diff --git a/core/src/main/scala/cats/Eval.scala b/core/src/main/scala/cats/Eval.scala
index 7834248b3c..476152e948 100644
--- a/core/src/main/scala/cats/Eval.scala
+++ b/core/src/main/scala/cats/Eval.scala
@@ -22,6 +22,7 @@
 package cats
 
 import org.typelevel.scalaccompat.annotation.uncheckedVariance2
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
 
 import scala.annotation.tailrec
 
@@ -479,6 +480,7 @@ trait EvalSemigroup[A] extends Semigroup[Eval[A]] {
 
 trait EvalMonoid[A] extends Monoid[Eval[A]] with EvalSemigroup[A] {
   implicit def algebra: Monoid[A]
+  @threadUnsafe3
   lazy val empty: Eval[A] = Eval.later(algebra.empty)
 }
 
diff --git a/core/src/main/scala/cats/data/Ior.scala b/core/src/main/scala/cats/data/Ior.scala
index f7aaf6a093..c98e33f3d1 100644
--- a/core/src/main/scala/cats/data/Ior.scala
+++ b/core/src/main/scala/cats/data/Ior.scala
@@ -24,6 +24,7 @@ package data
 
 import cats.arrow.FunctionK
 import cats.data.Validated.{Invalid, Valid}
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
 
 import scala.annotation.tailrec
 
@@ -946,6 +947,7 @@ sealed abstract private[data] class IorInstances extends IorInstances0 {
           }
       }
 
+      @threadUnsafe3
       lazy val monad: Monad[Ior[E, *]] = Monad[Ior[E, *]]
     }
 
diff --git a/core/src/main/scala/cats/data/IorT.scala b/core/src/main/scala/cats/data/IorT.scala
index 45712b664f..e3dccb407b 100644
--- a/core/src/main/scala/cats/data/IorT.scala
+++ b/core/src/main/scala/cats/data/IorT.scala
@@ -23,6 +23,7 @@ package cats
 package data
 
 import cats.arrow.FunctionK
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
 
 final case class IorT[F[_], A, B](value: F[Ior[A, B]]) {
 
@@ -533,6 +534,7 @@ abstract private[data] class IorTInstances extends IorTInstances1 {
           IorT(FA.map2(ff.value, fa.value)((f, a) => IorA.ap(f)(a)))
       }
 
+      @threadUnsafe3
       lazy val monad: Monad[IorT[M, E, *]] = {
         implicit def underlyingMonadM: Monad[M] = P.monad
         Monad[IorT[M, E, *]]
@@ -566,6 +568,7 @@ abstract private[data] class IorTInstances extends IorTInstances1 {
           IorT(FA.map2(ff.value, fa.value)((f, a) => IorA.ap(f)(a)))
       }
 
+      @threadUnsafe3
       lazy val monad: Monad[IorT[M, E, *]] = {
         implicit def underlyingMonadM: Monad[M] = P.monad
         Monad[IorT[M, E, *]]
@@ -611,6 +614,7 @@ abstract private[data] class IorTInstances1 extends IorTInstances2 {
           IorT(F.map2(ff.value, fa.value)((f, a) => underlyingParallel.applicative.ap[A, B](f)(a)))
       }
 
+      @threadUnsafe3
       lazy val monad: Monad[IorT[F0, E, *]] = Monad[IorT[F0, E, *]]
     }
 
diff --git a/core/src/main/scala/cats/data/Kleisli.scala b/core/src/main/scala/cats/data/Kleisli.scala
index 48a7ab34d1..483be49032 100644
--- a/core/src/main/scala/cats/data/Kleisli.scala
+++ b/core/src/main/scala/cats/data/Kleisli.scala
@@ -25,6 +25,7 @@ package data
 import cats.{Contravariant, Id}
 import cats.arrow._
 import cats.evidence.As
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
 
 /**
  * Represents a function `A => F[B]`.
@@ -372,7 +373,7 @@ sealed abstract private[data] class KleisliInstances extends KleisliInstances0 {
   implicit def catsDataDeferForKleisli[F[_], A](implicit F: Defer[F]): Defer[Kleisli[F, A, *]] =
     new Defer[Kleisli[F, A, *]] {
       def defer[B](fa: => Kleisli[F, A, B]): Kleisli[F, A, B] = {
-        lazy val cacheFa = fa
+        @threadUnsafe3 lazy val cacheFa = fa
         Kleisli[F, A, B] { a =>
           F.defer(cacheFa.run(a))
         }
diff --git a/core/src/main/scala/cats/data/RepresentableStore.scala b/core/src/main/scala/cats/data/RepresentableStore.scala
index 867e1dff40..da43f86f39 100644
--- a/core/src/main/scala/cats/data/RepresentableStore.scala
+++ b/core/src/main/scala/cats/data/RepresentableStore.scala
@@ -22,6 +22,7 @@
 package cats.data
 
 import cats.{Comonad, Functor, Representable}
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
 
