diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6d5a7d18e..07b7e3be7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,8 @@ Thank you!
 # 0.18.25
 
 * Fixes an issue in which refinements wouldn't work on custom simple shapes (newtypes) (see [#1595](https://github.com/disneystreaming/smithy4s/pull/1595))
+* Fixes an issue in which union members targetting Unit would fail to compile when used as traits (see [#1600](https://github.com/disneystreaming/smithy4s/pull/1600)).
+* Make the `transform` method in generated `*Gen` algebras final. This should make it possible to derive e.g. `FunctorK` instances in cats-tagless automatically (see [#1588](https://github.com/disneystreaming/smithy4s/pull/1588)).
 
 # 0.18.24
 
diff --git a/modules/bootstrapped/src/generated/com/amazonaws/dynamodb/DynamoDB.scala b/modules/bootstrapped/src/generated/com/amazonaws/dynamodb/DynamoDB.scala
index f41e79195..31ef79bf9 100644
--- a/modules/bootstrapped/src/generated/com/amazonaws/dynamodb/DynamoDB.scala
+++ b/modules/bootstrapped/src/generated/com/amazonaws/dynamodb/DynamoDB.scala
@@ -49,7 +49,7 @@ trait DynamoDBGen[F[_, _, _, _, _]] {
     */
   def listTables(exclusiveStartTableName: Option[TableName] = None, limit: Option[ListTablesInputLimit] = None): F[ListTablesInput, DynamoDBOperation.ListTablesError, ListTablesOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[DynamoDBGen[F]] = Transformation.of[DynamoDBGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[DynamoDBGen[F]] = Transformation.of[DynamoDBGen[F]](this)
 }
 
 object DynamoDBGen extends Service.Mixin[DynamoDBGen, DynamoDBOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/benchmark/BenchmarkService.scala b/modules/bootstrapped/src/generated/smithy4s/benchmark/BenchmarkService.scala
index e1ef29d50..e61d8593f 100644
--- a/modules/bootstrapped/src/generated/smithy4s/benchmark/BenchmarkService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/benchmark/BenchmarkService.scala
@@ -17,7 +17,7 @@ trait BenchmarkServiceGen[F[_, _, _, _, _]] {
   def createObject(key: String, bucketName: String, payload: S3Object): F[CreateObjectInput, Nothing, Unit, Nothing, Nothing]
   def sendString(key: String, bucketName: String, body: String): F[SendStringInput, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[BenchmarkServiceGen[F]] = Transformation.of[BenchmarkServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[BenchmarkServiceGen[F]] = Transformation.of[BenchmarkServiceGen[F]](this)
 }
 
 object BenchmarkServiceGen extends Service.Mixin[BenchmarkServiceGen, BenchmarkServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/BrandService.scala b/modules/bootstrapped/src/generated/smithy4s/example/BrandService.scala
index 5f9d88637..3ccfb0e5b 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/BrandService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/BrandService.scala
@@ -16,7 +16,7 @@ trait BrandServiceGen[F[_, _, _, _, _]] {
 
   def addBrands(brands: Option[List[String]] = None): F[AddBrandsInput, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[BrandServiceGen[F]] = Transformation.of[BrandServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[BrandServiceGen[F]] = Transformation.of[BrandServiceGen[F]](this)
 }
 
 object BrandServiceGen extends Service.Mixin[BrandServiceGen, BrandServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/DeprecatedService.scala b/modules/bootstrapped/src/generated/smithy4s/example/DeprecatedService.scala
index 189dfd330..6d000b0ac 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/DeprecatedService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/DeprecatedService.scala
@@ -18,7 +18,7 @@ trait DeprecatedServiceGen[F[_, _, _, _, _]] {
   @deprecated(message = "N/A", since = "N/A")
   def deprecatedOperation(): F[Unit, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[DeprecatedServiceGen[F]] = Transformation.of[DeprecatedServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[DeprecatedServiceGen[F]] = Transformation.of[DeprecatedServiceGen[F]](this)
 }
 
 object DeprecatedServiceGen extends Service.Mixin[DeprecatedServiceGen, DeprecatedServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/DiscriminatedService.scala b/modules/bootstrapped/src/generated/smithy4s/example/DiscriminatedService.scala
index 8c7cb21d2..a5a25f430 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/DiscriminatedService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/DiscriminatedService.scala
@@ -15,7 +15,7 @@ trait DiscriminatedServiceGen[F[_, _, _, _, _]] {
 
   def testDiscriminated(key: String): F[TestDiscriminatedInput, Nothing, TestDiscriminatedOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[DiscriminatedServiceGen[F]] = Transformation.of[DiscriminatedServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[DiscriminatedServiceGen[F]] = Transformation.of[DiscriminatedServiceGen[F]](this)
 }
 
