diff --git a/.scala-steward.conf b/.scala-steward.conf
index 0c8bf58e..b6b6f7d3 100644
--- a/.scala-steward.conf
+++ b/.scala-steward.conf
@@ -4,6 +4,6 @@ updates.ignore = [
   {groupId = "org.scala-lang", artifactId = "scala-compiler", version = "3."}
 ]
 updates.pin = [
-  {groupId = "org.scala-lang", artifactId = "scala3-library", version = "3.3."},
-  {groupId = "org.scala-lang", artifactId = "scala3-library_sjs1", version = "3.3."}
+  {groupId = "org.scala-lang", artifactId = "scala3-library", version = "3.9."},
+  {groupId = "org.scala-lang", artifactId = "scala3-library_sjs1", version = "3.9."}
 ]
diff --git a/.scalafmt.conf b/.scalafmt.conf
index e6196f88..7a43d8b3 100644
--- a/.scalafmt.conf
+++ b/.scalafmt.conf
@@ -1,4 +1,4 @@
-runner.dialect = scala213
+runner.dialect = scala213source3
 version = 3.11.5
 maxColumn = 120
 fileOverride {
diff --git a/build.sbt b/build.sbt
index 3dd5bb38..e37c94ce 100644
--- a/build.sbt
+++ b/build.sbt
@@ -5,7 +5,7 @@ import com.softwaremill.Publish.ossPublishSettings
 val scala2_12 = "2.12.21"
 val scala2_13 = "2.13.18"
 val scala2 = List(scala2_12, scala2_13)
-val scala3 = List("3.3.8")
+val scala3 = List("3.9.0")
 
 val scalaTestVersion = "3.2.20"
 val scalaTestPlusScalaCheckVersion = "3.2.20.0"
@@ -18,12 +18,13 @@ def dependenciesFor(version: String)(deps: (Option[(Long, Long)] => ModuleID)*):
 val commonSettings = commonSmlBuildSettings ++ ossPublishSettings ++ Seq(
   organization := "com.softwaremill.sttp.model",
   mimaPreviousArtifacts := Set.empty,
-  versionScheme := Some("semver-spec")
+  versionScheme := Some("semver-spec"),
+  scalacOptions ++= (if (ScalaArtifacts.isScala3(scalaVersion.value)) Seq.empty else Seq("-Xsource:3"))
 )
 
 val commonJvmSettings = commonSettings ++ Seq(
   scalacOptions ++=
-    (if (ScalaArtifacts.isScala3(scalaVersion.value)) Seq("-Yfuture-lazy-vals", "-java-output-version", "11")
+    (if (ScalaArtifacts.isScala3(scalaVersion.value)) Seq("-java-output-version", "17")
      else Seq("-release", "8")),
   ideSkipProject := (scalaVersion.value != scala2_13),
   libraryDependencies ++= Seq(
diff --git a/core/src/main/scala/sttp/model/Uri.scala b/core/src/main/scala/sttp/model/Uri.scala
index 8c5e0f1b..4c067080 100644
--- a/core/src/main/scala/sttp/model/Uri.scala
+++ b/core/src/main/scala/sttp/model/Uri.scala
@@ -124,7 +124,7 @@ case class Uri(
 
   /** Replace path with the given path segment. */
   @deprecated(message = "Use addPath, withPath or withWholePath", since = "1.2.0")
-  def pathSegments(s1: Segment, s2: Segment, ss: Segment*): Uri = withPathSegments(s1, s2, ss: _*)
+  def pathSegments(s1: Segment, s2: Segment, ss: Segment*): Uri = withPathSegments(s1 :: s2 :: ss.toList)
 
   /** Replace path with the given path segments. */
   @deprecated(message = "Use addPath, withPath or withWholePath", since = "1.2.0")
@@ -174,11 +174,11 @@ case class Uri(
 
   /** Adds the given parameters to the query. */
   @deprecated(message = "Use addParam or withParam", since = "1.2.0")
-  def params(ps: (String, String)*): Uri = addParams(ps: _*)
+  def params(ps: (String, String)*): Uri = addParams(ps*)
 
   def addParam(k: String, v: String): Uri = addParams(k -> v)
   def addParam(k: String, v: Option[String]): Uri = v.map(addParam(k, _)).getOrElse(this)
-  def addParams(ps: Map[String, String]): Uri = addParams(ps.toSeq: _*)
+  def addParams(ps: Map[String, String]): Uri = addParams(ps.toSeq*)
   def addParams(mqp: QueryParams): Uri = {
     this.copy(querySegments = querySegments ++ QuerySegment.fromQueryParams(mqp))
   }
@@ -195,7 +195,7 @@ case class Uri(
   def withParam(k: String, v: Option[String]): Uri = v.map(withParam(k, _)).getOrElse(this)
 
