diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Protocol.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Protocol.hs
index 08ce27780f6..03d2b63be6c 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Protocol.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Protocol.hs
@@ -59,18 +59,14 @@ import Shelley.Spec.Ledger.Keys (GenDelegs)
 import Shelley.Spec.Ledger.LedgerState
   ( EpochState (..),
     NewEpochState (..),
-    getGKeys,
     _delegationState,
     _dstate,
     _genDelegs,
   )
 import Shelley.Spec.Ledger.OCert (OCertSignable)
-import Shelley.Spec.Ledger.OverlaySchedule
-  ( OverlaySchedule,
-  )
-import Shelley.Spec.Ledger.PParams (PParams)
+import Shelley.Spec.Ledger.PParams (PParams, PParams' (..))
 import qualified Shelley.Spec.Ledger.STS.Prtcl as STS.Prtcl
-import Shelley.Spec.Ledger.STS.Tick (TICK, TickEnv (..))
+import Shelley.Spec.Ledger.STS.Tick (TICK)
 import qualified Shelley.Spec.Ledger.STS.Tickn as STS.Tickn
 import Shelley.Spec.Ledger.Serialization (decodeRecordNamed)
 import Shelley.Spec.Ledger.Slot (SlotNo)
@@ -78,7 +74,6 @@ import Shelley.Spec.Ledger.Slot (SlotNo)
 -- | Data required by the Transitional Praos protocol from the Shelley ledger.
 data LedgerView era = LedgerView
   { lvProtParams :: PParams era,
-    lvOverlaySched :: OverlaySchedule era,
     lvPoolDistr :: PoolDistr era,
     lvGenDelegs :: GenDelegs era
   }
@@ -90,26 +85,23 @@ instance Era era => FromCBOR (LedgerView era) where
   fromCBOR =
     decodeRecordNamed
       "LedgerView"
-      (const 4)
+      (const 3)
       ( LedgerView
           <$> fromCBOR
           <*> fromCBOR
           <*> fromCBOR
-          <*> fromCBOR
       )
 
 instance Era era => ToCBOR (LedgerView era) where
   toCBOR
     LedgerView
       { lvProtParams,
-        lvOverlaySched,
         lvPoolDistr,
         lvGenDelegs
       } =
       mconcat
-        [ encodeListLen 4,
+        [ encodeListLen 3,
           toCBOR lvProtParams,
-          toCBOR lvOverlaySched,
           toCBOR lvPoolDistr,
           toCBOR lvGenDelegs
         ]
@@ -124,12 +116,12 @@ mkPrtclEnv ::
   STS.Prtcl.PrtclEnv era
 mkPrtclEnv
   LedgerView
-    { lvOverlaySched,
+    { lvProtParams,
       lvPoolDistr,
       lvGenDelegs
     } =
     STS.Prtcl.PrtclEnv
-      lvOverlaySched
+      (_d lvProtParams)
       lvPoolDistr
       lvGenDelegs
 
@@ -137,13 +129,10 @@ view :: ShelleyState era -> LedgerView era
 view
   NewEpochState
     { nesPd,
-      nesOsched,
       nesEs
     } =
     LedgerView
       { lvProtParams = esPp nesEs,
-        lvOverlaySched =
-          nesOsched,
         lvPoolDistr = nesPd,
         lvGenDelegs =
           _genDelegs . _dstate
@@ -210,10 +199,7 @@ futureLedgerView globals ss slot =
     res =
       flip runReader globals
         . applySTS @(TICK era)
-        $ TRC (tickEnv, ss, slot)
-    tickEnv =
-      TickEnv
-        (getGKeys ss)
+        $ TRC ((), ss, slot)
 
 -- $chainstate
 --
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Types.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Types.hs
index 8e30072fb22..be58b38c550 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Types.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Types.hs
@@ -64,7 +64,6 @@ import Shelley.Spec.Ledger.LedgerState as X
     EpochState (..),
     KeyPairs,
     LedgerState (..),
-    NewEpochEnv (..),
     NewEpochState (..),
     PState (..),
     RewardUpdate (..),
@@ -95,7 +94,7 @@ import Shelley.Spec.Ledger.STS.Ocert as X (OCertEnv (..))
 import Shelley.Spec.Ledger.STS.Pool as X (POOL, PoolEnv (..))
 import Shelley.Spec.Ledger.STS.PoolReap as X (POOLREAP)
 import Shelley.Spec.Ledger.STS.Ppup as X (PPUP, PPUPEnv (..))
-import Shelley.Spec.Ledger.STS.Tick as X (TICK, TickEnv (..))
+import Shelley.Spec.Ledger.STS.Tick as X (TICK)
 import Shelley.Spec.Ledger.STS.Utxo as X (UTXO, UtxoEnv (..))
 import Shelley.Spec.Ledger.STS.Utxow as X (UTXOW)
 import Shelley.Spec.Ledger.Scripts as X
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Validation.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Validation.hs
index a03c343493c..cfe225d68b0 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Validation.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Validation.hs
@@ -54,22 +54,15 @@ chainChecks globals pp bh = STS.chainChecks (maxMajorPV globals) pp bh
   Applying blocks
 -------------------------------------------------------------------------------}
 
-mkTickEnv ::
-  ShelleyState era ->
-  STS.TickEnv era
-mkTickEnv = STS.TickEnv . LedgerState.getGKeys
-
 mkBbodyEnv ::
   ShelleyState era ->
   STS.BbodyEnv era
 mkBbodyEnv
   LedgerState.NewEpochState
-    { LedgerState.nesOsched,
-      LedgerState.nesEs
+    { LedgerState.nesEs
     } =
     STS.BbodyEnv
-      { STS.bbodySlots = nesOsched,
-        STS.bbodyPp = LedgerState.esPp nesEs,
+      { STS.bbodyPp = LedgerState.esPp nesEs,
         STS.bbodyAccount = LedgerState.esAccountState nesEs
       }
 
@@ -93,7 +86,7 @@ applyTickTransition ::
 applyTickTransition globals state hdr =
   (either err id) . flip runReader globals
     . applySTS @(STS.TICK era)
-    $ TRC (mkTickEnv state, state, hdr)
+    $ TRC ((), state, hdr)
   where
     err :: Show a => a -> b
     err msg = error $ "Panic! applyHeaderTransition failed: " <> (show msg)
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Wallet.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Wallet.hs
index 0f844f4e30f..86eeb778e51 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Wallet.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/Wallet.hs
@@ -44,6 +44,7 @@ import Shelley.Spec.Ledger.LedgerState
     stakeDistr,
   )
 import Shelley.Spec.Ledger.OverlaySchedule (isOverlaySlot)
+import Shelley.Spec.Ledger.PParams (PParams, PParams' (..))
 import Shelley.Spec.Ledger.Rewards
   ( NonMyopic (..),
     StakeShare (..),
@@ -153,20 +154,19 @@ getLeaderSchedule ::
   ChainDepState era ->
   KeyHash 'StakePool era ->
   SignKeyVRF era ->
+  PParams era ->
   Set SlotNo
-getLeaderSchedule globals ss cds poolHash key = Set.filter isLeader epochSlots
+getLeaderSchedule globals ss cds poolHash key pp = Set.filter isLeader epochSlots
   where
     isLeader slotNo =
       let y = VRF.evalCertified () (mkSeed seedL slotNo epochNonce) key
-       in not (isOverlaySlot slotNo overlaySched)
+       in not (isOverlaySlot a (_d pp) slotNo)
             && checkLeaderValue (VRF.certifiedOutput y) stake f
     stake = maybe 0 individualPoolStake $ Map.lookup poolHash poolDistr
-    overlaySched = nesOsched ss
     poolDistr = unPoolDistr $ nesPd ss
     TicknState epochNonce _ = csTickn cds
     currentEpoch = nesEL ss
     ei = epochInfo globals
     f = activeSlotCoeff globals
     epochSlots = Set.fromList [a .. b]
-      where
-        (a, b) = runIdentity $ epochInfoRange ei currentEpoch
+    (a, b) = runIdentity $ epochInfoRange ei currentEpoch
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/ByronTranslation.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/ByronTranslation.hs
index 0ee34210bf0..92f1e5be37f 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/ByronTranslation.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/ByronTranslation.hs
@@ -21,18 +21,15 @@ import qualified Cardano.Crypto.Hashing as Hashing
 import Cardano.Ledger.Crypto (ADDRHASH)
 import Cardano.Ledger.Era
 import qualified Cardano.Ledger.Val as Val
-import Control.Monad.Reader (runReader)
 import qualified Data.ByteString.Short as SBS
 import qualified Data.Map.Strict as Map
 import Data.Maybe (fromMaybe)
 import GHC.Stack (HasCallStack)
 import Shelley.Spec.Ledger.API
-import Shelley.Spec.Ledger.BaseTypes
 import Shelley.Spec.Ledger.Coin (word64ToCoin)
 import Shelley.Spec.Ledger.EpochBoundary
 import Shelley.Spec.Ledger.Genesis
 import Shelley.Spec.Ledger.LedgerState
-import Shelley.Spec.Ledger.OverlaySchedule
 import Shelley.Spec.Ledger.Rewards
 import Shelley.Spec.Ledger.Slot
 import Shelley.Spec.Ledger.UTxO
@@ -91,19 +88,17 @@ translateToShelleyLedgerState ::
   forall era.
   (Era era, ADDRHASH (Crypto era) ~ Crypto.Blake2b_224) =>
   ShelleyGenesis era ->
-  Globals ->
   EpochNo ->
   Byron.ChainValidationState ->
   ShelleyState era
-translateToShelleyLedgerState genesisShelley globals epochNo cvs =
+translateToShelleyLedgerState genesisShelley epochNo cvs =
   NewEpochState
     { nesEL = epochNo,
       nesBprev = BlocksMade Map.empty,
       nesBcur = BlocksMade Map.empty,
       nesEs = epochState,
       nesRu = SNothing,
-      nesPd = PoolDistr Map.empty,
-      nesOsched = oSchedule
+      nesPd = PoolDistr Map.empty
     }
   where
     pparams :: PParams era
@@ -159,34 +154,16 @@ translateToShelleyLedgerState genesisShelley globals epochNo cvs =
                 _pstate = emptyPState
               }
         }
-    oSchedule :: OverlaySchedule era
-    oSchedule =
-      flip runReader globals $
-        overlaySchedule
-          epochNo
-          (Map.keysSet (sgGenDelegs genesisShelley))
-          pparams
 
