diff --git a/bench-micro/src/main/scala/dotty/tools/benchmarks/TypeOpsBenchmark.scala b/bench-micro/src/main/scala/dotty/tools/benchmarks/TypeOpsBenchmark.scala
new file mode 100644
index 000000000000..2436fc10acfe
--- /dev/null
+++ b/bench-micro/src/main/scala/dotty/tools/benchmarks/TypeOpsBenchmark.scala
@@ -0,0 +1,56 @@
+package dotty.tools.benchmarks
+
+import org.openjdk.jmh.annotations.*
+import java.util.concurrent.TimeUnit.SECONDS
+import dotty.tools.dotc.{Driver, Run, Compiler}
+import dotty.tools.dotc.core.Mode
+import dotty.tools.dotc.core.Types.{TermRef, Type}
+import dotty.tools.dotc.core.Contexts.{ContextBase, Context, ctx, withMode}
+
+@Fork(value = 5)
+@Warmup(iterations = 5, time = 1, timeUnit = SECONDS)
+@Measurement(iterations = 5, time = 1, timeUnit = SECONDS)
+@State(Scope.Thread)
+class TypeOpsBenchmark:
+  var tp: Type = null
+  var context: Context = null
+
+  @Param(Array("int", "singletonsSum", "intsSum", "deepSingletonsSum", "deepIntsSum", "singletonsIntersection", "singletonsUnion"))
+  var valName: String = "int"
+
+  @Setup(Level.Iteration)
+  def setup(): Unit =
+    val driver = new Driver:
+      override def finish(compiler: Compiler, run: Run)(using Context): Unit =
+        withMode(Mode.Printing) {
+          val pkg = run.units(0).tpdTree.symbol
+          tp = pkg.requiredClass("Test").requiredValueRef(valName).underlying
+          context = ctx
+        }
+        super.finish(compiler, run)
+    driver.process(Array(
+      "-classpath", System.getProperty("BENCH_CLASS_PATH"),
+      "-Ystop-after:typer",
+      "tests/someTypes.scala"
+    ))
+
+  @Benchmark
+  def isStable(): Unit = tp.isStable(using context)
+
+  @Benchmark
+  def normalized(): Unit = tp.normalized(using context)
+
+  @Benchmark
+  def simplified(): Unit = tp.simplified(using context)
+
+  @Benchmark
+  def dealias(): Unit = tp.dealias(using context)
+
+  @Benchmark
+  def widen(): Unit = tp.widen(using context)
+
+  @Benchmark
+  def atoms(): Unit = tp.atoms(using context)
+
+  @Benchmark
+  def isProvisional(): Unit = tp.isProvisional(using context)
diff --git a/bench-micro/tests/someTypes.scala b/bench-micro/tests/someTypes.scala
new file mode 100644
index 000000000000..4631c6ba0750
--- /dev/null
+++ b/bench-micro/tests/someTypes.scala
@@ -0,0 +1,22 @@
+import compiletime.ops.int.+
+
+class Test:
+    val int: Int = 5
+
+    val int2: Int = 6
+
+    val singletonsSum: int.type + int2.type = ???
+
+    val intsSum: Int + Int = ???
+
+    val deepSingletonsSum:
+        ((int.type + int2.type) + (int.type + int2.type)) + ((int.type + int2.type) + (int.type + int2.type)) +
+        ((int.type + int2.type) + (int.type + int2.type)) + ((int.type + int2.type) + (int.type + int2.type)) = ???
+
+    val deepIntsSum:
+        ((Int + Int) + (Int + Int)) + ((Int + Int) + (Int + Int)) +
+        ((Int + Int) + (Int + Int)) + ((Int + Int) + (Int + Int)) = ???
+
+    val singletonsIntersection: int.type & int2.type = ???
+
+    val singletonsUnion: int.type | int2.type = ???
diff --git a/build.sbt b/build.sbt
index bae6deafd8cc..80a36739d5e8 100644
--- a/build.sbt
+++ b/build.sbt
@@ -13,6 +13,7 @@ val `scala3-tasty-inspector` = Build.`scala3-tasty-inspector`
 val `scala3-language-server` = Build.`scala3-language-server`
 val `scala3-bench` = Build.`scala3-bench`
 val `scala3-bench-bootstrapped` = Build.`scala3-bench-bootstrapped`
+val `scala3-bench-micro` = Build.`scala3-bench-micro`
 val `stdlib-bootstrapped` = Build.`stdlib-bootstrapped`
 val `stdlib-bootstrapped-tasty-tests` = Build.`stdlib-bootstrapped-tasty-tests`
 val `tasty-core` = Build.`tasty-core`
diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index 8b9f8690604e..21e72c1d918f 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -175,6 +175,7 @@ object Types {
         // see: tests/explicit-nulls/pos/flow-stable.scala.disabled
         tp.tp1.isStable && (realizability(tp.tp2) eq Realizable) ||
         tp.tp2.isStable && (realizability(tp.tp1) eq Realizable)
+      case tp: AppliedType => tp.cachedIsStable
       case _ => false
     }
 
