diff --git a/.scalafmt.conf b/.scalafmt.conf
index fcadd98d..e8563baf 100644
--- a/.scalafmt.conf
+++ b/.scalafmt.conf
@@ -1,4 +1,4 @@
-version = 3.9.4
+version = 3.9.8
 project.layout = StandardConvention
 runner.dialect = scala3
 maxColumn = 100
diff --git a/CLAUDE.md b/CLAUDE.md
index e01643b5..2e72e982 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -13,7 +13,7 @@ MessagePack-Java is a binary serialization library that provides a fast and comp
 ### Build and Compile
 ```bash
 ./sbt compile              # Compile source code
-./sbt test:compile         # Compile source and test code
+./sbt "Test / compile"     # Compile source and test code
 ./sbt package              # Create JAR files
 ```
 
@@ -31,7 +31,7 @@ MessagePack-Java is a binary serialization library that provides a fast and comp
 ### Code Quality
 ```bash
 ./sbt jcheckStyle          # Run checkstyle (Facebook Presto style)
-./sbt scalafmtAll          # Format Scala test code
+./sbt scalafmtAll          # Format all Scala and sbt code
 ```
 
 ### Publishing
@@ -66,7 +66,7 @@ The msgpack-jackson module provides:
 - Extension type support including timestamps
 
 ### Testing Structure
-- **msgpack-core tests**: Written in Scala using AirSpec framework
+- **msgpack-core tests**: Written in Scala (always use the latest Scala 3 version) using AirSpec framework
   - Location: `msgpack-core/src/test/scala/`
 - **msgpack-jackson tests**: Written in Java using JUnit
   - Location: `msgpack-jackson/src/test/java/`
@@ -81,7 +81,7 @@ For JDK 17+ compatibility, these options are automatically added:
 
 ## Code Style Requirements
 - Java code follows Facebook Presto style (enforced by checkstyle)
-- Scala test code uses Scalafmt with 180 character line limit
+- Scala test code uses Scalafmt with Scala 3 dialect and 100 character line limit
 - Checkstyle runs automatically during compilation
 - No external dependencies allowed in msgpack-core
 
diff --git a/README.md b/README.md
index 34a3f277..54d1877a 100644
--- a/README.md
+++ b/README.md
@@ -66,6 +66,7 @@ msgpack-java uses [sbt](http://www.scala-sbt.org/) for building the projects. Fo
 Coding style
  * msgpack-java uses [the same coding style](https://github.com/airlift/codestyle) with Facebook Presto
   * [IntelliJ setting file](https://raw.githubusercontent.com/airlift/codestyle/master/IntelliJIdea14/Airlift.xml)
+ * Scala test code uses Scalafmt with Scala 3 dialect (always use the latest Scala 3 version)
 
 ### Basic sbt commands
 Enter the sbt console:
@@ -76,14 +77,14 @@ $ ./sbt
 Here is a list of sbt commands for daily development:
 ```
 > ~compile                                 # Compile source codes
-> ~test:compile                            # Compile both source and test codes
+> ~"Test / compile"                        # Compile both source and test codes
 > ~test                                    # Run tests upon source code change
 > ~testOnly *MessagePackTest               # Run tests in the specified class
 > ~testOnly *MessagePackTest -- (pattern)  # Run tests matching the pattern 
 > project msgpack-core                     # Focus on a specific project
 > package                                  # Create a jar file in the target folder of each project
 > jcheckStyle                              # Run check style
-> scalafmtAll                              # Reformat code
+> scalafmtAll                              # Format all Scala and sbt code
 ```
 
