,16 @@
 import {sharedStyles} from '../../../styles/shared-styles';
 import {LitElement, PropertyValues, css, html} from 'lit';
 import {customElement, property, query, state} from 'lit/decorators';
+import {subscribe} from '../../lit/subscription-controller';
+import {changeComments$} from '../../../services/comments/comments-model';
 
 // Maximum length for patch set descriptions.
 const PATCH_DESC_MAX_LENGTH = 500;
 
+function getShaForPatch(patch: PatchSet) {
+  return patch.sha.substring(0, 10);
+}
+
 export interface PatchRangeChangeDetail {
   patchNum?: PatchSetNum;
   basePatchNum?: BasePatchSetNum;
@@ -95,9 +101,6 @@
   changeNum?: string;
 
   @property({type: Object})
-  changeComments?: ChangeComments;
-
-  @property({type: Object})
   filesWeblinks?: FilesWebLinks;
 
   @property({type: String})
@@ -106,18 +109,28 @@
   @property({type: String})
   basePatchNum?: BasePatchSetNum;
 
+  /** Not used directly. Translated into `sortedRevisions` in willUpdate(). */
   @property({type: Object})
-  revisions?: RevisionInfo[];
+  revisions: (RevisionInfo | EditRevisionInfo)[] = [];
 
   @property({type: Object})
   revisionInfo?: RevisionInfoClass;
 
-  @property({type: Array})
+  /** Private internal state, derived from `revisions` in willUpdate(). */
   @state()
-  protected sortedRevisions?: RevisionInfo[];
+  private sortedRevisions: (RevisionInfo | EditRevisionInfo)[] = [];
+
+  /** Private internal state, visible for testing. */
+  @state()
+  changeComments?: ChangeComments;
 
   private readonly reporting: ReportingService = appContext.reportingService;
 
+  constructor() {
+    super();
+    subscribe(this, changeComments$, x => (this.changeComments = x));
+  }
+
   static override get styles() {
     return [
       a11yStyles,
@@ -152,20 +165,6 @@
     ];
   }
 
-  private renderWeblinks(fileLink?: GeneratedWebLink[]) {
-    if (!fileLink) return;
-
-    return html`<span class="filesWeblinks">
-      ${fileLink.map(
-        weblink => html`
-          <a target="_blank" rel="noopener" href="${weblink.url}">
-            ${weblink.name}
-          </a>
-        `
-      )}</span
-    > `;
-  }
-
   override render() {
     return html`
       <h3 class="assistive-tech-only">Patchset Range Selection</h3>
@@ -173,14 +172,8 @@
         <gr-dropdown-list
           id="basePatchDropdown"
           .value="${convertToString(this.basePatchNum)}"
-          .items="${this._computeBaseDropdownContent(
-            this.availablePatches,
-            this.patchNum,
-            this.sortedRevisions,
-            this.changeComments,
-            this.revisionInfo
-          )}"
-          @value-change=${this._handlePatchChange}
+          .items="${this.computeBaseDropdownContent()}"
+          @value-change=${this.handlePatchChange}
         >
         </gr-dropdown-list>
       </span>
@@ -190,13 +183,8 @@
         <gr-dropdown-list
           id="patchNumDropdown"
           .value="${convertToString(this.patchNum)}"
-          .items="${this._computePatchDropdownContent(
-            this.availablePatches,
-            this.basePatchNum,
-            this.sortedRevisions,
-            this.changeComments
-          )}"
-          @value-change=${this._handlePatchChange}
+          .items="${this.computePatchDropdownContent()}"
+          @value-change=${this.handlePatchChange}
         >
         </gr-dropdown-list>
         ${this.renderWeblinks(this.filesWeblinks?.meta_b)}
@@ -204,63 +192,54 @@
     `;
   }
 
-  override updated(changedProperties: PropertyValues) {
+  private renderWeblinks(fileLinks?: GeneratedWebLink[]) {
+    if (!fileLinks) return;
+    return html`<span class="filesWeblinks">
+      ${fileLinks.map(
+        weblink => html`
+          <a target="_blank" rel="noopener" href="${weblink.url}">
+            ${weblink.name}
+          </a>
+        `
+      )}</span
+    > `;
+  }
+
+  override willUpdate(changedProperties: PropertyValues) {
     if (changedProperties.has('revisions')) {
-      this._updateSortedRevisions(this.revisions);
+      this.sortedRevisions = sortRevisions(Object.values(this.revisions || {}));
     }
   }
 
-  _updateSortedRevisions(revisions?: RevisionInfo[]) {
-    if (!revisions) return;
-    this.sortedRevisions = sortRevisions(Object.values(revisions));
-  }
-
-  _getShaForPatch(patch: PatchSet) {
-    return patch.sha.substring(0, 10);
-  }
-
-  _computeBaseDropdownContent(
-    availablePatches?: PatchSet[],
-    patchNum?: PatchSetNum,
-    sortedRevisions?: (RevisionInfo | EditRevisionInfo)[],
-    changeComments?: ChangeComments,
-    revisionInfo?: RevisionInfoClass
-  ): DropdownItem[] {
-    // Polymer 2: check for undefined
+  // Private method, but visible for testing.
+  computeBaseDropdownContent(): DropdownItem[] {
     if (
-      availablePatches === undefined ||
-      patchNum === undefined ||
-      sortedRevisions === undefined ||
-      changeComments === undefined ||
-      revisionInfo === undefined
+      this.availablePatches === undefined ||
+      this.patchNum === undefined ||
+      this.changeComments === undefined ||
+      this.revisionInfo === undefined
     ) {
       return [];
     }
 