 object DiscriminatedServiceGen extends Service.Mixin[DiscriminatedServiceGen, DiscriminatedServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/DummyService.scala b/modules/bootstrapped/src/generated/smithy4s/example/DummyService.scala
index e498cc779..d5648f46b 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/DummyService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/DummyService.scala
@@ -22,7 +22,7 @@ trait DummyServiceGen[F[_, _, _, _, _]] {
   def dummyHostPrefix(label1: String, label2: String, label3: HostLabelEnum): F[HostLabelInput, Nothing, Unit, Nothing, Nothing]
   def dummyPath(str: String, int: Int, ts1: Timestamp, ts2: Timestamp, ts3: Timestamp, ts4: Timestamp, b: Boolean, ie: Numbers): F[PathParams, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[DummyServiceGen[F]] = Transformation.of[DummyServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[DummyServiceGen[F]] = Transformation.of[DummyServiceGen[F]](this)
 }
 
 object DummyServiceGen extends Service.Mixin[DummyServiceGen, DummyServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/EmptyService.scala b/modules/bootstrapped/src/generated/smithy4s/example/EmptyService.scala
index a2c14736b..be71cd940 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/EmptyService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/EmptyService.scala
@@ -12,7 +12,7 @@ trait EmptyServiceGen[F[_, _, _, _, _]] {
   self =>
 
 
-  def transform: Transformation.PartiallyApplied[EmptyServiceGen[F]] = Transformation.of[EmptyServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[EmptyServiceGen[F]] = Transformation.of[EmptyServiceGen[F]](this)
 }
 
 object EmptyServiceGen extends Service.Mixin[EmptyServiceGen, EmptyServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/ErrorHandlingService.scala b/modules/bootstrapped/src/generated/smithy4s/example/ErrorHandlingService.scala
index 798bfdb62..ffdfb8b6f 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/ErrorHandlingService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/ErrorHandlingService.scala
@@ -18,7 +18,7 @@ trait ErrorHandlingServiceGen[F[_, _, _, _, _]] {
 
   def errorHandlingOperation(in: Option[String] = None): F[ErrorHandlingOperationInput, ErrorHandlingServiceOperation.ErrorHandlingOperationError, ErrorHandlingOperationOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[ErrorHandlingServiceGen[F]] = Transformation.of[ErrorHandlingServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[ErrorHandlingServiceGen[F]] = Transformation.of[ErrorHandlingServiceGen[F]](this)
 }
 
 object ErrorHandlingServiceGen extends Service.Mixin[ErrorHandlingServiceGen, ErrorHandlingServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/ErrorHandlingServiceExtraErrors.scala b/modules/bootstrapped/src/generated/smithy4s/example/ErrorHandlingServiceExtraErrors.scala
index a2c0da768..96c145144 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/ErrorHandlingServiceExtraErrors.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/ErrorHandlingServiceExtraErrors.scala
@@ -19,7 +19,7 @@ trait ErrorHandlingServiceExtraErrorsGen[F[_, _, _, _, _]] {
 
   def extraErrorOperation(in: Option[String] = None): F[ExtraErrorOperationInput, ErrorHandlingServiceExtraErrorsOperation.ExtraErrorOperationError, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[ErrorHandlingServiceExtraErrorsGen[F]] = Transformation.of[ErrorHandlingServiceExtraErrorsGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[ErrorHandlingServiceExtraErrorsGen[F]] = Transformation.of[ErrorHandlingServiceExtraErrorsGen[F]](this)
 }
 
 object ErrorHandlingServiceExtraErrorsGen extends Service.Mixin[ErrorHandlingServiceExtraErrorsGen, ErrorHandlingServiceExtraErrorsOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/FooService.scala b/modules/bootstrapped/src/generated/smithy4s/example/FooService.scala
index 52ba798dc..ed2fccdcf 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/FooService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/FooService.scala
@@ -23,7 +23,7 @@ trait FooServiceGen[F[_, _, _, _, _]] {
     */
   def getFoo(): F[Unit, Nothing, GetFooOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[FooServiceGen[F]] = Transformation.of[FooServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[FooServiceGen[F]] = Transformation.of[FooServiceGen[F]](this)
 }
 
