diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,14 @@
 # Changelog for extensible-effects-concurrent
 
+## 0.11.1
+
+- Fix a compilation error
+
+## 0.11.0
+
+- Change the return type of `spawnCallbackObserver` from
+  `Bool` to `ApiServerCmd`
+
 ## 0.10.0
 
 - Re-introduce a Logs Effect but keep the LogWriter Reader
diff --git a/examples/example-2/Main.hs b/examples/example-2/Main.hs
--- a/examples/example-2/Main.hs
+++ b/examples/example-2/Main.hs
@@ -43,7 +43,7 @@
   (\fromSvr msg -> do
     me <- self px
     logInfo (show me ++ " observed on: " ++ show fromSvr ++ ": " ++ show msg)
-    return True
+    return HandleNextRequest
   )
 
 counterHandler
diff --git a/extensible-effects-concurrent.cabal b/extensible-effects-concurrent.cabal
--- a/extensible-effects-concurrent.cabal
+++ b/extensible-effects-concurrent.cabal
@@ -1,5 +1,5 @@
 name:           extensible-effects-concurrent
-version:        0.10.0
+version:        0.11.1
 description:    Please see the README on GitHub at <https://github.com/sheyll/extensible-effects-concurrent#readme>
 synopsis:       Message passing concurrency as extensible-effect
 homepage:       https://github.com/sheyll/extensible-effects-concurrent#readme
diff --git a/src/Control/Eff/Concurrent/Api/Observer.hs b/src/Control/Eff/Concurrent/Api/Observer.hs
--- a/src/Control/Eff/Concurrent/Api/Observer.hs
+++ b/src/Control/Eff/Concurrent/Api/Observer.hs
@@ -188,17 +188,13 @@
      , HasCallStack
      )
   => SchedulerProxy q
-  -> (Server o -> Observation o -> Eff (Process q ': q) Bool)
+  -> (Server o -> Observation o -> Eff (Process q ': q) ApiServerCmd)
   -> Eff r (Server (CallbackObserver o))
 spawnCallbackObserver px onObserve = spawnServerWithEffects
   px
   (castHandler handleCastCbo)
   id
- where
-  handleCastCbo (CbObserved fromSvr v) = do
-    continueObservation <- onObserve fromSvr v
-    return
-      (if continueObservation then HandleNextRequest else StopApiServer Nothing)
+  where handleCastCbo (CbObserved fromSvr v) = onObserve fromSvr v
 
 -- | Start a new process for an 'Observer' that schedules
 -- all observations to an effectful callback.
@@ -218,4 +214,6 @@
   -> Eff r (Server (CallbackObserver o))
 spawnLoggingObserver px = spawnCallbackObserver
   px
-  (\s o -> logDebug (show s ++ " OBSERVED: " ++ show o) >> return True)
+  (\s o ->
+    logDebug (show s ++ " OBSERVED: " ++ show o) >> return HandleNextRequest
+  )
diff --git a/src/Control/Eff/Concurrent/Api/Observer/Queue.hs b/src/Control/Eff/Concurrent/Api/Observer/Queue.hs
--- a/src/Control/Eff/Concurrent/Api/Observer/Queue.hs
+++ b/src/Control/Eff/Concurrent/Api/Observer/Queue.hs
@@ -19,6 +19,7 @@
 import           Control.Eff.Concurrent.Api
 import           Control.Eff.Concurrent.Api.Client
 import           Control.Eff.Concurrent.Api.Observer
+import           Control.Eff.Concurrent.Api.Server
 import           Control.Eff.Reader.Strict
 import           Control.Exception
 import           Control.Monad.IO.Class
@@ -154,7 +155,7 @@
                     (show from)
             )
           liftIO (atomically (writeTBQueue q observation))
-          return True
+          return HandleNextRequest
         )
       logDebug
         (printf "%s started observer process %s"