diff --git a/README.md b/README.md
index c63d254..c0cc230 100644
--- a/README.md
+++ b/README.md
@@ -333,6 +333,12 @@ Known `async` backends include:
 ``none`` can be used when a library supports both a synchronous and
 asynchronous API, to disable the latter.
 
+### Compile-time configuration
+
+`chronos` contains several compile-time [configuration options](./chronos/config.nim) enabling stricter compile-time checks and debugging helpers whose runtime cost may be significant.
+
+Strictness options generally will become default in future chronos releases and allow adapting existing code without changing the new version - see the [`config.nim`](./chronos/config.nim) module for more information.
+
 ## TODO
   * Pipe/Subprocess Transports.
   * Multithreading Stream/Datagram servers
diff --git a/chronos.nimble b/chronos.nimble
index 18f7a47..dfb343c 100644
--- a/chronos.nimble
+++ b/chronos.nimble
@@ -32,10 +32,11 @@ proc run(args, path: string) =
 
 task test, "Run all tests":
   for args in [
-      "-d:useSysAssert -d:useGcAssert",
-      "-d:chronosStackTrace -d:chronosStrictException",
+      "-d:debug -d:chronosDebug",
+      "-d:debug -d:chronosPreviewV4",
+      "-d:debug -d:chronosDebug -d:useSysAssert -d:useGcAssert",
       "-d:release",
-      "-d:release -d:chronosFutureTracking",
+      "-d:release -d:chronosPreviewV4",
     ]: run args, "tests/testall"
 
 task test_libbacktrace, "test with libbacktrace":
diff --git a/chronos/asyncfutures2.nim b/chronos/asyncfutures2.nim
index 249bb98..bac4ba1 100644
--- a/chronos/asyncfutures2.nim
+++ b/chronos/asyncfutures2.nim
@@ -10,7 +10,7 @@
 
 import std/sequtils
 import stew/base10
-import ./srcloc
+import "."/[config, srcloc]
 export srcloc
 
 when defined(nimHasStacktracesModule):
@@ -24,7 +24,7 @@ const
   LocCreateIndex* = 0
   LocCompleteIndex* = 1
 
-when defined(chronosStackTrace):
+when chronosStackTrace:
   type StackTrace = string
 
 type
@@ -41,11 +41,11 @@ type
     mustCancel*: bool
     id*: uint
 
-    when defined(chronosStackTrace):
+    when chronosStackTrace:
       errorStackTrace*: StackTrace
       stackTrace: StackTrace ## For debugging purposes only.
 
-    when defined(chronosFutureTracking):
+    when chronosFutureTracking:
       next*: FutureBase
       prev*: FutureBase
 
@@ -54,7 +54,7 @@ type
   # How much refactoring is needed to make this a regular non-ref type?
   # Obviously, it will still be allocated on the heap when necessary.
   Future*[T] = ref object of FutureBase ## Typed future.
-    when defined(chronosStrictException):
+    when chronosStrictException:
       closure*: iterator(f: Future[T]): FutureBase {.raises: [Defect, CatchableError], gcsafe.}
     else:
       closure*: iterator(f: Future[T]): FutureBase {.raises: [Defect, CatchableError, Exception], gcsafe.}
@@ -80,23 +80,27 @@ type
     tail*: FutureBase
     count*: uint
 
-var currentID* {.threadvar.}: uint
-currentID = 0'u
+when chronosFutureId:
+  var currentID* {.threadvar.}: uint
+else:
+  template id*(f: FutureBase): uint =
+    cast[uint](addr f[])
 
-when defined(chronosFutureTracking):
+when chronosFutureTracking:
   var futureList* {.threadvar.}: FutureList
   futureList = FutureList()
 
 template setupFutureBase(loc: ptr SrcLoc) =
   new(result)
-  currentID.inc()
   result.state = FutureState.Pending
-  when defined(chronosStackTrace):
+  when chronosStackTrace:
     result.stackTrace = getStackTrace()
-  result.id = currentID
+  when chronosFutureId:
+    currentID.inc()
+    result.id = currentID
   result.location[LocCreateIndex] = loc
 
-  when defined(chronosFutureTracking):
+  when chronosFutureTracking:
     result.next = nil
     result.prev = futureList.tail
     if not(isNil(futureList.tail)):
@@ -160,7 +164,7 @@ proc done*(future: FutureBase): bool {.inline.} =
   ## This is an alias for ``completed(future)`` procedure.
   completed(future)
 