 object FooServiceGen extends Service.Mixin[FooServiceGen, FooServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/HasUnionUnitCaseTrait.scala b/modules/bootstrapped/src/generated/smithy4s/example/HasUnionUnitCaseTrait.scala
new file mode 100644
index 000000000..f96e4fa4c
--- /dev/null
+++ b/modules/bootstrapped/src/generated/smithy4s/example/HasUnionUnitCaseTrait.scala
@@ -0,0 +1,17 @@
+package smithy4s.example
+
+import smithy4s.Hints
+import smithy4s.Newtype
+import smithy4s.Schema
+import smithy4s.ShapeId
+import smithy4s.schema.Schema.bijection
+import smithy4s.schema.Schema.string
+
+object HasUnionUnitCaseTrait extends Newtype[String] {
+  val id: ShapeId = ShapeId("smithy4s.example", "HasUnionUnitCaseTrait")
+  val hints: Hints = Hints(
+    smithy4s.example.UnionTraitWithUnitCase.UCase.widen,
+  ).lazily
+  val underlyingSchema: Schema[String] = string.withId(id).addHints(hints)
+  implicit val schema: Schema[HasUnionUnitCaseTrait] = bijection(underlyingSchema, asBijection)
+}
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/KVStore.scala b/modules/bootstrapped/src/generated/smithy4s/example/KVStore.scala
index 96c88feed..15b069a7d 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/KVStore.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/KVStore.scala
@@ -21,7 +21,7 @@ trait KVStoreGen[F[_, _, _, _, _]] {
   def put(key: String, value: String): F[KeyValue, KVStoreOperation.PutError, Unit, Nothing, Nothing]
   def delete(key: String): F[Key, KVStoreOperation.DeleteError, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[KVStoreGen[F]] = Transformation.of[KVStoreGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[KVStoreGen[F]] = Transformation.of[KVStoreGen[F]](this)
 }
 
 object KVStoreGen extends Service.Mixin[KVStoreGen, KVStoreOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/Library.scala b/modules/bootstrapped/src/generated/smithy4s/example/Library.scala
index 15597ce1b..9ccf90dad 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/Library.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/Library.scala
@@ -18,7 +18,7 @@ trait LibraryGen[F[_, _, _, _, _]] {
   def getBook(): F[Unit, Nothing, Unit, Nothing, Nothing]
   def buyBook(): F[Unit, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[LibraryGen[F]] = Transformation.of[LibraryGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[LibraryGen[F]] = Transformation.of[LibraryGen[F]](this)
 }
 
 object LibraryGen extends Service.Mixin[LibraryGen, LibraryOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/NameCollision.scala b/modules/bootstrapped/src/generated/smithy4s/example/NameCollision.scala
index 00978821a..297a632d4 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/NameCollision.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/NameCollision.scala
@@ -19,7 +19,7 @@ trait NameCollisionGen[F[_, _, _, _, _]] {
   def myOp(): F[Unit, NameCollisionOperation.MyOpError, Unit, Nothing, Nothing]
   def endpoint(): F[Unit, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[NameCollisionGen[F]] = Transformation.of[NameCollisionGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[NameCollisionGen[F]] = Transformation.of[NameCollisionGen[F]](this)
 }
 
 object NameCollisionGen extends Service.Mixin[NameCollisionGen, NameCollisionOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/ObjectCollision.scala b/modules/bootstrapped/src/generated/smithy4s/example/ObjectCollision.scala
index 9de4e60ee..b1165cf9c 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/ObjectCollision.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/ObjectCollision.scala
@@ -24,7 +24,7 @@ trait ObjectCollisionGen[F[_, _, _, _, _]] {
   def _toString(): F[Unit, Nothing, Unit, Nothing, Nothing]
   def _wait(): F[Unit, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[ObjectCollisionGen[F]] = Transformation.of[ObjectCollisionGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[ObjectCollisionGen[F]] = Transformation.of[ObjectCollisionGen[F]](this)
 }
 
 object ObjectCollisionGen extends Service.Mixin[ObjectCollisionGen, ObjectCollisionOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/ObjectService.scala b/modules/bootstrapped/src/generated/smithy4s/example/ObjectService.scala
index eaadab04b..2a636dd80 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/ObjectService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/ObjectService.scala
@@ -27,7 +27,7 @@ trait ObjectServiceGen[F[_, _, _, _, _]] {
     */
   def getObject(key: ObjectKey, bucketName: BucketName): F[GetObjectInput, ObjectServiceOperation.GetObjectError, GetObjectOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[ObjectServiceGen[F]] = Transformation.of[ObjectServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[ObjectServiceGen[F]] = Transformation.of[ObjectServiceGen[F]](this)
 }
 
 object ObjectServiceGen extends Service.Mixin[ObjectServiceGen, ObjectServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/PackedInputsService.scala b/modules/bootstrapped/src/generated/smithy4s/example/PackedInputsService.scala
index 30834b45e..a0d084e90 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/PackedInputsService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/PackedInputsService.scala
@@ -16,7 +16,7 @@ trait PackedInputsServiceGen[F[_, _, _, _, _]] {
 
   def packedInputOperation(input: PackedInput): F[PackedInput, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[PackedInputsServiceGen[F]] = Transformation.of[PackedInputsServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[PackedInputsServiceGen[F]] = Transformation.of[PackedInputsServiceGen[F]](this)
 }
 
