diff --git a/.gitmodules b/.gitmodules
index 5f058d57..19d3c088 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -169,10 +169,11 @@
 	path = vendor/nim-codex-dht
 	url = https://github.com/codex-storage/nim-codex-dht.git
 	ignore = untracked
-	branch = master
+	branch = feat/chronos-v4
 [submodule "vendor/nim-datastore"]
 	path = vendor/nim-datastore
 	url = https://github.com/status-im/nim-datastore.git
+  branch = master
 [submodule "vendor/nim-sqlite3-abi"]
 	path = vendor/nim-sqlite3-abi
 	url = https://github.com/arnetheduck/nim-sqlite3-abi.git
diff --git a/codex.nimble b/codex.nimble
index 2156919f..5f989a95 100644
--- a/codex.nimble
+++ b/codex.nimble
@@ -7,10 +7,10 @@ srcDir = "."
 installFiles  = @["build.nims"]
 
 requires "nim >= 1.2.0"
-requires "asynctest >= 0.3.2 & < 0.4.0"
+requires "asynctest >= 0.4.3 & < 0.5.0"
 requires "bearssl >= 0.1.4"
 requires "chronicles >= 0.7.2"
-requires "chronos >= 2.5.2"
+requires "chronos#head"
 requires "confutils"
 requires "ethers >= 0.7.1 & < 0.8.0"
 requires "libbacktrace"
diff --git a/codex/blockexchange/engine/engine.nim b/codex/blockexchange/engine/engine.nim
index ec7b7f64..dacc7aa9 100644
--- a/codex/blockexchange/engine/engine.nim
+++ b/codex/blockexchange/engine/engine.nim
@@ -83,7 +83,7 @@ type
 proc scheduleTask(b: BlockExcEngine, task: BlockExcPeerCtx): bool {.gcsafe} =
   b.taskQueue.pushOrUpdateNoWait(task).isOk()
 
-proc blockexcTaskRunner(b: BlockExcEngine): Future[void] {.gcsafe.}
+proc blockexcTaskRunner(b: BlockExcEngine): Future[void] {.gcsafe, raises: [].}
 
 proc start*(b: BlockExcEngine) {.async.} =
   ## Start the blockexc task
diff --git a/codex/blockexchange/network/network.nim b/codex/blockexchange/network/network.nim
index 1a39364b..e829993d 100644
--- a/codex/blockexchange/network/network.nim
+++ b/codex/blockexchange/network/network.nim
@@ -34,11 +34,11 @@ const
   MaxInflight* = 100
 
 type
-  WantListHandler* = proc(peer: PeerId, wantList: WantList): Future[void] {.gcsafe.}
-  BlocksDeliveryHandler* = proc(peer: PeerId, blocks: seq[BlockDelivery]): Future[void] {.gcsafe.}
-  BlockPresenceHandler* = proc(peer: PeerId, precense: seq[BlockPresence]): Future[void] {.gcsafe.}
-  AccountHandler* = proc(peer: PeerId, account: Account): Future[void] {.gcsafe.}
-  PaymentHandler* = proc(peer: PeerId, payment: SignedState): Future[void] {.gcsafe.}
+  WantListHandler* = proc(peer: PeerId, wantList: WantList): Future[void] {.gcsafe, raises: [].}
+  BlocksDeliveryHandler* = proc(peer: PeerId, blocks: seq[BlockDelivery]): Future[void] {.gcsafe, raises: [].}
+  BlockPresenceHandler* = proc(peer: PeerId, precense: seq[BlockPresence]): Future[void] {.gcsafe, raises: [].}
+  AccountHandler* = proc(peer: PeerId, account: Account): Future[void] {.gcsafe, raises: [].}
+  PaymentHandler* = proc(peer: PeerId, payment: SignedState): Future[void] {.gcsafe, raises: [].}
   WantListSender* = proc(
     id: PeerId,
     addresses: seq[BlockAddress],
@@ -46,7 +46,7 @@ type
     cancel: bool = false,
     wantType: WantType = WantType.WantHave,
     full: bool = false,
-    sendDontHave: bool = false): Future[void] {.gcsafe.}
+    sendDontHave: bool = false): Future[void] {.gcsafe, raises: [].}
 
   BlockExcHandlers* = object
     onWantList*: WantListHandler
@@ -55,10 +55,10 @@ type
     onAccount*: AccountHandler
     onPayment*: PaymentHandler
 
