diff --git a/packages/@ember/-internals/glimmer/tests/integration/syntax/deprecated-in-element-test.js b/packages/@ember/-internals/glimmer/tests/integration/syntax/deprecated-in-element-test.js
deleted file mode 100644
index 84a6a5de9bb..00000000000
--- a/packages/@ember/-internals/glimmer/tests/integration/syntax/deprecated-in-element-test.js
+++ /dev/null
@@ -1,263 +0,0 @@
-import { moduleFor, RenderingTestCase, strip, equalTokens, runTask } from 'internal-test-helpers';
-import { Component } from '@ember/-internals/glimmer';
-import { set } from '@ember/-internals/metal';
-
-const deprecationMessage = /The use of the private `{{-in-element}}` is deprecated, please refactor to the public `{{in-element}}`/;
-
-moduleFor(
-  '{{-in-element}}',
-  class extends RenderingTestCase {
-    ['@test allows rendering into an external element']() {
-      expectDeprecation(deprecationMessage);
-
-      let someElement = document.createElement('div');
-
-      this.render(
-        strip`
-          {{#-in-element this.someElement}}
-            {{this.text}}
-          {{/-in-element}}
-        `,
-        {
-          someElement,
-          text: 'Whoop!',
-        }
-      );
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'Whoop!');
-
-      this.assertStableRerender();
-
-      runTask(() => set(this.context, 'text', 'Huzzah!!'));
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'Huzzah!!');
-
-      runTask(() => set(this.context, 'text', 'Whoop!'));
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'Whoop!');
-    }
-
-    ['@test it appends to the external element by default']() {
-      expectDeprecation(deprecationMessage);
-
-      let someElement = document.createElement('div');
-      someElement.appendChild(document.createTextNode('foo '));
-
-      this.render(
-        strip`
-          {{#-in-element this.someElement}}
-            {{this.text}}
-          {{/-in-element}}
-        `,
-        {
-          someElement,
-          text: 'bar',
-        }
-      );
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'foo bar');
-
-      this.assertStableRerender();
-
-      runTask(() => set(this.context, 'text', 'bar!!'));
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'foo bar!!');
-
-      runTask(() => set(this.context, 'text', 'bar'));
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'foo bar');
-    }
-
-    ['@test allows appending to the external element with insertBefore=null']() {
-      expectDeprecation(deprecationMessage);
-
-      let someElement = document.createElement('div');
-      someElement.appendChild(document.createTextNode('foo '));
-
-      this.render(
-        strip`
-          {{#-in-element this.someElement insertBefore=null}}
-            {{this.text}}
-          {{/-in-element}}
-        `,
-        {
-          someElement,
-          text: 'bar',
-        }
-      );
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'foo bar');
-
-      this.assertStableRerender();
-
-      runTask(() => set(this.context, 'text', 'bar!!'));
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'foo bar!!');
-
-      runTask(() => set(this.context, 'text', 'bar'));
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'foo bar');
-    }
-
-    ['@test allows clearing the external element with insertBefore=undefined']() {
-      expectDeprecation(deprecationMessage);
-
-      let someElement = document.createElement('div');
-      someElement.appendChild(document.createTextNode('foo '));
-
-      this.render(
-        strip`
-          {{#-in-element this.someElement insertBefore=undefined}}
-            {{this.text}}
-          {{/-in-element}}
-        `,
-        {
-          someElement,
-          text: 'bar',
-        }
-      );
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'bar');
-
-      this.assertStableRerender();
-
-      runTask(() => set(this.context, 'text', 'bar!!'));
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'bar!!');
-
-      runTask(() => set(this.context, 'text', 'bar'));
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, 'bar');
-    }
-
-    ['@test does not allow insertBefore=non-null-value']() {
-      expectDeprecation(deprecationMessage);
-
-      let someElement = document.createElement('div');
-
-      expectAssertion(() => {
-        this.render(
-          strip`
-            {{#-in-element this.someElement insertBefore=".foo"}}
-              {{this.text}}
-            {{/-in-element}}
-          `,
-          {
-            someElement,
-            text: 'Whoop!',
-          }
-        );
-      }, /Can only pass a null or undefined literals to insertBefore in -in-element, received:/);
-    }
-
-    ['@test components are cleaned up properly'](assert) {
-      expectDeprecation(deprecationMessage);
-
-      let hooks = [];
-
-      let someElement = document.createElement('div');
-
-      this.registerComponent('modal-display', {
-        ComponentClass: Component.extend({
-          didInsertElement() {
-            hooks.push('didInsertElement');
-          },
-
-          willDestroyElement() {
-            hooks.push('willDestroyElement');
-          },
-        }),
-
-        template: `{{this.text}}`,
-      });
-
-      this.render(
-        strip`
-          {{#if this.showModal}}
-            {{#-in-element this.someElement}}
-              {{modal-display text=this.text}}
-            {{/-in-element}}
-          {{/if}}
-        `,
-        {
-          someElement,
-          text: 'Whoop!',
-          showModal: false,
-        }
-      );
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, '');
-
-      this.assertStableRerender();
-
-      runTask(() => set(this.context, 'showModal', true));
-
-      equalTokens(this.element, '<!---->');
-      this.assertComponentElement(someElement.firstChild, {
-        content: 'Whoop!',
-      });
-
-      runTask(() => set(this.context, 'text', 'Huzzah!'));
-
-      equalTokens(this.element, '<!---->');
-      this.assertComponentElement(someElement.firstChild, {
-        content: 'Huzzah!',
-      });
-
-      runTask(() => set(this.context, 'text', 'Whoop!'));
-
-      equalTokens(this.element, '<!---->');
-      this.assertComponentElement(someElement.firstChild, {
-        content: 'Whoop!',
-      });
-
-      runTask(() => set(this.context, 'showModal', false));
-
-      equalTokens(this.element, '<!---->');
-      equalTokens(someElement, '');
-
-      assert.deepEqual(hooks, ['didInsertElement', 'willDestroyElement']);
-    }
-
-    ['@test appending to the root element should not cause double clearing']() {
-      expectDeprecation(deprecationMessage);
-
-      this.render(
-        strip`
-          Before
-          {{#-in-element this.rootElement insertBefore=null}}
-            {{this.text}}
-          {{/-in-element}}
-          After
-        `,
-        {
-          rootElement: this.element,
-          text: 'Whoop!',
-        }
-      );
-
-      equalTokens(this.element, 'BeforeWhoop!<!---->After');
-
-      this.assertStableRerender();
-
-      runTask(() => set(this.context, 'text', 'Huzzah!'));
-
-      equalTokens(this.element, 'BeforeHuzzah!<!---->After');
-
-      // teardown happens in afterEach and should not cause double-clearing error
-    }
-  }
-);
diff --git a/packages/ember-template-compiler/lib/plugins/transform-in-element.ts b/packages/ember-template-compiler/lib/plugins/transform-in-element.ts
index 6ef1ba31c94..43b135c2ba9 100644
--- a/packages/ember-template-compiler/lib/plugins/transform-in-element.ts
+++ b/packages/ember-template-compiler/lib/plugins/transform-in-element.ts
@@ -1,6 +1,5 @@
-import { assert, deprecate } from '@ember/debug';
+import { assert } from '@ember/debug';
 import { AST, ASTPlugin } from '@glimmer/syntax';
-import calculateLocationDisplay from '../system/calculate-location-display';
 import { EmberASTPluginEnvironment } from '../types';
 import { isPath } from './utils';
 
