diff --git a/packages/compiler-cli/src/ngtsc/annotations/src/component.ts b/packages/compiler-cli/src/ngtsc/annotations/src/component.ts
index 7706e29874..ead2eb8ab0 100644
--- a/packages/compiler-cli/src/ngtsc/annotations/src/component.ts
+++ b/packages/compiler-cli/src/ngtsc/annotations/src/component.ts
@@ -52,7 +52,7 @@ export class ComponentDecoratorHandler implements
       private scopeReader: ComponentScopeReader, private scopeRegistry: LocalModuleScopeRegistry,
       private isCore: boolean, private resourceLoader: ResourceLoader, private rootDirs: string[],
       private defaultPreserveWhitespaces: boolean, private i18nUseExternalIds: boolean,
-      private i18nLegacyMessageIdFormat: string, private moduleResolver: ModuleResolver,
+      private enableI18nLegacyMessageIdFormat: boolean, private moduleResolver: ModuleResolver,
       private cycleAnalyzer: CycleAnalyzer, private refEmitter: ReferenceEmitter,
       private defaultImportRecorder: DefaultImportRecorder,
       private annotateForClosureCompiler: boolean,
@@ -710,7 +710,7 @@ export class ComponentDecoratorHandler implements
         preserveWhitespaces,
         interpolationConfig: interpolation,
         range: templateRange, escapedString,
-        i18nLegacyMessageIdFormat: this.i18nLegacyMessageIdFormat, ...options,
+        enableI18nLegacyMessageIdFormat: this.enableI18nLegacyMessageIdFormat, ...options,
       }),
       template: templateStr, templateUrl,
       isInline: component.has('template'),
diff --git a/packages/compiler-cli/src/ngtsc/annotations/test/component_spec.ts b/packages/compiler-cli/src/ngtsc/annotations/test/component_spec.ts
index 5cb2b5b395..c44841cbe6 100644
--- a/packages/compiler-cli/src/ngtsc/annotations/test/component_spec.ts
+++ b/packages/compiler-cli/src/ngtsc/annotations/test/component_spec.ts
@@ -63,7 +63,7 @@ runInEachFileSystem(() => {
           reflectionHost, evaluator, metaRegistry, metaReader, scopeRegistry, scopeRegistry,
           /* isCore */ false, new NoopResourceLoader(), /* rootDirs */[''],
           /* defaultPreserveWhitespaces */ false, /* i18nUseExternalIds */ true,
-          /* i18nLegacyMessageIdFormat */ '', moduleResolver, cycleAnalyzer, refEmitter,
+          /* enableI18nLegacyMessageIdFormat */ false, moduleResolver, cycleAnalyzer, refEmitter,
           NOOP_DEFAULT_IMPORT_RECORDER, /* annotateForClosureCompiler */ false);
       const TestCmp = getDeclaration(program, _('/entry.ts'), 'TestCmp', isNamedClassDeclaration);
       const detected = handler.detect(TestCmp, reflectionHost.getDecoratorsOfDeclaration(TestCmp));
diff --git a/packages/compiler-cli/src/ngtsc/program.ts b/packages/compiler-cli/src/ngtsc/program.ts
index 9cc86026ee..7378985406 100644
--- a/packages/compiler-cli/src/ngtsc/program.ts
+++ b/packages/compiler-cli/src/ngtsc/program.ts
@@ -623,9 +623,9 @@ export class NgtscProgram implements api.Program {
           this.reflector, evaluator, metaRegistry, this.metaReader !, scopeReader, scopeRegistry,
           this.isCore, this.resourceManager, this.rootDirs,
           this.options.preserveWhitespaces || false, this.options.i18nUseExternalIds !== false,
-          this.getI18nLegacyMessageFormat(), this.moduleResolver, this.cycleAnalyzer,
-          this.refEmitter, this.defaultImportTracker, this.closureCompilerEnabled,
-          this.incrementalDriver),
+          this.options.enableI18nLegacyMessageIdFormat !== false, this.moduleResolver,
+          this.cycleAnalyzer, this.refEmitter, this.defaultImportTracker,
+          this.closureCompilerEnabled, this.incrementalDriver),
       new DirectiveDecoratorHandler(
           this.reflector, evaluator, metaRegistry, this.defaultImportTracker, this.isCore,
           this.closureCompilerEnabled),
@@ -648,11 +648,6 @@ export class NgtscProgram implements api.Program {
         this.options.compileNonExportedClasses !== false);
   }
 