   /** Replace query with the given parameters. */
-  def withParams(ps: Map[String, String]): Uri = withParams(ps.toSeq: _*)
+  def withParams(ps: Map[String, String]): Uri = withParams(ps.toSeq*)
 
   /** Replace query with the given parameters. */
   def withParams(mqp: QueryParams): Uri = this.copy(querySegments = QuerySegment.fromQueryParams(mqp).toList)
diff --git a/core/src/main/scala/sttp/model/UriInterpolator.scala b/core/src/main/scala/sttp/model/UriInterpolator.scala
index 58096758..5f62dc7a 100644
--- a/core/src/main/scala/sttp/model/UriInterpolator.scala
+++ b/core/src/main/scala/sttp/model/UriInterpolator.scala
@@ -36,7 +36,7 @@ trait UriInterpolator {
       * @throws IllegalArgumentException
       *   In case of a validation error. For a safe version, see [[Uri.parse()]].
       */
-    def uri(args: Any*): Uri = UriInterpolator.interpolate(sc, args: _*)
+    def uri(args: Any*): Uri = UriInterpolator.interpolate(sc, args*)
   }
 }
 
@@ -65,7 +65,7 @@ object UriInterpolator {
     if (isScEmptyString && areArgsEmptyString) {
       throw new IllegalArgumentException("empty string is not valid uri")
     }
-    val tokens = tokenize(sc, args: _*)
+    val tokens = tokenize(sc, args*)
 
     val (uri, leftTokens) =
       builders.foldLeft((startingUri, filterNulls(tokens))) { case ((u, t), builder) =>
@@ -178,9 +178,9 @@ object UriInterpolator {
   private object Tokenizer {
 
     object Scheme extends Tokenizer {
-      private val alphabet = Set(('a' to 'z'): _*) ++ Set(('A' to 'Z'): _*)
+      private val alphabet = ('a' to 'z').toSet ++ ('A' to 'Z').toSet
       private val firstChar = FastCharSet(alphabet)
-      private val nonFirstChars = FastCharSet(alphabet ++ Set(('0' to '9'): _*) ++ Set('+', '.', '-'))
+      private val nonFirstChars = FastCharSet(alphabet ++ ('0' to '9').toSet ++ Set('+', '.', '-'))
 
       // This is equivalent to such regular expression "[A-Za-z][A-Za-z0-9+.-]*"
       private def findPrefix(s: String): Option[String] = {
@@ -252,7 +252,7 @@ object UriInterpolator {
     }
 
     object Authority extends Tokenizer {
-      private val HexChars = FastCharSet(Set(('0' to '9'): _*) ++ Set(('a' to 'f'): _*) ++ Set(('A' to 'F'): _*) + ':')
+      private val HexChars = FastCharSet(('0' to '9').toSet ++ ('a' to 'f').toSet ++ ('A' to 'F').toSet + ':')
 
       private def isIpV6Like(str: String): Boolean = {
         val len = str.length()
@@ -626,7 +626,7 @@ object UriInterpolator {
             v <- anyToStringOpt(ve)
           } yield QF.KeyValue(k, v)
 
-        def seqToQueryFragments(s: Seq[_]): Vector[QF] = {
+        def seqToQueryFragments(s: Seq[Any]): Vector[QF] = {
           s.flatMap {
             case (ke, ve) => expressionPairToQueryFragment(ke, ve)
             case ve       => anyToStringOpt(ve).map(QF.Value(_))
diff --git a/core/src/main/scalanative/sttp/model/internal/idn/CIdn.scala b/core/src/main/scalanative/sttp/model/internal/idn/CIdn.scala
index ac0d0625..1dba40c8 100644
--- a/core/src/main/scalanative/sttp/model/internal/idn/CIdn.scala
+++ b/core/src/main/scalanative/sttp/model/internal/idn/CIdn.scala
@@ -12,5 +12,5 @@ private[idn] object CIdn {
   def errorMsg(rc: CInt): CString = extern
 
   @name("idn2_free")
-  def free(ptr: Ptr[_]): Unit = extern
+  def free(ptr: Ptr[Byte]): Unit = extern
 }