 -- | We construct a 'LedgerView' using the Shelley genesis config in the same
 -- way as 'translateToShelleyLedgerState'.
 mkInitialShelleyLedgerView ::
   forall era.
   ShelleyGenesis era ->
-  Globals ->
-  EpochNo ->
   LedgerView era
-mkInitialShelleyLedgerView genesisShelley globals epochNo =
+mkInitialShelleyLedgerView genesisShelley =
   LedgerView
     { lvProtParams = sgProtocolParams genesisShelley,
-      lvOverlaySched = oSchedule,
       lvPoolDistr = PoolDistr Map.empty,
       lvGenDelegs = GenDelegs $ sgGenDelegs genesisShelley
     }
-  where
-    oSchedule :: OverlaySchedule era
-    oSchedule =
-      flip runReader globals $
-        overlaySchedule
-          epochNo
-          (Map.keysSet (sgGenDelegs genesisShelley))
-          (sgProtocolParams genesisShelley)
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/LedgerState.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/LedgerState.hs
index 972152d6ce2..4e8d955ae99 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/LedgerState.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/LedgerState.hs
@@ -83,7 +83,6 @@ module Shelley.Spec.Ledger.LedgerState
     createRUpd,
     --
     NewEpochState (..),
-    NewEpochEnv (..),
     getGKeys,
     updateNES,
   )
@@ -154,7 +153,6 @@ import Shelley.Spec.Ledger.Keys
     VKey,
     asWitness,
   )
-import Shelley.Spec.Ledger.OverlaySchedule
 import Shelley.Spec.Ledger.PParams
   ( PParams,
     PParams' (..),
@@ -545,9 +543,7 @@ data NewEpochState era = NewEpochState
     -- | Possible reward update
     nesRu :: !(StrictMaybe (RewardUpdate era)),
     -- | Stake distribution within the stake pool
-    nesPd :: !(PoolDistr era),
-    -- | Overlay schedule for PBFT vs Praos
-    nesOsched :: !(OverlaySchedule era)
+    nesPd :: !(PoolDistr era)
   }
   deriving (Show, Eq, Generic)
 
@@ -556,41 +552,31 @@ instance (Era era) => NFData (NewEpochState era)
 instance NoUnexpectedThunks (NewEpochState era)
 
 instance Era era => ToCBOR (NewEpochState era) where
-  toCBOR (NewEpochState e bp bc es ru pd os) =
-    encodeListLen 7 <> toCBOR e <> toCBOR bp <> toCBOR bc <> toCBOR es
+  toCBOR (NewEpochState e bp bc es ru pd) =
+    encodeListLen 6 <> toCBOR e <> toCBOR bp <> toCBOR bc <> toCBOR es
       <> toCBOR ru
       <> toCBOR pd
-      <> toCBOR os
 
 instance Era era => FromCBOR (NewEpochState era) where
   fromCBOR = do
-    decodeRecordNamed "NewEpochState" (const 7) $ do
+    decodeRecordNamed "NewEpochState" (const 6) $ do
       e <- fromCBOR
       bp <- fromCBOR
       bc <- fromCBOR
       es <- fromCBOR
       ru <- fromCBOR
       pd <- fromCBOR
-      os <- fromCBOR
-      pure $ NewEpochState e bp bc es ru pd os
+      pure $ NewEpochState e bp bc es ru pd
 
 getGKeys ::
   NewEpochState era ->
   Set (KeyHash 'Genesis era)
 getGKeys nes = Map.keysSet genDelegs
   where
-    NewEpochState _ _ _ es _ _ _ = nes
+    NewEpochState _ _ _ es _ _ = nes
     EpochState _ _ ls _ _ _ = es
     LedgerState _ (DPState (DState _ _ _ _ (GenDelegs genDelegs) _) _) = ls
 
-data NewEpochEnv era = NewEpochEnv
-  { neeS :: SlotNo,
-    neeGkeys :: Set (KeyHash 'Genesis era)
-  }
-  deriving (Show, Eq, Generic)
-
-instance NoUnexpectedThunks (NewEpochEnv era)
-
 -- | The state associated with a 'Ledger'.
 data LedgerState era = LedgerState
   { -- | The current unspent transaction outputs.
@@ -965,8 +951,7 @@ updateNES
       (EpochState acnt ss _ pr pp nm)
       ru
       pd
-      osched
     )
   bcur
   ls =
-    NewEpochState eL bprev bcur (EpochState acnt ss ls pr pp nm) ru pd osched
+    NewEpochState eL bprev bcur (EpochState acnt ss ls pr pp nm) ru pd
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/OverlaySchedule.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/OverlaySchedule.hs
index d7b33e27475..0f1741242e2 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/OverlaySchedule.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/OverlaySchedule.hs
@@ -6,19 +6,15 @@
 
 module Shelley.Spec.Ledger.OverlaySchedule
   ( -- * Overlay schedule
-    OverlaySchedule,
-    compactOverlaySchedule,
-    decompactOverlaySchedule,
-    emptyOverlaySchedule,
     isOverlaySlot,
+    classifyOverlaySlot,
     lookupInOverlaySchedule,
-    overlaySchedule,
-    overlayScheduleHelper,
-    overlayScheduleIsEmpty,
-    overlayScheduleToMap,
 
     -- * OBftSlot
     OBftSlot (..),
+
+    -- * Testing
+    overlaySlots,
   )
 where
 
@@ -33,20 +29,12 @@ import Cardano.Binary
 import Cardano.Ledger.Era (Era)
 import Cardano.Prelude (NFData, NoUnexpectedThunks)
 import Cardano.Slotting.Slot
-import Control.Monad.Trans.Reader (asks)
-import Data.List.NonEmpty (NonEmpty)
-import qualified Data.List.NonEmpty as NonEmpty
-import Data.Map.Strict (Map)
-import qualified Data.Map.Strict as Map
-import Data.Set (Set)
-import qualified Data.Set as Set
 import GHC.Generics (Generic)
 import Shelley.Spec.Ledger.BaseTypes
 import Shelley.Spec.Ledger.Keys
   ( KeyHash (..),
     KeyRole (..),
   )
-import Shelley.Spec.Ledger.PParams (PParams, _d)
 import Shelley.Spec.Ledger.Slot
 
 data OBftSlot era
@@ -76,109 +64,62 @@ instance NoUnexpectedThunks (OBftSlot era)
 
 instance NFData (OBftSlot era)
 
