diff --git a/.changelog/hint-mostly-unused.md b/.changelog/hint-mostly-unused.md
new file mode 100644
index 00000000000..a77d16b0bc8
--- /dev/null
+++ b/.changelog/hint-mostly-unused.md
@@ -0,0 +1,11 @@
+---
+applies_to: ["client", "aws-sdk-rust"]
+authors: ["joshtriplett"]
+references: []
+breaking: false
+new_feature: true
+bug_fix: false
+---
+Use new `hints.mostly-unused` in Cargo to speed up compilation, given that most
+users of the AWS SDK crates will use a fraction of their API surface area. This
+speeds up compilation of `aws-sdk-ec2` from ~4m07s to ~2m04s, a ~50% speedup.
diff --git a/aws/sdk/build.gradle.kts b/aws/sdk/build.gradle.kts
index e41947a82e2..3630cd494a6 100644
--- a/aws/sdk/build.gradle.kts
+++ b/aws/sdk/build.gradle.kts
@@ -118,6 +118,7 @@ fun generateSmithyBuild(services: AwsServices): String {
                         "moduleRepository": "https://github.com/awslabs/aws-sdk-rust",
                         "license": "Apache-2.0",
                         "minimumSupportedRustVersion": "${getRustMSRV()}",
+                        "hintMostlyUnused": true,
                         "customizationConfig": {
                             "awsSdk": {
                                 "awsSdkBuild": true,
diff --git a/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/ClientRustSettings.kt b/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/ClientRustSettings.kt
index 6ef6cc5433f..47a64dfe966 100644
--- a/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/ClientRustSettings.kt
+++ b/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/ClientRustSettings.kt
@@ -37,6 +37,7 @@ data class ClientRustSettings(
     override val license: String?,
     override val examplesUri: String?,
     override val minimumSupportedRustVersion: String? = null,
+    override val hintMostlyUnused: Boolean = true,
     override val customizationConfig: ObjectNode?,
 ) : CoreRustSettings(
         service,
@@ -50,6 +51,7 @@ data class ClientRustSettings(
         license,
         examplesUri,
         minimumSupportedRustVersion,
+        hintMostlyUnused,
         customizationConfig,
     ) {
     companion object {
@@ -72,6 +74,7 @@ data class ClientRustSettings(
                 license = coreRustSettings.license,
                 examplesUri = coreRustSettings.examplesUri,
                 minimumSupportedRustVersion = coreRustSettings.minimumSupportedRustVersion,
+                hintMostlyUnused = coreRustSettings.hintMostlyUnused,
                 customizationConfig = coreRustSettings.customizationConfig,
             )
         }
diff --git a/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/testutil/TestHelpers.kt b/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/testutil/TestHelpers.kt
index b087d5078e4..c20cf09af51 100644
--- a/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/testutil/TestHelpers.kt
+++ b/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/testutil/TestHelpers.kt
@@ -37,6 +37,7 @@ fun testClientRustSettings(
     license: String? = null,
     examplesUri: String? = null,
     minimumSupportedRustVersion: String? = null,
+    hintMostlyUnused: Boolean = false,
     customizationConfig: ObjectNode? = null,
 ) = ClientRustSettings(
     service,
@@ -50,6 +51,7 @@ fun testClientRustSettings(
     license,
     examplesUri,
     minimumSupportedRustVersion,
+    hintMostlyUnused,
     customizationConfig,
 )
 
diff --git a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/CoreRustSettings.kt b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/CoreRustSettings.kt
index e320540b0de..a5bb8f6da76 100644
--- a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/CoreRustSettings.kt
+++ b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/CoreRustSettings.kt
@@ -27,6 +27,7 @@ private const val RUNTIME_CONFIG = "runtimeConfig"
 private const val LICENSE = "license"
 private const val EXAMPLES = "examples"
 private const val MINIMUM_SUPPORTED_RUST_VERSION = "minimumSupportedRustVersion"
+private const val HINT_MOSTLY_UNUSED = "hintMostlyUnused"
 private const val CUSTOMIZATION_CONFIG = "customizationConfig"
 const val CODEGEN_SETTINGS = "codegen"
 
@@ -90,6 +91,7 @@ open class CoreRustSettings(
     open val license: String?,
     open val examplesUri: String? = null,
     open val minimumSupportedRustVersion: String? = null,
+    open val hintMostlyUnused: Boolean = false,
     open val customizationConfig: ObjectNode? = null,
 ) {
     /**
@@ -179,6 +181,7 @@ open class CoreRustSettings(
                     EXAMPLES,
                     LICENSE,
                     MINIMUM_SUPPORTED_RUST_VERSION,
+                    HINT_MOSTLY_UNUSED,
                     CUSTOMIZATION_CONFIG,
                 ),
             )
@@ -201,6 +204,7 @@ open class CoreRustSettings(
                 license = config.getStringMember(LICENSE).orNull()?.value,
                 examplesUri = config.getStringMember(EXAMPLES).orNull()?.value,
                 minimumSupportedRustVersion = config.getStringMember(MINIMUM_SUPPORTED_RUST_VERSION).orNull()?.value,
+                hintMostlyUnused = config.getBooleanMemberOrDefault(HINT_MOSTLY_UNUSED, false),
                 customizationConfig = config.getObjectMember(CUSTOMIZATION_CONFIG).orNull(),
