diff --git a/Sources/ClientRuntime/Client/Client.swift b/Sources/ClientRuntime/Client/Client.swift
index 424d580fe..40742a4fd 100644
--- a/Sources/ClientRuntime/Client/Client.swift
+++ b/Sources/ClientRuntime/Client/Client.swift
@@ -4,7 +4,7 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 //
-public protocol Client {
+public protocol Client: Sendable {
     associatedtype Config: ClientConfiguration
     init(config: Config)
 }
diff --git a/Sources/ClientRuntime/Config/ClientConfiguration.swift b/Sources/ClientRuntime/Config/ClientConfiguration.swift
index 8b76fe7c5..f0a4129d7 100644
--- a/Sources/ClientRuntime/Config/ClientConfiguration.swift
+++ b/Sources/ClientRuntime/Config/ClientConfiguration.swift
@@ -5,6 +5,6 @@
 // SPDX-License-Identifier: Apache-2.0
 //
 
-public protocol ClientConfiguration {
+public protocol ClientConfiguration: Sendable {
     init() async throws
 }
diff --git a/Sources/ClientRuntime/Networking/Http/CRT/CRTClientEngine.swift b/Sources/ClientRuntime/Networking/Http/CRT/CRTClientEngine.swift
index 1b61a9467..699bef0dc 100644
--- a/Sources/ClientRuntime/Networking/Http/CRT/CRTClientEngine.swift
+++ b/Sources/ClientRuntime/Networking/Http/CRT/CRTClientEngine.swift
@@ -29,7 +29,7 @@ import Glibc
 import Darwin
 #endif
 
-public class CRTClientEngine: HTTPClient {
+public class CRTClientEngine: HTTPClient, @unchecked Sendable {
     public static let noOpCrtClientEngineTelemetry = HttpTelemetry(
         httpScope: "CRTClientEngine",
         telemetryProvider: DefaultTelemetry.provider
@@ -171,7 +171,7 @@ public class CRTClientEngine: HTTPClient {
 
     public typealias StreamContinuation = CheckedContinuation<HTTPResponse, Error>
     private let telemetry: HttpTelemetry
-    private var logger: LogAgent
+    private let logger: LogAgent
     private let serialExecutor: SerialExecutor
     private let CONTENT_LENGTH_HEADER = "Content-Length"
     private let AWS_COMMON_RUNTIME = "AwsCommonRuntime"
diff --git a/Sources/ClientRuntime/Networking/Http/SdkHttpClient.swift b/Sources/ClientRuntime/Networking/Http/SdkHttpClient.swift
index 827009df6..702dff0dc 100644
--- a/Sources/ClientRuntime/Networking/Http/SdkHttpClient.swift
+++ b/Sources/ClientRuntime/Networking/Http/SdkHttpClient.swift
@@ -9,7 +9,7 @@ import class SmithyHTTPAPI.HTTPRequest
 import class SmithyHTTPAPI.HTTPResponse
 
 /// this class will implement Handler per new middleware implementation
-public class SdkHttpClient: ExecuteRequest {
+public class SdkHttpClient: ExecuteRequest, @unchecked Sendable {
 
     let engine: HTTPClient
 
diff --git a/Sources/ClientRuntime/Networking/Http/URLSession/URLSessionHTTPClient.swift b/Sources/ClientRuntime/Networking/Http/URLSession/URLSessionHTTPClient.swift
index 2a0c6ea20..e3594c41d 100644
--- a/Sources/ClientRuntime/Networking/Http/URLSession/URLSessionHTTPClient.swift
+++ b/Sources/ClientRuntime/Networking/Http/URLSession/URLSessionHTTPClient.swift
@@ -56,7 +56,7 @@ import class SmithyStreams.BufferedStream
 /// for details about allowable modes of networking on the Apple Watch platform.)
 ///
 /// On Linux platforms, we recommend using the CRT-based HTTP client for its configurability and performance.
-public final class URLSessionHTTPClient: HTTPClient {
+public final class URLSessionHTTPClient: HTTPClient, @unchecked Sendable {
     public static let noOpURLSessionHTTPClientTelemetry = HttpTelemetry(
         httpScope: "URLSessionHTTPClient",
         telemetryProvider: DefaultTelemetry.provider
@@ -406,7 +406,7 @@ public final class URLSessionHTTPClient: HTTPClient {
     private let telemetry: HttpTelemetry
 
     /// The logger for this HTTP client.
-    private var logger: LogAgent
+    private let logger: LogAgent
 