-  BlocksDeliverySender* = proc(peer: PeerId, blocksDelivery: seq[BlockDelivery]): Future[void] {.gcsafe.}
-  PresenceSender* = proc(peer: PeerId, presence: seq[BlockPresence]): Future[void] {.gcsafe.}
-  AccountSender* = proc(peer: PeerId, account: Account): Future[void] {.gcsafe.}
-  PaymentSender* = proc(peer: PeerId, payment: SignedState): Future[void] {.gcsafe.}
+  BlocksDeliverySender* = proc(peer: PeerId, blocksDelivery: seq[BlockDelivery]): Future[void] {.gcsafe, raises: [].}
+  PresenceSender* = proc(peer: PeerId, presence: seq[BlockPresence]): Future[void] {.gcsafe, raises: [].}
+  AccountSender* = proc(peer: PeerId, account: Account): Future[void] {.gcsafe, raises: [].}
+  PaymentSender* = proc(peer: PeerId, payment: SignedState): Future[void] {.gcsafe, raises: [].}
 
   BlockExcRequest* = object
     sendWantList*: WantListSender
diff --git a/codex/blockexchange/network/networkpeer.nim b/codex/blockexchange/network/networkpeer.nim
index 69a19386..a13ba92a 100644
--- a/codex/blockexchange/network/networkpeer.nim
+++ b/codex/blockexchange/network/networkpeer.nim
@@ -22,9 +22,9 @@ logScope:
   topics = "codex blockexcnetworkpeer"
 
 type
-  ConnProvider* = proc(): Future[Connection] {.gcsafe, closure.}
+  ConnProvider* = proc (): Future[Connection] {.gcsafe, closure, raises: [].}
 
-  RPCHandler* = proc(peer: NetworkPeer, msg: Message): Future[void] {.gcsafe.}
+  RPCHandler* = proc (peer: NetworkPeer, msg: Message): Future[void] {.gcsafe, raises: [].}
 
   NetworkPeer* = ref object of RootObj
     id*: PeerId
diff --git a/codex/contracts/clock.nim b/codex/contracts/clock.nim
index 9102e5c2..88f627a2 100644
--- a/codex/contracts/clock.nim
+++ b/codex/contracts/clock.nim
@@ -2,6 +2,7 @@ import std/times
 import pkg/ethers
 import pkg/chronos
 import pkg/stint
+import pkg/upraises
 import ../clock
 import ../conf
 
@@ -46,7 +47,7 @@ method stop*(clock: OnChainClock) {.async.} =
   await clock.subscription.unsubscribe()
   clock.started = false
 
-method now*(clock: OnChainClock): SecondsSince1970 =
+method now*(clock: OnChainClock): SecondsSince1970 {.raises: [].}=
   when codex_use_hardhat:
     # hardhat's latest block.timestamp is usually 1s behind the block timestamp
     # in the newHeads event. When testing, always return the latest block.
diff --git a/codex/discovery.nim b/codex/discovery.nim
index ce0b4032..477a4bae 100644
--- a/codex/discovery.nim
+++ b/codex/discovery.nim
@@ -129,7 +129,7 @@ method provide*(d: Discovery, host: ca.Address) {.async, base.} =
 
 method removeProvider*(
   d: Discovery,
-  peerId: PeerId): Future[void] {.base.} =
+  peerId: PeerId): Future[void] {.base, raises: [].} =
   ## Remove provider from providers table
   ##
 
diff --git a/codex/stores/cachestore.nim b/codex/stores/cachestore.nim
index e670a093..0602fc6e 100644
--- a/codex/stores/cachestore.nim
+++ b/codex/stores/cachestore.nim
@@ -118,7 +118,7 @@ method hasBlock*(self: CacheStore, treeCid: Cid, index: Natural): Future[?!bool]
 
   await self.hasBlock(cidAndProof[0])
 
-func cids(self: CacheStore): (iterator: Cid {.gcsafe.}) =
+func cids(self: CacheStore): (iterator: Cid {.gcsafe, raises: [].}) =
   return iterator(): Cid =
     for cid in self.cache.keys:
       yield cid
diff --git a/codex/utils/exceptions.nim b/codex/utils/exceptions.nim
index 4aa2af95..1c51120a 100644
--- a/codex/utils/exceptions.nim
+++ b/codex/utils/exceptions.nim
@@ -4,4 +4,18 @@ proc msgDetail*(e: ref CatchableError): string =
   var msg = e.msg
   if e.parent != nil:
     msg = fmt"{msg} Inner exception: {e.parent.msg}"
-  return msg
\ No newline at end of file
+  return msg
+
+template launderBare*(body: untyped): untyped =
+  ## Launders bare Exceptions into CatchableError. This is typically used to
+  ## "fix" code that throws bare exceptions and won't compile with Chronos V4,
+  ## and which cannot be fixed otherise, e.g. in system APIs like json.parseJson
+  ## in Nim 1.6.x. It should only be used as a last resort.
+  try:
+    body
+  except Defect as ex:
+    raise ex
+  except CatchableError as ex:
+    raise ex
+  except Exception as ex:
+    raise newException(Defect, ex.msg, ex)
diff --git a/codex/utils/json.nim b/codex/utils/json.nim
index 080d4e89..9ff3addd 100644
--- a/codex/utils/json.nim
+++ b/codex/utils/json.nim
@@ -14,6 +14,7 @@ import pkg/stew/byteutils
 import pkg/stint
 import pkg/questionable/results
 import ../errors
+import exceptions
 
