diff --git a/packages/core/package.json b/packages/core/package.json
index a83524622de9..43d3e40cb6a0 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -79,6 +79,7 @@
   },
   "license": "Apache-2.0",
   "dependencies": {
+    "@aws-sdk/types": "*",
     "@smithy/core": "^2.4.7",
     "@smithy/node-config-provider": "^3.1.8",
     "@smithy/property-provider": "^3.1.7",
diff --git a/packages/core/src/submodules/client/index.ts b/packages/core/src/submodules/client/index.ts
index ed9af92686a2..2c463d5f978f 100644
--- a/packages/core/src/submodules/client/index.ts
+++ b/packages/core/src/submodules/client/index.ts
@@ -1 +1,2 @@
 export * from "./emitWarningIfUnsupportedVersion";
+export * from "./setFeature";
diff --git a/packages/core/src/submodules/client/setFeature.spec.ts b/packages/core/src/submodules/client/setFeature.spec.ts
new file mode 100644
index 000000000000..729867ce7d97
--- /dev/null
+++ b/packages/core/src/submodules/client/setFeature.spec.ts
@@ -0,0 +1,10 @@
+import { AwsHandlerExecutionContext } from "@aws-sdk/types";
+
+import { setFeature } from "./setFeature";
+
+describe(setFeature.name, () => {
+  it("creates the context object path if needed", () => {
+    const context: AwsHandlerExecutionContext = {};
+    setFeature(context, "ACCOUNT_ID_ENDPOINT", "O");
+  });
+});
diff --git a/packages/core/src/submodules/client/setFeature.ts b/packages/core/src/submodules/client/setFeature.ts
new file mode 100644
index 000000000000..01f0a436fca5
--- /dev/null
+++ b/packages/core/src/submodules/client/setFeature.ts
@@ -0,0 +1,26 @@
+import type { AwsHandlerExecutionContext, AwsSdkFeatures } from "@aws-sdk/types";
+
+/**
+ * @internal
+ * Indicates to the request context that a given feature is active.
+ *
+ * @param context - handler execution context.
+ * @param feature - readable name of feature.
+ * @param value - encoding value of feature. This is required because the
+ * specification asks the SDK not to include a runtime lookup of all
+ * the feature identifiers.
+ */
+export function setFeature<F extends keyof AwsSdkFeatures>(
+  context: AwsHandlerExecutionContext,
+  feature: F,
+  value: AwsSdkFeatures[F]
+) {
+  if (!context.__aws_sdk_context) {
+    context.__aws_sdk_context = {
+      features: {},
+    };
+  } else if (!context.__aws_sdk_context.features) {
+    context.__aws_sdk_context.features = {};
+  }
+  context.__aws_sdk_context.features![feature] = value;
+}
diff --git a/packages/middleware-user-agent/src/encode-features.spec.ts b/packages/middleware-user-agent/src/encode-features.spec.ts
new file mode 100644
index 000000000000..c9b01a0eb166
--- /dev/null
+++ b/packages/middleware-user-agent/src/encode-features.spec.ts
@@ -0,0 +1,26 @@
+import { encodeFeatures } from "./encode-features";
+
+describe(encodeFeatures.name, () => {
+  it("encodes empty features", () => {
+    expect(encodeFeatures({})).toEqual("");
+  });
+
+  it("encodes features", () => {
+    expect(
+      encodeFeatures({
+        A: "A",
+        z: "z",
+      } as any)
+    ).toEqual("A,z");
+  });
+
+  it("drops values that would exceed 1024 bytes", () => {
+    expect(
+      encodeFeatures({
+        A: "A".repeat(512),
+        B: "B".repeat(511),
+        z: "z",
+      } as any)
+    ).toEqual("A".repeat(512) + "," + "B".repeat(511));
+  });
+});
diff --git a/packages/middleware-user-agent/src/encode-features.ts b/packages/middleware-user-agent/src/encode-features.ts
new file mode 100644
index 000000000000..e1fc88c458d4
--- /dev/null
+++ b/packages/middleware-user-agent/src/encode-features.ts
@@ -0,0 +1,28 @@
+import type { AwsSdkFeatures } from "@aws-sdk/types";
+
+const BYTE_LIMIT = 1024;
+
+/**
+ * @internal
+ */
+export function encodeFeatures(features: AwsSdkFeatures): string {
+  let buffer = "";
+
+  // currently all possible values are 1 byte,
+  // so string length is used.