-  private getI18nLegacyMessageFormat(): string {
-    return this.options.enableI18nLegacyMessageIdFormat !== false && this.options.i18nInFormat ||
-        '';
-  }
-
   private get reflector(): TypeScriptReflectionHost {
     if (this._reflector === undefined) {
       this._reflector = new TypeScriptReflectionHost(this.tsProgram.getTypeChecker());
diff --git a/packages/compiler-cli/src/transformers/api.ts b/packages/compiler-cli/src/transformers/api.ts
index 0a806692e9..48c178363e 100644
--- a/packages/compiler-cli/src/transformers/api.ts
+++ b/packages/compiler-cli/src/transformers/api.ts
@@ -263,11 +263,10 @@ export interface CompilerOptions extends ts.CompilerOptions {
   i18nUseExternalIds?: boolean;
 
   /**
-   * Render `$localize` message ids with the legacy format (xlf, xlf2 or xmb) specified in
-   * `i18nInFormat`.
+   * Render `$localize` messages with legacy format ids.
    *
-   * This is only active if we are building with `enableIvy: true` and a valid
-   * `i18nInFormat` has been provided. The default value for now is `true`.
+   * This is only active if we are building with `enableIvy: true`.
+   * The default value for now is `true`.
    *
    * Use this option when use are using the `$localize` based localization messages but
    * have not migrated the translation files to use the new `$localize` message id format.
diff --git a/packages/compiler-cli/test/compliance/mock_compile.ts b/packages/compiler-cli/test/compliance/mock_compile.ts
index 6d55d1a376..e0c905ded7 100644
--- a/packages/compiler-cli/test/compliance/mock_compile.ts
+++ b/packages/compiler-cli/test/compliance/mock_compile.ts
@@ -210,7 +210,8 @@ export function compile(
       scripts, {
         target: ts.ScriptTarget.ES2015,
         module: ts.ModuleKind.ES2015,
-        moduleResolution: ts.ModuleResolutionKind.NodeJs, ...options,
+        moduleResolution: ts.ModuleResolutionKind.NodeJs,
+        enableI18nLegacyMessageIdFormat: false, ...options,
       },
       mockCompilerHost);
   program.emit();
diff --git a/packages/compiler-cli/test/compliance/r3_view_compiler_i18n_spec.ts b/packages/compiler-cli/test/compliance/r3_view_compiler_i18n_spec.ts
index b1af024abd..9133c2c705 100644
--- a/packages/compiler-cli/test/compliance/r3_view_compiler_i18n_spec.ts
+++ b/packages/compiler-cli/test/compliance/r3_view_compiler_i18n_spec.ts
@@ -3457,6 +3457,38 @@ describe('i18n support in the template compiler', () => {
     });
   });
 
+  describe('$localize legacy message ids', () => {
+    it('should add legacy message ids if `enableI18nLegacyMessageIdFormat` is true', () => {
+      const input = `<div i18n>Some Message</div>`;
+
+      const output = String.raw `
+        var $I18N_0$;
+        if (ngI18nClosureMode) { … }
+        else {
+            $I18N_0$ = $localize \`:␟ec93160d6d6a8822214060dd7938bf821c22b226␟6795333002533525253:Some Message\`;
+        }
+        …
+        `;
+
+      verify(input, output, {compilerOptions: {enableI18nLegacyMessageIdFormat: true}});
+    });
+
+    it('should add legacy message ids if `enableI18nLegacyMessageIdFormat` is undefined', () => {
+      const input = `<div i18n>Some Message</div>`;
+
+      const output = String.raw `
+        var $I18N_0$;
+        if (ngI18nClosureMode) { … }
+        else {
+            $I18N_0$ = $localize \`:␟ec93160d6d6a8822214060dd7938bf821c22b226␟6795333002533525253:Some Message\`;
+        }
+        …
+        `;
+
+      verify(input, output, {compilerOptions: {enableI18nLegacyMessageIdFormat: undefined}});
+    });
+  });
+
   describe('errors', () => {
     const verifyNestedSectionsError = (errorThrown: any, expectedErrorText: string) => {
       expect(errorThrown.ngParseErrors.length).toBe(1);
diff --git a/packages/compiler-cli/test/ngtsc/ngtsc_spec.ts b/packages/compiler-cli/test/ngtsc/ngtsc_spec.ts
index 88cdaaad29..877b8dc0c7 100644
--- a/packages/compiler-cli/test/ngtsc/ngtsc_spec.ts
+++ b/packages/compiler-cli/test/ngtsc/ngtsc_spec.ts
@@ -2454,82 +2454,23 @@ runInEachFileSystem(os => {
       expect(jsContents).not.toContain('MSG_EXTERNAL_');
     });
 
