diff --git a/build-system/externs/amp.extern.js b/build-system/externs/amp.extern.js
index 49ecd523debf..feee8fa5c411 100644
--- a/build-system/externs/amp.extern.js
+++ b/build-system/externs/amp.extern.js
@@ -483,7 +483,7 @@ let time;
 let AmpElement = function () {};
 
 /** @return {boolean} */
-AmpElement.prototype.V1 = function () {};
+AmpElement.prototype.R1 = function () {};
 
 /** @return {boolean} */
 AmpElement.prototype.deferredMount = function () {};
diff --git a/build-system/global-configs/experiments-config.json b/build-system/global-configs/experiments-config.json
index 5d1097ce8648..40e9e2f4360c 100644
--- a/build-system/global-configs/experiments-config.json
+++ b/build-system/global-configs/experiments-config.json
@@ -5,7 +5,7 @@
     "environment": "AMP",
     "issue": "https://github.com/ampproject/amphtml/issues/31915",
     "expiration_date_utc": "2021-06-30",
-    "define_experiment_constant": "V1_IMG_DEFERRED_BUILD"
+    "define_experiment_constant": "R1_IMG_DEFERRED_BUILD"
   },
   "experimentC": {}
 }
diff --git a/build-system/global-configs/experiments-const.json b/build-system/global-configs/experiments-const.json
index 935459c5e590..332a29fe9a9f 100644
--- a/build-system/global-configs/experiments-const.json
+++ b/build-system/global-configs/experiments-const.json
@@ -1,6 +1,6 @@
 {
   "INI_LOAD_INOB": true,
   "NO_SIGNING_RTV": true,
-  "V1_IMG_DEFERRED_BUILD": false,
+  "R1_IMG_DEFERRED_BUILD": false,
   "WITHIN_VIEWPORT_INOB": false
 }
diff --git a/builtins/amp-img.js b/builtins/amp-img.js
index 27683a280813..d99efc1b2017 100644
--- a/builtins/amp-img.js
+++ b/builtins/amp-img.js
@@ -47,8 +47,8 @@ const ATTRIBUTES_TO_PROPAGATE = [
 
 export class AmpImg extends BaseElement {
   /** @override @nocollapse */
-  static V1() {
-    return V1_IMG_DEFERRED_BUILD;
+  static R1() {
+    return R1_IMG_DEFERRED_BUILD;
   }
 
   /** @override @nocollapse */
@@ -141,7 +141,7 @@ export class AmpImg extends BaseElement {
         guaranteeSrcForSrcsetUnsupportedBrowsers(this.img_);
       }
 
-      if (AmpImg.V1() && !this.img_.complete) {
+      if (AmpImg.R1() && !this.img_.complete) {
         this.setReadyState(ReadyState.LOADING);
       }
     }
@@ -238,8 +238,8 @@ export class AmpImg extends BaseElement {
    * @private
    */
   maybeGenerateSizes_(sync) {
-    if (V1_IMG_DEFERRED_BUILD) {
-      // The `getLayoutSize()` is not available for a V1 element. Skip this
+    if (R1_IMG_DEFERRED_BUILD) {
+      // The `getLayoutSize()` is not available for a R1 element. Skip this
       // codepath. Also: is this feature at all useful? E.g. it doesn't even
       // execute in the `i-amphtml-ssr` mode.
       return;
@@ -367,8 +367,8 @@ export class AmpImg extends BaseElement {
 
   /** @override */
   unlayoutCallback() {
-    if (AmpImg.V1()) {
-      // TODO(#31915): Reconsider if this is still desired for V1. This helps
+    if (AmpImg.R1()) {
+      // TODO(#31915): Reconsider if this is still desired for R1. This helps
       // with network interruption when a document is inactivated.
       return;
     }
diff --git a/src/base-element.js b/src/base-element.js
index a5183a995777..c12902abb9f3 100644
--- a/src/base-element.js
+++ b/src/base-element.js
@@ -106,7 +106,7 @@ import {toWin} from './types';
  */
 export class BaseElement {
   /**
-   * Whether this element supports V1 protocol, which includes:
+   * Whether this element supports R1 protocol, which includes:
    * 1. Layout/unlayout are not managed by the runtime, but instead are
    *    implemented by the element as needed.
    * 2. The element can defer its build until later. See `deferredMount`.
@@ -119,7 +119,7 @@ export class BaseElement {
    * @return {boolean}
    * @nocollapse
    */
-  static V1() {
+  static R1() {
     return false;
   }
 