     /// The TLS options for this HTTP client.
     private let tlsConfiguration: URLSessionTLSOptions?
diff --git a/Sources/SmithyHTTPAPI/HTTPClient.swift b/Sources/SmithyHTTPAPI/HTTPClient.swift
index d6268ede5..067e5d6d1 100644
--- a/Sources/SmithyHTTPAPI/HTTPClient.swift
+++ b/Sources/SmithyHTTPAPI/HTTPClient.swift
@@ -6,7 +6,7 @@
 //
 
 /// The interface for a client that can be used to perform SDK operations over HTTP.
-public protocol HTTPClient {
+public protocol HTTPClient: Sendable {
 
     /// Executes an HTTP request to perform an SDK operation.
     ///
diff --git a/Sources/SmithyHTTPClientAPI/HttpClientConfiguration.swift b/Sources/SmithyHTTPClientAPI/HttpClientConfiguration.swift
index 9bec15b91..e3161d83a 100644
--- a/Sources/SmithyHTTPClientAPI/HttpClientConfiguration.swift
+++ b/Sources/SmithyHTTPClientAPI/HttpClientConfiguration.swift
@@ -9,7 +9,7 @@ import struct Foundation.TimeInterval
 import enum Smithy.URIScheme
 import struct SmithyHTTPAPI.Headers
 
-public class HTTPClientConfiguration {
+public class HTTPClientConfiguration: @unchecked Sendable {
 
     /// The timeout for establishing a connection, in seconds.
     ///
diff --git a/Sources/SmithyHTTPClientAPI/TLSConfiguration.swift b/Sources/SmithyHTTPClientAPI/TLSConfiguration.swift
index d4ed04ece..c957e8f95 100644
--- a/Sources/SmithyHTTPClientAPI/TLSConfiguration.swift
+++ b/Sources/SmithyHTTPClientAPI/TLSConfiguration.swift
@@ -10,7 +10,7 @@
  * All settings are optional.
  * Not specifying them will use the SDK defaults
  */
-public protocol TLSConfiguration {
+public protocol TLSConfiguration: Sendable {
 
     // Optional path to a PEM certificate
     var certificate: String? { get set }
diff --git a/Sources/SmithyIdentity/AWSCredentialIdentityResolver.swift b/Sources/SmithyIdentity/AWSCredentialIdentityResolver.swift
index 1e3e47a8b..9091cffc8 100644
--- a/Sources/SmithyIdentity/AWSCredentialIdentityResolver.swift
+++ b/Sources/SmithyIdentity/AWSCredentialIdentityResolver.swift
@@ -10,7 +10,7 @@ import struct Smithy.Attributes
 import protocol SmithyIdentityAPI.IdentityResolver
 
 /// A type that can provide credentials for authenticating with an AWS service
-public protocol AWSCredentialIdentityResolver: IdentityResolver where IdentityT == AWSCredentialIdentity {}
+public protocol AWSCredentialIdentityResolver: IdentityResolver, Sendable where IdentityT == AWSCredentialIdentity {}
 
 public extension AWSCredentialIdentityResolver {
 
diff --git a/Sources/SmithyIdentity/BearerTokenIdentityResolvers/BearerTokenIdentityResolver.swift b/Sources/SmithyIdentity/BearerTokenIdentityResolvers/BearerTokenIdentityResolver.swift
index 539c7cdbe..1759f9002 100644
--- a/Sources/SmithyIdentity/BearerTokenIdentityResolvers/BearerTokenIdentityResolver.swift
+++ b/Sources/SmithyIdentity/BearerTokenIdentityResolvers/BearerTokenIdentityResolver.swift
@@ -9,4 +9,4 @@ import protocol SmithyIdentityAPI.IdentityResolver
 
 /// The type that resolves a bearer token identity for authenticating with a service.
 /// All concrete implementations for bearer token identity resolver must conform to this protocol.
-public protocol BearerTokenIdentityResolver: IdentityResolver where IdentityT == BearerTokenIdentity {}
+public protocol BearerTokenIdentityResolver: IdentityResolver, Sendable where IdentityT == BearerTokenIdentity {}
diff --git a/Sources/SmithySwiftNIO/SwiftNIOHTTPClient.swift b/Sources/SmithySwiftNIO/SwiftNIOHTTPClient.swift
index 69761212c..560aadadb 100644
--- a/Sources/SmithySwiftNIO/SwiftNIOHTTPClient.swift
+++ b/Sources/SmithySwiftNIO/SwiftNIOHTTPClient.swift
@@ -37,7 +37,7 @@ public final class SwiftNIOHTTPClient: SmithyHTTPAPI.HTTPClient {
     private let telemetry: SmithyHTTPClientAPI.HttpTelemetry
 