@@ -4161,10 +4162,32 @@ object Types {
     private var myStableHash: Byte = 0
     private var myGround: Byte = 0
 
+    private var myIsStablePeriod: Period = Nowhere
+    private var myIsStable: Boolean = false
+
     def isGround(acc: TypeAccumulator[Boolean])(using Context): Boolean =
       if myGround == 0 then myGround = if acc.foldOver(true, this) then 1 else -1
       myGround > 0
 
+    private[Types] def cachedIsStable(using Context): Boolean =
+      // We need to invalidate the cache when the period changes because the
+      // case `TermRef` of `Type#isStable` reads denotations, which depend on
+      // the period. See docs/_docs/internals/periods.md for more information.
+      if myIsStablePeriod != ctx.period then
+        val res: Boolean = computeIsStable
+        // We don't cache if the type is provisional because `Type#isStable`
+        // calls `Type#stripTypeVar` which might return different results later.
+        if !isProvisional then
+          myIsStablePeriod = ctx.period
+          myIsStable = res
+        res
+      else
+        myIsStable
+
+    private def computeIsStable(using Context): Boolean = tycon match
+      case tycon: TypeRef if defn.isCompiletimeAppliedType(tycon.symbol) && args.forall(_.isStable) => true
+      case _ => false
+
     override def underlying(using Context): Type = tycon
 
     override def superType(using Context): Type =
@@ -4242,7 +4265,7 @@ object Types {
             // final val one = 1
             // type Two = one.type + one.type
             // ```
-            case tp: TermRef => tp.underlying
+            case tp: TypeProxy if tp.underlying.isStable => tp.underlying.fixForEvaluation
             case tp => tp
           }
 
diff --git a/compiler/src/dotty/tools/dotc/plugins/Plugins.scala b/compiler/src/dotty/tools/dotc/plugins/Plugins.scala
index bcc0c221f78b..3093a1c0460f 100644
--- a/compiler/src/dotty/tools/dotc/plugins/Plugins.scala
+++ b/compiler/src/dotty/tools/dotc/plugins/Plugins.scala
@@ -51,7 +51,7 @@ trait Plugins {
     }
     else _roughPluginsList
 
-  /** Load all available plugins.  Skips plugins that
+  /** Load all available plugins. Skips plugins that
    *  either have the same name as another one, or which
    *  define a phase name that another one does.
    */
diff --git a/library/src/scala/compiletime/ops/any.scala b/library/src/scala/compiletime/ops/any.scala
index ba3b6809fb49..c6eb7c075b14 100644
--- a/library/src/scala/compiletime/ops/any.scala
+++ b/library/src/scala/compiletime/ops/any.scala
@@ -10,7 +10,7 @@ object any:
    * ```
    * @syntax markdown
    */
-  type ==[+X, +Y] <: Boolean
+  type ==[X, Y] <: Boolean
 
   /** Inequality comparison of two singleton types.
    * ```scala
@@ -20,7 +20,7 @@ object any:
    * ```
    * @syntax markdown
    */
-  type !=[+X, +Y] <: Boolean
+  type !=[X, Y] <: Boolean
 
   /** Tests if a type is a constant.
    * ```scala
@@ -48,4 +48,4 @@ object any:
    *  ```
    *  @syntax markdown
    */
-  type ToString[+X] <: String
+  type ToString[X] <: String
diff --git a/library/src/scala/compiletime/ops/boolean.scala b/library/src/scala/compiletime/ops/boolean.scala
index c67ca28e5d22..323fd7d6d7ed 100644
--- a/library/src/scala/compiletime/ops/boolean.scala
+++ b/library/src/scala/compiletime/ops/boolean.scala
@@ -10,7 +10,7 @@ object boolean:
    *  ```
    *  @syntax markdown
    */
-  type ![+X <: Boolean] <: Boolean
+  type ![X <: Boolean] <: Boolean
 