@@ -128,7 +128,7 @@ export class BaseElement {
    * element's build will be deferred roughly based on the
    * `content-visibility: auto` rules.
    *
-   * Only used for V1 elements.
+   * Only used for R1 elements.
    *
    * @param {!AmpElement} unusedElement
    * @return {boolean}
@@ -284,7 +284,7 @@ export class BaseElement {
    *
    * The default priority for base elements is LayoutPriority.CONTENT.
    * @return {number}
-   * TODO(#31915): remove once V1 migration is complete.
+   * TODO(#31915): remove once R1 migration is complete.
    */
   getLayoutPriority() {
     return LayoutPriority.CONTENT;
@@ -317,7 +317,7 @@ export class BaseElement {
    * mainly affects fixed-position elements that are adjusted to be always
    * relative to the document position in the viewport.
    * @return {!./layout-rect.LayoutRectDef}
-   * TODO(#31915): remove once V1 migration is complete.
+   * TODO(#31915): remove once R1 migration is complete.
    */
   getLayoutBox() {
     return this.element.getLayoutBox();
@@ -326,7 +326,7 @@ export class BaseElement {
   /**
    * Returns a previously measured layout size.
    * @return {!./layout-rect.LayoutSizeDef}
-   * TODO(#31915): remove once V1 migration is complete.
+   * TODO(#31915): remove once R1 migration is complete.
    */
   getLayoutSize() {
     return this.element.getLayoutSize();
@@ -437,7 +437,7 @@ export class BaseElement {
    * hosts and prefetch resources it is likely to need. May be called
    * multiple times because connections can time out.
    * @param {boolean=} opt_onLayout
-   * TODO(#31915): remove once V1 migration is complete.
+   * TODO(#31915): remove once R1 migration is complete.
    */
   preconnectCallback(opt_onLayout) {
     // Subclasses may override.
@@ -463,7 +463,7 @@ export class BaseElement {
 
   /**
    * Set itself as a container element that can be monitored by the scheduler
-   * for auto-mounting. Scheduler is used for V1 elements. A container is
+   * for auto-mounting. Scheduler is used for R1 elements. A container is
    * usually a top-level scrollable overlay such as a lightbox or a sidebar.
    * The main scheduler (`IntersectionObserver`) cannot properly handle elements
    * inside a non-document scroller and this method instructs the scheduler
@@ -533,14 +533,14 @@ export class BaseElement {
   /**
    * Ensure that the element is being eagerly loaded.
    *
-   * Only used for V1 elements.
+   * Only used for R1 elements.
    */
   ensureLoaded() {}
 
   /**
    * Update the current `readyState`.
    *
-   * Only used for V1 elements.
+   * Only used for R1 elements.
    *
    * @param {!./ready-state.ReadyState} state
    * @param {*=} opt_failure
@@ -590,7 +590,7 @@ export class BaseElement {
    * {@link isRelayoutNeeded} method.
    *
    * @return {!Promise}
-   * TODO(#31915): remove once V1 migration is complete.
+   * TODO(#31915): remove once R1 migration is complete.
    */
   layoutCallback() {
     return Promise.resolve();
@@ -613,7 +613,7 @@ export class BaseElement {
    * Requests the element to stop its activity when the document goes into
    * inactive state. The scope is up to the actual component. Among other
    * things the active playback of video or audio content must be stopped.
-   * TODO(#31915): remove once V1 migration is complete.
+   * TODO(#31915): remove once R1 migration is complete.
    */
   pauseCallback() {}
 
@@ -621,7 +621,7 @@ export class BaseElement {
    * Requests the element to resume its activity when the document returns from
    * an inactive state. The scope is up to the actual component. Among other
    * things the active playback of video or audio content may be resumed.
-   * TODO(#31915): remove once V1 migration is complete.
+   * TODO(#31915): remove once R1 migration is complete.
    */
   resumeCallback() {}
 