 ### Publishing
diff --git a/msgpack-core/src/test/scala/org/msgpack/core/MessagePackTest.scala b/msgpack-core/src/test/scala/org/msgpack/core/MessagePackTest.scala
index 0a4328d8..b5541393 100644
--- a/msgpack-core/src/test/scala/org/msgpack/core/MessagePackTest.scala
+++ b/msgpack-core/src/test/scala/org/msgpack/core/MessagePackTest.scala
@@ -376,7 +376,7 @@ class MessagePackTest extends AirSpec with PropertyCheck with Benchmark:
   test("report errors when packing/unpacking malformed strings") {
     pending("We need to produce malformed utf-8 strings in Java 8")
     // Create 100 malformed UTF8 Strings
-    val r = new Random(0)
+    val r                = new Random(0)
     val malformedStrings = Iterator
       .continually {
         val b = new Array[Byte](10)
@@ -580,12 +580,12 @@ class MessagePackTest extends AirSpec with PropertyCheck with Benchmark:
 
             kvs
               .grouped(2)
-              .map((kvp: Array[Value]) =>
+              .map { (kvp: Array[Value]) =>
                 val k = kvp(0)
                 val v = kvp(1)
 
                 (k.asStringValue().asString, v.asStringValue().asString)
-              )
+              }
               .toMap
           }
           .toList
diff --git a/msgpack-core/src/test/scala/org/msgpack/core/MessagePackerTest.scala b/msgpack-core/src/test/scala/org/msgpack/core/MessagePackerTest.scala
index c1b4b0a4..7ff5d82e 100644
--- a/msgpack-core/src/test/scala/org/msgpack/core/MessagePackerTest.scala
+++ b/msgpack-core/src/test/scala/org/msgpack/core/MessagePackerTest.scala
@@ -211,7 +211,7 @@ class MessagePackerTest extends AirSpec with Benchmark:
   }
 
   test("compute totalWrittenBytes") {
-    val out = new ByteArrayOutputStream
+    val out                     = new ByteArrayOutputStream
     val packerTotalWrittenBytes =
       withResource(MessagePack.newDefaultPacker(out)) { packer =>
         packer
diff --git a/msgpack-core/src/test/scala/org/msgpack/core/MessageUnpackerTest.scala b/msgpack-core/src/test/scala/org/msgpack/core/MessageUnpackerTest.scala
index ae25d284..adab4708 100644
--- a/msgpack-core/src/test/scala/org/msgpack/core/MessageUnpackerTest.scala
+++ b/msgpack-core/src/test/scala/org/msgpack/core/MessageUnpackerTest.scala
@@ -30,7 +30,7 @@ import scala.util.Random
 
 object MessageUnpackerTest:
   class SplitMessageBufferInput(array: Array[Array[Byte]]) extends MessageBufferInput:
-    var cursor = 0
+    var cursor                         = 0
     override def next(): MessageBuffer =
       if cursor < array.length then
         val a = array(cursor)
@@ -45,7 +45,7 @@ import org.msgpack.core.MessageUnpackerTest.*
 
 class MessageUnpackerTest extends AirSpec with Benchmark:
 
-  private val universal = MessageBuffer.allocate(0).isInstanceOf[MessageBufferU]
+  private val universal             = MessageBuffer.allocate(0).isInstanceOf[MessageBufferU]
   private def testData: Array[Byte] =
     val out    = new ByteArrayOutputStream()
     val packer = MessagePack.newDefaultPacker(out)
@@ -435,7 +435,7 @@ class MessageUnpackerTest extends AirSpec with Benchmark:
       val t =
         time("skip performance", repeat = N) {
           block("v6") {
-            val v6 = new org.msgpack.MessagePack()
+            val v6       = new org.msgpack.MessagePack()
             val unpacker =
               new org.msgpack.unpacker.MessagePackUnpacker(v6, new ByteArrayInputStream(data))
             var count = 0
@@ -567,7 +567,7 @@ class MessageUnpackerTest extends AirSpec with Benchmark:
       val t =
         time("unpack performance", repeat = N) {
           block("v6") {
-            val v6 = new org.msgpack.MessagePack()
+            val v6       = new org.msgpack.MessagePack()
             val unpacker =
               new org.msgpack.unpacker.MessagePackUnpacker(v6, new ByteArrayInputStream(data))
             var count = 0
@@ -655,7 +655,7 @@ class MessageUnpackerTest extends AirSpec with Benchmark:
 
