diff --git a/extension.json b/extension.json
index 4a1b956a99..9bcaee6264 100644
--- a/extension.json
+++ b/extension.json
@@ -194,6 +194,7 @@
 			"services": [
 				"RevisionLookup",
 				"TempUserCreator",
+				"UserFactory",
 				"UserOptionsLookup",
 				"WatchlistManager",
 				"ContentTransformer",
diff --git a/includes/ApiVisualEditor.php b/includes/ApiVisualEditor.php
index ea7a841607..d6a4c5c731 100644
--- a/includes/ApiVisualEditor.php
+++ b/includes/ApiVisualEditor.php
@@ -35,10 +35,12 @@ use MediaWiki\Revision\RevisionLookup;
 use MediaWiki\SpecialPage\SpecialPageFactory;
 use MediaWiki\Title\Title;
 use MediaWiki\User\TempUser\TempUserCreator;
+use MediaWiki\User\UserFactory;
 use MediaWiki\User\UserOptionsLookup;
 use MediaWiki\Watchlist\WatchlistManager;
 use MessageLocalizer;
 use RequestContext;
+use User;
 use Wikimedia\ParamValidator\ParamValidator;
 use WikitextContent;
 
@@ -48,6 +50,7 @@ class ApiVisualEditor extends ApiBase {
 
 	private RevisionLookup $revisionLookup;
 	private TempUserCreator $tempUserCreator;
+	private UserFactory $userFactory;
 	private UserOptionsLookup $userOptionsLookup;
 	private WatchlistManager $watchlistManager;
 	private ContentTransformer $contentTransformer;
@@ -62,6 +65,7 @@ class ApiVisualEditor extends ApiBase {
 		string $name,
 		RevisionLookup $revisionLookup,
 		TempUserCreator $tempUserCreator,
+		UserFactory $userFactory,
 		UserOptionsLookup $userOptionsLookup,
 		WatchlistManager $watchlistManager,
 		ContentTransformer $contentTransformer,
@@ -77,6 +81,7 @@ class ApiVisualEditor extends ApiBase {
 		$this->setStats( $statsdDataFactory );
 		$this->revisionLookup = $revisionLookup;
 		$this->tempUserCreator = $tempUserCreator;
+		$this->userFactory = $userFactory;
 		$this->userOptionsLookup = $userOptionsLookup;
 		$this->watchlistManager = $watchlistManager;
 		$this->contentTransformer = $contentTransformer;
@@ -96,6 +101,20 @@ class ApiVisualEditor extends ApiBase {
 		);
 	}
 
+	/**
+	 * @see ApiParse::getUserForPreview
+	 * @return User
+	 */
+	private function getUserForPreview() {
+		$user = $this->getUser();
+		if ( $this->tempUserCreator->shouldAutoCreate( $user, 'edit' ) ) {
+			return $this->userFactory->newUnsavedTempUser(
+				$this->tempUserCreator->getStashedName( $this->getRequest()->getSession() )
+			);
+		}
+		return $user;
+	}
+
 	/**
 	 * Run wikitext through the parser's Pre-Save-Transform
 	 *
@@ -108,7 +127,7 @@ class ApiVisualEditor extends ApiBase {
 		return $this->contentTransformer->preSaveTransform(
 			$content,
 			$title,
-			$this->getUser(),
+			$this->getUserForPreview(),
 			$this->wikiPageFactory->newFromTitle( $title )->makeParserOptions( $this->getContext() )
 		)
 		->serialize( 'text/x-wiki' );
diff --git a/modules/ve-mw/ce/nodes/ve.ce.MWSignatureNode.js b/modules/ve-mw/ce/nodes/ve.ce.MWSignatureNode.js
index ed13a1e437..a61dd928dc 100644
--- a/modules/ve-mw/ce/nodes/ve.ce.MWSignatureNode.js
+++ b/modules/ve-mw/ce/nodes/ve.ce.MWSignatureNode.js
@@ -106,45 +106,62 @@ ve.ce.MWSignatureNode.prototype.onTeardown = function () {
  * @inheritdoc ve.ce.GeneratedContentNode
  */
 ve.ce.MWSignatureNode.prototype.generateContents = function () {
-	// Parsoid doesn't support pre-save transforms. PHP parser doesn't support Parsoid's
-	// meta attributes (that may or may not be required).
-
-	// We could try hacking up one (or even both) of these, but just calling the two parsers
-	// in order seems slightly saner.
-
-	// We must have only one top-level node, this is the easiest way.
-	var wikitext = '<span>~~~~</span>';
 	var doc = this.getModel().getDocument();
+	var abortable, aborted;
+	var abortedPromise = ve.createDeferred().reject( 'http',
+		{ textStatus: 'abort', exception: 'abort' } ).promise();
 