 object PackedInputsServiceGen extends Service.Mixin[PackedInputsServiceGen, PackedInputsServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/PizzaAdminService.scala b/modules/bootstrapped/src/generated/smithy4s/example/PizzaAdminService.scala
index 21a8c652e..0d4ecdbb1 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/PizzaAdminService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/PizzaAdminService.scala
@@ -32,7 +32,7 @@ trait PizzaAdminServiceGen[F[_, _, _, _, _]] {
   def headRequest(): F[Unit, Nothing, HeadRequestOutput, Nothing, Nothing]
   def noContentRequest(): F[Unit, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[PizzaAdminServiceGen[F]] = Transformation.of[PizzaAdminServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[PizzaAdminServiceGen[F]] = Transformation.of[PizzaAdminServiceGen[F]](this)
 }
 
 object PizzaAdminServiceGen extends Service.Mixin[PizzaAdminServiceGen, PizzaAdminServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/RecursiveInputService.scala b/modules/bootstrapped/src/generated/smithy4s/example/RecursiveInputService.scala
index 9c6dcc710..7697788f8 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/RecursiveInputService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/RecursiveInputService.scala
@@ -16,7 +16,7 @@ trait RecursiveInputServiceGen[F[_, _, _, _, _]] {
 
   def recursiveInputOperation(hello: Option[RecursiveInput] = None): F[RecursiveInput, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[RecursiveInputServiceGen[F]] = Transformation.of[RecursiveInputServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[RecursiveInputServiceGen[F]] = Transformation.of[RecursiveInputServiceGen[F]](this)
 }
 
 object RecursiveInputServiceGen extends Service.Mixin[RecursiveInputServiceGen, RecursiveInputServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/ServiceWithNullsAndDefaults.scala b/modules/bootstrapped/src/generated/smithy4s/example/ServiceWithNullsAndDefaults.scala
index 5fce0b700..1a96cdf5b 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/ServiceWithNullsAndDefaults.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/ServiceWithNullsAndDefaults.scala
@@ -17,7 +17,7 @@ trait ServiceWithNullsAndDefaultsGen[F[_, _, _, _, _]] {
   def defaultNullsOperation(input: DefaultNullsOperationInput): F[DefaultNullsOperationInput, Nothing, DefaultNullsOperationOutput, Nothing, Nothing]
   def timestampOperation(input: TimestampOperationInput): F[TimestampOperationInput, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[ServiceWithNullsAndDefaultsGen[F]] = Transformation.of[ServiceWithNullsAndDefaultsGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[ServiceWithNullsAndDefaultsGen[F]] = Transformation.of[ServiceWithNullsAndDefaultsGen[F]](this)
 }
 
 object ServiceWithNullsAndDefaultsGen extends Service.Mixin[ServiceWithNullsAndDefaultsGen, ServiceWithNullsAndDefaultsOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/StreamedObjects.scala b/modules/bootstrapped/src/generated/smithy4s/example/StreamedObjects.scala
index e6839fc7c..cde6022bc 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/StreamedObjects.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/StreamedObjects.scala
@@ -18,7 +18,7 @@ trait StreamedObjectsGen[F[_, _, _, _, _]] {
   def putStreamedObject(key: String): F[PutStreamedObjectInput, Nothing, Unit, StreamedBlob, Nothing]
   def getStreamedObject(key: String): F[GetStreamedObjectInput, Nothing, GetStreamedObjectOutput, Nothing, StreamedBlob]
 
-  def transform: Transformation.PartiallyApplied[StreamedObjectsGen[F]] = Transformation.of[StreamedObjectsGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[StreamedObjectsGen[F]] = Transformation.of[StreamedObjectsGen[F]](this)
 }
 