 export json except `%`, `%*`
 
@@ -27,12 +28,12 @@ proc newUnexpectedKindError(
   expectedType: type,
   expectedKinds: string,
   json: JsonNode
-): ref UnexpectedKindError =
+): ref UnexpectedKindError {.raises: [].} =
   let kind = if json.isNil: "nil"
              else: $json.kind
   newException(UnexpectedKindError,
-    &"deserialization to {$expectedType} failed: expected {expectedKinds} " &
-    &"but got {kind}")
+    "deserialization to " & $expectedType & " failed: expected " &
+    expectedKinds & " but got " & kind)
 
 proc newUnexpectedKindError(
   expectedType: type,
@@ -218,14 +219,16 @@ proc fromJson*[T: object](
   _: type T,
   bytes: seq[byte]
 ): ?!T =
-  let json = ?catch parseJson(string.fromBytes(bytes))
+  # FIXME remove launderBare when we upgrade to nim 2.0.0
+  let json = ?catch launderBare parseJson(string.fromBytes(bytes))
   T.fromJson(json)
 
 proc fromJson*[T: ref object](
   _: type T,
   bytes: seq[byte]
 ): ?!T =
-  let json = ?catch parseJson(string.fromBytes(bytes))
+  # FIXME remove launderBare when we upgrade to nim 2.0.0
+  let json = ?catch launderBare parseJson(string.fromBytes(bytes))
   T.fromJson(json)
 
 func `%`*(s: string): JsonNode = newJString(s)
diff --git a/codex/utils/timer.nim b/codex/utils/timer.nim
index 9361d07b..92f92451 100644
--- a/codex/utils/timer.nim
+++ b/codex/utils/timer.nim
@@ -35,12 +35,12 @@ proc timerLoop(timer: Timer) {.async.} =
     while true:
       await timer.callback()
       await sleepAsync(timer.interval)
-  except CancelledError:
-    raise
+  except CancelledError as exc:
+    raise exc
   except CatchableError as exc:
     error "Timer caught unhandled exception: ", name=timer.name, msg=exc.msg
 
-method start*(timer: Timer, callback: TimerCallback, interval: Duration) {.base.} =
+method start*(timer: Timer, callback: TimerCallback, interval: Duration) {.base, raises: [].} =
   if timer.loopFuture != nil:
     return
   trace "Timer starting: ", name=timer.name
diff --git a/codex/validation.nim b/codex/validation.nim
index b549997e..b29fa45f 100644
--- a/codex/validation.nim
+++ b/codex/validation.nim
@@ -75,8 +75,8 @@ proc markProofAsMissing(validation: Validation,
     else:
       let inDowntime {.used.} = await validation.market.inDowntime(slotId)
       trace "Proof not missing", checkedPeriod = period, inDowntime
-  except CancelledError:
-    raise
+  except CancelledError as e:
+    raise e
   except CatchableError as e:
     error "Marking proof as missing failed", msg = e.msg
 
diff --git a/config.nims b/config.nims
index dba6d9fe..a00ce831 100644
--- a/config.nims
+++ b/config.nims
@@ -67,7 +67,6 @@ else:
 --threads:on
 --opt:speed
 --excessiveStackTrace:on
---experimental:strictEffects
 # enable metric collection
 --define:metrics
 # for heap-usage-by-instance-type metrics and object base-type strings
diff --git a/vendor/nim-chronos b/vendor/nim-chronos
index c41599a6..e15dc3b4 160000
--- a/vendor/nim-chronos
+++ b/vendor/nim-chronos
@@ -1 +1 @@
-Subproject commit c41599a6d6d8b11c729032bf8913e06f4171e0fb
+Subproject commit e15dc3b41fea95348b58f32244962c1c6df310a7
diff --git a/vendor/nim-codex-dht b/vendor/nim-codex-dht
index a7f14bc9..71cc9298 160000
--- a/vendor/nim-codex-dht
+++ b/vendor/nim-codex-dht
@@ -1 +1 @@
-Subproject commit a7f14bc9b783f1b9e2d02cc85a338b1411058095
+Subproject commit 71cc92988968add33ddf0f517dff68f140feb68a