diff --git a/packages/apollo-server-core/src/__tests__/runQuery.test.ts b/packages/apollo-server-core/src/__tests__/runQuery.test.ts
index 69f50590d3f..ec6d83477dc 100644
--- a/packages/apollo-server-core/src/__tests__/runQuery.test.ts
+++ b/packages/apollo-server-core/src/__tests__/runQuery.test.ts
@@ -31,6 +31,7 @@ import {
 } from 'apollo-server-plugin-base';
 import { InMemoryLRUCache } from 'apollo-server-caching';
 import { generateSchemaHash } from "../utils/schemaHash";
+import { Logger } from "apollo-server-types";
 
 // This is a temporary kludge to ensure we preserve runQuery behavior with the
 // GraphQLRequestProcessor refactoring.
@@ -399,6 +400,88 @@ describe('runQuery', () => {
       }
     }
 
+    describe('deprecation warnings', () => {
+      const queryString = `{ testString }`;
+      async function runWithExtAndReturnLogger(
+        extensions: QueryOptions['extensions'],
+      ): Promise<Logger> {
+        const logger = {
+          warn: jest.fn(() => {}),
+          info: console.info,
+          debug: console.debug,
+          error: console.error,
+        };
+
+        await runQuery(
+          {
+            schema,
+            queryString,
+            extensions,
+            request: new MockReq(),
+          },
+          {
+            logger,
+          },
+        );
+
+        return logger;
+      }
+
+      it('warns about named extensions', async () => {
+        const logger = await runWithExtAndReturnLogger([
+          () => new (class NamedExtension implements GraphQLExtension<any> {})(),
+        ]);
+        expect(logger.warn).toHaveBeenCalledWith(
+          expect.stringMatching(/^\[deprecated\] A "NamedExtension" was/));
+      });
+
+      it('warns about anonymous extensions', async () => {
+        const logger = await runWithExtAndReturnLogger([
+          () => new (class implements GraphQLExtension<any> {})(),
+        ]);
+        expect(logger.warn).toHaveBeenCalledWith(
+          expect.stringMatching(/^\[deprecated\] An anonymous extension was/));
+      });
+
+      it('warns about anonymous class expressions', async () => {
+        // In other words, when the name is the name of the variable.
+        const anon = class implements GraphQLExtension<any> {};
+        const logger = await runWithExtAndReturnLogger([
+          () => new anon(),
+        ]);
+        expect(logger.warn).toHaveBeenCalledWith(
+          expect.stringMatching(/^\[deprecated\] A "anon" was/));
+      });
+
+      it('warns for multiple extensions', async () => {
+        const logger = await runWithExtAndReturnLogger([
+          () => new (class Name1Ext implements GraphQLExtension<any> {})(),
+          () => new (class Name2Ext implements GraphQLExtension<any> {})(),
+        ]);
+        expect(logger.warn).toHaveBeenCalledWith(
+          expect.stringMatching(/^\[deprecated\] A "Name1Ext" was/));
+        expect(logger.warn).toHaveBeenCalledWith(
+          expect.stringMatching(/^\[deprecated\] A "Name2Ext" was/));
+      });
+
+      it('warns only once', async () => {
+        // Will use the same extension across two invocations.
+        class NameExt implements GraphQLExtension<any> {};
+
+        const logger1 = await runWithExtAndReturnLogger([
+          () => new NameExt,
+        ]);
+        expect(logger1.warn).toHaveBeenCalledWith(
+          expect.stringMatching(/^\[deprecated\] A "NameExt" was/));
+
+        const logger2 = await runWithExtAndReturnLogger([
+          () => new NameExt,
+        ]);
+        expect(logger2.warn).not.toHaveBeenCalledWith(
+          expect.stringMatching(/^\[deprecated\] A "NameExt" 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..60962277b0c 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 +642,44 @@ 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 (
+        !extension.constructor ||
+        hasOwn.call(extension.constructor, symbolExtensionDeprecationDone)
+      ) {
+        return;
+      }
+
+      Object.defineProperty(
+        extension.constructor,
+        symbolExtensionDeprecationDone,
+        { value: true }
+      );
+
+      const extensionName = extension.constructor.name;
+      logger.warn(
+        '[deprecated] ' +
+          (extensionName
+            ? '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);
   }