-    const parentCounts = revisionInfo.getParentCountMap();
-    const currentParentCount = hasOwnProperty(parentCounts, patchNum)
-      ? parentCounts[patchNum as number]
+    const parentCounts = this.revisionInfo.getParentCountMap();
+    const currentParentCount = hasOwnProperty(parentCounts, this.patchNum)
+      ? parentCounts[this.patchNum as number]
       : 1;
-    const maxParents = revisionInfo.getMaxParents();
+    const maxParents = this.revisionInfo.getMaxParents();
     const isMerge = currentParentCount > 1;
 
     const dropdownContent: DropdownItem[] = [];
-    for (const basePatch of availablePatches) {
+    for (const basePatch of this.availablePatches) {
       const basePatchNum = basePatch.num;
-      const entry: DropdownItem = this._createDropdownEntry(
+      const entry: DropdownItem = this.createDropdownEntry(
         basePatchNum,
         'Patchset ',
-        sortedRevisions,
-        changeComments,
-        this._getShaForPatch(basePatch)
+        getShaForPatch(basePatch)
       );
       dropdownContent.push({
         ...entry,
-        disabled: this._computeLeftDisabled(
-          basePatch.num,
-          patchNum,
-          sortedRevisions
-        ),
+        disabled: this.computeLeftDisabled(basePatch.num, this.patchNum),
       });
     }
 
@@ -282,91 +261,61 @@
     return dropdownContent;
   }
 
-  _computeMobileText(
-    patchNum: PatchSetNum,
-    changeComments: ChangeComments,
-    revisions: (RevisionInfo | EditRevisionInfo)[]
-  ) {
+  private computeMobileText(patchNum: PatchSetNum) {
     return (
       `${patchNum}` +
-      `${this._computePatchSetCommentsString(changeComments, patchNum)}` +
-      `${this._computePatchSetDescription(revisions, patchNum, true)}`
+      `${this.computePatchSetCommentsString(patchNum)}` +
+      `${this.computePatchSetDescription(patchNum, true)}`
     );
   }
 
-  _computePatchDropdownContent(
-    availablePatches?: PatchSet[],
-    basePatchNum?: BasePatchSetNum,
-    sortedRevisions?: (RevisionInfo | EditRevisionInfo)[],
-    changeComments?: ChangeComments
-  ): DropdownItem[] {
-    // Polymer 2: check for undefined
+  // Private method, but visible for testing.
+  computePatchDropdownContent(): DropdownItem[] {
     if (
-      availablePatches === undefined ||
-      basePatchNum === undefined ||
-      sortedRevisions === undefined ||
-      changeComments === undefined
+      this.availablePatches === undefined ||
+      this.basePatchNum === undefined ||
+      this.changeComments === undefined
     ) {
       return [];
     }
 
     const dropdownContent: DropdownItem[] = [];
-    for (const patch of availablePatches) {
+    for (const patch of this.availablePatches) {
       const patchNum = patch.num;
-      const entry = this._createDropdownEntry(
+      const entry = this.createDropdownEntry(
         patchNum,
         patchNum === 'edit' ? '' : 'Patchset ',
-        sortedRevisions,
-        changeComments,
-        this._getShaForPatch(patch)
+        getShaForPatch(patch)
       );
       dropdownContent.push({
         ...entry,
-        disabled: this._computeRightDisabled(
-          basePatchNum,
-          patchNum,
-          sortedRevisions
-        ),
+        disabled: this.computeRightDisabled(this.basePatchNum, patchNum),
       });
     }
     return dropdownContent;
   }
 
-  _computeText(
-    patchNum: PatchSetNum,
-    prefix: string,
-    changeComments: ChangeComments,
-    sha: string
-  ) {
+  private computeText(patchNum: PatchSetNum, prefix: string, sha: string) {
     return (
       `${prefix}${patchNum}` +
-      `${this._computePatchSetCommentsString(changeComments, patchNum)}` +
+      `${this.computePatchSetCommentsString(patchNum)}` +
       ` | ${sha}`
     );
   }
 
-  _createDropdownEntry(
+  private createDropdownEntry(
     patchNum: PatchSetNum,
     prefix: string,
-    sortedRevisions: (RevisionInfo | EditRevisionInfo)[],
-    changeComments: ChangeComments,
     sha: string
   ) {
     const entry: DropdownItem = {
       triggerText: `${prefix}${patchNum}`,
-      text: this._computeText(patchNum, prefix, changeComments, sha),
-      mobileText: this._computeMobileText(
-        patchNum,
-        changeComments,
-        sortedRevisions
-      ),
-      bottomText: `${this._computePatchSetDescription(
-        sortedRevisions,
-        patchNum
-      )}`,
+      text: this.computeText(patchNum, prefix, sha),
+      mobileText: this.computeMobileText(patchNum),
+      bottomText: `${this.computePatchSetDescription(patchNum)}`,
       value: patchNum,
     };
-    const date = this._computePatchSetDate(sortedRevisions, patchNum);
+    const date = this.computePatchSetDate(patchNum);
     if (date) {
       entry.date = date;
     }
@@ -378,17 +327,18 @@
    * is sorted in reverse order (higher patchset nums first), invalid base
    * patch nums have an index greater than the index of patchNum.
    *
+   * Private method, but visible for testing.
+   *
    * @param basePatchNum The possible base patch num.
    * @param patchNum The current selected patch num.
    */
-  _computeLeftDisabled(
+  computeLeftDisabled(
     basePatchNum: PatchSetNum,
-    patchNum: PatchSetNum,
-    sortedRevisions: (RevisionInfo | EditRevisionInfo)[]
+    patchNum: PatchSetNum
   ): boolean {
     return (
-      findSortedIndex(basePatchNum, sortedRevisions) <=
-      findSortedIndex(patchNum, sortedRevisions)
+      findSortedIndex(basePatchNum, this.sortedRevisions) <=
+      findSortedIndex(patchNum, this.sortedRevisions)
     );
   }
 
@@ -403,13 +353,14 @@
    * If the current basePatchNum is a parent index, then only patches that have
    * at least that many parents are valid.
    *
+   * Private method, but visible for testing.
+   *
    * @param basePatchNum The current selected base patch num.
    * @param patchNum The possible patch num.
    */
-  _computeRightDisabled(
+  computeRightDisabled(
     basePatchNum: PatchSetNum,
-    patchNum: PatchSetNum,
-    sortedRevisions: (RevisionInfo | EditRevisionInfo)[]
+    patchNum: PatchSetNum
   ): boolean {
     if (basePatchNum === ParentPatchSetNum) {
       return false;
@@ -427,21 +378,17 @@
     }
 
     return (
-      findSortedIndex(basePatchNum, sortedRevisions) <=
-      findSortedIndex(patchNum, sortedRevisions)
+      findSortedIndex(basePatchNum, this.sortedRevisions) <=
+      findSortedIndex(patchNum, this.sortedRevisions)
     );
   }
 