-    it('should render legacy id when `enableI18nLegacyMessageIdFormat` is not false and `i18nInFormat` is set to "xlf"',
-       () => {
-         env.tsconfig({i18nInFormat: 'xlf'});
-         env.write(`test.ts`, `
+    it('should render legacy ids when `enableI18nLegacyMessageIdFormat` is not false', () => {
+      env.tsconfig({});
+      env.write(`test.ts`, `
         import {Component} from '@angular/core';
         @Component({
           selector: 'test',
           template: '<div i18n>Some text</div>'
         })
         class FooCmp {}`);
-         env.driveMain();
-         const jsContents = env.getContents('test.js');
-         expect(jsContents).toContain(':@@5dbba0a3da8dff890e20cf76eb075d58900fbcd3:Some text');
-       });
+      env.driveMain();
+      const jsContents = env.getContents('test.js');
+      expect(jsContents)
+          .toContain(
+              '":\\u241F5dbba0a3da8dff890e20cf76eb075d58900fbcd3\\u241F8321000940098097247:Some text"');
+    });
 
-    it('should render legacy id when `enableI18nLegacyMessageIdFormat` is not false and `i18nInFormat` is set to "xliff"',
-       () => {
-         env.tsconfig({i18nInFormat: 'xliff'});
-         env.write(`test.ts`, `
-        import {Component} from '@angular/core';
-        @Component({
-          selector: 'test',
-          template: '<div i18n>Some text</div>'
-        })
-        class FooCmp {}`);
-         env.driveMain();
-         const jsContents = env.getContents('test.js');
-         expect(jsContents).toContain(':@@5dbba0a3da8dff890e20cf76eb075d58900fbcd3:Some text');
-       });
-
-    it('should render legacy id when `enableI18nLegacyMessageIdFormat` is not false and `i18nInFormat` is set to "xlf2"',
-       () => {
-         env.tsconfig({i18nInFormat: 'xlf2'});
-         env.write(`test.ts`, `
-        import {Component} from '@angular/core';
-        @Component({
-          selector: 'test',
-          template: '<div i18n>Some text</div>'
-        })
-        class FooCmp {}`);
-         env.driveMain();
-         const jsContents = env.getContents('test.js');
-         expect(jsContents).toContain(':@@8321000940098097247:Some text');
-       });
-
-    it('should render legacy id when `enableI18nLegacyMessageIdFormat` is not false and `i18nInFormat` is set to "xliff2"',
-       () => {
-         env.tsconfig({i18nInFormat: 'xliff2'});
-         env.write(`test.ts`, `
-        import {Component} from '@angular/core';
-        @Component({
-          selector: 'test',
-          template: '<div i18n>Some text</div>'
-        })
-        class FooCmp {}`);
-         env.driveMain();
-         const jsContents = env.getContents('test.js');
-         expect(jsContents).toContain(':@@8321000940098097247:Some text');
-       });
-
-    it('should render legacy id when `enableI18nLegacyMessageIdFormat` is not false and `i18nInFormat` is set to "xmb"',
-       () => {
-         env.tsconfig({i18nInFormat: 'xmb'});
-         env.write(`test.ts`, `
-        import {Component} from '@angular/core';
-        @Component({
-          selector: 'test',
-          template: '<div i18n>Some text</div>'
-        })
-        class FooCmp {}`);
-         env.driveMain();
-         const jsContents = env.getContents('test.js');
-         expect(jsContents).toContain(':@@8321000940098097247:Some text');
-       });
-
-    it('should render custom id even if `enableI18nLegacyMessageIdFormat` is not false and `i18nInFormat` is set',
+    it('should render custom id and legacy ids if `enableI18nLegacyMessageIdFormat` is not false',
        () => {
          env.tsconfig({i18nFormatIn: 'xlf'});
          env.write(`test.ts`, `
@@ -2541,25 +2482,28 @@ runInEachFileSystem(os => {
         class FooCmp {}`);
          env.driveMain();
          const jsContents = env.getContents('test.js');
-         expect(jsContents).toContain(':@@custom:Some text');
+         expect(jsContents)
+             .toContain(
+                 ':@@custom\\u241F5dbba0a3da8dff890e20cf76eb075d58900fbcd3\\u241F8321000940098097247:Some text');
        });
 