-newtype OverlaySchedule era = OverlaySchedule (Map SlotNo (OBftSlot era))
-  deriving stock (Show, Eq)
-  deriving newtype (NoUnexpectedThunks, NFData)
-
-emptyOverlaySchedule :: OverlaySchedule era
-emptyOverlaySchedule = OverlaySchedule Map.empty
+isOverlaySlot ::
+  SlotNo -> -- starting slot
+  UnitInterval -> -- decentralization parameter
+  SlotNo -> -- slot to check
+  Bool
+isOverlaySlot firstSlotNo dval slot = step s < step (s + 1)
+  where
+    s = fromIntegral $ slot -* firstSlotNo
+    d = unitIntervalToRational dval
+    step :: Rational -> Integer
+    step x = ceiling (x * d)
+
+classifyOverlaySlot ::
+  SlotNo -> -- first slot of the epoch
+  [KeyHash 'Genesis era] -> -- genesis Nodes
+  UnitInterval -> -- decentralization parameter
+  ActiveSlotCoeff -> -- active slot coefficent
+  SlotNo -> -- overlay slot to classify
+  OBftSlot era
+classifyOverlaySlot firstSlotNo gkeys dval ascValue slot =
+  if isActive
+    then
+      let genesisIdx = (position `div` ascInv) `mod` (fromIntegral $ length gkeys)
+       in gkeys `getAtIndex` genesisIdx
+    else NonActiveSlot
+  where
+    d = unitIntervalToRational dval
+    position = ceiling (fromIntegral (slot -* firstSlotNo) * d)
+    isActive = position `mod` ascInv == 0
+    getAtIndex ls i = if i < length ls then ActiveSlot (ls !! i) else NonActiveSlot
+    ascInv = floor (1 / (unitIntervalToRational . activeSlotVal $ ascValue))
 
 lookupInOverlaySchedule ::
-  SlotNo ->
-  OverlaySchedule era ->
+  SlotNo -> -- first slot of the epoch
+  [KeyHash 'Genesis era] -> -- genesis Nodes
+  UnitInterval -> -- decentralization parameter
+  ActiveSlotCoeff -> -- active slot coefficent
+  SlotNo -> -- slot to lookup
   Maybe (OBftSlot era)
-lookupInOverlaySchedule slot (OverlaySchedule oSched) = Map.lookup slot oSched
-
-overlayScheduleIsEmpty :: OverlaySchedule era -> Bool
-overlayScheduleIsEmpty (OverlaySchedule oSched) = Map.null oSched
-
--- | Overlay schedule
--- This is just a very simple round-robin, evenly spaced schedule.
-overlaySchedule ::
-  EpochNo ->
-  Set (KeyHash 'Genesis era) ->
-  PParams era ->
-  ShelleyBase (OverlaySchedule era)
-overlaySchedule e gkeys pp = do
-  ei <- asks epochInfo
-  slotsPerEpoch <- epochInfoSize ei e
-  firstSlotNo <- epochInfoFirst ei e
-  asc <- asks activeSlotCoeff
-  pure $ overlayScheduleHelper slotsPerEpoch firstSlotNo gkeys (_d pp) asc
-
-overlayScheduleHelper ::
+lookupInOverlaySchedule firstSlotNo gkeys dval ascValue slot =
+  if isOverlaySlot firstSlotNo dval slot
+    then Just $ classifyOverlaySlot firstSlotNo gkeys dval ascValue slot
+    else Nothing
+
+-- | Return the list of overlaySlots for a given epoch.
+-- Note that this linear in the size of the epoch, and should probably
+-- only be used for testing.
+-- If something more performant is needed, we could probably use
+-- [start + floor(x/d) | x <- [0 .. (spe -1)], floor(x/d) < spe]
+-- but we would need to make sure that this is equivalent.
+overlaySlots ::
+  SlotNo -> -- starting slot
+  UnitInterval -> -- decentralization parameter
   EpochSize ->
-  -- | First slot of the epoch
-  SlotNo ->
-  Set (KeyHash 'Genesis era) ->
-  -- | Decentralization parameter @d@
-  UnitInterval ->
-  ActiveSlotCoeff ->
-  OverlaySchedule era
-overlayScheduleHelper slotsPerEpoch firstSlotNo gkeys d asc
-  | dval == 0 =
-    OverlaySchedule $ Map.empty
-  | otherwise =
-    OverlaySchedule $ Map.union active inactive
+  [SlotNo]
+overlaySlots start d (EpochSize spe) =
+  [SlotNo x | x <- [unSlotNo start .. end], isOverlaySlot start d (SlotNo x)]
   where
-    dval = intervalValue d
-    numActive = dval * fromIntegral slotsPerEpoch
-    dInv = 1 / dval
-    ascValue = (intervalValue . activeSlotVal) asc
-    toRelativeSlotNo x = (Duration . floor) (dInv * fromInteger x)
-    toSlotNo x = firstSlotNo +* toRelativeSlotNo x
-    genesisSlots = [toSlotNo x | x <- [0 .. (floor numActive - 1)]]
-    numInactivePerActive = floor (1 / ascValue) - 1
-    activitySchedule = cycle (True : replicate numInactivePerActive False)
-    unassignedSched = zip activitySchedule genesisSlots
-    genesisCycle = if Set.null gkeys then [] else cycle (Set.toList gkeys)
-    active =
-      Map.fromList $
-        fmap
-          (\(gk, (_, s)) -> (s, ActiveSlot gk))
-          (zip genesisCycle (filter fst unassignedSched))
-    inactive =
-      Map.fromList $
-        fmap
-          (\x -> (snd x, NonActiveSlot))
-          (filter (not . fst) unassignedSched)
-
-overlayScheduleToMap :: OverlaySchedule era -> Map SlotNo (OBftSlot era)
-overlayScheduleToMap (OverlaySchedule oSched) = oSched
-
--- | Convert the overlay schedule to a representation that is more compact
--- when serialised to a bytestring, but less efficient for lookups.
---
--- Each genesis key hash will only be stored once, instead of each time it is
--- assigned to a slot.
-compactOverlaySchedule ::
-  OverlaySchedule era ->
-  Map (OBftSlot era) (NonEmpty SlotNo)
-compactOverlaySchedule (OverlaySchedule oSched) =
-  Map.foldrWithKey'
-    ( \slot obftSlot ->
-        Map.insertWith (<>) obftSlot (pure slot)
-    )
-    Map.empty
-    oSched
-
--- | Inverse of 'compactOverlaySchedule'
-decompactOverlaySchedule ::
-  Map (OBftSlot era) (NonEmpty SlotNo) ->
-  OverlaySchedule era
-decompactOverlaySchedule compact =
-  OverlaySchedule $
-    Map.fromList
-      [ (slot, obftSlot)
-        | (obftSlot, slots) <- Map.toList compact,
-          slot <- NonEmpty.toList slots
-      ]
-
-instance Era era => ToCBOR (OverlaySchedule era) where
-  toCBOR = toCBOR . compactOverlaySchedule
-
-instance Era era => FromCBOR (OverlaySchedule era) where
-  fromCBOR = decompactOverlaySchedule <$> fromCBOR
-
-isOverlaySlot :: SlotNo -> OverlaySchedule c -> Bool
-isOverlaySlot slot (OverlaySchedule oslots) = Map.member slot oslots
+    end = unSlotNo start + spe - 1
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Bbody.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Bbody.hs
index 6b6f5d9c4d6..2330efd9f18 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Bbody.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Bbody.hs
@@ -20,18 +20,20 @@ where
 
 import Cardano.Ledger.Era (Era)
 import Cardano.Prelude (NoUnexpectedThunks (..))
+import Control.Monad.Trans.Reader (asks)
 import Control.State.Transition
   ( Embed (..),
     STS (..),
     TRC (..),
     TransitionRule,
     judgmentContext,
+    liftSTS,
     trans,
     (?!),
   )
 import qualified Data.Sequence.Strict as StrictSeq
 import GHC.Generics (Generic)
-import Shelley.Spec.Ledger.BaseTypes (ShelleyBase)
+import Shelley.Spec.Ledger.BaseTypes (ShelleyBase, epochInfo)
 import Shelley.Spec.Ledger.BlockChain
   ( BHBody (..),
     BHeader (..),
@@ -50,12 +52,10 @@ import Shelley.Spec.Ledger.LedgerState
   ( AccountState,
     LedgerState,
   )
-import Shelley.Spec.Ledger.OverlaySchedule
-  ( OverlaySchedule,
-    isOverlaySlot,
-  )
-import Shelley.Spec.Ledger.PParams (PParams)
+import Shelley.Spec.Ledger.OverlaySchedule (isOverlaySlot)
+import Shelley.Spec.Ledger.PParams (PParams, PParams' (..))
 import Shelley.Spec.Ledger.STS.Ledgers (LEDGERS, LedgersEnv (..))
+import Shelley.Spec.Ledger.Slot (epochInfoEpoch, epochInfoFirst)
 import Shelley.Spec.Ledger.Tx (TxBody)
 
 data BBODY era
@@ -65,8 +65,7 @@ data BbodyState era
   deriving (Eq, Show)
 
 data BbodyEnv era = BbodyEnv
-  { bbodySlots :: OverlaySchedule era,
-    bbodyPp :: PParams era,
+  { bbodyPp :: PParams era,
     bbodyAccount :: AccountState
   }
 
