diff --git a/packages/middleware-flexible-checksums/package.json b/packages/middleware-flexible-checksums/package.json
index 3a0dbcc9d20d..8254d604d6a4 100644
--- a/packages/middleware-flexible-checksums/package.json
+++ b/packages/middleware-flexible-checksums/package.json
@@ -28,6 +28,7 @@
   },
   "license": "Apache-2.0",
   "dependencies": {
+    "@smithy/node-config-provider": "^3.1.5",
     "@aws-crypto/crc32": "5.2.0",
     "@aws-crypto/crc32c": "5.2.0",
     "@aws-sdk/types": "*",
diff --git a/packages/middleware-flexible-checksums/src/NODE_REQUEST_CHECKSUM_CALCULATION_CONFIG_OPTIONS.ts b/packages/middleware-flexible-checksums/src/NODE_REQUEST_CHECKSUM_CALCULATION_CONFIG_OPTIONS.ts
new file mode 100644
index 000000000000..ac105c94d97a
--- /dev/null
+++ b/packages/middleware-flexible-checksums/src/NODE_REQUEST_CHECKSUM_CALCULATION_CONFIG_OPTIONS.ts
@@ -0,0 +1,16 @@
+import { LoadedConfigSelectors } from "@smithy/node-config-provider";
+
+import { RequestChecksumCalculation } from "./constants";
+import { SelectorType, stringUnionSelector } from "./stringUnionSelector";
+
+export const ENV_REQUEST_CHECKSUM_CALCULATION = "AWS_REQUEST_CHECKSUM_CALCULATION";
+export const CONFIG_REQUEST_CHECKSUM_CALCULATION = "request_checksum_calculation";
+export const DEFAULT_REQUEST_CHECKSUM_CALCULATION = RequestChecksumCalculation.WHEN_SUPPORTED;
+
+export const NODE_REQUEST_CHECKSUM_CALCULATION_CONFIG_OPTIONS: LoadedConfigSelectors<string> = {
+  environmentVariableSelector: (env) =>
+    stringUnionSelector(env, ENV_REQUEST_CHECKSUM_CALCULATION, RequestChecksumCalculation, SelectorType.ENV),
+  configFileSelector: (profile) =>
+    stringUnionSelector(profile, CONFIG_REQUEST_CHECKSUM_CALCULATION, RequestChecksumCalculation, SelectorType.CONFIG),
+  default: DEFAULT_REQUEST_CHECKSUM_CALCULATION,
+};
diff --git a/packages/middleware-flexible-checksums/src/NODE_RESPONSE_CHECKSUM_VALIDATION_CONFIG_OPTIONS.ts b/packages/middleware-flexible-checksums/src/NODE_RESPONSE_CHECKSUM_VALIDATION_CONFIG_OPTIONS.ts
new file mode 100644
index 000000000000..197b4ea6d052
--- /dev/null
+++ b/packages/middleware-flexible-checksums/src/NODE_RESPONSE_CHECKSUM_VALIDATION_CONFIG_OPTIONS.ts
@@ -0,0 +1,16 @@
+import { LoadedConfigSelectors } from "@smithy/node-config-provider";
+
+import { RequestChecksumCalculation } from "./constants";
+import { SelectorType, stringUnionSelector } from "./stringUnionSelector";
+
+export const ENV_RESPONSE_CHECKSUM_VALIDATION = "AWS_RESPONSE_CHECKSUM_VALIDATION";
+export const CONFIG_RESPONSE_CHECKSUM_VALIDATION = "response_checksum_validation";
+export const DEFAULT_RESPONSE_CHECKSUM_VALIDATION = RequestChecksumCalculation.WHEN_SUPPORTED;
+
+export const NODE_RESPONSE_CHECKSUM_VALIDATION_CONFIG_OPTIONS: LoadedConfigSelectors<string> = {
+  environmentVariableSelector: (env) =>
+    stringUnionSelector(env, ENV_RESPONSE_CHECKSUM_VALIDATION, RequestChecksumCalculation, SelectorType.ENV),
+  configFileSelector: (profile) =>
+    stringUnionSelector(profile, CONFIG_RESPONSE_CHECKSUM_VALIDATION, RequestChecksumCalculation, SelectorType.CONFIG),
+  default: DEFAULT_RESPONSE_CHECKSUM_VALIDATION,
+};
diff --git a/packages/middleware-flexible-checksums/src/constants.ts b/packages/middleware-flexible-checksums/src/constants.ts
index dc68086032c5..ac944f5fe23f 100644
--- a/packages/middleware-flexible-checksums/src/constants.ts
+++ b/packages/middleware-flexible-checksums/src/constants.ts
@@ -1,3 +1,49 @@
+/**
+ * Determines when a checksum will be calculated for request payloads.
+ */
+export const RequestChecksumCalculation = {
+  /**
+   * When set, a checksum will be calculated for all request payloads of operations
+   * modeled with the {@link httpChecksum} trait where `requestChecksumRequired` is `true`
+   * AND/OR a `requestAlgorithmMember` is modeled.
+   * {@link https://smithy.io/2.0/aws/aws-core.html#aws-protocols-httpchecksum-trait httpChecksum}
+   */
+  WHEN_SUPPORTED: "WHEN_SUPPORTED",
+
+  /**
+   * When set, a checksum will only be calculated for request payloads of operations
+   * modeled with the {@link httpChecksum} trait where `requestChecksumRequired` is `true`
+   * OR where a `requestAlgorithmMember` is modeled and the user sets it.