@@ -9,26 +8,7 @@ import { isPath } from './utils';
 */
 
 /**
-  A Glimmer2 AST transformation that handles the public `{{in-element}}` as per RFC287, and deprecates but still
-  continues support for the private `{{-in-element}}`.
-
-  Transforms:
-
-  ```handlebars
-  {{#-in-element someElement}}
-    {{modal-display text=text}}
-  {{/-in-element}}
-  ```
-
-  into:
-
-  ```handlebars
-  {{#in-element someElement}}
-    {{modal-display text=text}}
-  {{/in-element}}
-  ```
-
-  And issues a deprecation message.
+  A Glimmer2 AST transformation that handles the public `{{in-element}}` as per RFC287.
 
   Issues a build time assertion for:
 
@@ -42,7 +22,6 @@ import { isPath } from './utils';
   @class TransformInElement
 */
 export default function transformInElement(env: EmberASTPluginEnvironment): ASTPlugin {
-  let moduleName = env.meta?.moduleName;
   let { builders: b } = env.syntax;
 
   return {
@@ -72,47 +51,6 @@ export default function transformInElement(env: EmberASTPluginEnvironment): ASTP
               );
             }
           });
-        } else if (node.path.original === '-in-element') {
-          let sourceInformation = calculateLocationDisplay(moduleName, node.loc);
-          deprecate(
-            `The use of the private \`{{-in-element}}\` is deprecated, please refactor to the public \`{{in-element}}\`. ${sourceInformation}`,
-            false,
-            {
-              id: 'glimmer.private-in-element',
-              until: '3.25.0',
-              for: 'ember-source',
-              since: {
-                enabled: '3.20.0',
-              },
-            }
-          );
-
-          node.path.original = 'in-element';
-          node.path.parts = ['in-element'];
-
-          // replicate special hash arguments added here:
-          // https://github.com/glimmerjs/glimmer-vm/blob/ba9b37d44b85fa1385eeeea71910ff5798198c8e/packages/%40glimmer/syntax/lib/parser/handlebars-node-visitors.ts#L340-L363
-          let needsInsertBefore = true;
-          let hash = node.hash;
-          hash.pairs.forEach((pair) => {
-            if (pair.key === 'insertBefore') {
-              assert(
-                `Can only pass a null or undefined literals to insertBefore in -in-element, received: ${JSON.stringify(
-                  pair.value
-                )}`,
-                pair.value.type === 'NullLiteral' || pair.value.type === 'UndefinedLiteral'
-              );
-
-              needsInsertBefore = false;
-            }
-          });
-
-          // Maintain compatibility with previous -in-element behavior (defaults to append, not clear)
-          if (needsInsertBefore) {
-            let nullLiteral = b.literal('NullLiteral', null);
-            let nextSibling = b.pair('insertBefore', nullLiteral);
-            hash.pairs.push(nextSibling);
-          }
         }
       },
     },