@@ -632,7 +632,7 @@ export class BaseElement {
    * {@link layoutCallback} in case document becomes active again.
    *
    * @return {boolean}
-   * TODO(#31915): remove once V1 migration is complete.
+   * TODO(#31915): remove once R1 migration is complete.
    */
   unlayoutCallback() {
     return false;
@@ -642,7 +642,7 @@ export class BaseElement {
    * Subclasses can override this method to opt-in into calling
    * {@link unlayoutCallback} when paused.
    * @return {boolean}
-   * TODO(#31915): remove once V1 migration is complete.
+   * TODO(#31915): remove once R1 migration is complete.
    */
   unlayoutOnPause() {
     return false;
@@ -1099,7 +1099,7 @@ export class BaseElement {
    * This may currently not work with extended elements. Please file
    * an issue if that is required.
    * @public
-   * TODO(#31915): remove once V1 migration is complete.
+   * TODO(#31915): remove once R1 migration is complete.
    */
   onLayoutMeasure() {}
 
diff --git a/src/custom-element.js b/src/custom-element.js
index 0762dccf7f8a..caff48293417 100644
--- a/src/custom-element.js
+++ b/src/custom-element.js
@@ -393,7 +393,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
       this.classList.remove('i-amphtml-unresolved');
       this.assertLayout_();
       this.dispatchCustomEventForTesting(AmpEvents.ATTACHED);
-      if (!this.V1()) {
+      if (!this.R1()) {
         this.getResources().upgraded(this);
       }
       this.signals_.signal(CommonSignals.UPGRADED);
@@ -430,7 +430,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
     /**
      * Get the priority to load the element.
      * @return {number}
-     * TODO(#31915): remove once V1 migration is complete.
+     * TODO(#31915): remove once R1 migration is complete.
      */
     getLayoutPriority() {
       return this.impl_
@@ -543,7 +543,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
           this.classList.remove('amp-notbuilt');
           this.signals_.signal(CommonSignals.BUILT);
 
-          if (this.V1()) {
+          if (this.R1()) {
             this.setReadyStateInternal(
               this.readyState_ != ReadyState.BUILDING
                 ? this.readyState_
@@ -579,7 +579,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
             /** @type {!Error} */ (reason)
           );
 
-          if (this.V1()) {
+          if (this.R1()) {
             this.setReadyStateInternal(ReadyState.ERROR, reason);
           }
 
@@ -603,7 +603,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
         CommonSignals.READY_TO_UPGRADE
       );
       return readyPromise.then(() => {
-        if (this.V1()) {
+        if (this.R1()) {
           const scheduler = getSchedulerForDoc(this.getAmpDoc());
           scheduler.scheduleAsap(this);
         }
@@ -630,7 +630,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
       const {signal} = this.mountAbortController_;
       return (this.mountPromise_ = this.buildInternal()
         .then(() => {
-          devAssert(this.V1());
+          devAssert(this.R1());
           if (signal.aborted) {
             // Mounting has been canceled.
             return;
@@ -694,7 +694,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
         CommonSignals.READY_TO_UPGRADE
       );
       return readyPromise.then(() => {
-        if (!this.V1()) {
+        if (!this.R1()) {
           return this.whenBuilt();
         }
         if (signal.aborted) {
@@ -717,8 +717,8 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
         this.pause();
       }
 
-      // Legacy pre-V1 elements simply unlayout.
-      if (!this.V1()) {
+      // Legacy R0 elements simply unlayout.
+      if (!this.R1()) {
         this.unlayout_();
         return;
       }
@@ -775,7 +775,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
      */
     ensureLoaded(opt_parentPriority) {
       return this.mount().then(() => {
-        if (this.V1()) {
+        if (this.R1()) {
           if (this.implClass_.usesLoading(this)) {
             this.impl_.ensureLoaded();
           }
@@ -848,7 +848,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
 
       this.readyState_ = state;
 
-      if (!this.V1()) {
+      if (!this.R1()) {
         return;
       }
 
@@ -888,7 +888,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
      * Called to instruct the element to preconnect to hosts it uses during
      * layout.
      * @param {boolean} onLayout Whether this was called after a layout.
-     * TODO(#31915): remove once V1 migration is complete.
+     * TODO(#31915): remove once R1 migration is complete.
      */
     preconnect(onLayout) {
       devAssert(this.isUpgraded());
@@ -908,13 +908,13 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
     }
 
