diff --git a/build.sbt b/build.sbt
index 0f01fedb5..5ed7e29bd 100644
--- a/build.sbt
+++ b/build.sbt
@@ -373,7 +373,9 @@ lazy val codegen = projectMatrix
       Dependencies.Alloy.openapi,
       Dependencies.Smithytranslate.proto,
       "com.lihaoyi" %% "os-lib" % "0.9.3",
-      "com.lihaoyi" %% "upickle" % "3.2.0",
+      Dependencies.Circe.core.value,
+      Dependencies.Circe.parser.value,
+      Dependencies.Circe.generic.value,
       Dependencies.collectionsCompat.value,
       "org.scala-lang" % "scala-reflect" % scalaVersion.value,
       "io.get-coursier" %% "coursier" % "2.1.9"
diff --git a/modules/codegen/src/smithy4s/codegen/SmithyBuildJson.scala b/modules/codegen/src/smithy4s/codegen/SmithyBuildJson.scala
index c23488310..f871f2d60 100644
--- a/modules/codegen/src/smithy4s/codegen/SmithyBuildJson.scala
+++ b/modules/codegen/src/smithy4s/codegen/SmithyBuildJson.scala
@@ -19,10 +19,9 @@ package smithy4s.codegen
 import smithy4s.codegen.internals.SmithyBuild
 import smithy4s.codegen.internals.SmithyBuildMaven
 import smithy4s.codegen.internals.SmithyBuildMavenRepository
-import upickle.default._
+import io.circe.{Json, parser}
 
 private[codegen] object SmithyBuildJson {
-
   def toJson(
       imports: Seq[String],
       dependencies: Seq[String],
@@ -43,47 +42,29 @@ private[codegen] object SmithyBuildJson {
   def merge(
       json1: String,
       json2: String
-  ): String = {
-    val j1 = read[ujson.Value](json1)
-    val j2 = read[ujson.Value](json2)
-    val merged = mergeJs(j1, j2)
-    val finalJs = removeArrayDuplicates(merged)
-    finalJs.render(indent = 4)
-  }
+  ): String = (for {
+    j1 <- parser.parse(json1)
+    j2 <- parser.parse(json2)
+    merged = mergeJs(j1, j2)
+  } yield merged).left.map(err => throw err).merge.spaces4
 
   private def mergeJs(
-      v1: ujson.Value,
-      v2: ujson.Value
-  ): ujson.Value = {
-    (v1, v2) match {
-      case (ujson.Obj(obj1), ujson.Obj(obj2)) =>
-        val result = obj2.foldLeft(obj1.toMap) {
-          case (elements, (key, value2)) =>
-            val value = elements.get(key) match {
-              case None =>
-                value2
-              case Some(value1) =>
-                mergeJs(value1, value2)
+      v1: Json,
+      v2: Json
+  ): Json = {
+    (v1.asObject, v2.asObject, v1.asArray, v2.asArray) match {
+      // copied from circe's deepMerge method, however in order to handle concat + deduplication on arrays we need to do it manually here
+      case (Some(lhs), Some(rhs), _, _) =>
+        Json.fromJsonObject(
+          lhs.toIterable.foldLeft(rhs) { case (acc, (key, value)) =>
+            rhs(key).fold(acc.add(key, value)) { r =>
+              acc.add(key, mergeJs(value, r))
             }
-            elements.updated(key, value)
-        }
-        ujson.Obj.from(result)
-      case (arr1: ujson.Arr, arr2: ujson.Arr) =>
-        ujson.Arr(arr1.arr ++ arr2.arr)
-      case (_, _) => v1
-    }
-  }
-
-  private def removeArrayDuplicates(js: ujson.Value): ujson.Value = {
-    js match {
-      case ujson.Obj(obj1) =>
-        ujson.Obj.from(
-          obj1.toList.map { case (key, value) =>
-            key -> removeArrayDuplicates(value)
           }
         )
-      case (arr1: ujson.Arr) => arr1.arr.distinct
-      case x                 => x
+      case (_, _, Some(arr1), Some(arr2)) =>
+        Json.arr((arr1 ++ arr2).distinct: _*)
+      case _ => v1
     }
   }
 }
diff --git a/modules/codegen/src/smithy4s/codegen/internals/SmithyBuild.scala b/modules/codegen/src/smithy4s/codegen/internals/SmithyBuild.scala
index b600ed5d4..3cf6e4828 100644
--- a/modules/codegen/src/smithy4s/codegen/internals/SmithyBuild.scala
+++ b/modules/codegen/src/smithy4s/codegen/internals/SmithyBuild.scala
@@ -17,7 +17,9 @@
 package smithy4s.codegen
 package internals
 