 object StreamedObjectsGen extends Service.Mixin[StreamedObjectsGen, StreamedObjectsOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/UnionTraitWithUnitCase.scala b/modules/bootstrapped/src/generated/smithy4s/example/UnionTraitWithUnitCase.scala
new file mode 100644
index 000000000..b40bb9c3b
--- /dev/null
+++ b/modules/bootstrapped/src/generated/smithy4s/example/UnionTraitWithUnitCase.scala
@@ -0,0 +1,67 @@
+package smithy4s.example
+
+import UnionTraitWithUnitCase.UCaseAlt
+import smithy4s.Hints
+import smithy4s.Schema
+import smithy4s.ShapeId
+import smithy4s.ShapeTag
+import smithy4s.schema.Schema.bijection
+import smithy4s.schema.Schema.recursive
+import smithy4s.schema.Schema.string
+import smithy4s.schema.Schema.union
+
+sealed trait UnionTraitWithUnitCase extends scala.Product with scala.Serializable { self =>
+  @inline final def widen: UnionTraitWithUnitCase = this
+  def $ordinal: Int
+
+  object project {
+    def u: Option[UnionTraitWithUnitCase.UCase.type] = UCaseAlt.project.lift(self)
+    def s: Option[String] = UnionTraitWithUnitCase.SCase.alt.project.lift(self).map(_.s)
+  }
+
+  def accept[A](visitor: UnionTraitWithUnitCase.Visitor[A]): A = this match {
+    case value: UnionTraitWithUnitCase.UCase.type => visitor.u(value)
+    case value: UnionTraitWithUnitCase.SCase => visitor.s(value.s)
+  }
+}
+object UnionTraitWithUnitCase extends ShapeTag.Companion[UnionTraitWithUnitCase] {
+
+  def u(): UnionTraitWithUnitCase = UnionTraitWithUnitCase.UCase
+  def s(s: String): UnionTraitWithUnitCase = SCase(s)
+
+  val id: ShapeId = ShapeId("smithy4s.example", "unionTraitWithUnitCase")
+
+  val hints: Hints = Hints(
+    smithy.api.Trait(selector = None, structurallyExclusive = None, conflicts = None, breakingChanges = None),
+  ).lazily
+
+  case object UCase extends UnionTraitWithUnitCase { final def $ordinal: Int = 0 }
+  private val UCaseAlt = Schema.constant(UnionTraitWithUnitCase.UCase).oneOf[UnionTraitWithUnitCase]("u").addHints(hints)
+  final case class SCase(s: String) extends UnionTraitWithUnitCase { final def $ordinal: Int = 1 }
+
+  object SCase {
+    val hints: Hints = Hints.empty
+    val schema: Schema[UnionTraitWithUnitCase.SCase] = bijection(string.addHints(hints), UnionTraitWithUnitCase.SCase(_), _.s)
+    val alt = schema.oneOf[UnionTraitWithUnitCase]("s")
+  }
+
+  trait Visitor[A] {
+    def u(value: UnionTraitWithUnitCase.UCase.type): A
+    def s(value: String): A
+  }
+
+  object Visitor {
+    trait Default[A] extends Visitor[A] {
+      def default: A
+      def u(value: UnionTraitWithUnitCase.UCase.type): A = default
+      def s(value: String): A = default
+    }
+  }
+
+  implicit val schema: Schema[UnionTraitWithUnitCase] = recursive(union(
+    UCaseAlt,
+    UnionTraitWithUnitCase.SCase.alt,
+  ){
+    _.$ordinal
+  }.withId(id).addHints(hints))
+}
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/Weather.scala b/modules/bootstrapped/src/generated/smithy4s/example/Weather.scala
index 4015fa5f1..d0aba4cf6 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/Weather.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/Weather.scala
@@ -23,7 +23,7 @@ trait WeatherGen[F[_, _, _, _, _]] {
   def getForecast(cityId: CityId): F[GetForecastInput, Nothing, GetForecastOutput, Nothing, Nothing]
   def listCities(nextToken: Option[String] = None, pageSize: Option[Int] = None): F[ListCitiesInput, Nothing, ListCitiesOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[WeatherGen[F]] = Transformation.of[WeatherGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[WeatherGen[F]] = Transformation.of[WeatherGen[F]](this)
 }
 
 object WeatherGen extends Service.Mixin[WeatherGen, WeatherOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/aws/MyThing.scala b/modules/bootstrapped/src/generated/smithy4s/example/aws/MyThing.scala
index 807b7a8fa..6beba2804 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/aws/MyThing.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/aws/MyThing.scala
@@ -12,7 +12,7 @@ trait MyThingGen[F[_, _, _, _, _]] {
   self =>
 
 
-  def transform: Transformation.PartiallyApplied[MyThingGen[F]] = Transformation.of[MyThingGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[MyThingGen[F]] = Transformation.of[MyThingGen[F]](this)
 }
 
 object MyThingGen extends Service.Mixin[MyThingGen, MyThingOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/collision/ReservedNameService.scala b/modules/bootstrapped/src/generated/smithy4s/example/collision/ReservedNameService.scala
index eb4652255..197accd7a 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/collision/ReservedNameService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/collision/ReservedNameService.scala
@@ -19,7 +19,7 @@ trait ReservedNameServiceGen[F[_, _, _, _, _]] {
   def map(value: scala.collection.immutable.Map[smithy4s.example.collision.String, smithy4s.example.collision.String]): F[MapInput, Nothing, Unit, Nothing, Nothing]
   def option(value: scala.Option[smithy4s.example.collision.String] = None): F[OptionInput, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[ReservedNameServiceGen[F]] = Transformation.of[ReservedNameServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[ReservedNameServiceGen[F]] = Transformation.of[ReservedNameServiceGen[F]](this)
 }
 
 object ReservedNameServiceGen extends Service.Mixin[ReservedNameServiceGen, ReservedNameServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/greet/GreetService.scala b/modules/bootstrapped/src/generated/smithy4s/example/greet/GreetService.scala
index fdca3d8e4..3f4b90f6a 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/greet/GreetService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/greet/GreetService.scala
@@ -15,7 +15,7 @@ trait GreetServiceGen[F[_, _, _, _, _]] {
 
   def greet(name: String): F[GreetInput, Nothing, GreetOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[GreetServiceGen[F]] = Transformation.of[GreetServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[GreetServiceGen[F]] = Transformation.of[GreetServiceGen[F]](this)
 }
 
