diff --git a/build.sbt b/build.sbt
index 83fb8e4..0d347c4 100644
--- a/build.sbt
+++ b/build.sbt
@@ -3,7 +3,7 @@ import ReleaseTransformations._
 
 lazy val buildSettings = Seq(
   organization := "com.github.zainab-ali",
-  crossScalaVersions := List("2.12.4", "2.11.12"),
+  crossScalaVersions := List("2.12.6", "2.11.12"),
   scalaVersion := crossScalaVersions.value.head,
   name := "fs2-reactive-streams"
 )
@@ -28,9 +28,9 @@ lazy val commonSettings = Seq(
     resolvers ++= commonResolvers,
     scalacOptions ++= commonScalacOptions,
     libraryDependencies ++= Seq(
-      "co.fs2" %% "fs2-core" % "0.10.1",
+      "co.fs2" %% "fs2-core" % "1.0.0-M1",
       "org.reactivestreams" % "reactive-streams" % "1.0.2",
-      "org.scalatest" %% "scalatest" % "3.0.4" % "test",
+      "org.scalatest" %% "scalatest" % "3.0.5" % "test",
       "org.scalacheck" %% "scalacheck" % "1.13.5" % "test",
       "org.reactivestreams" % "reactive-streams-tck" % "1.0.2" % "test"
     )
diff --git a/core/src/main/scala/fs2/interop/reactivestreams/StreamSubscriber.scala b/core/src/main/scala/fs2/interop/reactivestreams/StreamSubscriber.scala
index ef2464a..489e797 100644
--- a/core/src/main/scala/fs2/interop/reactivestreams/StreamSubscriber.scala
+++ b/core/src/main/scala/fs2/interop/reactivestreams/StreamSubscriber.scala
@@ -4,8 +4,8 @@ package reactivestreams
 
 import cats._
 import cats.effect._
+import cats.effect.concurrent.{Deferred, Ref}
 import cats.implicits._
-import fs2.async.{Promise, Ref}
 import org.reactivestreams._
 
 import scala.concurrent.ExecutionContext
@@ -16,8 +16,8 @@ import scala.concurrent.ExecutionContext
   *
   * @see https://github.com/reactive-streams/reactive-streams-jvm#2-subscriber-code
   */
-final class StreamSubscriber[F[_], A](val sub: StreamSubscriber.FSM[F, A])(implicit A: Effect[F],
-                                                                           ec: ExecutionContext)
+final class StreamSubscriber[F[_], A](val sub: StreamSubscriber.FSM[F, A])(implicit F: ConcurrentEffect[F],
+                                                                           timer: Timer[F])
     extends Subscriber[A] {
 
   /** Called by an upstream reactivestreams system */
@@ -48,7 +48,7 @@ final class StreamSubscriber[F[_], A](val sub: StreamSubscriber.FSM[F, A])(impli
 }
 
 object StreamSubscriber {
-  def apply[F[_], A](implicit AA: Effect[F], ec: ExecutionContext): F[StreamSubscriber[F, A]] =
+  def apply[F[_], A](implicit AA: ConcurrentEffect[F], timer: Timer[F]): F[StreamSubscriber[F, A]] =
     fsm[F, A].map(new StreamSubscriber(_))
 
   /** A finite state machine describing the subscriber */
@@ -77,8 +77,7 @@ object StreamSubscriber {
       Stream.eval(dequeue1).repeat.rethrow.unNoneTerminate.onFinalize(onFinalize)
   }
 
-  private[reactivestreams] def fsm[F[_], A](implicit F: Effect[F],
-                                            ec: ExecutionContext): F[FSM[F, A]] = {
+  private[reactivestreams] def fsm[F[_], A](implicit F: Concurrent[F]): F[FSM[F, A]] = {
 
     type Out = Either[Throwable, Option[A]]
 
@@ -88,13 +87,13 @@ object StreamSubscriber {
     case class OnError(e: Throwable) extends Input
     case object OnComplete extends Input
     case object OnFinalize extends Input
-    case class OnDequeue(response: Promise[F, Out]) extends Input
+    case class OnDequeue(response: Deferred[F, Out]) extends Input
 
     sealed trait State
     case object Uninitialized extends State
     case class Idle(sub: Subscription) extends State
-    case class RequestBeforeSubscription(req: Promise[F, Out]) extends State
-    case class WaitingOnUpstream(sub: Subscription, elementRequest: Promise[F, Out]) extends State
+    case class RequestBeforeSubscription(req: Deferred[F, Out]) extends State
+    case class WaitingOnUpstream(sub: Subscription, elementRequest: Deferred[F, Out]) extends State
     case object UpstreamCompletion extends State
     case object DownstreamCancellation extends State
     case class UpstreamError(err: Throwable) extends State
@@ -135,17 +134,17 @@ object StreamSubscriber {
       }
     }
 