             )
         }
diff --git a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/CargoTomlGenerator.kt b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/CargoTomlGenerator.kt
index e5f49163489..3ddb2381f98 100644
--- a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/CargoTomlGenerator.kt
+++ b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/CargoTomlGenerator.kt
@@ -50,6 +50,7 @@ class CargoTomlGenerator(
     private val moduleLicense: String?,
     private val moduleRepository: String?,
     private val minimumSupportedRustVersion: String?,
+    private val hintMostlyUnused: Boolean,
     private val writer: RustWriter,
     private val manifestCustomizations: ManifestCustomizations = emptyMap(),
     private val dependencies: List<CargoDependency> = emptyList(),
@@ -69,6 +70,7 @@ class CargoTomlGenerator(
         settings.license,
         settings.moduleRepository,
         settings.minimumSupportedRustVersion,
+        settings.hintMostlyUnused,
         writer,
         manifestCustomizations,
         dependencies,
@@ -101,6 +103,7 @@ class CargoTomlGenerator(
                                     ).toMap(),
                             ).toMap(),
                     ).toMap(),
+                hintMostlyUnused.let { "hints" to listOfNotNull("mostly-unused" to true).toMap() },
                 "dependencies" to
                     dependencies.filter { it.scope == DependencyScope.Compile }
                         .associate { it.name to it.toMap() },
diff --git a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/Rust.kt b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/Rust.kt
index 368081e7643..f64fa377538 100644
--- a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/Rust.kt
+++ b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/Rust.kt
@@ -488,6 +488,7 @@ private fun String.intoCrate(
                 moduleLicense = null,
                 moduleRepository = null,
                 minimumSupportedRustVersion = null,
+                hintMostlyUnused = false,
                 writer = this,
                 dependencies = deps,
             ).render()
diff --git a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/TestHelpers.kt b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/TestHelpers.kt
index 42997a80127..28658827b65 100644
--- a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/TestHelpers.kt
+++ b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/TestHelpers.kt
@@ -127,6 +127,7 @@ fun testRustSettings(
     moduleAuthors: List<String> = listOf("notrelevant"),
     moduleDescription: String = "not relevant",
     moduleRepository: String? = null,
+    hintMostlyUnused: Boolean = false,
     runtimeConfig: RuntimeConfig = TestRuntimeConfig,
     codegenConfig: CoreCodegenConfig = CoreCodegenConfig(),
     license: String? = null,
@@ -138,6 +139,7 @@ fun testRustSettings(
     moduleAuthors,
     moduleDescription,
     moduleRepository,
+    hintMostlyUnused,
     runtimeConfig,
     codegenConfig,
     license,
diff --git a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/ServerRustSettings.kt b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/ServerRustSettings.kt
index b5949ad09c7..3c8c57b7b1d 100644
--- a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/ServerRustSettings.kt
+++ b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/ServerRustSettings.kt
@@ -39,6 +39,7 @@ data class ServerRustSettings(
     override val license: String?,
     override val examplesUri: String?,
     override val minimumSupportedRustVersion: String? = null,
+    override val hintMostlyUnused: Boolean = false,
     override val customizationConfig: ObjectNode?,
 ) : CoreRustSettings(
         service,
@@ -52,6 +53,7 @@ data class ServerRustSettings(
         license,
         examplesUri,
         minimumSupportedRustVersion,
+        hintMostlyUnused,
         customizationConfig,
     ) {
     companion object {
@@ -74,6 +76,7 @@ data class ServerRustSettings(
                 license = coreRustSettings.license,
                 examplesUri = coreRustSettings.examplesUri,
                 minimumSupportedRustVersion = coreRustSettings.minimumSupportedRustVersion,
+                hintMostlyUnused = coreRustSettings.hintMostlyUnused,
                 customizationConfig = coreRustSettings.customizationConfig,
             )
         }
diff --git a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/testutil/ServerTestHelpers.kt b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/testutil/ServerTestHelpers.kt
index a03dfbdd4e3..77cd8368cf1 100644
--- a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/testutil/ServerTestHelpers.kt
+++ b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/testutil/ServerTestHelpers.kt
@@ -82,6 +82,7 @@ fun serverTestRustSettings(
     license: String? = null,
     examplesUri: String? = null,
     minimumSupportedRustVersion: String? = null,
+    hintMostlyUnused: Boolean = false,
     customizationConfig: ObjectNode? = null,
 ) = ServerRustSettings(
     service,
@@ -95,6 +96,7 @@ fun serverTestRustSettings(
     license,
     examplesUri,
     minimumSupportedRustVersion,
+    hintMostlyUnused,
     customizationConfig,
 )