+   * {@link https://smithy.io/2.0/aws/aws-core.html#aws-protocols-httpchecksum-trait httpChecksum}
+   */
+  WHEN_REQUIRED: "WHEN_REQUIRED",
+} as const;
+
+export type RequestChecksumCalculation = (typeof RequestChecksumCalculation)[keyof typeof RequestChecksumCalculation];
+
+/**
+ * Determines when checksum validation will be performed on response payloads.
+ */
+export const ResponseChecksumValidation = {
+  /**
+   * When set, checksum validation MUST be performed on all response payloads of operations
+   * modeled with the {@link httpChecksum} trait where `responseAlgorithms` is modeled,
+   * except when no modeled checksum algorithms are supported by an SDK.
+   * {@link https://smithy.io/2.0/aws/aws-core.html#aws-protocols-httpchecksum-trait httpChecksum}
+   */
+  WHEN_SUPPORTED: "WHEN_SUPPORTED",
+
+  /**
+   * When set, checksum validation MUST NOT be performed on response payloads of operations UNLESS
+   * the SDK supports the modeled checksum algorithms AND the user has set the `requestValidationModeMember` to `ENABLED`.
+   * It is currently impossible to model an operation as requiring a response checksum,
+   * but this setting leaves the door open for future updates.
+   */
+  WHEN_REQUIRED: "WHEN_REQUIRED",
+} as const;
+
+export type ResponseChecksumValidation = (typeof ResponseChecksumValidation)[keyof typeof ResponseChecksumValidation];
+
 /**
  * Checksum Algorithms supported by the SDK.
  */
diff --git a/packages/middleware-flexible-checksums/src/index.ts b/packages/middleware-flexible-checksums/src/index.ts
index 26a8b50c93b2..8ff2b77d48e1 100644
--- a/packages/middleware-flexible-checksums/src/index.ts
+++ b/packages/middleware-flexible-checksums/src/index.ts
@@ -1,3 +1,5 @@
+export * from "./NODE_REQUEST_CHECKSUM_CALCULATION_CONFIG_OPTIONS";
+export * from "./NODE_RESPONSE_CHECKSUM_VALIDATION_CONFIG_OPTIONS";
 export * from "./constants";
 export * from "./flexibleChecksumsMiddleware";
 export * from "./getFlexibleChecksumsPlugin";
diff --git a/packages/middleware-flexible-checksums/src/stringUnionSelector.spec.ts b/packages/middleware-flexible-checksums/src/stringUnionSelector.spec.ts
new file mode 100644
index 000000000000..6bcfae43b0e8
--- /dev/null
+++ b/packages/middleware-flexible-checksums/src/stringUnionSelector.spec.ts
@@ -0,0 +1,40 @@
+import { SelectorType, stringUnionSelector } from "./stringUnionSelector";
+
+describe(stringUnionSelector.name, () => {
+  const key = "key";
+  const value = "VALUE";
+  const obj: { [key]: any } = {} as any;
+  const union = { [key]: value };
+
+  describe.each(Object.entries(SelectorType))(`Selector %s`, (selectorKey, selectorValue) => {
+    beforeEach(() => {
+      delete obj[key];
+    });
+
+    it(`should return undefined if ${key} is not defined`, () => {
+      // @ts-expect-error Element implicitly has an 'any' type
+      expect(stringUnionSelector(obj, key, union, SelectorType[selectorKey])).toBeUndefined();
+    });
+
+    it.each([
+      [value, value],
+      [value, value.toLowerCase()],
+      [value, [...value].map((c, i) => (i % 2 === 0 ? c.toLowerCase() : c.toUpperCase())).join("")],
+    ])(`should return number %s if ${key}="%s"`, (output, input) => {
+      obj[key] = input;
+      // @ts-expect-error Element implicitly has an 'any' type
+      expect(stringUnionSelector(obj, key, union, SelectorType[selectorKey])).toBe(output);
+    });
+
+    // Thows if the value is something other than different case.
+    it.each(["value1", "1value", [...value].reverse().join("")])(`should throw if ${key}=%s`, (input) => {
+      obj[key] = input;
+      // @ts-expect-error Element implicitly has an 'any' type
+      expect(() => stringUnionSelector(obj, key, union, SelectorType[selectorKey])).toThrow(
+        new TypeError(
+          `Cannot load ${selectorValue} '${key}'. Expected one of ${Object.values(union)}, got '${obj[key]}'.`
+        )
+      );
+    });
+  });
+});
diff --git a/packages/middleware-flexible-checksums/src/stringUnionSelector.ts b/packages/middleware-flexible-checksums/src/stringUnionSelector.ts
new file mode 100644
index 000000000000..2ad49baa50e8
--- /dev/null
+++ b/packages/middleware-flexible-checksums/src/stringUnionSelector.ts
@@ -0,0 +1,27 @@
+export enum SelectorType {
+  ENV = "env",
+  CONFIG = "shared config entry",
+}
+
+/**
+ * Returns undefined, if obj[key] is not defined.
+ * Returns string value, if the string is defined in obj[key] and it's uppercase matches union value.
+ * Throws error for all other cases.
+ *
+ * @internal
+ */
+export const stringUnionSelector = (
+  obj: Record<string, string | undefined>,
+  key: string,
+  union: Record<string, string>,
+  type: SelectorType
+) => {
+  if (!(key in obj)) return undefined;
+
+  const value = obj[key]!.toUpperCase();
+  if (!Object.values(union).includes(value)) {
+    throw new TypeError(`Cannot load ${type} '${key}'. Expected one of ${Object.values(union)}, got '${obj[key]}'.`);
+  }
+
+  return value;
+};