 /**
  * A generalization of `StoreT`, where the underlying functor `F` has a `Representable` instance.
@@ -53,12 +54,14 @@ final case class RepresentableStore[F[_], S, A](fa: F[A], index: S)(implicit R:
   /**
    * Extract the value at the current index.
    */
+  @threadUnsafe3
   lazy val extract: A = peek(index)
 
   /**
    * `coflatten` is the dual of `flatten` on `FlatMap`. Whereas flatten removes
    * a layer of `F`, coflatten adds a layer of `F`
    */
+  @threadUnsafe3
   lazy val coflatten: RepresentableStore[F, S, RepresentableStore[F, S, A]] =
     RepresentableStore(R.tabulate(idx => RepresentableStore(fa, idx)), index)
 
diff --git a/core/src/main/scala/cats/data/Tuple2K.scala b/core/src/main/scala/cats/data/Tuple2K.scala
index b5a1d88f4a..b03825de29 100644
--- a/core/src/main/scala/cats/data/Tuple2K.scala
+++ b/core/src/main/scala/cats/data/Tuple2K.scala
@@ -23,6 +23,7 @@ package cats
 package data
 
 import cats.arrow.FunctionK
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
 
 /**
  * [[Tuple2K]] is a product to two independent functor values.
@@ -89,7 +90,7 @@ sealed abstract private[data] class Tuple2KInstances extends Tuple2KInstances0 {
     new Defer[Tuple2K[F, G, *]] {
       def defer[A](fa: => Tuple2K[F, G, A]): Tuple2K[F, G, A] = {
         // Make sure we only evaluate once on both the first and second
-        lazy val cacheFa = fa
+        @threadUnsafe3 lazy val cacheFa = fa
 
         Tuple2K(F.defer(cacheFa.first), G.defer(cacheFa.second))
       }
diff --git a/core/src/main/scala/cats/instances/eq.scala b/core/src/main/scala/cats/instances/eq.scala
index 5c96a8c219..80958b24ce 100644
--- a/core/src/main/scala/cats/instances/eq.scala
+++ b/core/src/main/scala/cats/instances/eq.scala
@@ -22,6 +22,8 @@
 package cats
 package instances
 
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
+
 import scala.annotation.tailrec
 
 trait EqInstances extends kernel.instances.EqInstances {
@@ -52,6 +54,7 @@ object EqInstances {
   private val catsDeferForEqCache: Defer[Eq] =
     new Defer[Eq] {
       case class Deferred[A](fa: () => Eq[A]) extends Eq[A] {
+        @threadUnsafe3
         private lazy val resolved: Eq[A] = {
           @tailrec
           def loop(f: () => Eq[A]): Eq[A] =
@@ -66,7 +69,7 @@ object EqInstances {
       }
 
       override def defer[A](fa: => Eq[A]): Eq[A] = {
-        lazy val cachedFa = fa
+        @threadUnsafe3 lazy val cachedFa = fa
         Deferred(() => cachedFa)
       }
     }
diff --git a/core/src/main/scala/cats/instances/equiv.scala b/core/src/main/scala/cats/instances/equiv.scala
index 941fd6e911..85ad2ac42a 100644
--- a/core/src/main/scala/cats/instances/equiv.scala
+++ b/core/src/main/scala/cats/instances/equiv.scala
@@ -22,6 +22,8 @@
 package cats
 package instances
 
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
+
 import scala.annotation.tailrec
 
 trait EquivInstances {
@@ -61,6 +63,7 @@ object EquivInstances {
   private val catsDeferForEquivCache: Defer[Equiv] =
     new Defer[Equiv] {
       case class Deferred[A](fa: () => Equiv[A]) extends Equiv[A] {
+        @threadUnsafe3
         private lazy val resolved: Equiv[A] = {
           @tailrec
           def loop(f: () => Equiv[A]): Equiv[A] =
@@ -75,7 +78,7 @@ object EquivInstances {
       }
 
       override def defer[A](fa: => Equiv[A]): Equiv[A] = {
-        lazy val cachedFa = fa
+        @threadUnsafe3 lazy val cachedFa = fa
         Deferred(() => cachedFa)
       }
     }
diff --git a/core/src/main/scala/cats/instances/function.scala b/core/src/main/scala/cats/instances/function.scala
index 4233cd10a8..bbcbb231b6 100644
--- a/core/src/main/scala/cats/instances/function.scala
+++ b/core/src/main/scala/cats/instances/function.scala
@@ -25,6 +25,7 @@ package instances
 import cats.Contravariant
 import cats.arrow.{ArrowChoice, Category, CommutativeArrow}
 import cats.data.AndThen
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
 