     /**
-     * See `BaseElement.V1()`.
+     * See `BaseElement.R1()`.
      *
      * @return {boolean}
      * @final
      */
-    V1() {
-      return this.implClass_ ? this.implClass_.V1() : false;
+    R1() {
+      return this.implClass_ ? this.implClass_.R1() : false;
     }
 
     /**
@@ -1172,13 +1172,13 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
           this.reset_();
         }
         if (this.isUpgraded()) {
-          if (reconstruct && !this.V1()) {
+          if (reconstruct && !this.R1()) {
             this.getResources().upgraded(this);
           }
           this.connected_();
           this.dispatchCustomEventForTesting(AmpEvents.ATTACHED);
         }
-        if (this.implClass_ && this.V1()) {
+        if (this.implClass_ && this.R1()) {
           this.upgradeOrSchedule_();
         }
       } else {
@@ -1222,12 +1222,12 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
     }
 
     /**
-     * Upgrade or schedule element based on V1.
+     * Upgrade or schedule element based on R1.
      * @param {boolean=} opt_disablePreload
      * @private @final
      */
     upgradeOrSchedule_(opt_disablePreload) {
-      if (!this.V1()) {
+      if (!this.R1()) {
         this.tryUpgrade_();
         return;
       }
@@ -1374,7 +1374,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
       if (this.impl_) {
         this.impl_.detachedCallback();
       }
-      if (this.V1()) {
+      if (this.R1()) {
         this.unmount();
       }
       this.toggleLoading(false);
@@ -1526,7 +1526,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
      * should be called again when layout changes.
      * @return {boolean}
      * @package @final
-     * TODO(#31915): remove once V1 migration is complete.
+     * TODO(#31915): remove once R1 migration is complete.
      */
     isRelayoutNeeded() {
       return this.impl_ ? this.impl_.isRelayoutNeeded() : false;
@@ -1589,7 +1589,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
      * @param {!AbortSignal} signal
      * @return {!Promise}
      * @package @final
-     * TODO(#31915): remove once V1 migration is complete.
+     * TODO(#31915): remove once R1 migration is complete.
      */
     layoutCallback(signal) {
       assertNotTemplate(this);
@@ -1665,7 +1665,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
       this.impl_.pauseCallback();
 
       // Legacy unlayoutOnPause support.
-      if (!this.V1() && this.impl_.unlayoutOnPause()) {
+      if (!this.R1() && this.impl_.unlayoutOnPause()) {
         this.unlayout_();
       }
     }
@@ -1693,7 +1693,7 @@ function createBaseCustomElementClass(win, elementConnectedCallback) {
      *
      * @return {boolean}
      * @package @final
-     * TODO(#31915): remove once V1 migration is complete.
+     * TODO(#31915): remove once R1 migration is complete.
      */
     unlayoutCallback() {
       assertNotTemplate(this);
diff --git a/src/inabox/inabox-resources.js b/src/inabox/inabox-resources.js
index 024afbc84e79..c95166fd8ff6 100644
--- a/src/inabox/inabox-resources.js
+++ b/src/inabox/inabox-resources.js
@@ -209,7 +209,7 @@ export class InaboxResources {
     dev().fine(TAG, 'doPass');
     // measure in a batch
     this.resources_.forEach((resource) => {
-      if (!resource.isLayoutPending() || resource.element.V1()) {
+      if (!resource.isLayoutPending() || resource.element.R1()) {
         return;
       }
       resource.measure();
@@ -217,7 +217,7 @@ export class InaboxResources {
     // mutation in a batch
     this.resources_.forEach((resource) => {
       if (
-        !resource.element.V1() &&
+        !resource.element.R1() &&
         resource.getState() === ResourceState.READY_FOR_LAYOUT &&
         resource.isDisplayed()
       ) {
diff --git a/src/preact/base-element.js b/src/preact/base-element.js
index 8b3fe2bb4271..b469e892bc30 100644
--- a/src/preact/base-element.js
+++ b/src/preact/base-element.js
@@ -193,7 +193,7 @@ const IS_EMPTY_TEXT_NODE = (node) =>
  */
 export class PreactBaseElement extends AMP.BaseElement {
   /** @override @nocollapse */
-  static V1() {
+  static R1() {
     return true;
   }
 