   /** Exclusive disjunction of two `Boolean` singleton types.
    *  ```scala
@@ -19,7 +19,7 @@ object boolean:
    *  ```
    *  @syntax markdown
    */
-  type ^[+X <: Boolean, +Y <: Boolean] <: Boolean
+  type ^[X <: Boolean, Y <: Boolean] <: Boolean
 
   /** Conjunction of two `Boolean` singleton types.
    *  ```scala
@@ -28,7 +28,7 @@ object boolean:
    *  ```
    *  @syntax markdown
    */
-  type &&[+X <: Boolean, +Y <: Boolean] <: Boolean
+  type &&[X <: Boolean, Y <: Boolean] <: Boolean
 
   /** Disjunction of two `Boolean` singleton types.
    *  ```scala
@@ -37,4 +37,4 @@ object boolean:
    *  ```
    *  @syntax markdown
    */
-  type ||[+X <: Boolean, +Y <: Boolean] <: Boolean
+  type ||[X <: Boolean, Y <: Boolean] <: Boolean
diff --git a/library/src/scala/compiletime/ops/double.scala b/library/src/scala/compiletime/ops/double.scala
index 91f65f644e4b..74882b867e00 100644
--- a/library/src/scala/compiletime/ops/double.scala
+++ b/library/src/scala/compiletime/ops/double.scala
@@ -8,7 +8,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type +[+X <: Double, +Y <: Double] <: Double
+  type +[X <: Double, Y <: Double] <: Double
 
   /** Subtraction of two `Double` singleton types.
    *  ```scala
@@ -16,7 +16,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type -[+X <: Double, +Y <: Double] <: Double
+  type -[X <: Double, Y <: Double] <: Double
 
   /** Multiplication of two `Double` singleton types.
    *  ```scala
@@ -24,7 +24,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type *[+X <: Double, +Y <: Double] <: Double
+  type *[X <: Double, Y <: Double] <: Double
 
   /** Integer division of two `Double` singleton types.
    *  ```scala
@@ -32,7 +32,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type /[+X <: Double, +Y <: Double] <: Double
+  type /[X <: Double, Y <: Double] <: Double
 
   /** Remainder of the division of `X` by `Y`.
    *  ```scala
@@ -40,7 +40,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type %[+X <: Double, +Y <: Double] <: Double
+  type %[X <: Double, Y <: Double] <: Double
 
   /** Less-than comparison of two `Double` singleton types.
    *  ```scala
@@ -49,7 +49,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type <[+X <: Double, +Y <: Double] <: Boolean
+  type <[X <: Double, Y <: Double] <: Boolean
 
   /** Greater-than comparison of two `Double` singleton types.
    *  ```scala
@@ -58,7 +58,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type >[+X <: Double, +Y <: Double] <: Boolean
+  type >[X <: Double, Y <: Double] <: Boolean
 
   /** Greater-or-equal comparison of two `Double` singleton types.
    *  ```scala
@@ -67,7 +67,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type >=[+X <: Double, +Y <: Double] <: Boolean
+  type >=[X <: Double, Y <: Double] <: Boolean
 
   /** Less-or-equal comparison of two `Double` singleton types.
    *  ```scala
@@ -76,7 +76,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type <=[+X <: Double, +Y <: Double] <: Boolean
+  type <=[X <: Double, Y <: Double] <: Boolean
 
   /** Absolute value of an `Double` singleton type.
    *  ```scala
@@ -84,7 +84,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type Abs[+X <: Double] <: Double
+  type Abs[X <: Double] <: Double
 
   /** Negation of an `Double` singleton type.
    *  ```scala
@@ -93,7 +93,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type Negate[+X <: Double] <: Double
+  type Negate[X <: Double] <: Double
 
   /** Minimum of two `Double` singleton types.
    *  ```scala
@@ -101,7 +101,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type Min[+X <: Double, +Y <: Double] <: Double
+  type Min[X <: Double, Y <: Double] <: Double
 