+
+  for (const key in features) {
+    const val = features[key as keyof typeof features]!;
+    if (buffer.length + val!.length + 1 <= BYTE_LIMIT) {
+      if (buffer.length) {
+        buffer += "," + val;
+      } else {
+        buffer += val;
+      }
+      continue;
+    }
+    break;
+  }
+
+  return buffer;
+}
diff --git a/packages/middleware-user-agent/src/middleware-user-agent.integ.spec.ts b/packages/middleware-user-agent/src/middleware-user-agent.integ.spec.ts
index f95b8f78cf19..aa2c67fef18c 100644
--- a/packages/middleware-user-agent/src/middleware-user-agent.integ.spec.ts
+++ b/packages/middleware-user-agent/src/middleware-user-agent.integ.spec.ts
@@ -14,7 +14,7 @@ describe("middleware-user-agent", () => {
       requireRequestsFrom(client).toMatch({
         headers: {
           "x-amz-user-agent": /aws-sdk-js\/[\d\.]+/,
-          "user-agent": /aws-sdk-js\/[\d\.]+ (.*?)lang\/js md\/nodejs\#[\d\.]+ (.*?)api\/(.+)\#[\d\.]+/,
+          "user-agent": /aws-sdk-js\/[\d\.]+ (.*?)lang\/js md\/nodejs\#[\d\.]+ (.*?)api\/(.+)\#[\d\.]+ (.*?)m\//,
         },
       });
       await client.getUserDetails({
diff --git a/packages/middleware-user-agent/src/user-agent-middleware.spec.ts b/packages/middleware-user-agent/src/user-agent-middleware.spec.ts
index 3ea4d832f638..b01e90b967ea 100644
--- a/packages/middleware-user-agent/src/user-agent-middleware.spec.ts
+++ b/packages/middleware-user-agent/src/user-agent-middleware.spec.ts
@@ -89,6 +89,38 @@ describe("userAgentMiddleware", () => {
     expect(sdkUserAgent).toEqual(expect.stringContaining("custom_ua/abc"));
   });
 
+  describe("features", () => {
+    it("should collect features from the context", async () => {
+      const middleware = userAgentMiddleware({
+        defaultUserAgentProvider: async () => [
+          ["default_agent", "1.0.0"],
+          ["aws-sdk-js", "1.0.0"],
+        ],
+        runtime: "node",
+        userAgentAppId: async () => undefined,
+      });
+
+      const handler = middleware(mockNextHandler, {
+        __aws_sdk_context: {
+          features: {
+            "0": "0",
+            "9": "9",
+            A: "A",
+            B: "B",
+            y: "y",
+            z: "z",
+            "+": "+",
+            "/": "/",
+          },
+        },
+      });
+      await handler({ input: {}, request: new HttpRequest({ headers: {} }) });
+      expect(mockNextHandler.mock.calls[0][0].request.headers[USER_AGENT]).toEqual(
+        expect.stringContaining(`m/0,9,A,B,y,z,+,/`)
+      );
+    });
+  });
+
   describe("should sanitize the SDK user agent string", () => {
     const cases: { ua: UserAgentPair; expected: string }[] = [
       { ua: ["/name", "1.0.0"], expected: "name/1.0.0" },
diff --git a/packages/middleware-user-agent/src/user-agent-middleware.ts b/packages/middleware-user-agent/src/user-agent-middleware.ts
index 83fd46f26420..260151a13cb5 100644
--- a/packages/middleware-user-agent/src/user-agent-middleware.ts
+++ b/packages/middleware-user-agent/src/user-agent-middleware.ts