   // TODO(dhruvsri): have ported comments contribute to this count
-  _computePatchSetCommentsString(
-    changeComments: ChangeComments,
-    patchNum: PatchSetNum
-  ) {
-    if (!changeComments) {
-      return;
-    }
+  // Private method, but visible for testing.
+  computePatchSetCommentsString(patchNum: PatchSetNum): string {
+    if (!this.changeComments) return '';
 
-    const commentThreadCount = changeComments.computeCommentThreadCount(
+    const commentThreadCount = this.changeComments.computeCommentThreadCount(
       {
         patchNum,
       },
@@ -449,7 +396,7 @@
     );
     const commentThreadString = pluralize(commentThreadCount, 'comment');
 
-    const unresolvedCount = changeComments.computeUnresolvedNum(
+    const unresolvedCount = this.changeComments.computeUnresolvedNum(
       {patchNum},
       true
     );
@@ -468,23 +415,19 @@
     );
   }
 
-  _computePatchSetDescription(
-    revisions: (RevisionInfo | EditRevisionInfo)[],
+  private computePatchSetDescription(
     patchNum: PatchSetNum,
     addFrontSpace?: boolean
   ) {
-    const rev = getRevisionByPatchNum(revisions, patchNum);
+    const rev = getRevisionByPatchNum(this.sortedRevisions, patchNum);
     return rev?.description
       ? (addFrontSpace ? ' ' : '') +
           rev.description.substring(0, PATCH_DESC_MAX_LENGTH)
       : '';
   }
 
-  _computePatchSetDate(
-    revisions: (RevisionInfo | EditRevisionInfo)[],
-    patchNum: PatchSetNum
-  ): Timestamp | undefined {
-    const rev = getRevisionByPatchNum(revisions, patchNum);
+  private computePatchSetDate(patchNum: PatchSetNum): Timestamp | undefined {
+    const rev = getRevisionByPatchNum(this.sortedRevisions, patchNum);
     return rev ? rev.created : undefined;
   }
 
@@ -492,7 +435,7 @@
    * Catches value-change events from the patchset dropdowns and determines
    * whether or not a patch change event should be fired.
    */
-  _handlePatchChange(e: DropDownValueChangeEvent) {
+  private handlePatchChange(e: DropDownValueChangeEvent) {
     const detail: PatchRangeChangeDetail = {
       patchNum: this.patchNum,
       basePatchNum: this.basePatchNum,
diff --git a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.ts b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.ts
index a47b685..342fe3a 100644
--- a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.ts
+++ b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.ts
@@ -55,7 +55,7 @@
 suite('gr-patch-range-select tests', () => {
   let element: GrPatchRangeSelect;
 
-  function getInfo(revisions: RevisionInfo[]) {
+  function getInfo(revisions: (RevisionInfo | EditRevisionInfo)[]) {
     const revisionObj: Partial<RevIdToRevisionInfo> = {};
     for (let i = 0; i < revisions.length; i++) {
       revisionObj[i] = revisions[i];
@@ -78,97 +78,54 @@
     await element.updateComplete;
   });
 
-  test('enabled/disabled options', () => {
-    const patchRange = {
-      basePatchNum: 'PARENT' as PatchSetNum,
-      patchNum: 3 as PatchSetNum,
-    };
-    const sortedRevisions = [
+  test('enabled/disabled options', async () => {
+    element.revisions = [
       createRevision(3) as RevisionInfo,
       createEditRevision(2) as EditRevisionInfo,
       createRevision(2) as RevisionInfo,
       createRevision(1) as RevisionInfo,
     ];
+    await element.updateComplete;
+
+    const parent = 'PARENT' as PatchSetNum;
+    const edit = EditPatchSetNum;
+
     for (const patchNum of [1, 2, 3]) {
       assert.isFalse(
-        element._computeRightDisabled(
-          patchRange.basePatchNum,
-          patchNum as PatchSetNum,
-          sortedRevisions
-        )
+        element.computeRightDisabled(parent, patchNum as PatchSetNum)
       );
     }
     for (const basePatchNum of [1, 2]) {
-      assert.isFalse(
-        element._computeLeftDisabled(
-          basePatchNum as PatchSetNum,
-          patchRange.patchNum,
-          sortedRevisions
-        )
-      );
+      const base = basePatchNum as PatchSetNum;
+      assert.isFalse(element.computeLeftDisabled(base, 3 as PatchSetNum));
     }
     assert.isTrue(
-      element._computeLeftDisabled(3 as PatchSetNum, patchRange.patchNum, [])
+      element.computeLeftDisabled(3 as PatchSetNum, 3 as PatchSetNum)
     );
 
-    patchRange.basePatchNum = EditPatchSetNum;
     assert.isTrue(
-      element._computeLeftDisabled(
-        3 as PatchSetNum,
-        patchRange.patchNum,
-        sortedRevisions
-      )
+      element.computeLeftDisabled(3 as PatchSetNum, 3 as PatchSetNum)
     );
-    assert.isTrue(
-      element._computeRightDisabled(
-        patchRange.basePatchNum,
-        1 as PatchSetNum,
-        sortedRevisions
-      )
-    );
-    assert.isTrue(
-      element._computeRightDisabled(
-        patchRange.basePatchNum,
-        2 as PatchSetNum,
-        sortedRevisions
-      )
-    );
-    assert.isFalse(
-      element._computeRightDisabled(
-        patchRange.basePatchNum,
-        3 as PatchSetNum,
-        sortedRevisions
-      )
-    );
-    assert.isTrue(
-      element._computeRightDisabled(
-        patchRange.basePatchNum,
-        EditPatchSetNum,
-        sortedRevisions
-      )
-    );
+    assert.isTrue(element.computeRightDisabled(edit, 1 as PatchSetNum));
+    assert.isTrue(element.computeRightDisabled(edit, 2 as PatchSetNum));
+    assert.isFalse(element.computeRightDisabled(edit, 3 as PatchSetNum));
+    assert.isTrue(element.computeRightDisabled(edit, edit));
   });
 