 import annotation.tailrec
 
@@ -46,6 +47,7 @@ private[instances] trait FunctionInstancesBinCompat0 {
   implicit val catsSddDeferForFunction0: Defer[Function0] =
     new Defer[Function0] {
       case class Deferred[A](fa: () => Function0[A]) extends Function0[A] {
+        @threadUnsafe3
         private lazy val resolved: Function0[A] = {
           @annotation.tailrec
           def loop(f: () => Function0[A]): Function0[A] =
@@ -59,7 +61,7 @@ private[instances] trait FunctionInstancesBinCompat0 {
         def apply(): A = resolved()
       }
       def defer[A](fa: => Function0[A]): Function0[A] = {
-        lazy val cachedFa = fa
+        @threadUnsafe3 lazy val cachedFa = fa
         Deferred(() => cachedFa)
       }
     }
@@ -67,6 +69,7 @@ private[instances] trait FunctionInstancesBinCompat0 {
   implicit def catsStdDeferForFunction1[A]: Defer[A => *] =
     new Defer[A => *] {
       case class Deferred[B](fa: () => A => B) extends (A => B) {
+        @threadUnsafe3
         private lazy val resolved: A => B = {
           @annotation.tailrec
           def loop(f: () => A => B): A => B =
@@ -80,7 +83,7 @@ private[instances] trait FunctionInstancesBinCompat0 {
         def apply(a: A): B = resolved(a)
       }
       def defer[B](fa: => A => B): A => B = {
-        lazy val cachedFa = fa
+        @threadUnsafe3 lazy val cachedFa = fa
         Deferred(() => cachedFa)
       }
     }
diff --git a/core/src/main/scala/cats/instances/hash.scala b/core/src/main/scala/cats/instances/hash.scala
index 9175d0dd4f..3b89d6ea69 100644
--- a/core/src/main/scala/cats/instances/hash.scala
+++ b/core/src/main/scala/cats/instances/hash.scala
@@ -22,6 +22,8 @@
 package cats
 package instances
 
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
+
 import scala.annotation.tailrec
 
 trait HashInstances extends kernel.instances.HashInstances {
@@ -42,6 +44,7 @@ object HashInstances {
   private val catsDeferForHashCache: Defer[Hash] =
     new Defer[Hash] {
       case class Deferred[A](fa: () => Hash[A]) extends Hash[A] {
+        @threadUnsafe3
         private lazy val resolve: Hash[A] = {
           @tailrec
           def loop(f: () => Hash[A]): Hash[A] =
@@ -62,7 +65,7 @@ object HashInstances {
       }
 
       override def defer[A](fa: => Hash[A]): Hash[A] = {
-        lazy val cachedFa = fa
+        @threadUnsafe3 lazy val cachedFa = fa
         Deferred(() => cachedFa)
       }
     }
diff --git a/core/src/main/scala/cats/instances/order.scala b/core/src/main/scala/cats/instances/order.scala
index c1b4eab29b..978e750b1a 100644
--- a/core/src/main/scala/cats/instances/order.scala
+++ b/core/src/main/scala/cats/instances/order.scala
@@ -23,6 +23,7 @@ package cats
 package instances
 
 import cats.kernel.instances.unit._
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
 
 import scala.annotation.tailrec
 
@@ -56,6 +57,7 @@ object OrderInstances {
   private val catsDeferForOrderCache: Defer[Order] =
     new Defer[Order] {
       case class Deferred[A](fa: () => Order[A]) extends Order[A] {
+        @threadUnsafe3
         private lazy val resolved: Order[A] = {
           @tailrec
           def loop(f: () => Order[A]): Order[A] =
@@ -70,7 +72,7 @@ object OrderInstances {
       }
 
       override def defer[A](fa: => Order[A]): Order[A] = {
-        lazy val cachedFa = fa
+        @threadUnsafe3 lazy val cachedFa = fa
         Deferred(() => cachedFa)
       }
     }
diff --git a/core/src/main/scala/cats/instances/ordering.scala b/core/src/main/scala/cats/instances/ordering.scala
index 802e778e20..da35e2b691 100644
--- a/core/src/main/scala/cats/instances/ordering.scala
+++ b/core/src/main/scala/cats/instances/ordering.scala
@@ -23,6 +23,7 @@ package cats
 package instances
 