@@ -1,3 +1,4 @@
+import type { AwsHandlerExecutionContext } from "@aws-sdk/types";
 import { getUserAgentPrefix } from "@aws-sdk/util-endpoints";
 import { HttpRequest } from "@smithy/protocol-http";
 import {
@@ -22,6 +23,7 @@ import {
   USER_AGENT,
   X_AMZ_USER_AGENT,
 } from "./constants";
+import { encodeFeatures } from "./encode-features";
 
 /**
  * Build user agent header sections from:
@@ -39,14 +41,22 @@ export const userAgentMiddleware =
   (options: UserAgentResolvedConfig) =>
   <Output extends MetadataBearer>(
     next: BuildHandler<any, any>,
-    context: HandlerExecutionContext
+    context: HandlerExecutionContext | AwsHandlerExecutionContext
   ): BuildHandler<any, any> =>
   async (args: BuildHandlerArguments<any>): Promise<BuildHandlerOutput<Output>> => {
     const { request } = args;
-    if (!HttpRequest.isInstance(request)) return next(args);
+    if (!HttpRequest.isInstance(request)) {
+      return next(args);
+    }
     const { headers } = request;
     const userAgent = context?.userAgent?.map(escapeUserAgent) || [];
-    let defaultUserAgent = (await options.defaultUserAgentProvider()).map(escapeUserAgent);
+    const defaultUserAgent = (await options.defaultUserAgentProvider()).map(escapeUserAgent);
+    const awsContext = context as AwsHandlerExecutionContext;
+    defaultUserAgent.push(
+      `m/${encodeFeatures(
+        Object.assign({}, context.__smithy_context?.features, awsContext.__aws_sdk_context?.features)
+      )}`
+    );
     const customUserAgent = options?.customUserAgent?.map(escapeUserAgent) || [];
     const appId = await options.userAgentAppId();
     if (appId) {
diff --git a/packages/types/src/feature-ids.ts b/packages/types/src/feature-ids.ts
new file mode 100644
index 000000000000..7dc1b9078aed
--- /dev/null
+++ b/packages/types/src/feature-ids.ts
@@ -0,0 +1,58 @@
+/**
+ * @internal
+ */
+export type AwsSdkFeatures = Partial<{
+  RESOURCE_MODEL: "A";
+  WAITER: "B";
+  PAGINATOR: "C";
+  RETRY_MODE_LEGACY: "D";
+  RETRY_MODE_STANDARD: "E";
+  RETRY_MODE_ADAPTIVE: "F";
+  // S3_TRANSFER: "G"; // not applicable.
+  // S3_CRYPTO_V1N: "H"; // not applicable.
+  // S3_CRYPTO_V2: "I"; // not applicable.
+  S3_EXPRESS_BUCKET: "J";
+  S3_ACCESS_GRANTS: "K";
+  GZIP_REQUEST_COMPRESSION: "L";
+  PROTOCOL_RPC_V2_CBOR: "M";
+  ENDPOINT_OVERRIDE: "N";
+  ACCOUNT_ID_ENDPOINT: "O";
+  ACCOUNT_ID_MODE_PREFERRED: "P";
+  ACCOUNT_ID_MODE_DISABLED: "Q";
+  ACCOUNT_ID_MODE_REQUIRED: "R";
+  SIGV4A_SIGNING: "S";
+  RESOLVED_ACCOUNT_ID: "T";
+  FLEXIBLE_CHECKSUMS_REQ_CRC32: "U";
+  FLEXIBLE_CHECKSUMS_REQ_CRC32C: "V";
+  FLEXIBLE_CHECKSUMS_REQ_CRC64: "W";
+  FLEXIBLE_CHECKSUMS_REQ_SHA1: "X";
+  FLEXIBLE_CHECKSUMS_REQ_SHA256: "Y";
+  FLEXIBLE_CHECKSUMS_REQ_WHEN_SUPPORTED: "Z";
+  FLEXIBLE_CHECKSUMS_REQ_WHEN_REQUIRED: "a";
+  FLEXIBLE_CHECKSUMS_RES_WHEN_SUPPORTED: "b";
+  FLEXIBLE_CHECKSUMS_RES_WHEN_REQUIRED: "c";
+  DDB_MAPPER: "d";
+  CREDENTIALS_CODE: "e";
+  // CREDENTIALS_JVM_SYSTEM_PROPERTIES: "f"; // not applicable.