-  test('_computeBaseDropdownContent', () => {
-    const availablePatches = [
+  test('computeBaseDropdownContent', async () => {
+    element.availablePatches = [
       {num: 'edit', sha: '1'} as PatchSet,
       {num: 3, sha: '2'} as PatchSet,
       {num: 2, sha: '3'} as PatchSet,
       {num: 1, sha: '4'} as PatchSet,
     ];
-    const revisions: RevisionInfo[] = [
+    element.revisions = [
       createRevision(2),
       createRevision(3),
       createRevision(1),
       createRevision(4),
     ];
-    element.revisionInfo = getInfo(revisions);
-    const sortedRevisions = [
-      createRevision(3) as RevisionInfo,
-      createEditRevision(2) as EditRevisionInfo,
-      createRevision(2) as RevisionInfo,
-      createRevision(1) as RevisionInfo,
-    ];
+    element.revisionInfo = getInfo(element.revisions);
     const expectedResult: DropdownItem[] = [
       {
         disabled: true,
@@ -210,19 +167,14 @@
         value: 'PARENT',
       } as DropdownItem,
     ];
-    assert.deepEqual(
-      element._computeBaseDropdownContent(
-        availablePatches,
-        1 as PatchSetNum,
-        sortedRevisions,
-        element.changeComments,
-        element.revisionInfo
-      ),
-      expectedResult
-    );
+    element.patchNum = 1 as PatchSetNum;
+    element.basePatchNum = 'PARENT' as BasePatchSetNum;
+    await element.updateComplete;
+
+    assert.deepEqual(element.computeBaseDropdownContent(), expectedResult);
   });
 
-  test('_computeBaseDropdownContent called when patchNum updates', async () => {
+  test('computeBaseDropdownContent called when patchNum updates', async () => {
     element.revisions = [
       createRevision(2),
       createRevision(3),
@@ -240,7 +192,7 @@
     element.basePatchNum = 'PARENT' as BasePatchSetNum;
     await element.updateComplete;
 
-    const baseDropDownStub = sinon.stub(element, '_computeBaseDropdownContent');
+    const baseDropDownStub = sinon.stub(element, 'computeBaseDropdownContent');
 
     // Should be recomputed for each available patch
     element.patchNum = 1 as PatchSetNum;
@@ -248,7 +200,7 @@
     assert.equal(baseDropDownStub.callCount, 1);
   });
 
-  test('_computeBaseDropdownContent called when changeComments update', async () => {
+  test('computeBaseDropdownContent called when changeComments update', async () => {
     element.revisions = [
       createRevision(2),
       createRevision(3),
@@ -266,14 +218,14 @@
     await element.updateComplete;
 
     // Should be recomputed for each available patch
-    const baseDropDownStub = sinon.stub(element, '_computeBaseDropdownContent');
+    const baseDropDownStub = sinon.stub(element, 'computeBaseDropdownContent');
     assert.equal(baseDropDownStub.callCount, 0);
     element.changeComments = new ChangeComments();
     await element.updateComplete;
     assert.equal(baseDropDownStub.callCount, 1);
   });
 
-  test('_computePatchDropdownContent called when basePatchNum updates', async () => {
+  test('computePatchDropdownContent called when basePatchNum updates', async () => {
     element.revisions = [
       createRevision(2),
       createRevision(3),
@@ -292,29 +244,27 @@
     await element.updateComplete;
 
     // Should be recomputed for each available patch
-    const baseDropDownStub = sinon.stub(
-      element,
-      '_computePatchDropdownContent'
-    );
+    const baseDropDownStub = sinon.stub(element, 'computePatchDropdownContent');
     element.basePatchNum = 1 as BasePatchSetNum;
     await element.updateComplete;
     assert.equal(baseDropDownStub.callCount, 1);
   });
 
-  test('_computePatchDropdownContent', () => {
-    const availablePatches: PatchSet[] = [
+  test('computePatchDropdownContent', async () => {
+    element.availablePatches = [
       {num: 'edit', sha: '1'} as PatchSet,
       {num: 3, sha: '2'} as PatchSet,
       {num: 2, sha: '3'} as PatchSet,
       {num: 1, sha: '4'} as PatchSet,
     ];
-    const basePatchNum = 1;
-    const sortedRevisions = [
+    element.basePatchNum = 1 as BasePatchSetNum;
+    element.revisions = [
       createRevision(3) as RevisionInfo,
       createEditRevision(2) as EditRevisionInfo,
       createRevision(2, 'description') as RevisionInfo,
       createRevision(1) as RevisionInfo,
     ];
+    await element.updateComplete;
 
     const expectedResult: DropdownItem[] = [
       {
@@ -354,15 +304,7 @@
       } as DropdownItem,
     ];
 
-    assert.deepEqual(
-      element._computePatchDropdownContent(
-        availablePatches,
-        basePatchNum as BasePatchSetNum,
-        sortedRevisions,
-        element.changeComments
-      ),
-      expectedResult
-    );
+    assert.deepEqual(element.computePatchDropdownContent(), expectedResult);
   });
 
   test('filesWeblinks', async () => {
@@ -391,7 +333,7 @@
     );
   });
 
-  test('_computePatchSetCommentsString', () => {
+  test('computePatchSetCommentsString', () => {
     // Test string with unresolved comments.
     const comments: PathToCommentsInfoMap = {
       foo: [
@@ -432,10 +374,7 @@
     element.changeComments = new ChangeComments(comments);
 
     assert.equal(
-      element._computePatchSetCommentsString(
-        element.changeComments,
-        1 as PatchSetNum
-      ),
+      element.computePatchSetCommentsString(1 as PatchSetNum),
       ' (3 comments, 1 unresolved)'
     );
 
@@ -443,23 +382,14 @@
     delete comments['foo'];
     element.changeComments = new ChangeComments(comments);
     assert.equal(
-      element._computePatchSetCommentsString(
-        element.changeComments,
-        1 as PatchSetNum
-      ),
+      element.computePatchSetCommentsString(1 as PatchSetNum),
       ' (2 comments)'
     );
 