-    it('should not render legacy id when `enableI18nLegacyMessageIdFormat` is set to false', () => {
-      env.tsconfig({enableI18nLegacyMessageIdFormat: false, i18nInFormat: 'xmb'});
-      env.write(`test.ts`, `
+    it('should not render legacy ids when `enableI18nLegacyMessageIdFormat` is set to false',
+       () => {
+         env.tsconfig({enableI18nLegacyMessageIdFormat: false, i18nInFormat: 'xmb'});
+         env.write(`test.ts`, `
      import {Component} from '@angular/core';
      @Component({
        selector: 'test',
        template: '<div i18n>Some text</div>'
      })
      class FooCmp {}`);
-      env.driveMain();
-      const jsContents = env.getContents('test.js');
-      // Note that the colon would only be there if there is an id attached to the string.
-      expect(jsContents).not.toContain(':Some text');
-    });
+         env.driveMain();
+         const jsContents = env.getContents('test.js');
+         // Note that the colon would only be there if there is an id attached to the string.
+         expect(jsContents).not.toContain(':Some text');
+       });
 
-    it('should also render legacy id for ICUs when normal messages are using legacy ids', () => {
+    it('should also render legacy ids for ICUs when normal messages are using legacy ids', () => {
       env.tsconfig({i18nInFormat: 'xliff'});
       env.write(`test.ts`, `
      import {Component} from '@angular/core';
@@ -2572,8 +2516,10 @@ runInEachFileSystem(os => {
       const jsContents = env.getContents('test.js');
       expect(jsContents)
           .toContain(
-              ':@@720ba589d043a0497ac721ff972f41db0c919efb:{VAR_PLURAL, plural, 10 {ten} other {other}}');
-      expect(jsContents).toContain(':@@custom:Some text');
+              ':\\u241F720ba589d043a0497ac721ff972f41db0c919efb\\u241F3221232817843005870:{VAR_PLURAL, plural, 10 {ten} other {other}}');
+      expect(jsContents)
+          .toContain(
+              ':@@custom\\u241Fdcb6170595f5d548a3d00937e87d11858f51ad04\\u241F7419139165339437596:Some text');
     });
 
     it('@Component\'s `interpolation` should override default interpolation config', () => {
diff --git a/packages/compiler/src/i18n/i18n_ast.ts b/packages/compiler/src/i18n/i18n_ast.ts
index 0476214f41..9ec6afe1ba 100644
--- a/packages/compiler/src/i18n/i18n_ast.ts
+++ b/packages/compiler/src/i18n/i18n_ast.ts
@@ -11,8 +11,8 @@ import {ParseSourceSpan} from '../parse_util';
 export class Message {
   sources: MessageSpan[];
   id: string = this.customId;
-  /** The id to use if there is no custom id and if `i18nLegacyMessageIdFormat` is not empty */
-  legacyId?: string = '';
+  /** The ids to use if there are no custom id and if `i18nLegacyMessageIdFormat` is not empty */
+  legacyIds: string[] = [];
 