@@ -114,7 +113,7 @@ bbodyTransition ::
 bbodyTransition =
   judgmentContext
     >>= \( TRC
-             ( BbodyEnv oslots pp account,
+             ( BbodyEnv pp account,
                BbodyState ls b,
                Block (BHeader bhb _) txsSeq
                )
@@ -136,7 +135,19 @@ bbodyTransition =
         -- delegate. However, this would only entail an overhead of 7 counts, and it's
         -- easier than differentiating here.
         let hkAsStakePool = coerceKeyRole . poolIDfromBHBody $ bhb
-        pure $ BbodyState ls' (incrBlocks (isOverlaySlot (bheaderSlotNo bhb) oslots) hkAsStakePool b)
+            slot = bheaderSlotNo bhb
+        firstSlotNo <- liftSTS $ do
+          ei <- asks epochInfo
+          e <- epochInfoEpoch ei slot
+          epochInfoFirst ei e
+        pure $
+          BbodyState
+            ls'
+            ( incrBlocks
+                (isOverlaySlot firstSlotNo (_d pp) slot)
+                hkAsStakePool
+                b
+            )
 
 instance
   ( Era era,
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Chain.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Chain.hs
index bfe68f33bec..d942bf4e88f 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Chain.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Chain.hs
@@ -95,18 +95,14 @@ import Shelley.Spec.Ledger.LedgerState
     emptyDState,
     emptyPPUPState,
     emptyPState,
-    getGKeys,
     updateNES,
     _genDelegs,
   )
 import Shelley.Spec.Ledger.OCert (OCertSignable)
-import Shelley.Spec.Ledger.OverlaySchedule
 import Shelley.Spec.Ledger.PParams
   ( PParams,
+    PParams' (..),
     ProtVer (..),
-    _maxBBSize,
-    _maxBHSize,
-    _protocolVersion,
   )
 import Shelley.Spec.Ledger.Rewards (emptyNonMyopic)
 import Shelley.Spec.Ledger.STS.Bbody (BBODY, BbodyEnv (..), BbodyState (..))
@@ -117,7 +113,7 @@ import Shelley.Spec.Ledger.STS.Prtcl
     PrtlSeqFailure,
     prtlSeqChecks,
   )
-import Shelley.Spec.Ledger.STS.Tick (TICK, TickEnv (..))
+import Shelley.Spec.Ledger.STS.Tick (TICK)
 import Shelley.Spec.Ledger.STS.Tickn
 import Shelley.Spec.Ledger.Slot (EpochNo)
 import Shelley.Spec.Ledger.Tx (TxBody)
@@ -162,11 +158,10 @@ initialShelleyState ::
   UTxO era ->
   Coin ->
   Map (KeyHash 'Genesis era) (GenDelegPair era) ->
-  OverlaySchedule era ->
   PParams era ->
   Nonce ->
   ChainState era
-initialShelleyState lab e utxo reserves genDelegs os pp initNonce =
+initialShelleyState lab e utxo reserves genDelegs pp initNonce =
   ChainState
     ( NewEpochState
         e
@@ -190,7 +185,6 @@ initialShelleyState lab e utxo reserves genDelegs os pp initNonce =
         )
         SNothing
         (PoolDistr Map.empty)
-        os
     )
     cs
     initNonce
@@ -261,7 +255,7 @@ chainTransition =
         Right () -> pure ()
         Left e -> failBecause $ PrtclSeqFailure e
 
-      let NewEpochState _ _ _ (EpochState _ _ _ _ pp _) _ _ _ = nes
+      let NewEpochState _ _ _ (EpochState _ _ _ _ pp _) _ _ = nes
 
       maxpv <- liftSTS $ asks maxMajorPV
       case chainChecks maxpv pp bh of
@@ -269,13 +263,12 @@ chainTransition =
         Left e -> failBecause e
 
       let s = bheaderSlotNo $ bhbody bh
-      let gkeys = getGKeys nes
 
       nes' <-
-        trans @(TICK era) $ TRC (TickEnv gkeys, nes, s)
+        trans @(TICK era) $ TRC ((), nes, s)
 
-      let NewEpochState e1 _ _ _ _ _ _ = nes
-          NewEpochState e2 _ bcur es _ _pd osched = nes'
+      let NewEpochState e1 _ _ _ _ _ = nes
+          NewEpochState e2 _ bcur es _ _pd = nes'
       let EpochState account _ ls _ pp' _ = es
       let LedgerState _ (DPState (DState _ _ _ _ _genDelegs _) (PState _ _ _)) = ls
 
@@ -293,14 +286,14 @@ chainTransition =
       PrtclState cs' etaV' etaC' <-
         trans @(PRTCL era) $
           TRC
-            ( PrtclEnv osched _pd _genDelegs eta0',
+            ( PrtclEnv (_d pp') _pd _genDelegs eta0',
               PrtclState cs etaV etaC,
               bh
             )
 
       BbodyState ls' bcur' <-
         trans @(BBODY era) $
-          TRC (BbodyEnv osched pp' account, BbodyState ls bcur, block)
+          TRC (BbodyEnv pp' account, BbodyState ls bcur, block)
 
       let nes'' = updateNES nes' bcur' ls'
           bhb = bhbody bh
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/NewEpoch.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/NewEpoch.hs
index a826709c754..d94b28414b0 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/NewEpoch.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/NewEpoch.hs
@@ -28,7 +28,6 @@ import Shelley.Spec.Ledger.Coin
 import Shelley.Spec.Ledger.Delegation.Certificates
 import Shelley.Spec.Ledger.EpochBoundary
 import Shelley.Spec.Ledger.LedgerState
-import Shelley.Spec.Ledger.OverlaySchedule
 import Shelley.Spec.Ledger.STS.Epoch
 import Shelley.Spec.Ledger.STS.Mir
 import Shelley.Spec.Ledger.Slot
@@ -53,7 +52,7 @@ instance
 
   type Signal (NEWEPOCH era) = EpochNo
 
-  type Environment (NEWEPOCH era) = NewEpochEnv era
+  type Environment (NEWEPOCH era) = ()
 
   type BaseM (NEWEPOCH era) = ShelleyBase
   type PredicateFailure (NEWEPOCH era) = NewEpochPredicateFailure era
@@ -67,7 +66,6 @@ instance
           emptyEpochState
           SNothing
           (PoolDistr Map.empty)
-          emptyOverlaySchedule
     ]
 
   transitionRules = [newEpochTransition]
@@ -78,8 +76,8 @@ newEpochTransition ::
   TransitionRule (NEWEPOCH era)
 newEpochTransition = do
   TRC
-    ( NewEpochEnv _s gkeys,
-      src@(NewEpochState (EpochNo eL) _ bcur es ru _pd _osched),
+    ( _,
+      src@(NewEpochState (EpochNo eL) _ bcur es ru _pd),
       e@(EpochNo e_)
       ) <-
     judgmentContext
@@ -95,9 +93,8 @@ newEpochTransition = do
 
       es'' <- trans @(MIR era) $ TRC ((), es', ())
       es''' <- trans @(EPOCH era) $ TRC ((), es'', e)
-      let EpochState _acnt ss _ls _pr pp _ = es'''
+      let EpochState _acnt ss _ls _pr _ _ = es'''
           pd' = calculatePoolDistr (_pstakeSet ss)
-      osched' <- liftSTS $ overlaySchedule e gkeys pp
       pure $
         NewEpochState
           e
@@ -106,7 +103,6 @@ newEpochTransition = do
           es'''
           SNothing
           pd'
-          osched'
 