     // Test string with no comments.
     delete comments['bar'];
     element.changeComments = new ChangeComments(comments);
-    assert.equal(
-      element._computePatchSetCommentsString(
-        element.changeComments,
-        1 as PatchSetNum
-      ),
-      ''
-    );
+    assert.equal(element.computePatchSetCommentsString(1 as PatchSetNum), '');
   });
 
   test('patch-range-change fires', () => {
diff --git a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.ts b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.ts
index 595de34..9e0027a 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.ts
@@ -50,7 +50,6 @@
   stubReporting,
   stubRestApi,
 } from '../../../test/test-utils';
-import {_testOnly_resetState} from '../../../services/comments/comments-model';
 import {SinonStub} from 'sinon';
 
 const basicFixture = fixtureFromElement('gr-comment-thread');
@@ -63,7 +62,6 @@
 
     setup(() => {
       stubRestApi('getLoggedIn').returns(Promise.resolve(false));
-      _testOnly_resetState();
       element = basicFixture.instantiate();
       element.patchNum = 3 as PatchSetNum;
       element.changeNum = 1 as NumericChangeId;
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.ts b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.ts
index 00edc07..09ac95b 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.ts
@@ -384,11 +384,7 @@
 
     test('delete comment', async () => {
       const stub = stubRestApi('deleteComment').returns(
-        Promise.resolve({
-          id: '1' as UrlEncodedCommentId,
-          updated: '1' as Timestamp,
-          ...createComment(),
-        })
+        Promise.resolve(createComment())
       );
       const openSpy = sinon.spy(element.confirmDeleteOverlay!, 'open');
       element.changeNum = 42 as NumericChangeId;
@@ -1183,6 +1179,7 @@
 
     test('draft prevent save when disabled', async () => {
       const saveStub = sinon.stub(element, 'save').returns(Promise.resolve());
+      sinon.stub(element, '_fireEdit');
       element.showActions = true;
       element.draft = true;
       await flush();
diff --git a/polygerrit-ui/app/services/browser/browser-model.ts b/polygerrit-ui/app/services/browser/browser-model.ts
index db790f6..8cb6575 100644
--- a/polygerrit-ui/app/services/browser/browser-model.ts
+++ b/polygerrit-ui/app/services/browser/browser-model.ts
@@ -33,11 +33,13 @@
 
 const initialState: BrowserState = {};
 
-// Mutable for testing
-let privateState$ = new BehaviorSubject(initialState);
+const privateState$ = new BehaviorSubject(initialState);
 
 export function _testOnly_resetState() {
-  privateState$ = new BehaviorSubject(initialState);
+  // We cannot assign a new subject to privateState$, because all the selectors
+  // have already subscribed to the original subject. So we have to emit the
+  // initial state on the existing subject.
+  privateState$.next({...initialState});
 }
 
 export function _testOnly_setState(state: BrowserState) {
diff --git a/polygerrit-ui/app/services/change/change-model.ts b/polygerrit-ui/app/services/change/change-model.ts
index 962ef4d..7df0c22 100644
--- a/polygerrit-ui/app/services/change/change-model.ts
+++ b/polygerrit-ui/app/services/change/change-model.ts
@@ -40,6 +40,13 @@
 
 const privateState$ = new BehaviorSubject(initialState);
 
+export function _testOnly_resetState() {
+  // We cannot assign a new subject to privateState$, because all the selectors
+  // have already subscribed to the original subject. So we have to emit the
+  // initial state on the existing subject.
+  privateState$.next({...initialState});
+}
+
 // Re-exporting as Observable so that you can only subscribe, but not emit.
 export const changeState$: Observable<ChangeState> = privateState$;
 
diff --git a/polygerrit-ui/app/services/checks/checks-model.ts b/polygerrit-ui/app/services/checks/checks-model.ts
index 75c24b6d..6435252 100644
--- a/polygerrit-ui/app/services/checks/checks-model.ts
+++ b/polygerrit-ui/app/services/checks/checks-model.ts
@@ -126,11 +126,13 @@
   pluginStateSelected: {},
 };
 
-// Mutable for testing
-let privateState$ = new BehaviorSubject(initialState);
+const privateState$ = new BehaviorSubject(initialState);
 
 export function _testOnly_resetState() {
-  privateState$ = new BehaviorSubject(initialState);
+  // We cannot assign a new subject to privateState$, because all the selectors
+  // have already subscribed to the original subject. So we have to emit the
+  // initial state on the existing subject.
+  privateState$.next({...initialState});
 }
 
 export function _testOnly_setState(state: ChecksState) {
diff --git a/polygerrit-ui/app/services/checks/checks-model_test.ts b/polygerrit-ui/app/services/checks/checks-model_test.ts
index dbd3f86..0be0451 100644
--- a/polygerrit-ui/app/services/checks/checks-model_test.ts
+++ b/polygerrit-ui/app/services/checks/checks-model_test.ts
@@ -18,7 +18,6 @@
 import './checks-model';
 import {
   _testOnly_getState,
-  _testOnly_resetState,
   ChecksPatchset,
   updateStateSetLoading,
   updateStateSetProvider,
@@ -52,7 +51,6 @@
 
 suite('checks-model tests', () => {
   test('updateStateSetProvider', () => {
-    _testOnly_resetState();
     updateStateSetProvider(PLUGIN_NAME, ChecksPatchset.LATEST);
     assert.deepEqual(current(), {
       pluginName: PLUGIN_NAME,
@@ -65,7 +63,6 @@
   });
 
   test('loading and first time load', () => {
-    _testOnly_resetState();
     updateStateSetProvider(PLUGIN_NAME, ChecksPatchset.LATEST);
     assert.isFalse(current().loading);
     assert.isTrue(current().firstTimeLoad);
@@ -84,14 +81,12 @@
   });
 
   test('updateStateSetResults', () => {
-    _testOnly_resetState();
     updateStateSetResults(PLUGIN_NAME, RUNS, [], [], ChecksPatchset.LATEST);
     assert.lengthOf(current().runs, 1);
     assert.lengthOf(current().runs[0].results!, 1);
   });
 
   test('updateStateUpdateResult', () => {
-    _testOnly_resetState();
     updateStateSetResults(PLUGIN_NAME, RUNS, [], [], ChecksPatchset.LATEST);
     assert.equal(
       current().runs[0].results![0].summary,
diff --git a/polygerrit-ui/app/services/comments/comments-model.ts b/polygerrit-ui/app/services/comments/comments-model.ts
index 850acbc..5b32465 100644
--- a/polygerrit-ui/app/services/comments/comments-model.ts
+++ b/polygerrit-ui/app/services/comments/comments-model.ts
@@ -51,7 +51,10 @@
 const privateState$ = new BehaviorSubject(initialState);
 
 export function _testOnly_resetState() {
-  privateState$.next(initialState);
+  // We cannot assign a new subject to privateState$, because all the selectors
+  // have already subscribed to the original subject. So we have to emit the
+  // initial state on the existing subject.
+  privateState$.next({...initialState});
 }
 