-    async.refOf[F, State](Uninitialized).map { ref =>
+    Ref.of[F, State](Uninitialized).map { ref =>
       new FSM[F, A] {
-        def nextState(in: Input): F[Unit] = ref.modify2(step(in)).flatMap(_._2)
+        def nextState(in: Input): F[Unit] = ref.modify(step(in)).flatten
         def onSubscribe(s: Subscription): F[Unit] = nextState(OnSubscribe(s))
         def onNext(a: A): F[Unit] = nextState(OnNext(a))
         def onError(t: Throwable): F[Unit] = nextState(OnError(t))
         def onComplete: F[Unit] = nextState(OnComplete)
         def onFinalize: F[Unit] = nextState(OnFinalize)
         def dequeue1: F[Either[Throwable, Option[A]]] =
-          async.promise[F, Out].flatMap { p =>
-            ref.modify2(step(OnDequeue(p))).flatMap(_._2) *> p.get
+          Deferred[F, Out].flatMap { p =>
+            ref.modify(step(OnDequeue(p))).flatten *> p.get
           }
       }
     }
diff --git a/core/src/main/scala/fs2/interop/reactivestreams/StreamSubscription.scala b/core/src/main/scala/fs2/interop/reactivestreams/StreamSubscription.scala
index b5da5ad..104b096 100644
--- a/core/src/main/scala/fs2/interop/reactivestreams/StreamSubscription.scala
+++ b/core/src/main/scala/fs2/interop/reactivestreams/StreamSubscription.scala
@@ -20,7 +20,7 @@ final class StreamSubscription[F[_], A](
   cancelled: Signal[F, Boolean],
   sub: Subscriber[A],
   stream: Stream[F, A]
-)(implicit F: Effect[F], ec: ExecutionContext)
+)(implicit F: ConcurrentEffect[F], timer: Timer[F])
     extends Subscription {
   import StreamSubscription._
 
@@ -92,8 +92,8 @@ object StreamSubscription {
   case object Infinite extends Request
   case class Finite(n: Long) extends Request
 
-  def apply[F[_]: Effect, A](sub: Subscriber[A], stream: Stream[F, A])(
-    implicit ec: ExecutionContext
+  def apply[F[_]: ConcurrentEffect, A](sub: Subscriber[A], stream: Stream[F, A])(
+    implicit timer: Timer[F]
   ): F[StreamSubscription[F, A]] =
     async.signalOf[F, Boolean](false).flatMap { cancelled =>
       async.unboundedQueue[F, Request].map { requests =>
diff --git a/core/src/main/scala/fs2/interop/reactivestreams/StreamUnicastPublisher.scala b/core/src/main/scala/fs2/interop/reactivestreams/StreamUnicastPublisher.scala
index ff5b624..940c6c5 100644
--- a/core/src/main/scala/fs2/interop/reactivestreams/StreamUnicastPublisher.scala
+++ b/core/src/main/scala/fs2/interop/reactivestreams/StreamUnicastPublisher.scala
@@ -15,9 +15,9 @@ import scala.concurrent.ExecutionContext
   * @see https://github.com/reactive-streams/reactive-streams-jvm#1-publisher-code
   *
   */
-final class StreamUnicastPublisher[F[_]: Effect, A](
+final class StreamUnicastPublisher[F[_]: ConcurrentEffect, A](
   val s: Stream[F, A]
-)(implicit ec: ExecutionContext)
+)(implicit timer: Timer[F])
     extends Publisher[A] {
 
   def subscribe(subscriber: Subscriber[_ >: A]): Unit = {
@@ -37,8 +37,8 @@ final class StreamUnicastPublisher[F[_]: Effect, A](
 }
 