 calculatePoolDistr :: SnapShot era -> PoolDistr era
 calculatePoolDistr (SnapShot (Stake stake) delegs poolParams) =
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Overlay.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Overlay.hs
index 29cd209d419..ce74a10993c 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Overlay.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Overlay.hs
@@ -24,10 +24,10 @@ import Cardano.Ledger.Era
 import Cardano.Prelude
   ( MonadError (..),
     NoUnexpectedThunks (..),
-    asks,
     unless,
   )
 import Control.Iterate.SetAlgebra (dom, eval, range)
+import Control.Monad.Trans.Reader (asks)
 import Control.State.Transition
 import Data.Coerce (coerce)
 import Data.Map.Strict (Map)
@@ -40,7 +40,9 @@ import Shelley.Spec.Ledger.BaseTypes
     Nonce,
     Seed,
     ShelleyBase,
+    UnitInterval,
     activeSlotCoeff,
+    epochInfo,
   )
 import Shelley.Spec.Ledger.BlockChain
   ( BHBody (..),
@@ -71,17 +73,16 @@ import Shelley.Spec.Ledger.Keys
 import Shelley.Spec.Ledger.OCert (OCertSignable)
 import Shelley.Spec.Ledger.OverlaySchedule
   ( OBftSlot (..),
-    OverlaySchedule,
     lookupInOverlaySchedule,
   )
 import Shelley.Spec.Ledger.STS.Ocert (OCERT, OCertEnv (..))
-import Shelley.Spec.Ledger.Slot (SlotNo)
+import Shelley.Spec.Ledger.Slot (SlotNo, epochInfoEpoch, epochInfoFirst)
 
 data OVERLAY era
 
 data OverlayEnv era
   = OverlayEnv
-      (OverlaySchedule era)
+      UnitInterval -- the decentralization paramater @d@ from the protocal parameters
       (PoolDistr era)
       (GenDelegs era)
       Nonce
@@ -245,17 +246,22 @@ overlayTransition ::
 overlayTransition =
   judgmentContext
     >>= \( TRC
-             ( OverlayEnv osched pd (GenDelegs genDelegs) eta0,
+             ( OverlayEnv dval pd (GenDelegs genDelegs) eta0,
                cs,
                bh@(BHeader bhb _)
                )
            ) -> do
         let vk = bheaderVk bhb
             vkh = hashKey vk
+            slot = bheaderSlotNo bhb
 
         asc <- liftSTS $ asks activeSlotCoeff
+        firstSlotNo <- liftSTS $ do
+          ei <- asks epochInfo
+          e <- epochInfoEpoch ei slot
+          epochInfoFirst ei e
 
-        case lookupInOverlaySchedule (bheaderSlotNo bhb) osched of
+        case lookupInOverlaySchedule firstSlotNo (Map.keys genDelegs) dval asc slot of
           Nothing ->
             praosVrfChecks eta0 pd asc bhb ?!: id
           Just NonActiveSlot ->
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Prtcl.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Prtcl.hs
index da64a0633c2..ab717cb4fdf 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Prtcl.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Prtcl.hs
@@ -41,6 +41,7 @@ import Shelley.Spec.Ledger.BaseTypes
   ( Nonce,
     Seed,
     ShelleyBase,
+    UnitInterval,
   )
 import Shelley.Spec.Ledger.BlockChain
   ( BHBody (..),
@@ -61,7 +62,6 @@ import Shelley.Spec.Ledger.Keys
     VRFSignable,
   )
 import Shelley.Spec.Ledger.OCert (OCertSignable)
-import Shelley.Spec.Ledger.OverlaySchedule (OverlaySchedule)
 import Shelley.Spec.Ledger.STS.Overlay (OVERLAY, OverlayEnv (..))
 import Shelley.Spec.Ledger.STS.Updn (UPDN, UpdnEnv (..), UpdnState (..))
 import Shelley.Spec.Ledger.Serialization (decodeRecordNamed)
@@ -103,7 +103,7 @@ instance Era era => NoUnexpectedThunks (PrtclState era)
 
 data PrtclEnv era
   = PrtclEnv
-      (OverlaySchedule era)
+      UnitInterval -- the decentralization paramater @d@ from the protocal parameters
       (PoolDistr era)
       (GenDelegs era)
       Nonce
@@ -161,7 +161,7 @@ prtclTransition ::
   TransitionRule (PRTCL era)
 prtclTransition = do
   TRC
-    ( PrtclEnv osched pd dms eta0,
+    ( PrtclEnv dval pd dms eta0,
       PrtclState cs etaV etaC,
       bh
       ) <-
@@ -179,7 +179,7 @@ prtclTransition = do
         )
   cs' <-
     trans @(OVERLAY era) $
-      TRC (OverlayEnv osched pd dms eta0, cs, bh)
+      TRC (OverlayEnv dval pd dms eta0, cs, bh)
 
   pure $
     PrtclState
diff --git a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Tick.hs b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Tick.hs
index 259ead0fff6..85a7930002a 100644
--- a/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Tick.hs
+++ b/shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/STS/Tick.hs
@@ -9,7 +9,6 @@
 
 module Shelley.Spec.Ledger.STS.Tick
   ( TICK,
-    TickEnv (..),
     State,
     TickPredicateFailure (..),
     PredicateFailure,
@@ -22,17 +21,15 @@ import Control.Iterate.SetAlgebra (eval, (⨃))
 import Control.Monad.Trans.Reader (asks)
 import Control.State.Transition
 import qualified Data.Map.Strict as Map
-import Data.Set (Set)
 import GHC.Generics (Generic)
 import Shelley.Spec.Ledger.BaseTypes (ShelleyBase, epochInfo)
-import Shelley.Spec.Ledger.Keys (GenDelegs (..), KeyHash, KeyRole (..))
+import Shelley.Spec.Ledger.Keys (GenDelegs (..))
 import Shelley.Spec.Ledger.LedgerState
   ( DPState (..),
     DState (..),
     EpochState (..),
     FutureGenDeleg (..),
     LedgerState (..),
-    NewEpochEnv (..),
     NewEpochState (..),
   )
 import Shelley.Spec.Ledger.STS.NewEpoch (NEWEPOCH)
@@ -41,9 +38,6 @@ import Shelley.Spec.Ledger.Slot (SlotNo, epochInfoEpoch)
 
 data TICK era
 
-data TickEnv era
-  = TickEnv (Set (KeyHash 'Genesis era))
-
 data TickPredicateFailure era
   = NewEpochFailure (PredicateFailure (NEWEPOCH era)) -- Subtransition Failures
   | RupdFailure (PredicateFailure (RUPD era)) -- Subtransition Failures
@@ -61,7 +55,7 @@ instance
   type
     Signal (TICK era) =
       SlotNo
-  type Environment (TICK era) = TickEnv era
+  type Environment (TICK era) = ()
   type BaseM (TICK era) = ShelleyBase
   type PredicateFailure (TICK era) = TickPredicateFailure era
 
@@ -102,16 +96,14 @@ bheadTransition ::
   (Era era) =>
   TransitionRule (TICK era)
 bheadTransition = do
-  TRC (TickEnv gkeys, nes@(NewEpochState _ bprev _ es _ _ _), slot) <-
+  TRC ((), nes@(NewEpochState _ bprev _ es _ _), slot) <-
     judgmentContext
 
   epoch <- liftSTS $ do
     ei <- asks epochInfo
     epochInfoEpoch ei slot
 
-  nes' <-
-    trans @(NEWEPOCH era) $
-      TRC (NewEpochEnv slot gkeys, nes, epoch)
+  nes' <- trans @(NEWEPOCH era) $ TRC ((), nes, epoch)
 
   ru'' <- trans @(RUPD era) $ TRC (RupdEnv bprev es, nesRu nes', slot)
 