 // Re-exporting as Observable so that you can only subscribe, but not emit.
@@ -65,11 +68,21 @@
   privateState$.next(state);
 }
 
+export const comments$ = commentState$.pipe(
+  map(commentState => commentState.comments),
+  distinctUntilChanged()
+);
+
 export const drafts$ = commentState$.pipe(
   map(commentState => commentState.drafts),
   distinctUntilChanged()
 );
 
+export const portedComments$ = commentState$.pipe(
+  map(commentState => commentState.portedComments),
+  distinctUntilChanged()
+);
+
 export const discardedDrafts$ = commentState$.pipe(
   map(commentState => commentState.discardedDrafts),
   distinctUntilChanged()
@@ -87,14 +100,22 @@
         commentState.portedComments,
         commentState.portedDrafts
       )
-  ),
-  distinctUntilChanged()
+  )
+);
+
+export const threads$ = changeComments$.pipe(
+  map(changeComments => changeComments.getAllThreadsForChange())
 );
 
 function publishState(state: CommentState) {
   privateState$.next(state);
 }
 
+/** Called when the change number changes. Wipes out all data from the state. */
+export function updateStateReset() {
+  publishState({...initialState});
+}
+
 export function updateStateComments(comments?: {
   [path: string]: CommentInfo[];
 }) {
diff --git a/polygerrit-ui/app/services/comments/comments-model_test.ts b/polygerrit-ui/app/services/comments/comments-model_test.ts
index e389254..30fc7cf 100644
--- a/polygerrit-ui/app/services/comments/comments-model_test.ts
+++ b/polygerrit-ui/app/services/comments/comments-model_test.ts
@@ -22,13 +22,11 @@
 import {
   updateStateDeleteDraft,
   _testOnly_getState,
-  _testOnly_resetState,
   _testOnly_setState,
 } from './comments-model';
 
 suite('comments model tests', () => {
   test('updateStateDeleteDraft', () => {
-    _testOnly_resetState();
     const draft = createDraft();
     draft.id = '1' as UrlEncodedCommentId;
     _testOnly_setState({
diff --git a/polygerrit-ui/app/services/comments/comments-service.ts b/polygerrit-ui/app/services/comments/comments-service.ts
index 16ee2f7..5896b52 100644
--- a/polygerrit-ui/app/services/comments/comments-service.ts
+++ b/polygerrit-ui/app/services/comments/comments-service.ts
@@ -31,7 +31,10 @@
   updateStatePortedDrafts,
   updateStateUndoDiscardedDraft,
   discardedDrafts$,
+  updateStateReset,
 } from './comments-model';
+import {changeNum$, currentPatchNum$} from '../change/change-model';
+import {combineLatest} from 'rxjs';
 
 export class CommentsService {
   private discardedDrafts?: UIDraft[] = [];
@@ -40,31 +43,55 @@
     discardedDrafts$.subscribe(
       discardedDrafts => (this.discardedDrafts = discardedDrafts)
     );
+    changeNum$.subscribe(changeNum => {
+      updateStateReset();
+      if (!changeNum) return;
+      this.reloadComments(changeNum);
+      this.reloadRobotComments(changeNum);
+      this.reloadDrafts(changeNum);
+    });
+    combineLatest([changeNum$, currentPatchNum$]).subscribe(
+      ([changeNum, currentPatchNum]) => {
+        if (!changeNum || !currentPatchNum) return;
+        this.reloadPortedComments(changeNum, currentPatchNum);
+        this.reloadPortedDrafts(changeNum, currentPatchNum);
+      }
+    );
   }
 
-  /**
-   * Load all comments (with drafts and robot comments) for the given change
-   * number. The returned promise resolves when the comments have loaded, but
-   * does not yield the comment data.
-   */
-  // TODO(dhruvsri): listen to changeNum changes or reload event to update
-  // automatically
-  loadAll(changeNum: NumericChangeId, patchNum = CURRENT as RevisionId) {
-    const revision = patchNum;
-    this.restApiService
+  reloadComments(changeNum: NumericChangeId): Promise<void> {
+    return this.restApiService
       .getDiffComments(changeNum)
       .then(comments => updateStateComments(comments));
-    this.restApiService
+  }
+
+  reloadRobotComments(changeNum: NumericChangeId): Promise<void> {
+    return this.restApiService
       .getDiffRobotComments(changeNum)
       .then(robotComments => updateStateRobotComments(robotComments));
-    this.restApiService
+  }
+
+  reloadDrafts(changeNum: NumericChangeId): Promise<void> {
+    return this.restApiService
       .getDiffDrafts(changeNum)
       .then(drafts => updateStateDrafts(drafts));
-    this.restApiService
-      .getPortedComments(changeNum, revision)
+  }
+
+  reloadPortedComments(
+    changeNum: NumericChangeId,
+    patchNum = CURRENT as RevisionId
+  ): Promise<void> {
+    return this.restApiService
+      .getPortedComments(changeNum, patchNum)
       .then(portedComments => updateStatePortedComments(portedComments));
-    this.restApiService
-      .getPortedDrafts(changeNum, revision)
+  }
+
+  reloadPortedDrafts(
+    changeNum: NumericChangeId,
+    patchNum = CURRENT as RevisionId
+  ): Promise<void> {
+    return this.restApiService
+      .getPortedDrafts(changeNum, patchNum)
       .then(portedDrafts => updateStatePortedDrafts(portedDrafts));
   }
 