-	var deferred = ve.createDeferred();
-	var xhr = ve.init.target.getContentApi( doc ).post( {
-		action: 'parse',
-		text: wikitext,
-		contentmodel: 'wikitext',
-		prop: 'text',
-		onlypst: true
-	} )
-		.done( function ( resp ) {
-			var wt = ve.getProp( resp, 'parse', 'text' );
-			if ( wt ) {
-				ve.init.target.parseWikitextFragment( wt, true, doc ).then( function ( response ) {
-					if ( ve.getProp( response, 'visualeditor', 'result' ) !== 'success' ) {
-						deferred.reject();
-						return;
-					}
+	function abort() {
+		aborted = true;
+		if ( abortable && abortable.abort ) {
+			abortable.abort();
+		}
+	}
 
-					// Simplified case of template rendering, don't need to worry about filtering etc
-					deferred.resolve( $( response.visualeditor.content ).contents().toArray() );
-				} );
-			} else {
-				deferred.reject();
+	// Acquire a temporary user username before previewing, so that signatures
+	// display the temp user instead of IP user. (T331397)
+	return mw.user.acquireTempUserName()
+		.then( function () {
+			if ( aborted ) {
+				return abortedPromise;
 			}
-		} )
-		.fail( function () {
-			deferred.reject();
-		} );
 
-	return deferred.promise( { abort: xhr.abort } );
+			// We must have only one top-level node, this is the easiest way.
+			var wikitext = '<span>~~~~</span>';
+
+			// Parsoid doesn't support pre-save transforms. PHP parser doesn't support Parsoid's
+			// meta attributes (that may or may not be required).
+			// We could try hacking up one (or even both) of these, but just calling the two parsers
+			// in order seems slightly saner.
+			return ( abortable = ve.init.target.getContentApi( doc ).post( {
+				action: 'parse',
+				text: wikitext,
+				contentmodel: 'wikitext',
+				prop: 'text',
+				onlypst: true
+			} ) );
+		} )
+		.then( function ( pstResponse ) {
+			if ( aborted ) {
+				return abortedPromise;
+			}
+			var wikitext = ve.getProp( pstResponse, 'parse', 'text' );
+			if ( !wikitext ) {
+				return ve.createDeferred().reject();
+			}
+			return ( abortable = ve.init.target.parseWikitextFragment( wikitext, true, doc ) );
+		} )
+		.then( function ( parseResponse ) {
+			if ( aborted ) {
+				return abortedPromise;
+			}
+			if ( ve.getProp( parseResponse, 'visualeditor', 'result' ) !== 'success' ) {
+				return ve.createDeferred().reject();
+			}
+			// Simplified case of template rendering, don't need to worry about filtering etc
+			return $( parseResponse.visualeditor.content ).contents().toArray();
+		} )
+		.promise( { abort: abort } );
 };
 
 /* Registration */
diff --git a/modules/ve-mw/init/targets/ve.init.mw.ArticleTarget.js b/modules/ve-mw/init/targets/ve.init.mw.ArticleTarget.js
index 1e413e452a..c3b59c847e 100644
--- a/modules/ve-mw/init/targets/ve.init.mw.ArticleTarget.js
+++ b/modules/ve-mw/init/targets/ve.init.mw.ArticleTarget.js
@@ -915,14 +915,18 @@ ve.init.mw.ArticleTarget.prototype.onSaveDialogReview = function () {
 	if ( !this.saveDialog.hasDiff ) {
 		this.emit( 'saveReview' );
 		this.saveDialog.pushPending();
-		if ( this.pageExists ) {
-			// Has no callback, handled via target.showChangesDiff
-			this.showChanges( this.getDocToSave() );
-		} else {
-			this.serialize( this.getDocToSave() ).then( function ( data ) {
-				target.onSaveDialogReviewComplete( data.content );
-			} );
-		}
+		// Acquire a temporary user username before diffing, so that signatures and
+		// user-related magic words display the temp user instead of IP user in the diff. (T331397)
+		mw.user.acquireTempUserName().then( function () {
+			if ( target.pageExists ) {
+				// Has no callback, handled via target.showChangesDiff
+				target.showChanges( target.getDocToSave() );
+			} else {
+				target.serialize( target.getDocToSave() ).then( function ( data ) {
+					target.onSaveDialogReviewComplete( data.content );
+				} );
+			}
+		} );
 	} else {
 		this.saveDialog.swapPanel( 'review' );
 	}
@@ -952,19 +956,23 @@ ve.init.mw.ArticleTarget.prototype.onSaveDialogPreview = function () {
 			params.variant = mw.config.get( 'wgUserVariant' );
 		}
 