   /** Maximum of two `Double` singleton types.
    *  ```scala
@@ -109,7 +109,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type Max[+X <: Double, +Y <: Double] <: Double
+  type Max[X <: Double, Y <: Double] <: Double
 
   /** Int conversion of a `Double` singleton type.
    *  ```scala
@@ -117,7 +117,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type ToInt[+X <: Double] <: Int
+  type ToInt[X <: Double] <: Int
 
   /** Long conversion of a `Double` singleton type.
    *  ```scala
@@ -125,7 +125,7 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type ToLong[+X <: Double] <: Long
+  type ToLong[X <: Double] <: Long
 
   /** Float conversion of a `Double` singleton type.
    *  ```scala
@@ -133,4 +133,4 @@ object double:
    *  ```
    *  @syntax markdown
    */
-  type ToFloat[+X <: Double] <: Float
+  type ToFloat[X <: Double] <: Float
\ No newline at end of file
diff --git a/library/src/scala/compiletime/ops/float.scala b/library/src/scala/compiletime/ops/float.scala
index c42aa4aec70f..29e02992a8df 100644
--- a/library/src/scala/compiletime/ops/float.scala
+++ b/library/src/scala/compiletime/ops/float.scala
@@ -8,7 +8,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type +[+X <: Float, +Y <: Float] <: Float
+  type +[X <: Float, Y <: Float] <: Float
 
   /** Subtraction of two `Float` singleton types.
    *  ```scala
@@ -16,7 +16,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type -[+X <: Float, +Y <: Float] <: Float
+  type -[X <: Float, Y <: Float] <: Float
 
   /** Multiplication of two `Float` singleton types.
    *  ```scala
@@ -24,7 +24,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type *[+X <: Float, +Y <: Float] <: Float
+  type *[X <: Float, Y <: Float] <: Float
 
   /** Integer division of two `Float` singleton types.
    *  ```scala
@@ -32,7 +32,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type /[+X <: Float, +Y <: Float] <: Float
+  type /[X <: Float, Y <: Float] <: Float
 
   /** Remainder of the division of `X` by `Y`.
    *  ```scala
@@ -40,7 +40,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type %[+X <: Float, +Y <: Float] <: Float
+  type %[X <: Float, Y <: Float] <: Float
 
   /** Less-than comparison of two `Float` singleton types.
    *  ```scala
@@ -49,7 +49,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type <[+X <: Float, +Y <: Float] <: Boolean
+  type <[X <: Float, Y <: Float] <: Boolean
 
   /** Greater-than comparison of two `Float` singleton types.
    *  ```scala
@@ -58,7 +58,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type >[+X <: Float, +Y <: Float] <: Boolean
+  type >[X <: Float, Y <: Float] <: Boolean
 
   /** Greater-or-equal comparison of two `Float` singleton types.
    *  ```scala
@@ -67,7 +67,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type >=[+X <: Float, +Y <: Float] <: Boolean
+  type >=[X <: Float, Y <: Float] <: Boolean
 
   /** Less-or-equal comparison of two `Float` singleton types.
    *  ```scala
@@ -76,7 +76,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type <=[+X <: Float, +Y <: Float] <: Boolean
+  type <=[X <: Float, Y <: Float] <: Boolean
 
   /** Absolute value of an `Float` singleton type.
    *  ```scala
@@ -84,7 +84,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type Abs[+X <: Float] <: Float
+  type Abs[X <: Float] <: Float
 
   /** Negation of an `Float` singleton type.
    *  ```scala
@@ -93,7 +93,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type Negate[+X <: Float] <: Float
+  type Negate[X <: Float] <: Float
 
   /** Minimum of two `Float` singleton types.
    *  ```scala
@@ -101,7 +101,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type Min[+X <: Float, +Y <: Float] <: Float
+  type Min[X <: Float, Y <: Float] <: Float
 
   /** Maximum of two `Float` singleton types.
    *  ```scala
@@ -109,7 +109,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type Max[+X <: Float, +Y <: Float] <: Float
+  type Max[X <: Float, Y <: Float] <: Float
 
   /** Int conversion of a `Float` singleton type.
    *  ```scala
@@ -117,7 +117,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type ToInt[+X <: Float] <: Int
+  type ToInt[X <: Float] <: Int
 
   /** Long conversion of a `Float` singleton type.
    *  ```scala
@@ -125,7 +125,7 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type ToLong[+X <: Float] <: Long
+  type ToLong[X <: Float] <: Long
 