diff --git a/polygerrit-ui/app/services/comments/comments-service_test.ts b/polygerrit-ui/app/services/comments/comments-service_test.ts
index 604b5c4..a35768e 100644
--- a/polygerrit-ui/app/services/comments/comments-service_test.ts
+++ b/polygerrit-ui/app/services/comments/comments-service_test.ts
@@ -18,109 +18,63 @@
 import '../../test/common-test-setup-karma';
 import {
   createComment,
-  createFixSuggestionInfo,
+  createParsedChange,
+  TEST_NUMERIC_CHANGE_ID,
 } from '../../test/test-data-generators';
-import {stubRestApi} from '../../test/test-utils';
-import {
-  NumericChangeId,
-  RobotId,
-  RobotRunId,
-  Timestamp,
-  UrlEncodedCommentId,
-} from '../../types/common';
+import {stubRestApi, waitUntil, waitUntilCalled} from '../../test/test-utils';
 import {appContext} from '../app-context';
 import {CommentsService} from './comments-service';
+import {updateState as updateChangeState} from '../change/change-model';
+import {
+  GerritView,
+  updateState as updateRouterState,
+} from '../router/router-model';
+import {comments$, portedComments$} from './comments-model';
+import {PathToCommentsInfoMap} from '../../types/common';
 
 suite('change service tests', () => {
-  let commentsService: CommentsService;
-
-  test('loads logged-out', () => {
-    const changeNum = 1234 as NumericChangeId;
-    commentsService = new CommentsService(appContext.restApiService);
-    stubRestApi('getLoggedIn').returns(Promise.resolve(false));
+  test('loads comments', async () => {
+    new CommentsService(appContext.restApiService);
     const diffCommentsSpy = stubRestApi('getDiffComments').returns(
-      Promise.resolve({
-        'foo.c': [
-          {
-            ...createComment(),
-            id: '123' as UrlEncodedCommentId,
-            message: 'Done',
-            updated: '2017-02-08 16:40:49' as Timestamp,
-          },
-        ],
-      })
+      Promise.resolve({'foo.c': [createComment()]})
     );
     const diffRobotCommentsSpy = stubRestApi('getDiffRobotComments').returns(
-      Promise.resolve({
-        'foo.c': [
-          {
-            ...createComment(),
-            id: '321' as UrlEncodedCommentId,
-            message: 'Done',
-            updated: '2017-02-08 16:40:49' as Timestamp,
-            robot_id: 'robot_1' as RobotId,
-            robot_run_id: 'run_1' as RobotRunId,
-            properties: {},
-            fix_suggestions: [
-              createFixSuggestionInfo('fix_1'),
-              createFixSuggestionInfo('fix_2'),
-            ],
-          },
-        ],
-      })
+      Promise.resolve({})
     );
     const diffDraftsSpy = stubRestApi('getDiffDrafts').returns(
       Promise.resolve({})
     );
-
-    commentsService.loadAll(changeNum);
-    assert.isTrue(diffCommentsSpy.calledWithExactly(changeNum));
-    assert.isTrue(diffRobotCommentsSpy.calledWithExactly(changeNum));
-    assert.isTrue(diffDraftsSpy.calledWithExactly(changeNum));
-  });
-
-  test('loads logged-in', () => {
-    const changeNum = 1234 as NumericChangeId;
-
-    stubRestApi('getLoggedIn').returns(Promise.resolve(true));
-    const diffCommentsSpy = stubRestApi('getDiffComments').returns(
-      Promise.resolve({
-        'foo.c': [
-          {
-            ...createComment(),
-            id: '123' as UrlEncodedCommentId,
-            message: 'Done',
-            updated: '2017-02-08 16:40:49' as Timestamp,
-          },
-        ],
-      })
+    const portedCommentsSpy = stubRestApi('getPortedComments').returns(
+      Promise.resolve({'foo.c': [createComment()]})
     );
-    const diffRobotCommentsSpy = stubRestApi('getDiffRobotComments').returns(
-      Promise.resolve({
-        'foo.c': [
-          {
-            ...createComment(),
-            id: '321' as UrlEncodedCommentId,
-            message: 'Done',
-            updated: '2017-02-08 16:40:49' as Timestamp,
-            robot_id: 'robot_1' as RobotId,
-            robot_run_id: 'run_1' as RobotRunId,
-            properties: {},
-            fix_suggestions: [
-              createFixSuggestionInfo('fix_1'),
-              createFixSuggestionInfo('fix_2'),
-            ],
-          },
-        ],
-      })
-    );
-    const diffDraftsSpy = stubRestApi('getDiffDrafts').returns(
+    const portedDraftsSpy = stubRestApi('getPortedDrafts').returns(
       Promise.resolve({})
     );
+    let comments: PathToCommentsInfoMap = {};
+    comments$.subscribe(c => (comments = c));
+    let portedComments: PathToCommentsInfoMap = {};
+    portedComments$.subscribe(c => (portedComments = c));
 
-    commentsService.loadAll(changeNum);
-    assert.isTrue(diffCommentsSpy.calledWithExactly(changeNum));
-    assert.isTrue(diffRobotCommentsSpy.calledWithExactly(changeNum));
-    assert.isTrue(diffDraftsSpy.calledWithExactly(changeNum));
+    updateRouterState(GerritView.CHANGE, TEST_NUMERIC_CHANGE_ID);
+    updateChangeState(createParsedChange());
+
+    await waitUntilCalled(diffCommentsSpy, 'diffCommentsSpy');
+    await waitUntilCalled(diffRobotCommentsSpy, 'diffRobotCommentsSpy');
+    await waitUntilCalled(diffDraftsSpy, 'diffDraftsSpy');
+    await waitUntilCalled(portedCommentsSpy, 'portedCommentsSpy');
+    await waitUntilCalled(portedDraftsSpy, 'portedDraftsSpy');
+    await waitUntil(
+      () => Object.keys(comments).length > 0,
+      'comment in model not set'
+    );
+    await waitUntil(
+      () => Object.keys(portedComments).length > 0,
+      'ported comment in model not set'
+    );
+
+    assert.equal(comments['foo.c'].length, 1);
+    assert.equal(comments['foo.c'][0].id, '12345');
+    assert.equal(portedComments['foo.c'].length, 1);
+    assert.equal(portedComments['foo.c'][0].id, '12345');
   });
 });
diff --git a/polygerrit-ui/app/services/router/router-model.ts b/polygerrit-ui/app/services/router/router-model.ts
index b3cdf9e..ae3d848 100644
--- a/polygerrit-ui/app/services/router/router-model.ts
+++ b/polygerrit-ui/app/services/router/router-model.ts
@@ -47,6 +47,13 @@
 
 const privateState$ = new BehaviorSubject<RouterState>(initialState);
 