-when defined(chronosFutureTracking):
+when chronosFutureTracking:
   proc futureDestructor(udata: pointer) =
     ## This procedure will be called when Future[T] got finished, cancelled or
     ## failed and all Future[T].callbacks are already scheduled and processed.
@@ -188,7 +192,7 @@ proc checkFinished(future: FutureBase, loc: ptr SrcLoc) =
     msg.add("\n    " & $future.location[LocCompleteIndex])
     msg.add("\n  Second completion location:")
     msg.add("\n    " & $loc)
-    when defined(chronosStackTrace):
+    when chronosStackTrace:
       msg.add("\n  Stack trace to moment of creation:")
       msg.add("\n" & indent(future.stackTrace.strip(), 4))
       msg.add("\n  Stack trace to moment of secondary completion:")
@@ -212,7 +216,7 @@ proc finish(fut: FutureBase, state: FutureState) =
     item = default(AsyncCallback) # release memory as early as possible
   fut.callbacks = default(seq[AsyncCallback]) # release seq as well
 
-  when defined(chronosFutureTracking):
+  when chronosFutureTracking:
     scheduleDestructor(fut)
 
 proc complete[T](future: Future[T], val: T, loc: ptr SrcLoc) =
@@ -240,7 +244,7 @@ proc fail[T](future: Future[T], error: ref CatchableError, loc: ptr SrcLoc) =
   if not(future.cancelled()):
     checkFinished(FutureBase(future), loc)
     future.error = error
-    when defined(chronosStackTrace):
+    when chronosStackTrace:
       future.errorStackTrace = if getStackTrace(error) == "":
                                  getStackTrace()
                                else:
@@ -258,7 +262,7 @@ proc cancelAndSchedule(future: FutureBase, loc: ptr SrcLoc) =
   if not(future.finished()):
     checkFinished(future, loc)
     future.error = newCancelledError()
-    when defined(chronosStackTrace):
+    when chronosStackTrace:
       future.errorStackTrace = getStackTrace()
     future.finish(FutureState.Cancelled)
 
@@ -472,7 +476,7 @@ proc `$`(stackTraceEntries: seq[StackTraceEntry]): string =
     return exc.msg # Shouldn't actually happen since we set the formatting
                    # string
 
-when defined(chronosStackTrace):
+when chronosStackTrace:
   proc injectStacktrace(future: FutureBase) =
     const header = "\nAsync traceback:\n"
 
@@ -500,7 +504,7 @@ proc internalCheckComplete*(fut: FutureBase) {.
      raises: [Defect, CatchableError].} =
   # For internal use only. Used in asyncmacro
   if not(isNil(fut.error)):
-    when defined(chronosStackTrace):
+    when chronosStackTrace:
       injectStacktrace(fut)
     raise fut.error
 
diff --git a/chronos/asyncloop.nim b/chronos/asyncloop.nim
index ca16554..abf3edc 100644
--- a/chronos/asyncloop.nim
+++ b/chronos/asyncloop.nim
@@ -14,9 +14,9 @@ else:
   {.push raises: [].}
 
 from nativesockets import Port
-import std/[tables, strutils, heapqueue, lists, options, deques]
+import std/[tables, strutils, heapqueue, options, deques]
 import stew/results
-import "."/[osdefs, osutils, timer]
+import "."/[config, osdefs, osutils, timer]
 
 export Port
 export timer, results
@@ -1263,7 +1263,7 @@ proc getTracker*(id: string): TrackerBase =
   let loop = getThreadDispatcher()
   result = loop.trackers.getOrDefault(id, nil)
 
-when defined(chronosFutureTracking):
+when chronosFutureTracking:
   iterator pendingFutures*(): FutureBase =
     ## Iterates over the list of pending Futures (Future[T] objects which not
     ## yet completed, cancelled or failed).
diff --git a/chronos/asyncmacro2.nim b/chronos/asyncmacro2.nim
index 61bf3b5..3fb0bb7 100644
--- a/chronos/asyncmacro2.nim
+++ b/chronos/asyncmacro2.nim
@@ -193,12 +193,12 @@ proc asyncSingleProc(prc: NimNode): NimNode {.compileTime.} =
       #      here the possibility of transporting more specific error types here
       #      for example by casting exceptions coming out of `await`..
       let raises = nnkBracket.newTree()
-      when not defined(chronosStrictException):
-        raises.add(newIdentNode("Exception"))
-      else:
+      when chronosStrictException:
         raises.add(newIdentNode("CatchableError"))
         when (NimMajor, NimMinor) < (1, 4):
           raises.add(newIdentNode("Defect"))
+      else:
+        raises.add(newIdentNode("Exception"))
 
