diff --git a/packages/credential-provider-http/src/fromHttp/fromHttp.spec.ts b/packages/credential-provider-http/src/fromHttp/fromHttp.spec.ts
index f88c6e0ffd2c6..903bb9c12d968 100644
--- a/packages/credential-provider-http/src/fromHttp/fromHttp.spec.ts
+++ b/packages/credential-provider-http/src/fromHttp/fromHttp.spec.ts
@@ -25,7 +25,7 @@ const mockHandle = jest.fn().mockResolvedValue({
   response: new HttpResponse({
     statusCode: 200,
     headers: {
-      "Content-Type": "application/json",
+      "content-type": "application/json",
     },
     body: Readable.from([""]),
   }),
diff --git a/packages/credential-provider-http/src/fromHttp/requestHelpers.spec.ts b/packages/credential-provider-http/src/fromHttp/requestHelpers.spec.ts
index ddb1d4b069d17..df2f52cc07191 100644
--- a/packages/credential-provider-http/src/fromHttp/requestHelpers.spec.ts
+++ b/packages/credential-provider-http/src/fromHttp/requestHelpers.spec.ts
@@ -17,7 +17,7 @@ describe(getCredentials.name, () => {
     const response = new HttpResponse({
       statusCode: 200,
       headers: {
-        "Content-Type": "application/json",
+        "content-type": "application/json",
       },
       body: Readable.from(JSON.stringify(data)),
     });
@@ -34,7 +34,7 @@ describe(getCredentials.name, () => {
     const response = new HttpResponse({
       statusCode: 400,
       headers: {
-        "Content-Type": "application/json",
+        "content-type": "application/json",
       },
       body: Readable.from(
         JSON.stringify({
@@ -57,7 +57,7 @@ describe(getCredentials.name, () => {
     const response = new HttpResponse({
       statusCode: 500,
       headers: {
-        "Content-Type": "json",
+        "content-type": "json",
       },
       body: Readable.from(JSON.stringify({})),
     });
diff --git a/packages/middleware-eventstream/src/eventStreamHeaderMiddleware.ts b/packages/middleware-eventstream/src/eventStreamHeaderMiddleware.ts
index 6e52508d839da..1ffe2a36ee541 100644
--- a/packages/middleware-eventstream/src/eventStreamHeaderMiddleware.ts
+++ b/packages/middleware-eventstream/src/eventStreamHeaderMiddleware.ts
@@ -5,7 +5,7 @@ export const eventStreamHeaderMiddleware: BuildMiddleware<any, any> = (next) =>
   if (!HttpRequest.isInstance(request)) return next(args);
   request.headers = {
     ...request.headers,
-    "Content-Type": "application/vnd.amazon.eventstream",
+    "content-type": "application/vnd.amazon.eventstream",
     "x-amz-content-sha256": "STREAMING-AWS4-HMAC-SHA256-EVENTS",
   };
   return next({
diff --git a/packages/middleware-eventstream/src/middleware-eventstream.integ.spec.ts b/packages/middleware-eventstream/src/middleware-eventstream.integ.spec.ts
index 8bafcb49fe091..2216bdda63bc9 100644
--- a/packages/middleware-eventstream/src/middleware-eventstream.integ.spec.ts
+++ b/packages/middleware-eventstream/src/middleware-eventstream.integ.spec.ts
@@ -20,7 +20,7 @@ describe("middleware-eventstream", () => {
 
       requireRequestsFrom(client).toMatch({
         headers: {
-          "Content-Type": "application/vnd.amazon.eventstream",
+          "content-type": "application/vnd.amazon.eventstream",
           "x-amz-content-sha256": "STREAMING-AWS4-HMAC-SHA256-EVENTS",
         },
       });
@@ -51,7 +51,7 @@ describe("middleware-eventstream", () => {
 
       requireRequestsFrom(client).toMatch({
         headers: {
-          "Content-Type": "application/vnd.amazon.eventstream",
+          "content-type": "application/vnd.amazon.eventstream",
           "x-amz-content-sha256": "STREAMING-AWS4-HMAC-SHA256-EVENTS",
         },
       });
@@ -83,7 +83,7 @@ describe("middleware-eventstream", () => {
 
       requireRequestsFrom(client).toMatch({
         headers: {
-          "Content-Type": "application/vnd.amazon.eventstream",
+          "content-type": "application/vnd.amazon.eventstream",
           "x-amz-content-sha256": "STREAMING-AWS4-HMAC-SHA256-EVENTS",
         },
       });
diff --git a/packages/middleware-sdk-transcribe-streaming/src/middleware-sdk-transcribe-streaming.integ.spec.ts b/packages/middleware-sdk-transcribe-streaming/src/middleware-sdk-transcribe-streaming.integ.spec.ts
index af595d18996f1..1e01f09cffd9d 100644
--- a/packages/middleware-sdk-transcribe-streaming/src/middleware-sdk-transcribe-streaming.integ.spec.ts
+++ b/packages/middleware-sdk-transcribe-streaming/src/middleware-sdk-transcribe-streaming.integ.spec.ts
@@ -12,7 +12,7 @@ describe("middleware-sdk-transcribe-streaming", () => {
 
