diff --git a/packages/apollo-server-core/src/__tests__/runQuery.test.ts b/packages/apollo-server-core/src/__tests__/runQuery.test.ts
index 69f50590d3f..e9a5f1915c5 100644
--- a/packages/apollo-server-core/src/__tests__/runQuery.test.ts
+++ b/packages/apollo-server-core/src/__tests__/runQuery.test.ts
@@ -399,6 +399,27 @@ describe('runQuery', () => {
       }
     }
 
+    it('warns that they are deprecated', async () => {
+      const queryString = `{ testString }`;
+      const logger = {
+        warn: jest.fn(console.warn),
+        info: console.info,
+        debug: console.debug,
+        error: console.error,
+      };
+      const extensions = [() => new CustomExtension()];
+      await runQuery({
+        schema,
+        queryString,
+        extensions,
+        request: new MockReq(),
+      }, {
+        logger,
+      });
+      expect(logger.warn).toHaveBeenCalledWith(
+        expect.stringMatching(/^\[deprecated\] A "CustomExtension" was/));
+    });
+
     it('creates the extension stack', async () => {
       const queryString = `{ testString }`;
       const extensions = [() => new CustomExtension()];
diff --git a/packages/apollo-server-core/src/requestPipeline.ts b/packages/apollo-server-core/src/requestPipeline.ts
index 09d4d4517fe..5398ce6f79e 100644
--- a/packages/apollo-server-core/src/requestPipeline.ts
+++ b/packages/apollo-server-core/src/requestPipeline.ts
@@ -113,6 +113,14 @@ export type DataSources<TContext> = {
 
 type Mutable<T> = { -readonly [P in keyof T]: T[P] };
 
+/**
+ * We attach this symbol to the constructor of extensions to mark that we've
+ * already warned about the deprecation of the `graphql-extensions` API for that
+ * particular definition.
+ */
+const symbolExtensionDeprecationDone =
+  Symbol("apolloServerExtensionDeprecationDone");
+
 export async function processGraphQLRequest<TContext>(
   config: GraphQLRequestPipelineConfig<TContext>,
   requestContext: Mutable<GraphQLRequestContext<TContext>>,
@@ -634,6 +642,39 @@ export async function processGraphQLRequest<TContext>(
     // objects.
     const extensions = config.extensions ? config.extensions.map(f => f()) : [];
 
+    // Warn about usage of (deprecated) `graphql-extensions` implementations.
+    // Since extensions are often provided as factory functions which
+    // instantiate an extension on each request, we'll attach a symbol to the
+    // constructor after we've warned to ensure that we don't do it on each
+    // request.  Another option here might be to keep a `Map` of constructor
+    // instances within this module, but I hope this will do the trick.
+    const hasOwn = Object.prototype.hasOwnProperty;
+    extensions.forEach((extension) => {
+      // Using `hasOwn` just in case there is a user-land `hasOwnProperty`
+      // defined on the `constructor` object.
+      if (hasOwn.call(extension.constructor, symbolExtensionDeprecationDone)) {
+        return;
+      }
+
+      Object.defineProperty(
+        extension.constructor,
+        symbolExtensionDeprecationDone,
+        { value: true }
+      );
+
+      const extensionName = extension.constructor.name;
+      logger.warn(
+        '[deprecated] ' +
+          ('A "' + extensionName + '" ' || 'An anonymous extension ') +
+          'was defined within the "extensions" configuration for ' +
+          'Apollo Server.  The API on which this extension is built ' +
+          '("graphql-extensions") is being deprecated in the next major ' +
+          'version of Apollo Server in favor of the new plugin API.  See ' +
+          'https://go.apollo.dev/s/plugins for the documentation on how ' +
+          'these plugins are to be defined and used.',
+      );
+    });
+
     return new GraphQLExtensionStack(extensions);
   }