   /** Double conversion of a `Float` singleton type.
    *  ```scala
@@ -133,4 +133,4 @@ object float:
    *  ```
    *  @syntax markdown
    */
-  type ToDouble[+X <: Float] <: Double
+  type ToDouble[X <: Float] <: Double
diff --git a/library/src/scala/compiletime/ops/int.scala b/library/src/scala/compiletime/ops/int.scala
index ef7707173a00..f041576faa86 100644
--- a/library/src/scala/compiletime/ops/int.scala
+++ b/library/src/scala/compiletime/ops/int.scala
@@ -15,7 +15,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type S[+N <: Int] <: Int
+  type S[N <: Int] <: Int
 
   /** Addition of two `Int` singleton types.
    *  ```scala
@@ -23,7 +23,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type +[+X <: Int, +Y <: Int] <: Int
+  type +[X <: Int, Y <: Int] <: Int
 
   /** Subtraction of two `Int` singleton types.
    *  ```scala
@@ -31,7 +31,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type -[+X <: Int, +Y <: Int] <: Int
+  type -[X <: Int, Y <: Int] <: Int
 
   /** Multiplication of two `Int` singleton types.
    *  ```scala
@@ -39,7 +39,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type *[+X <: Int, +Y <: Int] <: Int
+  type *[X <: Int, Y <: Int] <: Int
 
   /** Integer division of two `Int` singleton types.
    *  ```scala
@@ -47,7 +47,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type /[+X <: Int, +Y <: Int] <: Int
+  type /[X <: Int, Y <: Int] <: Int
 
   /** Remainder of the division of `X` by `Y`.
    *  ```scala
@@ -55,7 +55,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type %[+X <: Int, +Y <: Int] <: Int
+  type %[X <: Int, Y <: Int] <: Int
 
   /** Binary left shift of `X` by `Y`.
    *  ```scala
@@ -63,7 +63,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type <<[+X <: Int, +Y <: Int] <: Int
+  type <<[X <: Int, Y <: Int] <: Int
 
   /** Binary right shift of `X` by `Y`.
    *  ```scala
@@ -71,7 +71,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type >>[+X <: Int, +Y <: Int] <: Int
+  type >>[X <: Int, Y <: Int] <: Int
 
   /** Binary right shift of `X` by `Y`, filling the left with zeros.
    *  ```scala
@@ -79,7 +79,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type >>>[+X <: Int, +Y <: Int] <: Int
+  type >>>[X <: Int, Y <: Int] <: Int
 
   /** Bitwise xor of `X` and `Y`.
    *  ```scala
@@ -87,7 +87,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type ^[+X <: Int, +Y <: Int] <: Int
+  type ^[X <: Int, Y <: Int] <: Int
 
   /** Less-than comparison of two `Int` singleton types.
    *  ```scala
@@ -96,7 +96,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type <[+X <: Int, +Y <: Int] <: Boolean
+  type <[X <: Int, Y <: Int] <: Boolean
 
   /** Greater-than comparison of two `Int` singleton types.
    *  ```scala
@@ -105,7 +105,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type >[+X <: Int, +Y <: Int] <: Boolean
+  type >[X <: Int, Y <: Int] <: Boolean
 
   /** Greater-or-equal comparison of two `Int` singleton types.
    *  ```scala
@@ -114,7 +114,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type >=[+X <: Int, +Y <: Int] <: Boolean
+  type >=[X <: Int, Y <: Int] <: Boolean
 
   /** Less-or-equal comparison of two `Int` singleton types.
    *  ```scala
@@ -123,7 +123,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type <=[+X <: Int, +Y <: Int] <: Boolean
+  type <=[X <: Int, Y <: Int] <: Boolean
 
   /** Bitwise and of `X` and `Y`.
    *  ```scala
@@ -132,7 +132,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type BitwiseAnd[+X <: Int, +Y <: Int] <: Int
+  type BitwiseAnd[X <: Int, Y <: Int] <: Int
 
   /** Bitwise or of `X` and `Y`.
    *  ```scala
@@ -140,7 +140,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type BitwiseOr[+X <: Int, +Y <: Int] <: Int
+  type BitwiseOr[X <: Int, Y <: Int] <: Int
 