     /// Logger for HTTP-related events.
-    private var logger: LogAgent
+    private let logger: LogAgent
 
     /// Creates a new `SwiftNIOHTTPClient`.
     ///
diff --git a/Sources/SmithyTestUtil/ProtocolTestClient.swift b/Sources/SmithyTestUtil/ProtocolTestClient.swift
index c3d591fb8..026547680 100644
--- a/Sources/SmithyTestUtil/ProtocolTestClient.swift
+++ b/Sources/SmithyTestUtil/ProtocolTestClient.swift
@@ -8,7 +8,7 @@ import class SmithyHTTPAPI.HTTPRequest
 import class SmithyHTTPAPI.HTTPResponse
 import ClientRuntime
 
-public class ProtocolTestClient {
+public final class ProtocolTestClient {
     public init() {}
 }
 
diff --git a/smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/endpoints/EndpointResolverGenerator.kt b/smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/endpoints/EndpointResolverGenerator.kt
index 0b5c9179c..2969eb668 100644
--- a/smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/endpoints/EndpointResolverGenerator.kt
+++ b/smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/endpoints/EndpointResolverGenerator.kt
@@ -64,7 +64,7 @@ class EndpointResolverGenerator(
             }
         }
         writer.write("")
-        writer.write("extension DefaultEndpointResolver: EndpointResolver {}")
+        writer.write("extension DefaultEndpointResolver: EndpointResolver where Params == EndpointParams {}")
     }
 
     private fun renderStaticResolver(writer: SwiftWriter) {
diff --git a/smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/integration/HttpProtocolServiceClient.kt b/smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/integration/HttpProtocolServiceClient.kt
index 99ba1847e..39a4d3803 100644
--- a/smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/integration/HttpProtocolServiceClient.kt
+++ b/smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/integration/HttpProtocolServiceClient.kt
@@ -26,7 +26,7 @@ open class HttpProtocolServiceClient(
 
     fun render(serviceSymbol: Symbol) {
         writer.openBlock(
-            "${ctx.settings.visibility} class \$L: \$N {",
+            "${ctx.settings.visibility} final class \$L: \$N, Sendable {",
             "}",
             serviceSymbol.name,
             clientProtocolSymbol,
@@ -119,7 +119,7 @@ open class HttpProtocolServiceClient(
                 .joinToString(" & ")
 
         writer.openBlock(
-            "public class \$LConfiguration: \$L {",
+            "public final class \$LConfiguration: \$L, @unchecked Sendable {",
             "}",
             serviceConfig.clientName.toUpperCamelCase(),
             clientConfigurationProtocols,
diff --git a/smithy-swift-codegen/src/test/kotlin/software/amazon/smithy/swift/codegen/HttpProtocolClientGeneratorTests.kt b/smithy-swift-codegen/src/test/kotlin/software/amazon/smithy/swift/codegen/HttpProtocolClientGeneratorTests.kt
index 800f64fd3..41e19ecb4 100644
--- a/smithy-swift-codegen/src/test/kotlin/software/amazon/smithy/swift/codegen/HttpProtocolClientGeneratorTests.kt
+++ b/smithy-swift-codegen/src/test/kotlin/software/amazon/smithy/swift/codegen/HttpProtocolClientGeneratorTests.kt
@@ -17,7 +17,7 @@ class HttpProtocolClientGeneratorTests {
         val contents = getFileContents(context.manifest, "Sources/RestJson/RestJsonProtocolClient.swift")
         contents.shouldSyntacticSanityCheck()
         val expected = """
-public class RestJsonProtocolClient: ClientRuntime.Client {
+public final class RestJsonProtocolClient: ClientRuntime.Client, Sendable {
     public static let clientName = "RestJsonProtocolClient"
     public static let version = "2019-12-16"
     let client: ClientRuntime.SdkHttpClient
@@ -38,7 +38,7 @@ public class RestJsonProtocolClient: ClientRuntime.Client {
 
 extension RestJsonProtocolClient {
 
-    public class RestJsonProtocolClientConfiguration: ClientRuntime.DefaultClientConfiguration & ClientRuntime.DefaultHttpClientConfiguration {
+    public final class RestJsonProtocolClientConfiguration: ClientRuntime.DefaultClientConfiguration & ClientRuntime.DefaultHttpClientConfiguration, @unchecked Sendable {
         public var telemetryProvider: ClientRuntime.TelemetryProvider
         public var retryStrategyOptions: SmithyRetriesAPI.RetryStrategyOptions
         public var clientLogMode: ClientRuntime.ClientLogMode