   /**
    * @param nodes message AST
diff --git a/packages/compiler/src/output/output_ast.ts b/packages/compiler/src/output/output_ast.ts
index 1071ae554e..5e6660af2f 100644
--- a/packages/compiler/src/output/output_ast.ts
+++ b/packages/compiler/src/output/output_ast.ts
@@ -509,12 +509,20 @@ export class LocalizedString extends Expression {
    * @param messagePart The first part of the tagged string
    */
   serializeI18nHead(): {cooked: string, raw: string} {
+    const MEANING_SEPARATOR = '|';
+    const ID_SEPARATOR = '@@';
+    const LEGACY_ID_INDICATOR = '␟';
+
     let metaBlock = this.metaBlock.description || '';
     if (this.metaBlock.meaning) {
-      metaBlock = `${this.metaBlock.meaning}|${metaBlock}`;
+      metaBlock = `${this.metaBlock.meaning}${MEANING_SEPARATOR}${metaBlock}`;
     }
-    if (this.metaBlock.customId || this.metaBlock.legacyId) {
-      metaBlock = `${metaBlock}@@${this.metaBlock.customId || this.metaBlock.legacyId}`;
+    if (this.metaBlock.customId) {
+      metaBlock = `${metaBlock}${ID_SEPARATOR}${this.metaBlock.customId}`;
+    }
+    if (this.metaBlock.legacyIds) {
+      this.metaBlock.legacyIds.forEach(
+          legacyId => { metaBlock = `${metaBlock}${LEGACY_ID_INDICATOR}${legacyId}`; });
     }
     return createCookedRawString(metaBlock, this.messageParts[0]);
   }
diff --git a/packages/compiler/src/render3/view/i18n/meta.ts b/packages/compiler/src/render3/view/i18n/meta.ts
index a1122d0357..fb4d5fc9d5 100644
--- a/packages/compiler/src/render3/view/i18n/meta.ts
+++ b/packages/compiler/src/render3/view/i18n/meta.ts
@@ -18,7 +18,7 @@ import {I18N_ATTR, I18N_ATTR_PREFIX, hasI18nAttrs, icuFromI18nMessage} from './u
 export type I18nMeta = {
   id?: string,
   customId?: string,
-  legacyId?: string,
+  legacyIds?: string[],
   description?: string,
   meaning?: string
 };
@@ -52,7 +52,7 @@ export class I18nMetaVisitor implements html.Visitor {
 
   constructor(
       private interpolationConfig: InterpolationConfig = DEFAULT_INTERPOLATION_CONFIG,
-      private keepI18nAttrs: boolean = false, private i18nLegacyMessageIdFormat: string = '') {}
+      private keepI18nAttrs = false, private enableI18nLegacyMessageIdFormat = false) {}
 
   private _generateI18nMessage(
       nodes: html.Node[], meta: string|i18n.I18nMeta = '',
@@ -60,7 +60,7 @@ export class I18nMetaVisitor implements html.Visitor {
     const {meaning, description, customId} = this._parseMetadata(meta);
     const message = this._createI18nMessage(nodes, meaning, description, customId, visitNodeFn);
     this._setMessageId(message, meta);
-    this._setLegacyId(message, meta);
+    this._setLegacyIds(message, meta);
     return message;
   }
 