 import cats.kernel.instances.unit._
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
 
 import scala.annotation.tailrec
 
@@ -52,6 +53,7 @@ object OrderingInstances {
   private val catsStdDeferForOrderingCache: Defer[Ordering] =
     new Defer[Ordering] {
       case class Deferred[A](fa: () => Ordering[A]) extends Ordering[A] {
+        @threadUnsafe3
         private lazy val resolved: Ordering[A] = {
           @tailrec
           def loop(f: () => Ordering[A]): Ordering[A] =
@@ -66,7 +68,7 @@ object OrderingInstances {
       }
 
       override def defer[A](fa: => Ordering[A]): Ordering[A] = {
-        lazy val cachedFa = fa
+        @threadUnsafe3 lazy val cachedFa = fa
         Deferred(() => cachedFa)
       }
     }
diff --git a/core/src/main/scala/cats/instances/partialOrder.scala b/core/src/main/scala/cats/instances/partialOrder.scala
index 81bdce03e1..cb1f67b286 100644
--- a/core/src/main/scala/cats/instances/partialOrder.scala
+++ b/core/src/main/scala/cats/instances/partialOrder.scala
@@ -23,6 +23,8 @@ package cats
 package instances
 import cats.kernel.instances.unit._
 
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
+
 import scala.annotation.tailrec
 
 trait PartialOrderInstances extends kernel.instances.PartialOrderInstances {
@@ -50,6 +52,7 @@ object PartialOrderInstances {
   private val catsDeferForPartialOrderCache: Defer[PartialOrder] =
     new Defer[PartialOrder] {
       case class Deferred[A](fa: () => PartialOrder[A]) extends PartialOrder[A] {
+        @threadUnsafe3
         private lazy val resolved: PartialOrder[A] = {
           @tailrec
           def loop(f: () => PartialOrder[A]): PartialOrder[A] =
@@ -64,7 +67,7 @@ object PartialOrderInstances {
       }
 
       override def defer[A](fa: => PartialOrder[A]): PartialOrder[A] = {
-        lazy val cachedFa = fa
+        @threadUnsafe3 lazy val cachedFa = fa
         Deferred(() => cachedFa)
       }
     }
diff --git a/core/src/main/scala/cats/instances/partialOrdering.scala b/core/src/main/scala/cats/instances/partialOrdering.scala
index 586c9492dd..7c957186df 100644
--- a/core/src/main/scala/cats/instances/partialOrdering.scala
+++ b/core/src/main/scala/cats/instances/partialOrdering.scala
@@ -22,6 +22,8 @@
 package cats
 package instances
 
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
+
 import scala.annotation.tailrec
 
 trait PartialOrderingInstances {
@@ -60,6 +62,7 @@ object PartialOrderingInstances {
   private val catsStdDeferForPartialOrderingCache: Defer[PartialOrdering] =
     new Defer[PartialOrdering] {
       case class Deferred[A](fa: () => PartialOrdering[A]) extends PartialOrdering[A] {
+        @threadUnsafe3
         private lazy val resolve: PartialOrdering[A] = {
           @tailrec
           def loop(f: () => PartialOrdering[A]): PartialOrdering[A] =
@@ -77,7 +80,7 @@ object PartialOrderingInstances {
       }
 
       override def defer[A](fa: => PartialOrdering[A]): PartialOrdering[A] = {
-        lazy val cachedFa = fa
+        @threadUnsafe3 lazy val cachedFa = fa
         Deferred(() => cachedFa)
       }
     }
diff --git a/core/src/main/scala/cats/instances/show.scala b/core/src/main/scala/cats/instances/show.scala
index 2f2c01907a..971b6b95a4 100644
--- a/core/src/main/scala/cats/instances/show.scala
+++ b/core/src/main/scala/cats/instances/show.scala
@@ -22,6 +22,8 @@
 package cats
 package instances
 
+import org.typelevel.scalaccompat.annotation.threadUnsafe3
+
 import scala.annotation.tailrec
 
 trait ShowInstances {
@@ -31,6 +33,7 @@ object ShowInstances {
   private val catsDeferForShowCache: Defer[Show] =
     new Defer[Show] {
       case class Deferred[A](fa: () => Show[A]) extends Show[A] {
+        @threadUnsafe3
         private lazy val resolved: Show[A] = {
           @tailrec
           def loop(f: () => Show[A]): Show[A] =
@@ -45,7 +48,7 @@ object ShowInstances {
       }
 
       override def defer[A](fa: => Show[A]): Show[A] = {
-        lazy val cachedFa = fa
+        @threadUnsafe3 lazy val cachedFa = fa
         Deferred(() => cachedFa)
       }
     }