       closureIterator.addPragma(nnkExprColonExpr.newTree(
         newIdentNode("raises"),
@@ -328,5 +328,5 @@ macro async*(prc: untyped): untyped =
       result.add asyncSingleProc(oneProc)
   else:
     result = asyncSingleProc(prc)
-  when defined(nimDumpAsync):
+  when chronosDumpAsync:
     echo repr result
diff --git a/chronos/config.nim b/chronos/config.nim
new file mode 100644
index 0000000..abc9c37
--- /dev/null
+++ b/chronos/config.nim
@@ -0,0 +1,57 @@
+## Compile-time configuration options for chronos that control the availability
+## of various strictness and debuggability options. In general, debug helpers
+## are enabled when `debug` is defined while strictness options are introduced
+## in transition periods leading up to a breaking release that starts enforcing
+## them and removes the option.
+##
+## `chronosPreviewV4` is a preview flag to enable v4 semantics - in particular,
+## it enables strict exception checking and disables parts of the deprecated
+## API and other changes being prepared for the upcoming release
+##
+## `chronosDebug` can be defined to enable several debugging helpers that come
+## with a runtime cost - it is recommeneded to not enable these in production
+## code.
+when (NimMajor, NimMinor) >= (1, 4):
+  const
+    chronosStrictException* {.booldefine.}: bool = defined(chronosPreviewV4)
+      ## Require that `async` code raises only derivatives of `CatchableError` and
+      ## not `Exception` - forward declarations, methods and `proc` types used
+      ## from within `async` code may need to be be explicitly annotated with
+      ## `raises: [CatchableError]` when this mode is enabled.
+
+    chronosStackTrace* {.booldefine.}: bool = defined(chronosDebug)
+      ## Include stack traces in futures for creation and completion points
+
+    chronosFutureId* {.booldefine.}: bool = defined(chronosDebug)
+      ## Generate a unique `id` for every future - when disabled, the address of
+      ## the future will be used instead
+
+    chronosFutureTracking* {.booldefine.}: bool = defined(chronosDebug)
+      ## Keep track of all pending futures and allow iterating over them -
+      ## useful for detecting hung tasks
+
+    chronosDumpAsync* {.booldefine.}: bool = defined(nimDumpAsync)
+      ## Print code generated by {.async.} transformation
+else:
+  # 1.2 doesn't support `booldefine` in `when` properly
+  const
+    chronosStrictException*: bool =
+      defined(chronosPreviewV4) or defined(chronosStrictException)
+    chronosStackTrace*: bool = defined(chronosDebug) or defined(chronosStackTrace)
+    chronosFutureId*: bool = defined(chronosDebug) or defined(chronosFutureId)
+    chronosFutureTracking*: bool =
+      defined(chronosDebug) or defined(chronosFutureTracking)
+    chronosDumpAsync*: bool = defined(nimDumpAsync)
+
+when defined(debug) or defined(chronosConfig):
+  import std/macros
+
+  static:
+    hint("Chronos configuration:")
+    template printOption(name: string, value: untyped) =
+      hint(name & ": " & $value)
+    printOption("chronosStrictException", chronosStrictException)
+    printOption("chronosStackTrace", chronosStackTrace)
+    printOption("chronosFutureId", chronosFutureId)
+    printOption("chronosFutureTracking", chronosFutureTracking)
+    printOption("chronosDumpAsync", chronosDumpAsync)
diff --git a/chronos/debugutils.nim b/chronos/debugutils.nim
index 451189a..17d6412 100644
--- a/chronos/debugutils.nim
+++ b/chronos/debugutils.nim
@@ -12,10 +12,10 @@ when (NimMajor, NimMinor) < (1, 4):
 else:
   {.push raises: [].}
 