+export function _testOnly_resetState() {
+  // We cannot assign a new subject to privateState$, because all the selectors
+  // have already subscribed to the original subject. So we have to emit the
+  // initial state on the existing subject.
+  privateState$.next({...initialState});
+}
+
 // Re-exporting as Observable so that you can only subscribe, but not emit.
 export const routerState$: Observable<RouterState> = privateState$;
 
diff --git a/polygerrit-ui/app/services/user/user-model.ts b/polygerrit-ui/app/services/user/user-model.ts
index 000887c..df307d6 100644
--- a/polygerrit-ui/app/services/user/user-model.ts
+++ b/polygerrit-ui/app/services/user/user-model.ts
@@ -37,11 +37,13 @@
   diffPreferences: createDefaultDiffPrefs(),
 };
 
-// Mutable for testing
-let privateState$ = new BehaviorSubject(initialState);
+const privateState$ = new BehaviorSubject(initialState);
 
 export function _testOnly_resetState() {
-  privateState$ = new BehaviorSubject(initialState);
+  // We cannot assign a new subject to privateState$, because all the selectors
+  // have already subscribed to the original subject. So we have to emit the
+  // initial state on the existing subject.
+  privateState$.next({...initialState});
 }
 
 export function _testOnly_setState(state: UserState) {
diff --git a/polygerrit-ui/app/test/common-test-setup.ts b/polygerrit-ui/app/test/common-test-setup.ts
index bd5504a..05adb41 100644
--- a/polygerrit-ui/app/test/common-test-setup.ts
+++ b/polygerrit-ui/app/test/common-test-setup.ts
@@ -45,6 +45,12 @@
 import {updatePreferences} from '../services/user/user-model';
 import {createDefaultPreferences} from '../constants/constants';
 import {appContext} from '../services/app-context';
+import {_testOnly_resetState as resetBrowserState} from '../services/browser/browser-model';
+import {_testOnly_resetState as resetChangeState} from '../services/change/change-model';
+import {_testOnly_resetState as resetChecksState} from '../services/checks/checks-model';
+import {_testOnly_resetState as resetCommentsState} from '../services/comments/comments-model';
+import {_testOnly_resetState as resetRouterState} from '../services/router/router-model';
+import {_testOnly_resetState as resetUserState} from '../services/user/user-model';
 
 declare global {
   interface Window {
@@ -106,6 +112,14 @@
   // tests.
   initGlobalVariables();
   _testOnly_initGerritPluginApi();
+
+  resetBrowserState();
+  resetChangeState();
+  resetChecksState();
+  resetCommentsState();
+  resetRouterState();
+  resetUserState();
+
   const shortcuts = appContext.shortcutsService;
   assert.isTrue(shortcuts._testOnly_isEmpty());
   const selection = document.getSelection();
diff --git a/polygerrit-ui/app/test/test-data-generators.ts b/polygerrit-ui/app/test/test-data-generators.ts
index dd56ce2..91cd2f3 100644
--- a/polygerrit-ui/app/test/test-data-generators.ts
+++ b/polygerrit-ui/app/test/test-data-generators.ts
@@ -95,7 +95,12 @@
 import {AppElementChangeViewParams} from '../elements/gr-app-types';
 import {CommitInfoWithRequiredCommit} from '../elements/change/gr-change-metadata/gr-change-metadata';
 import {WebLinkInfo} from '../types/diff';
-import {createCommentThreads, UIComment, UIDraft} from '../utils/comment-util';
+import {
+  createCommentThreads,
+  UIComment,
+  UIDraft,
+  UIHuman,
+} from '../utils/comment-util';
 import {GerritView} from '../services/router/router-model';
 import {ChangeComments} from '../elements/diff/gr-comment-api/gr-comment-api';
 import {EditRevisionInfo, ParsedChangeInfo} from '../types/types';
@@ -488,7 +493,7 @@
   };
 }
 
-export function createComment(): UIComment {
+export function createComment(): UIHuman {
   return {
     patch_set: 1 as PatchSetNum,
     id: '12345' as UrlEncodedCommentId,
diff --git a/polygerrit-ui/app/test/test-utils.ts b/polygerrit-ui/app/test/test-utils.ts
index 4a513f8..63c125e 100644
--- a/polygerrit-ui/app/test/test-utils.ts
+++ b/polygerrit-ui/app/test/test-utils.ts
@@ -19,7 +19,7 @@
 import {_testOnly_resetEndpoints} from '../elements/shared/gr-js-api-interface/gr-plugin-endpoints';
 import {appContext} from '../services/app-context';
 import {RestApiService} from '../services/gr-rest-api/gr-rest-api';
-import {SinonSpy} from 'sinon';
+import {SinonSpy, SinonStub} from 'sinon';
 import {StorageService} from '../services/storage/gr-storage';
 import {AuthService} from '../services/gr-auth/gr-auth';
 import {ReportingService} from '../services/gr-reporting/gr-reporting';
@@ -185,6 +185,7 @@
 ): Promise<void> {
   const start = Date.now();
   let sleep = 0;
+  if (predicate()) return Promise.resolve();
   return new Promise((resolve, reject) => {
     const waiter = () => {
       if (predicate()) {
@@ -200,6 +201,10 @@
   });
 }
 
+export function waitUntilCalled(stub: SinonStub, name: string) {
+  return waitUntil(() => stub.called, `${name} was not called`);
+}
+
 /**
  * Promisify an event callback to simplify async...await tests.
  *
diff --git a/polygerrit-ui/app/utils/patch-set-util.ts b/polygerrit-ui/app/utils/patch-set-util.ts
index ee4ed8b..921850a 100644
--- a/polygerrit-ui/app/utils/patch-set-util.ts
+++ b/polygerrit-ui/app/utils/patch-set-util.ts
@@ -103,7 +103,7 @@
       return rev;
     }
   }
-  console.warn('no revision found');
+  if (revisions.length > 0) console.warn('no revision found');
   return;
 }