 object GreetServiceGen extends Service.Mixin[GreetServiceGen, GreetServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/guides/auth/HelloWorldAuthService.scala b/modules/bootstrapped/src/generated/smithy4s/example/guides/auth/HelloWorldAuthService.scala
index a678023e3..59e2159eb 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/guides/auth/HelloWorldAuthService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/guides/auth/HelloWorldAuthService.scala
@@ -20,7 +20,7 @@ trait HelloWorldAuthServiceGen[F[_, _, _, _, _]] {
   def sayWorld(): F[Unit, HelloWorldAuthServiceOperation.SayWorldError, World, Nothing, Nothing]
   def healthCheck(): F[Unit, HelloWorldAuthServiceOperation.HealthCheckError, HealthCheckOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[HelloWorldAuthServiceGen[F]] = Transformation.of[HelloWorldAuthServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[HelloWorldAuthServiceGen[F]] = Transformation.of[HelloWorldAuthServiceGen[F]](this)
 }
 
 object HelloWorldAuthServiceGen extends Service.Mixin[HelloWorldAuthServiceGen, HelloWorldAuthServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/guides/hello/HelloWorldService.scala b/modules/bootstrapped/src/generated/smithy4s/example/guides/hello/HelloWorldService.scala
index 32fdf7701..c14524aac 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/guides/hello/HelloWorldService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/guides/hello/HelloWorldService.scala
@@ -16,7 +16,7 @@ trait HelloWorldServiceGen[F[_, _, _, _, _]] {
 
   def sayWorld(): F[Unit, Nothing, World, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[HelloWorldServiceGen[F]] = Transformation.of[HelloWorldServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[HelloWorldServiceGen[F]] = Transformation.of[HelloWorldServiceGen[F]](this)
 }
 
 object HelloWorldServiceGen extends Service.Mixin[HelloWorldServiceGen, HelloWorldServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/hello/HelloWorldService.scala b/modules/bootstrapped/src/generated/smithy4s/example/hello/HelloWorldService.scala
index 1ef9acb62..5069303bf 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/hello/HelloWorldService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/hello/HelloWorldService.scala
@@ -18,7 +18,7 @@ trait HelloWorldServiceGen[F[_, _, _, _, _]] {
 
   def hello(name: String, town: Option[String] = None): F[Person, HelloWorldServiceOperation.HelloError, Greeting, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[HelloWorldServiceGen[F]] = Transformation.of[HelloWorldServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[HelloWorldServiceGen[F]] = Transformation.of[HelloWorldServiceGen[F]](this)
 }
 
 object HelloWorldServiceGen extends Service.Mixin[HelloWorldServiceGen, HelloWorldServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/imp/ImportService.scala b/modules/bootstrapped/src/generated/smithy4s/example/imp/ImportService.scala
index 3c6d39aa5..67b4248d4 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/imp/ImportService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/imp/ImportService.scala
@@ -21,7 +21,7 @@ trait ImportServiceGen[F[_, _, _, _, _]] {
 
   def importOperation(): F[Unit, ImportServiceOperation.ImportOperationError, OpOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[ImportServiceGen[F]] = Transformation.of[ImportServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[ImportServiceGen[F]] = Transformation.of[ImportServiceGen[F]](this)
 }
 
 object ImportServiceGen extends Service.Mixin[ImportServiceGen, ImportServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/package.scala b/modules/bootstrapped/src/generated/smithy4s/example/package.scala
index a914f9cf4..568c337a0 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/package.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/package.scala
@@ -66,6 +66,7 @@ package object example {
   type ExtraData = smithy4s.example.ExtraData.Type
   type FancyList = smithy4s.example.FancyList.Type
   type FreeForm = smithy4s.example.FreeForm.Type
+  type HasUnionUnitCaseTrait = smithy4s.example.HasUnionUnitCaseTrait.Type
   type Ingredients = smithy4s.example.Ingredients.Type
   /** @param member
     *   listFoo
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/product/ExampleService.scala b/modules/bootstrapped/src/generated/smithy4s/example/product/ExampleService.scala
index b9c15a600..4a09388e5 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/product/ExampleService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/product/ExampleService.scala
@@ -16,7 +16,7 @@ trait ExampleServiceGen[F[_, _, _, _, _]] {
 
   def exampleOperation(a: String): F[ExampleOperationInput, Nothing, ExampleOperationOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[ExampleServiceGen[F]] = Transformation.of[ExampleServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[ExampleServiceGen[F]] = Transformation.of[ExampleServiceGen[F]](this)
 }
 