       time("unpackBinary", repeat = 100) {
         block("v6") {
-          val v6 = new org.msgpack.MessagePack()
+          val v6       = new org.msgpack.MessagePack()
           val unpacker =
             new org.msgpack.unpacker.MessagePackUnpacker(v6, new ByteArrayInputStream(b))
           var i = 0
diff --git a/msgpack-core/src/test/scala/org/msgpack/value/VariableTest.scala b/msgpack-core/src/test/scala/org/msgpack/value/VariableTest.scala
index 4eabdbd7..2f3cbf9c 100644
--- a/msgpack-core/src/test/scala/org/msgpack/value/VariableTest.scala
+++ b/msgpack-core/src/test/scala/org/msgpack/value/VariableTest.scala
@@ -181,39 +181,39 @@ class VariableTest extends AirSpec with PropertyCheck:
 
     test("read integers") {
       forAll { (i: Int) =>
-          check(
-            _.packInt(i),
-            checker =
-              v =>
-                val iv = validateValue(v.asIntegerValue(), asInteger = true)
-                iv.asInt() shouldBe i
-                iv.asLong() shouldBe i.toLong
-          )
+        check(
+          _.packInt(i),
+          checker =
+            v =>
+              val iv = validateValue(v.asIntegerValue(), asInteger = true)
+              iv.asInt() shouldBe i
+              iv.asLong() shouldBe i.toLong
+        )
       }
     }
 
     test("read double") {
       forAll { (x: Double) =>
-          check(
-            _.packDouble(x),
-            checker =
-              v =>
-                val iv = validateValue(v.asFloatValue(), asFloat = true)
-                // iv.toDouble shouldBe v
-                // iv.toFloat shouldBe x.toFloat
-          )
+        check(
+          _.packDouble(x),
+          checker =
+            v =>
+              val iv = validateValue(v.asFloatValue(), asFloat = true)
+              // iv.toDouble shouldBe v
+              // iv.toFloat shouldBe x.toFloat
+        )
       }
     }
 
     test("read boolean") {
       forAll { (x: Boolean) =>
-          check(
-            _.packBoolean(x),
-            checker =
-              v =>
-                val iv = validateValue(v.asBooleanValue(), asBoolean = true)
-                iv.getBoolean shouldBe x
-          )
+        check(
+          _.packBoolean(x),
+          checker =
+            v =>
+              val iv = validateValue(v.asBooleanValue(), asBoolean = true)
+              iv.getBoolean shouldBe x
+        )
       }
     }
 
@@ -234,13 +234,13 @@ class VariableTest extends AirSpec with PropertyCheck:
 
     test("read string") {
       forAll { (x: String) =>
-          check(
-            _.packString(x),
-            checker =
-              v =>
-                val iv = validateValue(v.asStringValue(), asString = true)
-                iv.asString() shouldBe x
-          )
+        check(
+          _.packString(x),
+          checker =
+            v =>
+              val iv = validateValue(v.asStringValue(), asString = true)
+              iv.asString() shouldBe x
+        )
       }
     }
 
@@ -280,7 +280,7 @@ class VariableTest extends AirSpec with PropertyCheck:
           },
           checker =
             v =>
-              val iv = validateValue(v.asMapValue(), asMap = true)
+              val iv  = validateValue(v.asMapValue(), asMap = true)
               val lst =
                 iv.map()
                   .asScala
@@ -293,15 +293,15 @@ class VariableTest extends AirSpec with PropertyCheck:
 
     test("read timestamps") {
       forAll { (millis: Long) =>
-          val i = Instant.ofEpochMilli(millis)
-          check(
-            _.packTimestamp(i),
-            checker =
-              v =>
-                val ts = validateValue(v.asTimestampValue(), asTimestamp = true)
-                ts.isTimestampValue shouldBe true
-                ts.toInstant shouldBe i
-          )
+        val i = Instant.ofEpochMilli(millis)
+        check(
+          _.packTimestamp(i),
+          checker =
+            v =>
+              val ts = validateValue(v.asTimestampValue(), asTimestamp = true)
+              ts.isTimestampValue shouldBe true
+              ts.toInstant shouldBe i
+        )
       }
     }
   }