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/bench/BenchValidation.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/bench/BenchValidation.hs
index 4b77a239f02..60f36fde06d 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/bench/BenchValidation.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/bench/BenchValidation.hs
@@ -172,7 +172,7 @@ instance Show UpdateInputs where
   show (UpdateInputs _globals vl bh st) = show vl ++ "\n" ++ show bh ++ "\n" ++ show st
 
 instance NFData (LedgerView era) where
-  rnf (LedgerView _pp _ov _pool _delegs) = ()
+  rnf (LedgerView _pp _pool _delegs) = ()
 
 instance Era era => NFData (BHeader era) where
   rnf (BHeader _ _) = ()
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/shelley-spec-ledger-test.cabal b/shelley/chain-and-ledger/shelley-spec-ledger-test/shelley-spec-ledger-test.cabal
index d436693c26f..719d7eb4d95 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/shelley-spec-ledger-test.cabal
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/shelley-spec-ledger-test.cabal
@@ -114,6 +114,7 @@ test-suite shelley-spec-ledger-test
       Test.Shelley.Spec.Ledger.Examples.PoolReReg
       Test.Shelley.Spec.Ledger.Examples.Updates
       Test.Shelley.Spec.Ledger.Fees
+      Test.Shelley.Spec.Ledger.LegacyOverlay
       Test.Shelley.Spec.Ledger.MultiSigExamples
       Test.Shelley.Spec.Ledger.PropertyTests
       Test.Shelley.Spec.Ledger.Rewards
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Generator/Block.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Generator/Block.hs
index 84b3ee3bd1c..c920cc4f334 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Generator/Block.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Generator/Block.hs
@@ -43,7 +43,7 @@ import Shelley.Spec.Ledger.Keys
     hashKey,
   )
 import Shelley.Spec.Ledger.OCert (KESPeriod (..), currentIssueNo, kesPeriod)
-import Shelley.Spec.Ledger.OverlaySchedule
+import Shelley.Spec.Ledger.OverlaySchedule (lookupInOverlaySchedule)
 import Shelley.Spec.Ledger.STS.Prtcl (PrtclState (..))
 import Shelley.Spec.Ledger.STS.Tickn (TicknState (..))
 import Shelley.Spec.Ledger.Slot (SlotNo (..))
@@ -89,7 +89,7 @@ genBlock
             $ selectNextSlotWithLeader ge origChainState firstConsideredSlot
 
     -- Now we need to compute the KES period and get the set of hot keys.
-    let NewEpochState _ _ _ es _ _ _ = chainNes chainSt
+    let NewEpochState _ _ _ es _ _ = chainNes chainSt
         EpochState acnt _ ls _ pp _ = es
         kp@(KESPeriod kesPeriod_) = runShelleyBase $ kesPeriod nextSlot
         cs = chainOCertIssue chainSt
@@ -174,7 +174,7 @@ selectNextSlotWithLeader
         Maybe (ChainState era, AllIssuerKeys era 'BlockIssuer)
       selectLeaderForSlot slotNo =
         (chainSt,)
-          <$> case lookupInOverlaySchedule slotNo overlaySched of
+          <$> case lookupInOverlaySchedule firstEpochSlot (Map.keys cores) d f slotNo of
             Nothing ->
               coerce
                 <$> List.find
@@ -190,16 +190,17 @@ selectNextSlotWithLeader
         where
           chainSt = tickChainState slotNo origChainState
           epochNonce = chainEpochNonce chainSt
-          overlaySched = nesOsched $ chainNes chainSt
           poolDistr = unPoolDistr . nesPd . chainNes $ chainSt
           dpstate = (_delegationState . esLState . nesEs . chainNes) chainSt
           (GenDelegs cores) = (_genDelegs . _dstate) dpstate
+          firstEpochSlot = slotFromEpoch (epochFromSlotNo slotNo)
+          f = activeSlotCoeff testGlobals
+          d = (_d . esPp . nesEs . chainNes) chainSt
 
           isLeader poolHash vrfKey =
             let y = VRF.evalCertified @(VRF (Crypto era)) () (mkSeed seedL slotNo epochNonce) vrfKey
                 stake = maybe 0 individualPoolStake $ Map.lookup poolHash poolDistr
-                f = activeSlotCoeff testGlobals
-             in case lookupInOverlaySchedule slotNo overlaySched of
+             in case lookupInOverlaySchedule firstEpochSlot (Map.keys cores) d f slotNo of
                   Nothing -> checkLeaderValue (VRF.certifiedOutput y) stake f
                   Just (ActiveSlot x) | coerceKeyRole x == poolHash -> True
                   _ -> False
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Generator/Trace/Chain.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Generator/Trace/Chain.hs
index 7259f548b96..a90a98b7b24 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Generator/Trace/Chain.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Generator/Trace/Chain.hs
@@ -29,7 +29,7 @@ import Control.State.Transition.Trace.Generator.QuickCheck
   )
 import Data.Functor.Identity (runIdentity)
 import Data.Map.Strict (Map)
-import qualified Data.Map.Strict as Map (elems, fromList, keysSet)
+import qualified Data.Map.Strict as Map (elems, fromList)
 import Data.Proxy
 import Numeric.Natural (Natural)
 import Shelley.Spec.Ledger.API
@@ -51,7 +51,6 @@ import Shelley.Spec.Ledger.Keys
     coerceKeyRole,
   )
 import Shelley.Spec.Ledger.LedgerState (esAccountState, nesEs, _treasury)
-import Shelley.Spec.Ledger.OverlaySchedule (overlaySchedule)
 import Shelley.Spec.Ledger.STS.Chain (chainNes, initialShelleyState)
 import qualified Shelley.Spec.Ledger.STS.Chain as STS (ChainState (ChainState))
 import Shelley.Spec.Ledger.Slot (BlockNo (..), EpochNo (..), SlotNo (..))
@@ -67,7 +66,7 @@ import Test.Shelley.Spec.Ledger.Generator.Core (GenEnv (..))
 import Test.Shelley.Spec.Ledger.Generator.Presets (genUtxo0, genesisDelegs0)
 import Test.Shelley.Spec.Ledger.Generator.Update (genPParams)
 import Test.Shelley.Spec.Ledger.Shrinkers (shrinkBlock)
-import Test.Shelley.Spec.Ledger.Utils (maxLLSupply, mkHash, runShelleyBase)
+import Test.Shelley.Spec.Ledger.Utils (maxLLSupply, mkHash)
 
 -- The CHAIN STS at the root of the STS allows for generating blocks of transactions
 -- with meaningful delegation certificates, protocol and application updates, withdrawals etc.
@@ -105,12 +104,6 @@ mkGenesisChainState constants (IRC _slotNo) = do
   utxo0 <- genUtxo0 constants
 
   pParams <- genPParams constants
-  let osched_ =
-        runShelleyBase $
-          overlaySchedule
-            epoch0
-            (Map.keysSet delegs0)
-            pParams
 
   pure . Right . withRewards $
     initialShelleyState
@@ -119,7 +112,6 @@ mkGenesisChainState constants (IRC _slotNo) = do
       utxo0
       (maxLLSupply Val.~~ balance utxo0)
       delegs0
-      osched_
       pParams
       (hashHeaderToNonce (lastByronHeaderHash p))
   where
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Serialisation/Generators.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Serialisation/Generators.hs
index 24572127c1b..1000151e035 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Serialisation/Generators.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Serialisation/Generators.hs
@@ -38,7 +38,7 @@ import qualified Cardano.Crypto.Hash as Hash
 import Cardano.Ledger.Crypto (DSIGN)
 import Cardano.Ledger.Era (Crypto, Era)
 import Cardano.Slotting.Block (BlockNo (..))
-import Cardano.Slotting.Slot (EpochNo (..), EpochSize (..), SlotNo (..))
+import Cardano.Slotting.Slot (EpochNo (..), SlotNo (..))
 import Control.Iterate.SetAlgebra (biMapFromList)
 import qualified Data.ByteString.Char8 as BS
 import Data.Coerce (coerce)
@@ -85,7 +85,6 @@ import Shelley.Spec.Ledger.MetaData
   )
 import qualified Shelley.Spec.Ledger.MetaData as MD
 import Shelley.Spec.Ledger.OCert (KESPeriod (..))
-import Shelley.Spec.Ledger.OverlaySchedule
 import Shelley.Spec.Ledger.PParams (ProtVer)
 import Shelley.Spec.Ledger.Rewards
   ( Likelihood (..),
@@ -578,16 +577,6 @@ instance Era era => Arbitrary (OBftSlot era) where
 instance Arbitrary ActiveSlotCoeff where
   arbitrary = mkActiveSlotCoeff <$> arbitrary
 
-instance Era era => Arbitrary (OverlaySchedule era) where
-  arbitrary =
-    -- Pick the parameters from specific random to avoid huge overlay schedules
-    overlayScheduleHelper
-      <$> (EpochSize <$> choose (1, 100))
-      <*> (SlotNo <$> choose (0, 100000))
-      <*> arbitrary
-      <*> arbitrary
-      <*> arbitrary
-
 instance Arbitrary Likelihood where
   arbitrary = Likelihood <$> arbitrary
 