   /** Absolute value of an `Int` singleton type.
    *  ```scala
@@ -148,7 +148,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type Abs[+X <: Int] <: Int
+  type Abs[X <: Int] <: Int
 
   /** Negation of an `Int` singleton type.
    *  ```scala
@@ -157,7 +157,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type Negate[+X <: Int] <: Int
+  type Negate[X <: Int] <: Int
 
   /** Minimum of two `Int` singleton types.
    *  ```scala
@@ -165,7 +165,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type Min[+X <: Int, +Y <: Int] <: Int
+  type Min[X <: Int, Y <: Int] <: Int
 
   /** Maximum of two `Int` singleton types.
    *  ```scala
@@ -173,7 +173,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type Max[+X <: Int, +Y <: Int] <: Int
+  type Max[X <: Int, Y <: Int] <: Int
 
   /** String conversion of an `Int` singleton type.
    *  ```scala
@@ -182,7 +182,7 @@ object int:
    *  @syntax markdown
    */
   //@deprecated("Use compiletime.ops.any.ToString instead.","3.2.0") // uncomment when reaching 3.2.0
-  type ToString[+X <: Int] <: String
+  type ToString[X <: Int] <: String
 
   /** Long conversion of an `Int` singleton type.
    *  ```scala
@@ -190,7 +190,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type ToLong[+X <: Int] <: Long
+  type ToLong[X <: Int] <: Long
 
   /** Float conversion of an `Int` singleton type.
    *  ```scala
@@ -198,7 +198,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type ToFloat[+X <: Int] <: Float
+  type ToFloat[X <: Int] <: Float
 
   /** Double conversion of an `Int` singleton type.
    *  ```scala
@@ -206,7 +206,7 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type ToDouble[+X <: Int] <: Double
+  type ToDouble[X <: Int] <: Double
 
   /** Number of zero bits preceding the highest-order ("leftmost")
    * one-bit in the two's complement binary representation of the specified `Int` singleton type.
@@ -220,4 +220,4 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  type NumberOfLeadingZeros[+X <: Int] <: Int
+  type NumberOfLeadingZeros[X <: Int] <: Int
diff --git a/library/src/scala/compiletime/ops/long.scala b/library/src/scala/compiletime/ops/long.scala
index 1d10e3bf3213..3ab7841faedd 100644
--- a/library/src/scala/compiletime/ops/long.scala
+++ b/library/src/scala/compiletime/ops/long.scala
@@ -15,7 +15,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type S[+N <: Long] <: Long
+  type S[N <: Long] <: Long
 
   /** Addition of two `Long` singleton types.
    *  ```scala
@@ -23,7 +23,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type +[+X <: Long, +Y <: Long] <: Long
+  type +[X <: Long, Y <: Long] <: Long
 
   /** Subtraction of two `Long` singleton types.
    *  ```scala
@@ -31,7 +31,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type -[+X <: Long, +Y <: Long] <: Long
+  type -[X <: Long, Y <: Long] <: Long
 
   /** Multiplication of two `Long` singleton types.
    *  ```scala
@@ -39,7 +39,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type *[+X <: Long, +Y <: Long] <: Long
+  type *[X <: Long, Y <: Long] <: Long
 
   /** Integer division of two `Long` singleton types.
    *  ```scala
@@ -47,7 +47,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type /[+X <: Long, +Y <: Long] <: Long
+  type /[X <: Long, Y <: Long] <: Long
 
   /** Remainder of the division of `X` by `Y`.
    *  ```scala
@@ -55,7 +55,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type %[+X <: Long, +Y <: Long] <: Long
+  type %[X <: Long, Y <: Long] <: Long
 
   /** Binary left shift of `X` by `Y`.
    *  ```scala
@@ -63,7 +63,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type <<[+X <: Long, +Y <: Long] <: Long
+  type <<[X <: Long, Y <: Long] <: Long
 
   /** Binary right shift of `X` by `Y`.
    *  ```scala
@@ -71,7 +71,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type >>[+X <: Long, +Y <: Long] <: Long
+  type >>[X <: Long, Y <: Long] <: Long
 
   /** Binary right shift of `X` by `Y`, filling the left with zeros.
    *  ```scala
@@ -79,7 +79,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type >>>[+X <: Long, +Y <: Long] <: Long
+  type >>>[X <: Long, Y <: Long] <: Long
 