-import ./asyncloop
+import "."/[asyncloop, config]
 export asyncloop
 
-when defined(chronosFutureTracking):
+when chronosFutureTracking:
   import stew/base10
 
 const
@@ -34,7 +34,7 @@ proc dumpPendingFutures*(filter = AllFutureStates): string =
   ##    not yet finished).
   ## 2. Future[T] objects with ``FutureState.Finished/Cancelled/Failed`` state
   ##    which callbacks are scheduled, but not yet fully processed.
-  when defined(chronosFutureTracking):
+  when chronosFutureTracking:
     var count = 0'u
     var res = ""
     for item in pendingFutures():
@@ -62,7 +62,7 @@ proc pendingFuturesCount*(filter: set[FutureState]): uint =
   ##
   ## If ``filter`` is equal to ``AllFutureStates`` Operation's complexity is
   ## O(1), otherwise operation's complexity is O(n).
-  when defined(chronosFutureTracking):
+  when chronosFutureTracking:
     if filter == AllFutureStates:
       pendingFuturesCount()
     else:
diff --git a/tests/testaddress.nim b/tests/testaddress.nim
index 040fc28..e505ff5 100644
--- a/tests/testaddress.nim
+++ b/tests/testaddress.nim
@@ -8,7 +8,7 @@
 import unittest2
 import ../chronos
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 suite "TransportAddress test suite":
   test "initTAddress(string)":
diff --git a/tests/testasyncstream.nim b/tests/testasyncstream.nim
index b8c729b..fd581cb 100644
--- a/tests/testasyncstream.nim
+++ b/tests/testasyncstream.nim
@@ -10,7 +10,7 @@ import bearssl/[x509]
 import ../chronos
 import ../chronos/streams/[tlsstream, chunkstream, boundstream]
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 # To create self-signed certificate and key you can use openssl
 # openssl req -new -x509 -sha256 -newkey rsa:2048 -nodes \
diff --git a/tests/testbugs.nim b/tests/testbugs.nim
index d31ea99..19a8edb 100644
--- a/tests/testbugs.nim
+++ b/tests/testbugs.nim
@@ -8,7 +8,7 @@
 import unittest2
 import ../chronos
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 suite "Asynchronous issues test suite":
   const HELLO_PORT = 45679
diff --git a/tests/testdatagram.nim b/tests/testdatagram.nim
index 149ce9d..1eea489 100644
--- a/tests/testdatagram.nim
+++ b/tests/testdatagram.nim
@@ -9,7 +9,7 @@ import std/[strutils, net]
 import unittest2
 import ../chronos
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 suite "Datagram Transport test suite":
   const
diff --git a/tests/testfut.nim b/tests/testfut.nim
index 23015b9..fa250a1 100644
--- a/tests/testfut.nim
+++ b/tests/testfut.nim
@@ -8,7 +8,7 @@
 import unittest2
 import ../chronos, ../chronos/unittest2/asynctests
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 suite "Future[T] behavior test suite":
   proc testFuture1(): Future[int] {.async.} =
diff --git a/tests/testhttpclient.nim b/tests/testhttpclient.nim
index 15f77d3..e04e2ab 100644
--- a/tests/testhttpclient.nim
+++ b/tests/testhttpclient.nim
@@ -10,7 +10,7 @@ import unittest2
 import ../chronos, ../chronos/apps/http/[httpserver, shttpserver, httpclient]
 import stew/base10
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 # To create self-signed certificate and key you can use openssl
 # openssl req -new -x509 -sha256 -newkey rsa:2048 -nodes \
diff --git a/tests/testhttpserver.nim b/tests/testhttpserver.nim
index b200040..8b71ca2 100644
--- a/tests/testhttpserver.nim
+++ b/tests/testhttpserver.nim
@@ -11,7 +11,7 @@ import ../chronos, ../chronos/apps/http/httpserver,
        ../chronos/apps/http/httpcommon
 import stew/base10
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 suite "HTTP server testing suite":
   type
diff --git a/tests/testmacro.nim b/tests/testmacro.nim
index e6c9812..f50015f 100644
--- a/tests/testmacro.nim
+++ b/tests/testmacro.nim
@@ -9,7 +9,7 @@ import unittest2
 import macros
 import ../chronos
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 type
   RetValueType = proc(n: int): Future[int] {.async.}
diff --git a/tests/testnet.nim b/tests/testnet.nim
index ff78429..419195d 100644
--- a/tests/testnet.nim
+++ b/tests/testnet.nim
@@ -8,7 +8,7 @@
 import unittest2
 import ../chronos/transports/[osnet, ipnet]
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 suite "Network utilities test suite":
 
diff --git a/tests/testratelimit.nim b/tests/testratelimit.nim
index 32b8e95..4c78664 100644
--- a/tests/testratelimit.nim
+++ b/tests/testratelimit.nim
@@ -6,7 +6,9 @@
 #  Apache License, version 2.0, (LICENSE-APACHEv2)
 #              MIT license (LICENSE-MIT)
 