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Combinators.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Combinators.hs
index 96e2f4e9b90..65f0685e5af 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Combinators.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Combinators.hs
@@ -92,7 +92,6 @@ import Shelley.Spec.Ledger.STS.Chain (ChainState (..))
 import Shelley.Spec.Ledger.TxBody (MIRPot (..), PoolParams (..), RewardAcnt (..), TxBody (..))
 import Shelley.Spec.Ledger.UTxO (txins, txouts)
 import qualified Cardano.Ledger.Val as Val
-import Test.Shelley.Spec.Ledger.Examples.Federation (overlayScheduleFor)
 import Test.Shelley.Spec.Ledger.Utils (epochFromSlotNo, getBlockNonce)
 
 -- | = Evolve Nonces - Frozen
@@ -579,7 +578,6 @@ newEpoch b cs = cs'
     nes' =
       nes
         { nesEL = e,
-          nesOsched = overlayScheduleFor e pp,
           nesBprev = (nesBcur nes),
           nesBcur = BlocksMade Map.empty
         }
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Federation.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Federation.hs
index baff8476415..db5f5d8b877 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Federation.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Federation.hs
@@ -15,7 +15,6 @@ module Test.Shelley.Spec.Ledger.Examples.Federation
     coreNodeIssuerKeys,
     coreNodeKeysBySchedule,
     genDelegs,
-    overlayScheduleFor,
   )
 where
 
@@ -37,15 +36,11 @@ import Shelley.Spec.Ledger.Keys
     hashVerKeyVRF,
     vKey,
   )
+import Shelley.Spec.Ledger.BaseTypes (Globals (..))
 import Shelley.Spec.Ledger.OCert (KESPeriod (..))
 import Shelley.Spec.Ledger.OverlaySchedule
-import Shelley.Spec.Ledger.PParams
-  ( PParams,
-  )
-import Shelley.Spec.Ledger.Slot
-  ( EpochNo (..),
-    SlotNo (..),
-  )
+import Shelley.Spec.Ledger.PParams (PParams, PParams' (..))
+import Shelley.Spec.Ledger.Slot (SlotNo (..))
 import Test.Shelley.Spec.Ledger.Generator.Core
   ( AllIssuerKeys (..),
   )
@@ -103,51 +98,36 @@ coreNodeIssuerKeys ::
   AllIssuerKeys era 'GenesisDelegate
 coreNodeIssuerKeys = snd . (coreNodes @era !!)
 
-coreNodeKeysForSlot ::
-  forall era.
-  (HasCallStack, Era era) =>
-  Map SlotNo (OBftSlot era) ->
-  Word64 ->
-  AllIssuerKeys era 'GenesisDelegate
-coreNodeKeysForSlot overlay slot = case Map.lookup (SlotNo slot) overlay of
-  Nothing -> error $ "coreNodesForSlot: Cannot find keys for slot " <> show slot
-  Just NonActiveSlot -> error $ "coreNodesForSlot: Non-active slot " <> show slot
-  Just (ActiveSlot gkh) ->
-    case Data.List.find (\((_, gk), _) -> hashKey gk == gkh) coreNodes of
-      Nothing ->
-        error $
-          "coreNodesForSlot: Cannot find key hash in coreNodes: "
-            <> show gkh
-      Just ((_, _), ak) -> ak
-
--- | === Overlay Schedule
--- Retrieve the overlay schedule for a given epoch and protocol parameters.
-overlayScheduleFor :: Era era => EpochNo -> PParams era -> OverlaySchedule era
-overlayScheduleFor e pp =
-  runShelleyBase $
-    overlaySchedule
-      e
-      (Map.keysSet genDelegs)
-      pp
-
 -- | === Keys by Overlay Schedule
 -- Retrieve all the keys associated with a core node
 -- for a given slot and protocol parameters.
 -- It will return an error if there is not a core node scheduled
 -- for the given slot.
 coreNodeKeysBySchedule ::
+  forall era.
   (HasCallStack, Era era) =>
   PParams era ->
   Word64 ->
   AllIssuerKeys era 'GenesisDelegate
-coreNodeKeysBySchedule = coreNodeKeysForSlot . fullOSched
+coreNodeKeysBySchedule pp slot =
+  case lookupInOverlaySchedule
+         firstSlot
+         (Map.keys genDelegs)
+         (_d pp)
+         (activeSlotCoeff testGlobals)
+         slot' of
+    Nothing -> error $ "coreNodesForSlot: Cannot find keys for slot " <> show slot
+    Just NonActiveSlot -> error $ "coreNodesForSlot: Non-active slot " <> show slot
+    Just (ActiveSlot gkh) ->
+      case Data.List.find (\((_, gk), _) -> hashKey gk == gkh) coreNodes of
+        Nothing ->
+          error $
+            "coreNodesForSlot: Cannot find key hash in coreNodes: "
+              <> show gkh
+        Just ((_, _), ak) -> ak
   where
-    fullOSched pp =
-      Map.unions $
-        [ overlayScheduleToMap $
-            overlayScheduleFor e pp
-          | e <- [0 .. 10]
-        ]
+    slot' = SlotNo slot
+    firstSlot = slotFromEpoch . epochFromSlotNo $ slot'
 
 -- | === Genesis Delegation Mapping
 -- The map from genesis/core node (verification) key hashes
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Init.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Init.hs
index ab1fa154598..b2c0376983d 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Init.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Examples/Init.hs
@@ -42,7 +42,7 @@ import Shelley.Spec.Ledger.Slot
   )
 import Shelley.Spec.Ledger.UTxO (UTxO (..), balance)
 import qualified Cardano.Ledger.Val as Val
-import Test.Shelley.Spec.Ledger.Examples.Federation (genDelegs, overlayScheduleFor)
+import Test.Shelley.Spec.Ledger.Examples.Federation (genDelegs)
 import Test.Shelley.Spec.Ledger.Utils (maxLLSupply, mkHash, unsafeMkUnitInterval)
 