 trait ExampleServiceProductGen[F[_, _, _, _, _]] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/reservedNameOverride/ReservedNameOverrideService.scala b/modules/bootstrapped/src/generated/smithy4s/example/reservedNameOverride/ReservedNameOverrideService.scala
index 5f67990e6..549ab9968 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/reservedNameOverride/ReservedNameOverrideService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/reservedNameOverride/ReservedNameOverrideService.scala
@@ -16,7 +16,7 @@ trait ReservedNameOverrideServiceGen[F[_, _, _, _, _]] {
 
   def setOp(set: Set): F[SetOpInput, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[ReservedNameOverrideServiceGen[F]] = Transformation.of[ReservedNameOverrideServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[ReservedNameOverrideServiceGen[F]] = Transformation.of[ReservedNameOverrideServiceGen[F]](this)
 }
 
 object ReservedNameOverrideServiceGen extends Service.Mixin[ReservedNameOverrideServiceGen, ReservedNameOverrideServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/test/HelloService.scala b/modules/bootstrapped/src/generated/smithy4s/example/test/HelloService.scala
index 518557b0a..81dc62293 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/test/HelloService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/test/HelloService.scala
@@ -21,7 +21,7 @@ trait HelloServiceGen[F[_, _, _, _, _]] {
   def listen(): F[Unit, Nothing, Unit, Nothing, Nothing]
   def testPath(path: String): F[TestPathInput, Nothing, Unit, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[HelloServiceGen[F]] = Transformation.of[HelloServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[HelloServiceGen[F]] = Transformation.of[HelloServiceGen[F]](this)
 }
 
 object HelloServiceGen extends Service.Mixin[HelloServiceGen, HelloServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/smithy4s/example/test/HelloWorldService.scala b/modules/bootstrapped/src/generated/smithy4s/example/test/HelloWorldService.scala
index e1135ef1c..603453601 100644
--- a/modules/bootstrapped/src/generated/smithy4s/example/test/HelloWorldService.scala
+++ b/modules/bootstrapped/src/generated/smithy4s/example/test/HelloWorldService.scala
@@ -15,7 +15,7 @@ trait HelloWorldServiceGen[F[_, _, _, _, _]] {
 
   def hello(name: String): F[HelloInput, Nothing, HelloOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[HelloWorldServiceGen[F]] = Transformation.of[HelloWorldServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[HelloWorldServiceGen[F]] = Transformation.of[HelloWorldServiceGen[F]](this)
 }
 
 object HelloWorldServiceGen extends Service.Mixin[HelloWorldServiceGen, HelloWorldServiceOperation] {
diff --git a/modules/bootstrapped/src/generated/weather/WeatherService.scala b/modules/bootstrapped/src/generated/weather/WeatherService.scala
index 3258c14e9..c118be625 100644
--- a/modules/bootstrapped/src/generated/weather/WeatherService.scala
+++ b/modules/bootstrapped/src/generated/weather/WeatherService.scala
@@ -15,7 +15,7 @@ trait WeatherServiceGen[F[_, _, _, _, _]] {
 
   def getWeather(city: String): F[GetWeatherInput, Nothing, GetWeatherOutput, Nothing, Nothing]
 
-  def transform: Transformation.PartiallyApplied[WeatherServiceGen[F]] = Transformation.of[WeatherServiceGen[F]](this)
+  final def transform: Transformation.PartiallyApplied[WeatherServiceGen[F]] = Transformation.of[WeatherServiceGen[F]](this)
 }
 
 object WeatherServiceGen extends Service.Mixin[WeatherServiceGen, WeatherServiceOperation] {
diff --git a/modules/codegen/src/smithy4s/codegen/internals/IR.scala b/modules/codegen/src/smithy4s/codegen/internals/IR.scala
index fbdc20cdc..3519c1d3a 100644
--- a/modules/codegen/src/smithy4s/codegen/internals/IR.scala
+++ b/modules/codegen/src/smithy4s/codegen/internals/IR.scala
@@ -31,6 +31,7 @@ import TypedNode.FieldTN.OptionalSomeTN
 import TypedNode.FieldTN.RequiredTN
 import TypedNode.AltValueTN.ProductAltTN
 import TypedNode.AltValueTN.TypeAltTN
+import TypedNode.AltValueTN.UnitAltTN
 import UnionMember._
 import LineSegment.{NameDef, NameRef}
 
@@ -426,6 +427,7 @@ private[internals] object TypedNode {
     def map[B](f: A => B): AltValueTN[B] = this match {
       case ProductAltTN(value) => ProductAltTN(f(value))
       case TypeAltTN(value)    => TypeAltTN(f(value))
+      case UnitAltTN           => UnitAltTN
     }
   }
   object AltValueTN {
@@ -437,6 +439,7 @@ private[internals] object TypedNode {
           fa match {
             case ProductAltTN(value) => f(value).map(ProductAltTN(_))
             case TypeAltTN(value)    => f(value).map(TypeAltTN(_))
+            case UnitAltTN           => Applicative[G].pure(UnitAltTN)
           }
         def foldLeft[A, B](fa: AltValueTN[A], b: B)(f: (B, A) => B): B = ???
         def foldRight[A, B](fa: AltValueTN[A], lb: Eval[B])(
@@ -446,6 +449,7 @@ private[internals] object TypedNode {
 