+  CREDENTIALS_ENV_VARS: "g";
+  CREDENTIALS_ENV_VARS_STS_WEB_ID_TOKEN: "h";
+  CREDENTIALS_STS_ASSUME_ROLE: "i";
+  CREDENTIALS_STS_ASSUME_ROLE_SAML: "j";
+  CREDENTIALS_STS_ASSUME_ROLE_WEB_ID: "k";
+  CREDENTIALS_STS_FEDERATION_TOKEN: "l";
+  CREDENTIALS_STS_SESSION_TOKEN: "m";
+  CREDENTIALS_PROFILE: "n";
+  CREDENTIALS_PROFILE_SOURCE_PROFILE: "o";
+  CREDENTIALS_PROFILE_NAMED_PROVIDER: "p";
+  CREDENTIALS_PROFILE_STS_WEB_ID_TOKEN: "q";
+  CREDENTIALS_PROFILE_SSO: "r";
+  CREDENTIALS_SSO: "s";
+  CREDENTIALS_PROFILE_SSO_LEGACY: "t";
+  CREDENTIALS_SSO_LEGACY: "u";
+  CREDENTIALS_PROFILE_PROCESS: "v";
+  CREDENTIALS_PROCESS: "w";
+  CREDENTIALS_BOTO2_CONFIG_FILE: "x";
+  CREDENTIALS_AWS_SDK_STORE: "y";
+  CREDENTIALS_HTTP: "z";
+  CREDENTIALS_IMDS: "0";
+}>;
diff --git a/packages/types/src/index.ts b/packages/types/src/index.ts
index ab64cd947b8c..ce32277d0364 100644
--- a/packages/types/src/index.ts
+++ b/packages/types/src/index.ts
@@ -12,6 +12,7 @@ export * from "./encode";
 export * from "./endpoint";
 export * from "./eventStream";
 export * from "./extensions";
+export * from "./feature-ids";
 export * from "./http";
 export * from "./identity";
 export * from "./logger";
diff --git a/packages/types/src/middleware.ts b/packages/types/src/middleware.ts
index 3ae51bd9a83d..9cdc79fe2e60 100644
--- a/packages/types/src/middleware.ts
+++ b/packages/types/src/middleware.ts
@@ -1,3 +1,7 @@
+import { HandlerExecutionContext } from "@smithy/types";
+
+import { AwsSdkFeatures } from "./feature-ids";
+
 export {
   AbsoluteLocation,
   BuildHandler,
@@ -38,3 +42,14 @@ export {
   Step,
   Terminalware,
 } from "@smithy/types";
+
+/**
+ * @internal
+ * Contains reserved keys for AWS SDK internal usage of the
+ * handler execution context object.
+ */
+export interface AwsHandlerExecutionContext extends HandlerExecutionContext {
+  __aws_sdk_context?: {
+    features?: AwsSdkFeatures;
+  };
+}
diff --git a/packages/util-user-agent-browser/src/index.native.spec.ts b/packages/util-user-agent-browser/src/index.native.spec.ts
index 56313e41305f..b7d60589d116 100644
--- a/packages/util-user-agent-browser/src/index.native.spec.ts
+++ b/packages/util-user-agent-browser/src/index.native.spec.ts
@@ -6,7 +6,7 @@ it("should response basic browser default user agent", async () => {
   jest.spyOn(window.navigator, "userAgent", "get").mockReturnValue(undefined);
   const userAgent = await defaultUserAgent({ serviceId: "s3", clientVersion: "0.1.0" })();
   expect(userAgent[0]).toEqual(["aws-sdk-js", "0.1.0"]);
-  expect(userAgent[1]).toEqual(["ua", "2.0"]);
+  expect(userAgent[1]).toEqual(["ua", "2.1"]);
   expect(userAgent[2]).toEqual(["os/other"]);
   expect(userAgent[3]).toEqual(["lang/js"]);
   expect(userAgent[4]).toEqual(["md/rn"]);
diff --git a/packages/util-user-agent-browser/src/index.native.ts b/packages/util-user-agent-browser/src/index.native.ts
index 2d54ad3de29e..aca09d7ce7f3 100644
--- a/packages/util-user-agent-browser/src/index.native.ts
+++ b/packages/util-user-agent-browser/src/index.native.ts
@@ -15,7 +15,7 @@ export const defaultUserAgent =
       // sdk-metadata
       ["aws-sdk-js", clientVersion],
       // ua-metadata
-      ["ua", "2.0"],
+      ["ua", "2.1"],