-		api.post( ve.extendObject( params, {
-			action: 'parse',
-			title: this.getPageName(),
-			text: this.getDocToSave(),
-			pst: true,
-			preview: true,
-			sectionpreview: this.section !== null,
-			disableeditsection: true,
-			uselang: mw.config.get( 'wgUserLanguage' ),
-			useskin: mw.config.get( 'skin' ),
-			mobileformat: OO.ui.isMobile(),
-			prop: [ 'text', 'categorieshtml', 'displaytitle', 'subtitle', 'modules', 'jsconfigvars' ]
-		} ) ).then( function ( response ) {
+		// Acquire a temporary user username before previewing, so that signatures and
+		// user-related magic words display the temp user instead of IP user in the preview. (T331397)
+		mw.user.acquireTempUserName().then( function () {
+			return api.post( ve.extendObject( params, {
+				action: 'parse',
+				title: target.getPageName(),
+				text: target.getDocToSave(),
+				pst: true,
+				preview: true,
+				sectionpreview: target.section !== null,
+				disableeditsection: true,
+				uselang: mw.config.get( 'wgUserLanguage' ),
+				useskin: mw.config.get( 'skin' ),
+				mobileformat: OO.ui.isMobile(),
+				prop: [ 'text', 'categorieshtml', 'displaytitle', 'subtitle', 'modules', 'jsconfigvars' ]
+			} ) );
+		} ).then( function ( response ) {
 			target.saveDialog.showPreview( response );
 		}, function ( errorCode, details ) {
 			target.saveDialog.showPreview( target.extractErrorMessages( details ) );
@@ -1035,14 +1043,18 @@ ve.init.mw.ArticleTarget.prototype.getVisualDiffGeneratorPromise = function () {
 		}
 
 		if ( mode === 'source' ) {
-			var newRevPromise = target.getContentApi().post( {
-				action: 'visualeditor',
-				paction: 'parse',
-				page: target.getPageName(),
-				wikitext: target.getSurface().getDom(),
-				section: target.section,
-				stash: 0,
-				pst: true
+			// Acquire a temporary user username before diffing, so that signatures and
+			// user-related magic words display the temp user instead of IP user in the diff. (T331397)
+			var newRevPromise = mw.user.acquireTempUserName().then( function () {
+				return target.getContentApi().post( {
+					action: 'visualeditor',
+					paction: 'parse',
+					page: target.getPageName(),
+					wikitext: target.getSurface().getDom(),
+					section: target.section,
+					stash: 0,
+					pst: true
+				} );
 			} ).then( function ( response ) {
 				// Source mode always fetches the whole document, so set section=null to unwrap sections
 				return mw.libs.ve.diffLoader.getModelFromResponse( response, null );
diff --git a/modules/ve-mw/init/targets/ve.init.mw.Target.js b/modules/ve-mw/init/targets/ve.init.mw.Target.js
index 3749c8a331..9cda401d68 100644
--- a/modules/ve-mw/init/targets/ve.init.mw.Target.js
+++ b/modules/ve-mw/init/targets/ve.init.mw.Target.js
@@ -615,13 +615,41 @@ ve.init.mw.Target.prototype.getWikitextFragment = function ( doc, useRevision )
  * @return {jQuery.Promise} Abortable promise
  */
 ve.init.mw.Target.prototype.parseWikitextFragment = function ( wikitext, pst, doc ) {
-	return this.getContentApi( doc ).post( {
-		action: 'visualeditor',
-		paction: 'parsefragment',
-		page: this.getPageName( doc ),
-		wikitext: wikitext,
-		pst: pst
-	} );
+	var target = this;
+	var abortable, aborted;
+	var abortedPromise = ve.createDeferred().reject( 'http',
+		{ textStatus: 'abort', exception: 'abort' } ).promise();
+
+	function abort() {
+		aborted = true;
+		if ( abortable && abortable.abort ) {
+			abortable.abort();
+		}
+	}
+
+	// Acquire a temporary user username before previewing or diffing, so that signatures and
+	// user-related magic words display the temp user instead of IP user in the preview. (T331397)
+	var tempUserNamePromise;
+	if ( pst ) {
+		tempUserNamePromise = mw.user.acquireTempUserName();
+	} else {
+		tempUserNamePromise = ve.createDeferred().resolve( null );
+	}
+
+	return tempUserNamePromise
+		.then( function () {
+			if ( aborted ) {
+				return abortedPromise;
+			}
+			return ( abortable = target.getContentApi( doc ).post( {
+				action: 'visualeditor',
+				paction: 'parsefragment',
+				page: target.getPageName( doc ),
+				wikitext: wikitext,
+				pst: pst
+			} ) );
+		} )
+		.promise( { abort: abort } );
 };
 
 /**