diff --git a/build.sbt b/build.sbt
index 49525d5..ab99c08 100755
--- a/build.sbt
+++ b/build.sbt
@@ -1,7 +1,7 @@
 ThisBuild / organization       := "org.scala-exercises"
 ThisBuild / githubOrganization := "47degrees"
-ThisBuild / scalaVersion       := "2.13.3"
-ThisBuild / crossScalaVersions := Seq("2.13.3", "2.12.15")
+ThisBuild / scalaVersion       := "2.13.8"
+ThisBuild / crossScalaVersions := Seq("2.13.8", "2.12.15")
 
 publish / skip := true
 
@@ -13,7 +13,7 @@ lazy val V = new {
   val cats: String      = "2.7.0"
   val circe: String     = "0.14.1"
   val classutil: String = "1.5.1"
-  val http4s: String    = "0.21.31"
+  val http4s: String    = "0.23.7"
   val scalatest: String = "3.2.10"
 }
 
diff --git a/evaluator-client/src/main/scala/org/scalaexercises/evaluator/EvaluatorClient.scala b/evaluator-client/src/main/scala/org/scalaexercises/evaluator/EvaluatorClient.scala
index 60d2c69..b9ca513 100644
--- a/evaluator-client/src/main/scala/org/scalaexercises/evaluator/EvaluatorClient.scala
+++ b/evaluator-client/src/main/scala/org/scalaexercises/evaluator/EvaluatorClient.scala
@@ -16,19 +16,17 @@
 
 package org.scalaexercises.evaluator
 
-import cats.effect.{ConcurrentEffect, Resource}
+import cats.effect.{Async, Resource}
 import org.http4s.client.Client
-import org.http4s.client.blaze.BlazeClientBuilder
+import org.http4s.blaze.client.BlazeClientBuilder
 import org.scalaexercises.evaluator.service.{HttpClientHandler, HttpClientService}
 
-import scala.concurrent.ExecutionContext
-
 object EvaluatorClient {
 
-  private def clientResource[F[_]: ConcurrentEffect]: Resource[F, Client[F]] =
-    BlazeClientBuilder[F](ExecutionContext.global).resource
+  private def clientResource[F[_]: Async]: Resource[F, Client[F]] =
+    BlazeClientBuilder[F].resource
 
-  def apply[F[_]: ConcurrentEffect](url: String, authKey: String): HttpClientService[F] =
+  def apply[F[_]: Async](url: String, authKey: String): HttpClientService[F] =
     HttpClientHandler[F](url, authKey, clientResource[F])
 
 }
diff --git a/evaluator-client/src/main/scala/org/scalaexercises/evaluator/service/HttpClientHandler.scala b/evaluator-client/src/main/scala/org/scalaexercises/evaluator/service/HttpClientHandler.scala
index c0ddd61..c74d1bf 100644
--- a/evaluator-client/src/main/scala/org/scalaexercises/evaluator/service/HttpClientHandler.scala
+++ b/evaluator-client/src/main/scala/org/scalaexercises/evaluator/service/HttpClientHandler.scala
@@ -16,20 +16,21 @@
 
 package org.scalaexercises.evaluator.service
 
-import cats.effect.{Resource, Sync}
+import cats.effect.{Async, Resource, Sync}
 import cats.implicits._
 import org.http4s.client.Client
 import org.http4s.{Header, Method, Request, Uri}
 import org.scalaexercises.evaluator.types._
 import org.scalaexercises.evaluator.util.Codecs._
+import org.typelevel.ci._
 
 object HttpClientHandler {
 
-  private def headerToken(value: String) = Header("x-scala-eval-api-token", value)
+  private def headerToken(value: String) = Header.Raw(ci"x-scala-eval-api-token", value)
 
-  private val headerContentType = Header("content-type", "application/json")
+  private val headerContentType = Header.Raw(ci"content-type", "application/json")
 
-  def apply[F[_]](uri: String, authString: String, resource: Resource[F, Client[F]])(implicit
+  def apply[F[_]: Async](uri: String, authString: String, resource: Resource[F, Client[F]])(implicit
       F: Sync[F]
   ): HttpClientService[F] =
     new HttpClientService[F] {
diff --git a/evaluator-client/src/main/scala/org/scalaexercises/evaluator/util/Codecs.scala b/evaluator-client/src/main/scala/org/scalaexercises/evaluator/util/Codecs.scala
index a7b7ee7..f59d20d 100644
--- a/evaluator-client/src/main/scala/org/scalaexercises/evaluator/util/Codecs.scala
+++ b/evaluator-client/src/main/scala/org/scalaexercises/evaluator/util/Codecs.scala
@@ -16,7 +16,7 @@
 
 package org.scalaexercises.evaluator.util
 
-import cats.effect.Sync
+import cats.effect.Concurrent
 import io.circe.generic.semiauto
 import io.circe.generic.semiauto.deriveDecoder
 import io.circe.syntax.EncoderOps
@@ -52,8 +52,8 @@ object Codecs {
 
   implicit val encodeExclusion: Encoder[Exclusion] = semiauto.deriveEncoder[Exclusion]
 
-  implicit def decoder[F[_]: Sync, A: Decoder]: EntityDecoder[F, A] = jsonOf[F, A]
+  implicit def decoder[F[_]: Concurrent, A: Decoder]: EntityDecoder[F, A] = jsonOf[F, A]
 
-  implicit def encoder[F[_]: Sync, A: Encoder]: EntityEncoder[F, A] = jsonEncoderOf[F, A]
+  implicit def encoder[F[_], A: Encoder]: EntityEncoder[F, A] = jsonEncoderOf[F, A]
 
 }