   /** Bitwise xor of `X` and `Y`.
    *  ```scala
@@ -87,7 +87,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type ^[+X <: Long, +Y <: Long] <: Long
+  type ^[X <: Long, Y <: Long] <: Long
 
   /** Less-than comparison of two `Long` singleton types.
    *  ```scala
@@ -96,7 +96,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type <[+X <: Long, +Y <: Long] <: Boolean
+  type <[X <: Long, Y <: Long] <: Boolean
 
   /** Greater-than comparison of two `Long` singleton types.
    *  ```scala
@@ -105,7 +105,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type >[+X <: Long, +Y <: Long] <: Boolean
+  type >[X <: Long, Y <: Long] <: Boolean
 
   /** Greater-or-equal comparison of two `Long` singleton types.
    *  ```scala
@@ -114,7 +114,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type >=[+X <: Long, +Y <: Long] <: Boolean
+  type >=[X <: Long, Y <: Long] <: Boolean
 
   /** Less-or-equal comparison of two `Long` singleton types.
    *  ```scala
@@ -123,7 +123,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type <=[+X <: Long, +Y <: Long] <: Boolean
+  type <=[X <: Long, Y <: Long] <: Boolean
 
   /** Bitwise and of `X` and `Y`.
    *  ```scala
@@ -132,7 +132,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type BitwiseAnd[+X <: Long, +Y <: Long] <: Long
+  type BitwiseAnd[X <: Long, Y <: Long] <: Long
 
   /** Bitwise or of `X` and `Y`.
    *  ```scala
@@ -140,7 +140,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type BitwiseOr[+X <: Long, +Y <: Long] <: Long
+  type BitwiseOr[X <: Long, Y <: Long] <: Long
 
   /** Absolute value of an `Long` singleton type.
    *  ```scala
@@ -148,7 +148,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type Abs[+X <: Long] <: Long
+  type Abs[X <: Long] <: Long
 
   /** Negation of an `Long` singleton type.
    *  ```scala
@@ -157,7 +157,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type Negate[+X <: Long] <: Long
+  type Negate[X <: Long] <: Long
 
   /** Minimum of two `Long` singleton types.
    *  ```scala
@@ -165,7 +165,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type Min[+X <: Long, +Y <: Long] <: Long
+  type Min[X <: Long, Y <: Long] <: Long
 
   /** Maximum of two `Long` singleton types.
    *  ```scala
@@ -173,7 +173,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type Max[+X <: Long, +Y <: Long] <: Long
+  type Max[X <: Long, Y <: Long] <: Long
 
   /** Number of zero bits preceding the highest-order ("leftmost")
    * one-bit in the two's complement binary representation of the specified `Long` singleton type.
@@ -187,7 +187,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type NumberOfLeadingZeros[+X <: Long] <: Int
+  type NumberOfLeadingZeros[X <: Long] <: Int
 
   /** Int conversion of a `Long` singleton type.
    *  ```scala
@@ -195,7 +195,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type ToInt[+X <: Long] <: Int
+  type ToInt[X <: Long] <: Int
 
   /** Float conversion of a `Long` singleton type.
    *  ```scala
@@ -203,7 +203,7 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type ToFloat[+X <: Long] <: Float
+  type ToFloat[X <: Long] <: Float
 
   /** Double conversion of a `Long` singleton type.
    *  ```scala
@@ -211,4 +211,4 @@ object long:
    *  ```
    *  @syntax markdown
    */
-  type ToDouble[+X <: Long] <: Double
+  type ToDouble[X <: Long] <: Double
diff --git a/library/src/scala/compiletime/ops/string.scala b/library/src/scala/compiletime/ops/string.scala
index 18c5b13871b1..35562cfd6261 100644
--- a/library/src/scala/compiletime/ops/string.scala
+++ b/library/src/scala/compiletime/ops/string.scala
@@ -8,7 +8,7 @@ object string:
    *  ```
    *  @syntax markdown
    */
-  type +[+X <: String, +Y <: String] <: String
+  type +[X <: String, Y <: String] <: String
 
   /** Length of a `String` singleton type.
    *  ```scala
@@ -16,7 +16,7 @@ object string:
    *  ```
    *  @syntax markdown
    */
-  type Length[+X <: String] <: Int
+  type Length[X <: String] <: Int
 