diff --git a/src/service/resource.js b/src/service/resource.js
index 3cdf8fed48a3..631b547ab5c8 100644
--- a/src/service/resource.js
+++ b/src/service/resource.js
@@ -960,7 +960,7 @@ export class Resource {
    * @return {!Promise}
    */
   loadedOnce() {
-    if (this.element.V1()) {
+    if (this.element.R1()) {
       return this.element.whenLoaded();
     }
     return this.loadPromise_;
diff --git a/src/service/resources-impl.js b/src/service/resources-impl.js
index 6b149604d00a..73bb3ad0391e 100644
--- a/src/service/resources-impl.js
+++ b/src/service/resources-impl.js
@@ -1071,7 +1071,7 @@ export class ResourcesImpl {
       if (
         r.getState() == ResourceState.NOT_BUILT &&
         !r.isBuilding() &&
-        !r.element.V1()
+        !r.element.R1()
       ) {
         this.buildOrScheduleBuildForResource_(r, /* checkForDupes */ true);
       }
@@ -1101,7 +1101,7 @@ export class ResourcesImpl {
     ) {
       for (let i = 0; i < this.resources_.length; i++) {
         const r = this.resources_[i];
-        if ((r.hasOwner() && !r.isMeasureRequested()) || r.element.V1()) {
+        if ((r.hasOwner() && !r.isMeasureRequested()) || r.element.R1()) {
           // If element has owner, and measure is not requested, do nothing.
           continue;
         }
@@ -1165,7 +1165,7 @@ export class ResourcesImpl {
       if (
         r.getState() == ResourceState.NOT_BUILT ||
         r.hasOwner() ||
-        r.element.V1()
+        r.element.R1()
       ) {
         continue;
       }
@@ -1191,7 +1191,7 @@ export class ResourcesImpl {
           !r.isBuilt() &&
           !r.isBuilding() &&
           !r.hasOwner() &&
-          !r.element.V1() &&
+          !r.element.R1() &&
           r.hasBeenMeasured() &&
           r.isDisplayed() &&
           r.overlaps(loadRect)
@@ -1227,7 +1227,7 @@ export class ResourcesImpl {
         if (
           r.getState() == ResourceState.READY_FOR_LAYOUT &&
           !r.hasOwner() &&
-          !r.element.V1() &&
+          !r.element.R1() &&
           r.isDisplayed() &&
           r.idleRenderOutsideViewport()
         ) {
@@ -1247,7 +1247,7 @@ export class ResourcesImpl {
         if (
           r.getState() == ResourceState.READY_FOR_LAYOUT &&
           !r.hasOwner() &&
-          !r.element.V1() &&
+          !r.element.R1() &&
           r.isDisplayed()
         ) {
           dev().fine(TAG_, 'idle layout:', r.debugid);
@@ -1537,7 +1537,7 @@ export class ResourcesImpl {
     opt_parentPriority,
     opt_forceOutsideViewport
   ) {
-    if (resource.element.V1()) {
+    if (resource.element.R1()) {
       return;
     }
     const isBuilt = resource.getState() != ResourceState.NOT_BUILT;
diff --git a/test/integration/test-visibility-states.js b/test/integration/test-visibility-states.js
index 9a9bdb0c2cb7..db7dbb46cac4 100644
--- a/test/integration/test-visibility-states.js
+++ b/test/integration/test-visibility-states.js
@@ -85,7 +85,7 @@ t.run('Viewer Visibility State', () => {
           shouldPass = true;
           resources.schedulePass();
         }).then(() => {
-          if (V1_IMG_DEFERRED_BUILD) {
+          if (R1_IMG_DEFERRED_BUILD) {
             return new Promise((resolve) => setTimeout(resolve, 20));
           }
         });
@@ -127,8 +127,8 @@ t.run('Viewer Visibility State', () => {
             img.setAttribute('width', 100);
             img.setAttribute('height', 100);
             img.setAttribute('layout', 'fixed');
-            // TODO(#31915): Cleanup when V1_IMG_DEFERRED_BUILD is complete.
-            if (!V1_IMG_DEFERRED_BUILD) {
+            // TODO(#31915): Cleanup when R1_IMG_DEFERRED_BUILD is complete.
+            if (!R1_IMG_DEFERRED_BUILD) {
               win.document.body.appendChild(img);
             }
 