       requireRequestsFrom(client).toMatch({
         headers: {
-          "Content-Type": /undefined/,
+          "content-type": /undefined/,
           host: "transcribestreaming.us-west-2.amazonaws.com:8443",
         },
         query: {
diff --git a/packages/middleware-websocket/src/middleware-websocket-endpoint.spec.ts b/packages/middleware-websocket/src/middleware-websocket-endpoint.spec.ts
index 0472fc1f1efee..fe4658023d324 100644
--- a/packages/middleware-websocket/src/middleware-websocket-endpoint.spec.ts
+++ b/packages/middleware-websocket/src/middleware-websocket-endpoint.spec.ts
@@ -38,7 +38,7 @@ describe(websocketEndpointMiddleware.name, () => {
     mw(next as any, {} as any)({ request, input: {} });
   });
 
-  it("should remove content-type and sha256 hash header", (done) => {
+  it("should remove content-type and sha256 hash header without transferring them to query parameters", (done) => {
     const request = new HttpRequest({
       headers: {
         "content-type": "application/vnd.amazon.eventstream",
@@ -50,21 +50,22 @@ describe(websocketEndpointMiddleware.name, () => {
     const next = (args: BuildHandlerArguments<any>) => {
       expect(HttpRequest.isInstance(args.request)).toBeTruthy();
       const processed = args.request as HttpRequest;
-      expect(processed.headers["content-type"]).toBeUndefined();
-      expect(processed.headers["Content-Type"]).toBeUndefined();
-      expect(processed.headers["x-amz-content-sha256"]).toBeUndefined();
-      expect(processed.headers["X-Amz-Content-Sha256"]).toBeUndefined();
+      const queryKeys = Object.keys(processed.query).map((key) => key.toLowerCase());
+      expect(queryKeys).not.toContain("content-type");
+      expect(queryKeys).not.toContain("x-amz-content-sha256");
       done();
     };
     const mw = websocketEndpointMiddleware(config, handlerOption);
     mw(next as any, {} as any)({ request, input: {} });
   });
 
-  it("should contains host header after adjustment", (done) => {
+  it("should contain only a host header after adjustment", (done) => {
     const request = new HttpRequest({});
     const next = (args: BuildHandlerArguments<any>) => {
       expect(HttpRequest.isInstance(args.request)).toBeTruthy();
       const processed = args.request as HttpRequest;
+      const headerKeys = Object.keys(processed.headers).map((key) => key.toLowerCase());
+      expect(headerKeys).toEqual(["host"]);
       expect(processed.headers["host"]).toBeDefined();
       done();
     };
diff --git a/packages/middleware-websocket/src/middleware-websocket-endpoint.ts b/packages/middleware-websocket/src/middleware-websocket-endpoint.ts
index ed36f4a1ef321..af5b168d173fc 100644
--- a/packages/middleware-websocket/src/middleware-websocket-endpoint.ts
+++ b/packages/middleware-websocket/src/middleware-websocket-endpoint.ts
@@ -37,7 +37,7 @@ export const websocketEndpointMiddleware =
       // 'Content-Type' and 'x-amz-content-sha256' headers are normally set for
       // event stream, but WebSocket doesn't require it.
       // See: 'eventStreamHeaderMiddleware' in @aws-sdk/middleware-eventstream
-      delete headers["Content-Type"];
+      delete headers["content-type"];
       delete headers["x-amz-content-sha256"];
 
       for (const name of Object.keys(headers)) {
diff --git a/packages/middleware-websocket/src/middleware-websocket.integ.spec.ts b/packages/middleware-websocket/src/middleware-websocket.integ.spec.ts
index 2c4b888ca4c5f..7155b92c4979d 100644
--- a/packages/middleware-websocket/src/middleware-websocket.integ.spec.ts
+++ b/packages/middleware-websocket/src/middleware-websocket.integ.spec.ts
@@ -21,7 +21,7 @@ describe("middleware-websocket", () => {
         path: "/start-face-liveness-session-websocket",
         headers: {
           host: "streaming-rekognition.us-west-2.amazonaws.com",
-          "Content-Type": /^undefined$/,
+          "content-type": /^undefined$/,
           "x-amz-content-sha256": /^undefined$/,
           "user-agent": /^aws-sdk-js/,
         },
diff --git a/packages/s3-request-presigner/src/presigner.spec.ts b/packages/s3-request-presigner/src/presigner.spec.ts
index 016d873f211e4..73220f9015f65 100644
--- a/packages/s3-request-presigner/src/presigner.spec.ts
+++ b/packages/s3-request-presigner/src/presigner.spec.ts
@@ -71,7 +71,7 @@ describe("s3 presigner", () => {
       ...minimalRequest,
       headers: {
         ...minimalRequest.headers,
-        "Content-Type": "application/octet-stream",
+        "content-type": "application/octet-stream",
       },
     };
     const signed = await signer.presign(requestWithContentTypeHeader, presigningOptions);