-import unittest
+{.used.}
+
+import unittest2
 import ../chronos
 import ../chronos/ratelimit
 
diff --git a/tests/testserver.nim b/tests/testserver.nim
index 8828bb2..e7e834e 100644
--- a/tests/testserver.nim
+++ b/tests/testserver.nim
@@ -8,7 +8,7 @@
 import unittest2
 import ../chronos
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 suite "Server's test suite":
   type
diff --git a/tests/testshttpserver.nim b/tests/testshttpserver.nim
index 596a8da..4b55b27 100644
--- a/tests/testshttpserver.nim
+++ b/tests/testshttpserver.nim
@@ -10,7 +10,7 @@ import unittest2
 import ../chronos, ../chronos/apps/http/shttpserver
 import stew/base10
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 # To create self-signed certificate and key you can use openssl
 # openssl req -new -x509 -sha256 -newkey rsa:2048 -nodes \
diff --git a/tests/testsignal.nim b/tests/testsignal.nim
index 1163a8c..5eca5a9 100644
--- a/tests/testsignal.nim
+++ b/tests/testsignal.nim
@@ -8,7 +8,7 @@
 import unittest2
 import ../chronos
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 when not defined(windows):
   import posix
diff --git a/tests/testsoon.nim b/tests/testsoon.nim
index 8b76113..69bffd4 100644
--- a/tests/testsoon.nim
+++ b/tests/testsoon.nim
@@ -8,7 +8,7 @@
 import unittest2
 import ../chronos
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 suite "callSoon() tests suite":
   const CallSoonTests = 10
diff --git a/tests/teststream.nim b/tests/teststream.nim
index e0ee9f3..90fd55d 100644
--- a/tests/teststream.nim
+++ b/tests/teststream.nim
@@ -9,7 +9,7 @@ import std/[strutils, os]
 import unittest2
 import ".."/chronos, ".."/chronos/osdefs
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 when defined(windows):
   proc get_osfhandle*(fd: FileHandle): HANDLE {.
diff --git a/tests/testsync.nim b/tests/testsync.nim
index 9acea50..4e09682 100644
--- a/tests/testsync.nim
+++ b/tests/testsync.nim
@@ -8,7 +8,7 @@
 import unittest2
 import ../chronos
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 suite "Asynchronous sync primitives test suite":
   var testLockResult {.threadvar.}: string
diff --git a/tests/testtime.nim b/tests/testtime.nim
index 430db8f..aac926e 100644
--- a/tests/testtime.nim
+++ b/tests/testtime.nim
@@ -9,7 +9,7 @@ import std/os
 import unittest2
 import ../chronos, ../chronos/timer
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 static:
   doAssert Moment.high - Moment.low == Duration.high
diff --git a/tests/testutils.nim b/tests/testutils.nim
index 67a59ab..f458190 100644
--- a/tests/testutils.nim
+++ b/tests/testutils.nim
@@ -6,12 +6,12 @@
 #  Apache License, version 2.0, (LICENSE-APACHEv2)
 #              MIT license (LICENSE-MIT)
 import unittest2
-import ../chronos
+import ../chronos, ../chronos/config
 
-when defined(nimHasUsed): {.used.}
+{.used.}
 
 suite "Asynchronous utilities test suite":
-  when defined(chronosFutureTracking):
+  when chronosFutureTracking:
     proc getCount(): uint =
       # This procedure counts number of Future[T] in double-linked list via list
       # iteration.
@@ -21,7 +21,7 @@ suite "Asynchronous utilities test suite":
       res
 
   test "Future clean and leaks test":
-    when defined(chronosFutureTracking):
+    when chronosFutureTracking:
       if pendingFuturesCount(WithoutFinished) == 0'u:
         if pendingFuturesCount(OnlyFinished) > 0'u:
           poll()
@@ -33,7 +33,7 @@ suite "Asynchronous utilities test suite":
       skip()
 
   test "FutureList basics test":
-    when defined(chronosFutureTracking):
+    when chronosFutureTracking:
       var fut1 = newFuture[void]()
       check:
         getCount() == 1'u
@@ -65,7 +65,7 @@ suite "Asynchronous utilities test suite":
       skip()
 
   test "FutureList async procedure test":
-    when defined(chronosFutureTracking):
+    when chronosFutureTracking:
       proc simpleProc() {.async.} =
         await sleepAsync(10.milliseconds)