-import upickle.default._
+import io.circe.Codec
+import io.circe.generic.semiauto._
+import io.circe.syntax._
 
 private[internals] final case class SmithyBuild(
     version: String,
@@ -25,8 +27,8 @@ private[internals] final case class SmithyBuild(
     maven: SmithyBuildMaven
 )
 private[codegen] object SmithyBuild {
-  implicit val codecs: ReadWriter[SmithyBuild] = macroRW
-  def writeJson(sb: SmithyBuild): String = write(sb, indent = 4)
+  implicit val codecs: Codec[SmithyBuild] = deriveCodec
+  def writeJson(sb: SmithyBuild): String = sb.asJson.spaces4
 }
 
 private[internals] final case class SmithyBuildMaven(
@@ -34,12 +36,12 @@ private[internals] final case class SmithyBuildMaven(
     repositories: Seq[SmithyBuildMavenRepository]
 )
 private[codegen] object SmithyBuildMaven {
-  implicit val codecs: ReadWriter[SmithyBuildMaven] = macroRW
+  implicit val codecs: Codec[SmithyBuildMaven] = deriveCodec
 }
 
 private[internals] final case class SmithyBuildMavenRepository(
     url: String
 )
 private[codegen] object SmithyBuildMavenRepository {
-  implicit val codecs: ReadWriter[SmithyBuildMavenRepository] = macroRW
+  implicit val codecs: Codec[SmithyBuildMavenRepository] = deriveCodec
 }
diff --git a/modules/codegen/test/src/smithy4s/codegen/internals/SmithyBuildSpec.scala b/modules/codegen/test/src/smithy4s/codegen/internals/SmithyBuildSpec.scala
index d8b8801ed..a9ce64144 100644
--- a/modules/codegen/test/src/smithy4s/codegen/internals/SmithyBuildSpec.scala
+++ b/modules/codegen/test/src/smithy4s/codegen/internals/SmithyBuildSpec.scala
@@ -30,17 +30,17 @@ final class SmithyBuildSpec extends munit.FunSuite {
     assertEquals(
       actual,
       """|{
-         |    "version": "1.0",
-         |    "imports": [
+         |    "version" : "1.0",
+         |    "imports" : [
          |        "src/"
          |    ],
-         |    "maven": {
-         |        "dependencies": [
+         |    "maven" : {
+         |        "dependencies" : [
          |            "dep"
          |        ],
-         |        "repositories": [
+         |        "repositories" : [
          |            {
-         |                "url": "repo"
+         |                "url" : "repo"
          |            }
          |        ]
          |    }
@@ -73,18 +73,61 @@ final class SmithyBuildSpec extends munit.FunSuite {
     assertEquals(
       actual,
       """|{
-         |    "version": "1.0",
-         |    "imports": [
+         |    "version" : "1.0",
+         |    "imports" : [
          |        "src/main/smithy"
          |    ],
-         |    "maven": {
-         |        "dependencies": [
+         |    "maven" : {
+         |        "dependencies" : [
          |            "oterh",
          |            "dep1"
          |        ],
-         |        "repositories": []
+         |        "repositories" : [
+         |        ]
+         |    },
+         |    "custom" : "attribute"
+         |}""".stripMargin
+    )
+  }
+
+  test("merge two json de-duplicating arrays") {
+    val actual = SmithyBuildJson.merge(
+      """|{
+         |  "version": "1.0",
+         |  "imports": ["src/main/smithy"],
+         |  "maven": {
+         |    "dependencies": ["oterh", "dep1"],
+         |    "repositories": []
+         |  }
+         |}
+         |""".stripMargin,
+      """|{
+         |  "version": "1.0",
+         |  "imports": ["src/main/smithy"],
+         |  "maven": {
+         |    "dependencies": ["dep1"],
+         |    "repositories": []
+         |  },
+         |  "custom": "attribute"
+         |}
+         |""".stripMargin
+    )
+    assertEquals(
+      actual,
+      """|{
+         |    "version" : "1.0",
+         |    "imports" : [
+         |        "src/main/smithy"
+         |    ],
+         |    "maven" : {
+         |        "dependencies" : [
+         |            "oterh",
+         |            "dep1"
+         |        ],
+         |        "repositories" : [
+         |        ]
          |    },
-         |    "custom": "attribute"
+         |    "custom" : "attribute"
          |}""".stripMargin
     )
   }