       // os-metadata
       ["os/other"],
       // language-metadata
diff --git a/packages/util-user-agent-browser/src/index.spec.ts b/packages/util-user-agent-browser/src/index.spec.ts
index 5454ca3f2e22..a0ed2582bf58 100644
--- a/packages/util-user-agent-browser/src/index.spec.ts
+++ b/packages/util-user-agent-browser/src/index.spec.ts
@@ -19,7 +19,7 @@ describe("defaultUserAgent", () => {
   it("should populate metrics", async () => {
     const userAgent = await defaultUserAgent({ serviceId: "s3", clientVersion: "0.1.0" })(mockConfig);
     expect(userAgent[0]).toEqual(["aws-sdk-js", "0.1.0"]);
-    expect(userAgent[1]).toEqual(["ua", "2.0"]);
+    expect(userAgent[1]).toEqual(["ua", "2.1"]);
     expect(userAgent[2]).toEqual(["os/macOS", "10.15.7"]);
     expect(userAgent[3]).toEqual(["lang/js"]);
     expect(userAgent[4]).toEqual(["md/browser", "Chrome_86.0.4240.111"]);
@@ -47,4 +47,4 @@ describe("defaultUserAgent", () => {
     expect(userAgent).not.toContainEqual(expect.arrayContaining(["app/"]));
     expect(userAgent.length).toBe(6);
   });
-});
\ No newline at end of file
+});
diff --git a/packages/util-user-agent-browser/src/index.ts b/packages/util-user-agent-browser/src/index.ts
index 1f59b7f1a1bc..5153db33cf3d 100644
--- a/packages/util-user-agent-browser/src/index.ts
+++ b/packages/util-user-agent-browser/src/index.ts
@@ -24,7 +24,7 @@ export const defaultUserAgent =
       // sdk-metadata
       ["aws-sdk-js", clientVersion],
       // ua-metadata
-      ["ua", "2.0"],
+      ["ua", "2.1"],
       // os-metadata
       [`os/${parsedUA?.os?.name || "other"}`, parsedUA?.os?.version],
       // language-metadata
diff --git a/packages/util-user-agent-node/src/defaultUserAgent.spec.ts b/packages/util-user-agent-node/src/defaultUserAgent.spec.ts
index 1be9bee84b28..86c662588306 100644
--- a/packages/util-user-agent-node/src/defaultUserAgent.spec.ts
+++ b/packages/util-user-agent-node/src/defaultUserAgent.spec.ts
@@ -39,7 +39,7 @@ describe("createDefaultUserAgentProvider", () => {
 
   const basicUserAgent: UserAgent = [
     ["aws-sdk-js", "0.1.0"],
-    ["ua", "2.0"],
+    ["ua", "2.1"],
     ["api/s3", "0.1.0"],
     ["os/darwin", "19.6.0"],
     ["lang/js"],
diff --git a/packages/util-user-agent-node/src/defaultUserAgent.ts b/packages/util-user-agent-node/src/defaultUserAgent.ts
index 12d371ccc4d8..df23988414c2 100644
--- a/packages/util-user-agent-node/src/defaultUserAgent.ts
+++ b/packages/util-user-agent-node/src/defaultUserAgent.ts
@@ -26,7 +26,7 @@ export const createDefaultUserAgentProvider = ({ serviceId, clientVersion }: Def
       // sdk-metadata
       ["aws-sdk-js", clientVersion],
       // ua-metadata
-      ["ua", "2.0"],
+      ["ua", "2.1"],
       // os-metadata
       [`os/${platform()}`, release()],
       // language-metadata
diff --git a/packages/util-user-agent-node/src/index.ts b/packages/util-user-agent-node/src/index.ts
index 8aeee67f65c7..cbf37f23bbca 100644
--- a/packages/util-user-agent-node/src/index.ts
+++ b/packages/util-user-agent-node/src/index.ts
@@ -1,2 +1,2 @@
 export * from "./defaultUserAgent";
-export * from "./nodeAppIdConfigOptions";
\ No newline at end of file
+export * from "./nodeAppIdConfigOptions";