@@ -138,16 +138,16 @@ t.run('Viewer Visibility State', () => {
             prerenderAllowed = env.sandbox.stub(img, 'prerenderAllowed');
             prerenderAllowed.returns(false);
 
-            if (V1_IMG_DEFERRED_BUILD) {
+            if (R1_IMG_DEFERRED_BUILD) {
               win.document.body.appendChild(img);
             }
             return img.getImpl(false);
           })
           .then((impl) => {
-            layoutCallback = V1_IMG_DEFERRED_BUILD
+            layoutCallback = R1_IMG_DEFERRED_BUILD
               ? env.sandbox.stub(impl, 'mountCallback')
               : env.sandbox.stub(impl, 'layoutCallback');
-            unlayoutCallback = V1_IMG_DEFERRED_BUILD
+            unlayoutCallback = R1_IMG_DEFERRED_BUILD
               ? env.sandbox.stub(impl, 'unmountCallback')
               : env.sandbox.stub(impl, 'unlayoutCallback');
             pauseCallback = env.sandbox.stub(impl, 'pauseCallback');
@@ -260,7 +260,7 @@ t.run('Viewer Visibility State', () => {
             });
             changeVisibility('hidden');
             return waitForNextPass().then(() => {
-              if (V1_IMG_DEFERRED_BUILD) {
+              if (R1_IMG_DEFERRED_BUILD) {
                 expect(layoutCallback).to.have.been.called;
               } else {
                 expect(layoutCallback).not.to.have.been.called;
@@ -439,7 +439,7 @@ t.run('Viewer Visibility State', () => {
           });
           changeVisibility('hidden');
           return waitForNextPass().then(() => {
-            if (V1_IMG_DEFERRED_BUILD) {
+            if (R1_IMG_DEFERRED_BUILD) {
               expect(layoutCallback).to.have.been.called;
             } else {
               expect(layoutCallback).not.to.have.been.called;
diff --git a/test/unit/inabox/test-inabox-resources.js b/test/unit/inabox/test-inabox-resources.js
index d7a05ec3d1a3..94f5d33a7444 100644
--- a/test/unit/inabox/test-inabox-resources.js
+++ b/test/unit/inabox/test-inabox-resources.js
@@ -149,10 +149,10 @@ describes.realWin('inabox-resources', {amp: true}, (env) => {
     expect(resource2.unload).to.be.calledOnce;
   });
 
-  it('should ignore V1 resources for layout pass', async () => {
+  it('should ignore R1 resources for layout pass', async () => {
     const element1 = env.createAmpElement('amp-foo');
     const element2 = env.createAmpElement('amp-bar');
-    env.sandbox.stub(element2, 'V1').returns(true);
+    env.sandbox.stub(element2, 'R1').returns(true);
 
     win.document.body.appendChild(element1);
     win.document.body.appendChild(element2);
diff --git a/test/unit/preact/test-base-element-mapping.js b/test/unit/preact/test-base-element-mapping.js
index 41dbdee7d14f..9334295f3b1b 100644
--- a/test/unit/preact/test-base-element-mapping.js
+++ b/test/unit/preact/test-base-element-mapping.js
@@ -20,7 +20,7 @@ import {Slot} from '../../../src/preact/slot';
 import {createElementWithAttributes} from '../../../src/dom';
 import {htmlFor} from '../../../src/static-template';
 import {omit} from '../../../src/core/types/object';
-import {testElementV1} from '../../../testing/element-v1';
+import {testElementR1} from '../../../testing/element-v1';
 import {upgradeOrRegisterElement} from '../../../src/service/custom-element-registry';
 import {waitFor} from '../../../testing/test-helper';
 
@@ -75,9 +75,9 @@ describes.realWin('PreactBaseElement', spec, (env) => {
     });
   }
 