     case class ProductAltTN[A](value: A) extends AltValueTN[A]
     case class TypeAltTN[A](value: A) extends AltValueTN[A]
+    case object UnitAltTN extends AltValueTN[Nothing]
   }
 
   implicit val typedNodeTraverse: Traverse[TypedNode] =
diff --git a/modules/codegen/src/smithy4s/codegen/internals/Renderer.scala b/modules/codegen/src/smithy4s/codegen/internals/Renderer.scala
index 1adccaf79..ae4de8862 100644
--- a/modules/codegen/src/smithy4s/codegen/internals/Renderer.scala
+++ b/modules/codegen/src/smithy4s/codegen/internals/Renderer.scala
@@ -355,7 +355,7 @@ private[internals] class Renderer(compilationUnit: CompilationUnit) { self =>
           )
         },
         newline,
-        line"def $transform_: $Transformation.PartiallyApplied[$genName[F]] = $Transformation.of[$genName[F]](this)"
+        line"final def $transform_: $Transformation.PartiallyApplied[$genName[F]] = $Transformation.of[$genName[F]](this)"
       ),
       newline,
       lines(
@@ -1613,6 +1613,9 @@ private[internals] class Renderer(compilationUnit: CompilationUnit) { self =>
     case AltTN(ref, altName, AltValueTN.TypeAltTN(alt)) =>
       line"${ref.show}.${altName.capitalize}Case(${alt.runDefault}).widen".write
 
+    case AltTN(ref, altName, AltValueTN.UnitAltTN) =>
+      line"${ref.show}.${altName.capitalize}Case.widen".write
+
     case AltTN(_, _, AltValueTN.ProductAltTN(alt)) =>
       alt.runDefault.write
 
diff --git a/modules/codegen/src/smithy4s/codegen/internals/SmithyToIR.scala b/modules/codegen/src/smithy4s/codegen/internals/SmithyToIR.scala
index bee39fb2e..0ccc14bd2 100644
--- a/modules/codegen/src/smithy4s/codegen/internals/SmithyToIR.scala
+++ b/modules/codegen/src/smithy4s/codegen/internals/SmithyToIR.scala
@@ -1048,7 +1048,9 @@ private[codegen] class SmithyToIR(
       maybeTypeclassesHint(shape)
   }
 
-  case class AltInfo(name: String, tpe: Type, isAdtMember: Boolean)
+  case class AltInfo(name: String, tpe: Type, isAdtMember: Boolean) {
+    def isUnit: Boolean = tpe == Type.unit
+  }
 
   implicit class ShapeExt(shape: Shape) {
     def name = shape.getId().getName()
@@ -1151,21 +1153,17 @@ private[codegen] class SmithyToIR(
       shape
         .members()
         .asScala
-        .map { member =>
-          val memberTarget =
-            model.expectShape(member.getTarget)
-          if (isPartOfAdt(memberTarget)) {
-            (member.getMemberName(), member.tpe.map(Left(_)))
-          } else {
-            (member.getMemberName(), member.tpe.map(Right(_)))
+        .flatMap { member =>
+          member.tpe.map { tpe =>
+            val memberTarget = model.expectShape(member.getTarget)
+
+            AltInfo(
+              member.getMemberName(),
+              tpe,
+              isAdtMember = isPartOfAdt(memberTarget)
+            )
           }
         }
-        .collect {
-          case (name, Some(Left(tpe))) =>
-            AltInfo(name, tpe, isAdtMember = true)
-          case (name, Some(Right(tpe))) =>
-            AltInfo(name, tpe, isAdtMember = false)
-        }
         .toList
     }
 
@@ -1302,6 +1300,8 @@ private[codegen] class SmithyToIR(
         val a = if (alt.isAdtMember) {
           val t = NodeAndType(node, alt.tpe)
           TypedNode.AltValueTN.ProductAltTN(t)
+        } else if (alt.isUnit) {
+          TypedNode.AltValueTN.UnitAltTN
         } else {
           val t = NodeAndType(node, alt.tpe)
           TypedNode.AltValueTN.TypeAltTN(t)
diff --git a/sampleSpecs/misc.smithy b/sampleSpecs/misc.smithy
index 27f8f3f9d..a5392c2a8 100644
--- a/sampleSpecs/misc.smithy
+++ b/sampleSpecs/misc.smithy
@@ -110,3 +110,14 @@ structure RangeCheck {
 // face with sunglasses emoji
 @pattern("^\\uD83D\\uDE0E$")
 string UnicodeRegexString
+
+@trait
+union unionTraitWithUnitCase {
+    u: Unit
+    s: String
+}
+
+@unionTraitWithUnitCase(u: {
+
+})
+string HasUnionUnitCaseTrait