 object StreamUnicastPublisher {
-  def apply[F[_]: Effect, A](
+  def apply[F[_]: ConcurrentEffect, A](
     s: Stream[F, A]
-  )(implicit ec: ExecutionContext): StreamUnicastPublisher[F, A] =
+  )(implicit timer: Timer[F]): StreamUnicastPublisher[F, A] =
     new StreamUnicastPublisher(s)
 }
diff --git a/core/src/main/scala/fs2/interop/reactivestreams/package.scala b/core/src/main/scala/fs2/interop/reactivestreams/package.scala
index 3f8847f..a8f85f1 100644
--- a/core/src/main/scala/fs2/interop/reactivestreams/package.scala
+++ b/core/src/main/scala/fs2/interop/reactivestreams/package.scala
@@ -13,9 +13,9 @@ package object reactivestreams {
     *
     * The publisher only receives a subscriber when the stream is run.
     */
-  def fromPublisher[F[_]: Effect, A](
+  def fromPublisher[F[_]: ConcurrentEffect, A](
     p: Publisher[A]
-  )(implicit ec: ExecutionContext): Stream[F, A] =
+  )(implicit timer: Timer[F]): Stream[F, A] =
     Stream
       .eval(StreamSubscriber[F, A].map { s =>
         p.subscribe(s)
@@ -26,7 +26,7 @@ package object reactivestreams {
   implicit final class PublisherOps[A](val pub: Publisher[A]) extends AnyVal {
 
     /** Creates a lazy stream from an org.reactivestreams.Publisher */
-    def toStream[F[_]]()(implicit F: Effect[F], ec: ExecutionContext): Stream[F, A] =
+    def toStream[F[_]]()(implicit F: ConcurrentEffect[F], timer: Timer[F]): Stream[F, A] =
       fromPublisher(pub)
   }
 
@@ -37,8 +37,8 @@ package object reactivestreams {
       * This publisher can only have a single subscription.
       * The stream is only ran when elements are requested.
       */
-    def toUnicastPublisher()(implicit F: Effect[F],
-                             ec: ExecutionContext): StreamUnicastPublisher[F, A] =
+    def toUnicastPublisher()(implicit F: ConcurrentEffect[F],
+                             timer: Timer[F]): StreamUnicastPublisher[F, A] =
       StreamUnicastPublisher(stream)
   }
 }
diff --git a/core/src/test/scala/fs2/interop/reactivestreams/SubscriberSpec.scala b/core/src/test/scala/fs2/interop/reactivestreams/SubscriberSpec.scala
index e4e448e..39757c0 100644
--- a/core/src/test/scala/fs2/interop/reactivestreams/SubscriberSpec.scala
+++ b/core/src/test/scala/fs2/interop/reactivestreams/SubscriberSpec.scala
@@ -5,6 +5,7 @@ package reactivestreams
 import java.util.concurrent.atomic.AtomicInteger
 
 import cats.effect._
+import cats.implicits._
 import org.reactivestreams._
 import org.reactivestreams.tck.SubscriberWhiteboxVerification.{
   SubscriberPuppet,
@@ -77,10 +78,7 @@ class SubscriberBlackboxSpec
     with TestNGSuiteLike {
   implicit val ec: ExecutionContext = ExecutionContext.global
 
-  val (scheduler: Scheduler, _) =
-    Scheduler
-      .allocate[IO](corePoolSize = 2, threadPrefix = "subscriber-blackbox-spec-scheduler")
-      .unsafeRunSync()
+  val timer = Timer[IO]
 
   private val counter = new AtomicInteger()
 
@@ -88,7 +86,7 @@ class SubscriberBlackboxSpec
 
   override def triggerRequest(s: Subscriber[_ >: Int]): Unit = {
     val req = s.asInstanceOf[StreamSubscriber[IO, Int]].sub.dequeue1
-    (scheduler.sleep_[IO](100 milliseconds) ++ Stream.eval(req)).compile.drain.unsafeRunAsync(_ => ())
+    (Stream.eval(timer.sleep(100.milliseconds) *> req)).compile.drain.unsafeRunAsync(_ => ())
   }
 
   def createElement(i: Int): Int = counter.incrementAndGet()
diff --git a/core/version.sbt b/core/version.sbt
index f943617..3f478e0 100644
--- a/core/version.sbt
+++ b/core/version.sbt
@@ -1 +1 @@
-version in ThisBuild := "0.5.2-SNAPSHOT"
+version in ThisBuild := "0.6.0-SNAPSHOT"
diff --git a/project/build.properties b/project/build.properties
index 394cb75..d6e3507 100644
--- a/project/build.properties
+++ b/project/build.properties
@@ -1 +1 @@
-sbt.version=1.0.4
+sbt.version=1.1.6