   /** Substring of a `String` singleton type, with a singleton type
    * begin inclusive index `IBeg`, and a singleton type exclusive end index `IEnd`.
@@ -28,7 +28,7 @@ object string:
    *  ```
    *  @syntax markdown
    */
-  type Substring[+S <: String, +IBeg <: Int, +IEnd <: Int] <: String
+  type Substring[S <: String, IBeg <: Int, IEnd <: Int] <: String
 
   /** Tests if this `String` singleton type matches the given
    * regular expression `String` singleton type.
@@ -37,7 +37,7 @@ object string:
    *  ```
    *  @syntax markdown
    */
-  type Matches[+S <: String, +Regex <: String] <: Boolean
+  type Matches[S <: String, Regex <: String] <: Boolean
 
   /** Returns the Char type at the specified index.
    *  An index ranges from 0 to Length[S] - 1. The first Char of
@@ -47,4 +47,4 @@ object string:
    *  ```
    *  @syntax markdown
    */
-  type CharAt[+S <: String, +Idx <: Int] <: Char
+  type CharAt[S <: String, Idx <: Int] <: Char
diff --git a/project/Build.scala b/project/Build.scala
index 5d02e9870253..9ae3c477ffd5 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -1247,6 +1247,10 @@ object Build {
   lazy val `scala3-bench-bootstrapped` = project.in(file("bench")).asDottyBench(Bootstrapped)
   lazy val `scala3-bench-run` = project.in(file("bench-run")).asDottyBench(Bootstrapped)
 
+  lazy val `scala3-bench-micro` = project.in(file("bench-micro"))
+    .asDottyBench(Bootstrapped)
+    .settings(Jmh / run / mainClass := Some("org.openjdk.jmh.Main"))
+
   val testcasesOutputDir = taskKey[Seq[String]]("Root directory where tests classses are generated")
   val testcasesSourceRoot = taskKey[String]("Root directory where tests sources are generated")
   val testDocumentationRoot = taskKey[String]("Root directory where tests documentation are stored")
diff --git a/project/plugins.sbt b/project/plugins.sbt
index f0b13c6cb7c4..bb43d75d44da 100644
--- a/project/plugins.sbt
+++ b/project/plugins.sbt
@@ -10,7 +10,7 @@ addSbtPlugin("com.jsuereth" % "sbt-pgp" % "2.0.0")
 
 addSbtPlugin("org.xerial.sbt" % "sbt-pack" % "0.13")
 
-addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.3.2")
+addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.4.3")
 
 addSbtPlugin("com.eed3si9n" % "sbt-buildinfo" % "0.9.0")
 
diff --git a/tests/neg/singleton-ops-int.scala b/tests/neg/singleton-ops-int.scala
index f7081342a4ee..bdceb5bad5e3 100644
--- a/tests/neg/singleton-ops-int.scala
+++ b/tests/neg/singleton-ops-int.scala
@@ -117,11 +117,23 @@ object Test {
   val t83: ToDouble[1] = 1.0
   val t84: ToDouble[2] = 2 // error
 
-  // Singleton operations are covariant.
-  type Plus2[X <: Int] = X + 2
-  val x: Int = 5
-  val xPlus2: Plus2[x.type] = (x + 2).asInstanceOf
-  summon[xPlus2.type + 1 <:< Plus2[x.type] + 1]
+  // Singletons are dereferenced
+  val t85: Int = 5
+  val t86: t85.type = t85
+  summon[t85.type + t85.type =:= t86.type + t86.type]
+
+  // Singletons are dereferenced recursively
+  val t87: t86.type = t87
+  summon[t85.type + t85.type =:= t87.type + t87.type]
+
+  // Skolems of compile-time types are dereferenced:
+  // (?1 : (Test.x : Int) * (Test.x : Int)) --> (Test.x : Int) * (Test.x : Int)
   def mult(x: Int, y: Int): x.type * y.type = (x * y).asInstanceOf
-  val y: x.type * x.type * x.type = mult(mult(x, x), x)
+  val t88: t85.type * t85.type * t85.type = mult(mult(t85, t85), t85)
+
+  // Compile-time operations with singleton arguments are singletons
+  summon[t85.type + t86.type <:< Singleton]
+
+  // Compile-time operations with non-singleton arguments are not singletons  
+  summon[t85.type + Int <:< Singleton] // error
 }