@@ -171,13 +171,9 @@ export class I18nMetaVisitor implements html.Visitor {
    * @param message the message whose legacy id should be set
    * @param meta information about the message being processed
    */
-  private _setLegacyId(message: i18n.Message, meta: string|i18n.I18nMeta): void {
-    if (this.i18nLegacyMessageIdFormat === 'xlf' || this.i18nLegacyMessageIdFormat === 'xliff') {
-      message.legacyId = computeDigest(message);
-    } else if (
-        this.i18nLegacyMessageIdFormat === 'xlf2' || this.i18nLegacyMessageIdFormat === 'xliff2' ||
-        this.i18nLegacyMessageIdFormat === 'xmb') {
-      message.legacyId = computeDecimalDigest(message);
+  private _setLegacyIds(message: i18n.Message, meta: string|i18n.I18nMeta): void {
+    if (this.enableI18nLegacyMessageIdFormat) {
+      message.legacyIds = [computeDigest(message), computeDecimalDigest(message)];
     } else if (typeof meta !== 'string') {
       // This occurs if we are doing the 2nd pass after whitespace removal (see `parseTemplate()` in
       // `packages/compiler/src/render3/view/template.ts`).
@@ -186,7 +182,7 @@ export class I18nMetaVisitor implements html.Visitor {
       const previousMessage = meta instanceof i18n.Message ?
           meta :
           meta instanceof i18n.IcuPlaceholder ? meta.previousMessage : undefined;
-      message.legacyId = previousMessage && previousMessage.legacyId;
+      message.legacyIds = previousMessage ? previousMessage.legacyIds : [];
     }
   }
 }
@@ -195,7 +191,7 @@ export function metaFromI18nMessage(message: i18n.Message, id: string | null = n
   return {
     id: typeof id === 'string' ? id : message.id || '',
     customId: message.customId,
-    legacyId: message.legacyId,
+    legacyIds: message.legacyIds,
     meaning: message.meaning || '',
     description: message.description || ''
   };
diff --git a/packages/compiler/src/render3/view/template.ts b/packages/compiler/src/render3/view/template.ts
index 957935241d..897957aec9 100644
--- a/packages/compiler/src/render3/view/template.ts
+++ b/packages/compiler/src/render3/view/template.ts
@@ -1945,17 +1945,14 @@ export interface ParseTemplateOptions {
   leadingTriviaChars?: string[];
 
   /**
-   * Render `$localize` message ids with the specified legacy format (xlf, xlf2 or xmb).
+   * Render `$localize` message ids with additional legacy message ids.
    *
-   * Use this option when use are using the `$localize` based localization messages but
-   * have not migrated the translation files to use the new `$localize` message id format.
+   * This option defaults to `true` but in the future the defaul will be flipped.
    *
-   * @deprecated
-   * `i18nLegacyMessageIdFormat` should only be used while migrating from legacy message id
-   * formatted translation files and will be removed at the same time as ViewEngine support is
-   * removed.
+   * For now set this option to false if you have migrated the translation files to use the new
+   * `$localize` message id format and you are not using compile time translation merging.
    */
-  i18nLegacyMessageIdFormat?: string;
+  enableI18nLegacyMessageIdFormat?: boolean;
 }
 
 /**
@@ -1968,7 +1965,7 @@ export interface ParseTemplateOptions {
 export function parseTemplate(
     template: string, templateUrl: string, options: ParseTemplateOptions = {}):
     {errors?: ParseError[], nodes: t.Node[], styleUrls: string[], styles: string[]} {
-  const {interpolationConfig, preserveWhitespaces, i18nLegacyMessageIdFormat} = options;
+  const {interpolationConfig, preserveWhitespaces, enableI18nLegacyMessageIdFormat} = options;
   const bindingParser = makeBindingParser(interpolationConfig);
   const htmlParser = new HtmlParser();
   const parseResult = htmlParser.parse(
@@ -1986,7 +1983,8 @@ export function parseTemplate(
   // extraction process (ng xi18n) relies on a raw content to generate
   // message ids
   const i18nMetaVisitor = new I18nMetaVisitor(
-      interpolationConfig, /* keepI18nAttrs */ !preserveWhitespaces, i18nLegacyMessageIdFormat);
+      interpolationConfig, /* keepI18nAttrs */ !preserveWhitespaces,
+      enableI18nLegacyMessageIdFormat);
   rootNodes = html.visitAll(i18nMetaVisitor, rootNodes);
 
   if (!preserveWhitespaces) {
diff --git a/packages/compiler/test/i18n/digest_spec.ts b/packages/compiler/test/i18n/digest_spec.ts
index 9cb788efac..e77e49735f 100644
--- a/packages/compiler/test/i18n/digest_spec.ts
+++ b/packages/compiler/test/i18n/digest_spec.ts
@@ -14,6 +14,7 @@ import {computeMsgId, digest, sha1} from '../../src/i18n/digest';
       it('must return the ID if it\'s explicit', () => {
         expect(digest({
           id: 'i',
+          legacyIds: [],
           nodes: [],
           placeholders: {},
           placeholderToMessage: {},