-  describe('V1', () => {
-    it('testElementV1', () => {
-      testElementV1(PreactBaseElement);
+  describe('R1', () => {
+    it('testElementR1', () => {
+      testElementR1(PreactBaseElement);
     });
 
     it('by default prerenderAllowed is tied to the "loadable" flag', () => {
diff --git a/test/unit/test-amp-img-v1.js b/test/unit/test-amp-img-v1.js
index 4d5be1f2513f..901611452ec5 100644
--- a/test/unit/test-amp-img-v1.js
+++ b/test/unit/test-amp-img-v1.js
@@ -18,9 +18,9 @@ import {AmpImg} from '../../builtins/amp-img';
 import {BaseElement} from '../../src/base-element';
 import {Layout, LayoutPriority} from '../../src/layout';
 import {createElementWithAttributes, dispatchCustomEvent} from '../../src/dom';
-import {testElementV1} from '../../testing/element-v1';
+import {testElementR1} from '../../testing/element-v1';
 
-describes.realWin('amp-img V1', {amp: true}, (env) => {
+describes.realWin('amp-img R1', {amp: true}, (env) => {
   let win, doc;
   let sandbox;
   let windowWidth;
@@ -33,7 +33,7 @@ describes.realWin('amp-img V1', {amp: true}, (env) => {
     doc = win.document;
     sandbox = env.sandbox;
 
-    sandbox.stub(AmpImg, 'V1').returns(true);
+    sandbox.stub(AmpImg, 'R1').returns(true);
 
     windowWidth = 320;
     sandbox.stub(BaseElement.prototype, 'getViewport').callsFake(() => {
@@ -65,8 +65,8 @@ describes.realWin('amp-img V1', {amp: true}, (env) => {
     return img;
   }
 
-  it('testElementV1', () => {
-    testElementV1(AmpImg, {
+  it('testElementR1', () => {
+    testElementR1(AmpImg, {
       exceptions: [
         'Must not have preconnectCallback',
         'Must not have layoutCallback',
diff --git a/test/unit/test-custom-element-v1.js b/test/unit/test-custom-element-v1.js
index cc0f546fd0d0..0ab8f9a39959 100644
--- a/test/unit/test-custom-element-v1.js
+++ b/test/unit/test-custom-element-v1.js
@@ -69,7 +69,7 @@ describes.realWin('CustomElement V1', {amp: true}, (env) => {
   });
 
   class TestElement extends BaseElement {
-    static V1() {
+    static R1() {
       return true;
     }
 
diff --git a/test/unit/test-resources.js b/test/unit/test-resources.js
index 56993443d8c4..4ec50e292cd2 100644
--- a/test/unit/test-resources.js
+++ b/test/unit/test-resources.js
@@ -76,7 +76,7 @@ describes.realWin('Resources', {amp: true}, (env) => {
     };
 
     const element = document.createElement('amp-el');
-    element.V1 = () => false;
+    element.R1 = () => false;
     element.isBuilt = () => isBuilt;
     element.isBuilding = () => isBuilding;
     element.pause = () => {};
@@ -619,7 +619,7 @@ describes.realWin('Resources discoverWork', {amp: true}, (env) => {
   function createElement(rect) {
     const element = env.win.document.createElement('amp-test');
     element.classList.add('i-amphtml-element');
-    element.V1 = () => false;
+    element.R1 = () => false;
     element.signals = () => new Signals();
     element.whenBuilt = () => Promise.resolve();
     element.isBuilt = () => true;
diff --git a/testing/element-v1.js b/testing/element-v1.js
index 7ddbf7f558cc..4fecb3278022 100644
--- a/testing/element-v1.js
+++ b/testing/element-v1.js
@@ -24,8 +24,8 @@ import {BaseElement} from '../src/base-element';
  */
 const RULES = [
   {
-    name: 'V1=true',
-    test: (implClass) => implClass.V1() === true,
+    name: 'R1=true',
+    test: (implClass) => implClass.R1() === true,
   },
 
   {
@@ -138,7 +138,7 @@ const RULES = [
  *   exceptions: (!Array<string>|undefined),
  * }=} options
  */
-export function testElementV1(implClass, options = {}) {
+export function testElementR1(implClass, options = {}) {
   const exceptions = options.exceptions || [];
   RULES.forEach(({name, notes, test}) => {
     if (exceptions.includes(name)) {