 -- === Initial Protocol Parameters
@@ -105,6 +105,5 @@ initSt utxo =
     utxo
     (maxLLSupply Val.~~ (balance utxo))
     genDelegs
-    (overlayScheduleFor (EpochNo 0) ppEx)
     ppEx
     (nonce0 @era)
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/LegacyOverlay.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/LegacyOverlay.hs
new file mode 100644
index 00000000000..d4662e5d0d6
--- /dev/null
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/LegacyOverlay.hs
@@ -0,0 +1,94 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeApplications #-}
+
+module Test.Shelley.Spec.Ledger.LegacyOverlay
+  ( legacyOverlayTest,
+  )
+where
+
+import Cardano.Slotting.Slot
+import qualified Data.Map.Strict as Map
+import Data.Map.Strict (Map)
+import Data.Ratio ((%))
+import qualified Data.Set as Set
+import Data.Set (Set)
+import Shelley.Spec.Ledger.BaseTypes
+import Shelley.Spec.Ledger.Keys
+  ( KeyHash (..),
+    KeyRole (..),
+  )
+import Shelley.Spec.Ledger.OverlaySchedule (OBftSlot (..), classifyOverlaySlot, overlaySlots)
+import Shelley.Spec.Ledger.Slot
+import Test.Shelley.Spec.Ledger.ConcreteCryptoTypes (C)
+import Test.Shelley.Spec.Ledger.Examples.Federation (genDelegs)
+import Test.Shelley.Spec.Ledger.Utils
+import Test.Tasty.QuickCheck
+
+legacyOverlay ::
+  EpochSize ->
+  SlotNo ->
+  -- | First slot of the epoch
+  Set (KeyHash 'Genesis era) ->
+  UnitInterval ->
+  -- | Decentralization parameter @d@
+  ActiveSlotCoeff ->
+  Map SlotNo (OBftSlot era)
+legacyOverlay slotsPerEpoch firstSlotNo gkeys d asc
+  | dval == 0 = Map.empty
+  | otherwise = Map.union active inactive
+  where
+    dval = intervalValue d
+    numActive = dval * fromIntegral slotsPerEpoch
+    dInv = 1 / dval
+    ascValue = (intervalValue . activeSlotVal) asc
+    toRelativeSlotNo x = (Duration . floor) (dInv * fromInteger x)
+    toSlotNo x = firstSlotNo +* toRelativeSlotNo x
+    genesisSlots = [toSlotNo x | x <- [0 .. (floor numActive - 1)]]
+    numInactivePerActive = floor (1 / ascValue) - 1
+    activitySchedule = cycle (True : replicate numInactivePerActive False)
+    unassignedSched = zip activitySchedule genesisSlots
+    genesisCycle = if Set.null gkeys then [] else cycle (Set.toList gkeys)
+    active =
+      Map.fromList $
+        fmap
+          (\(gk, (_, s)) -> (s, ActiveSlot gk))
+          (zip genesisCycle (filter fst unassignedSched))
+    inactive =
+      Map.fromList $
+        fmap
+          (\x -> (snd x, NonActiveSlot))
+          (filter (not . fst) unassignedSched)
+
+mainnetEpochSize :: EpochSize
+mainnetEpochSize = EpochSize 432000
+
+makeConcreteOverlay ::
+  SlotNo -> -- first slot of the epoch
+  [KeyHash 'Genesis era] -> -- genesis Nodes
+  UnitInterval -> -- decentralization parameter
+  ActiveSlotCoeff -> -- active slot coefficent
+  EpochSize -> -- slots per epoch
+  Map SlotNo (OBftSlot era)
+makeConcreteOverlay start gkeys dval asc spe =
+  Map.fromList $
+    map
+      (\s -> (s, classifyOverlaySlot start gkeys dval asc s))
+      (overlaySlots start dval spe)
+
+legacyOverlayTest :: Property
+legacyOverlayTest = property $ do
+  d <- choose (0, 100)
+  e <- choose (0, 100)
+  let dval = unsafeMkUnitInterval (d % 100)
+      asc = mkActiveSlotCoeff . unsafeMkUnitInterval $ 1 % 20
+      EpochSize spe = mainnetEpochSize
+      start = SlotNo $ e * spe
+      os =
+        legacyOverlay
+          mainnetEpochSize
+          start
+          (Map.keysSet (genDelegs @C))
+          dval
+          asc
+  pure $ os === makeConcreteOverlay start (Map.keys (genDelegs @C)) dval asc mainnetEpochSize
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/PropertyTests.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/PropertyTests.hs
index 33868720478..94fc40405dc 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/PropertyTests.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/PropertyTests.hs
@@ -8,6 +8,7 @@ import Test.Shelley.Spec.Ledger.Address.Bootstrap
   ( bootstrapHashTest,
   )
 import Test.Shelley.Spec.Ledger.ByronTranslation (testGroupByronTranslation)
+import Test.Shelley.Spec.Ledger.LegacyOverlay (legacyOverlayTest)
 import Test.Shelley.Spec.Ledger.Rules.ClassifyTraces
   ( onlyValidChainSignalsAreGenerated,
     onlyValidLedgerSignalsAreGenerated,
@@ -55,7 +56,8 @@ minimalPropertyTests =
         "Deserialize stake address reference"
         [ TQC.testProperty "wstake reference from bytestrings" propDeserializeAddrStakeReference,
           TQC.testProperty "stake reference from short bytestring" propDeserializeAddrStakeReferenceShortIncrediblyLongName
-        ]
+        ],
+      TQC.testProperty "legacy overlay schedule" legacyOverlayTest
     ]
 
 -- | 'TestTree' of property-based testing properties.
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Rules/TestChain.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Rules/TestChain.hs
index 5dd4b373d36..55bc666c88f 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Rules/TestChain.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Rules/TestChain.hs
@@ -50,7 +50,6 @@ import Shelley.Spec.Ledger.LedgerState
 import Shelley.Spec.Ledger.STS.Chain (ChainState (..), totalAda, totalAdaPots)
 import Shelley.Spec.Ledger.STS.Ledger (LedgerEnv (..))
 import Shelley.Spec.Ledger.STS.PoolReap (PoolreapState (..))
-import Shelley.Spec.Ledger.STS.Tick (TickEnv (TickEnv))
 import Shelley.Spec.Ledger.Tx
 import Shelley.Spec.Ledger.TxBody
 import Shelley.Spec.Ledger.UTxO (balance, totalDeposits, txins, txouts, pattern UTxO)
@@ -465,7 +464,7 @@ chainSstWithTick ledgerTr =
           _
           b@(Block bh _)
         ) =
-        case runShelleyBase (applySTSTest @(TICK C) (TRC (TickEnv (getGKeys nes), nes, (bheaderSlotNo . bhbody) bh))) of
+        case runShelleyBase (applySTSTest @(TICK C) (TRC ((), nes, (bheaderSlotNo . bhbody) bh))) of
           Left pf ->
             error ("chainSstWithTick.applyTick Predicate failure " <> show pf)
           Right nes' ->
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Serialisation/Golden/Encoding.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Serialisation/Golden/Encoding.hs
index a4931aca6f9..26d548cfab2 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Serialisation/Golden/Encoding.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/Serialisation/Golden/Encoding.hs
@@ -33,7 +33,6 @@ import qualified Data.ByteString.Base16.Lazy as Base16
 import qualified Data.ByteString.Char8 as BS (pack)
 import Data.Coerce (coerce)
 import Data.IP (toIPv4)
-import Data.List.NonEmpty (NonEmpty ((:|)))
 import qualified Data.Map.Strict as Map
 import qualified Data.Maybe as Maybe (fromJust)
 import Data.Proxy
@@ -131,7 +130,6 @@ import Shelley.Spec.Ledger.LedgerState
   )
 import qualified Shelley.Spec.Ledger.MetaData as MD
 import Shelley.Spec.Ledger.OCert (KESPeriod (..), OCertSignable (..), pattern OCert)
-import Shelley.Spec.Ledger.OverlaySchedule
 import Shelley.Spec.Ledger.PParams
   ( PParams' (..),
     PParamsUpdate,
@@ -1296,8 +1294,6 @@ tests =
             ) ::
               StrictMaybe (RewardUpdate C)
           pd = (PoolDistr Map.empty) :: PoolDistr C
-          compactOs = Map.singleton (ActiveSlot (testGKeyHash p)) (SlotNo 1 :| [])
-          os = decompactOverlaySchedule compactOs
           nes =
             NewEpochState
               e
@@ -1306,18 +1302,16 @@ tests =
               es
               ru
               pd
-              os
        in checkEncodingCBOR
             "new_epoch_state"
             nes
-            ( T (TkListLen 7)
+            ( T (TkListLen 6)
                 <> S e
                 <> S (BlocksMade bs)
                 <> S (BlocksMade bs)
                 <> S es
                 <> S ru
                 <> S pd
-                <> S compactOs
             )
     ]
   where
diff --git a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/UnitTests.hs b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/UnitTests.hs
index ff55144ea4d..2d464905baa 100644
--- a/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/UnitTests.hs
+++ b/shelley/chain-and-ledger/shelley-spec-ledger-test/test/Test/Shelley/Spec/Ledger/UnitTests.hs
@@ -60,7 +60,6 @@ import Shelley.Spec.Ledger.LedgerState
     _dstate,
     _rewards,
   )
-import Shelley.Spec.Ledger.OverlaySchedule
 import Shelley.Spec.Ledger.PParams
 import Shelley.Spec.Ledger.STS.Delegs (DelegsPredicateFailure (..))
 import Shelley.Spec.Ledger.STS.Delpl (DelplPredicateFailure (..))
@@ -155,26 +154,6 @@ pp =
       _minPoolCost = Coin 100
     }
 
-testOverlayScheduleZero :: Assertion
-testOverlayScheduleZero =
-  let os =
-        runShelleyBase $
-          overlaySchedule
-            (EpochNo 0)
-            mempty
-            (emptyPParams {_d = unsafeMkUnitInterval 0})
-   in assertBool "Overlay schedule is not empty" (overlayScheduleIsEmpty os)
-
-testNoGenesisOverlay :: Assertion
-testNoGenesisOverlay =
-  let os =
-        runShelleyBase $
-          overlaySchedule
-            (EpochNo 0)
-            mempty
-            (emptyPParams {_d = unsafeMkUnitInterval 0.5})
-   in assertBool "Overlay schedule is not empty" (overlayScheduleIsEmpty os)
-
 testVRFCheckWithActiveSlotCoeffOne :: Assertion
 testVRFCheckWithActiveSlotCoeffOne =
   checkLeaderValue
@@ -187,11 +166,7 @@ testsPParams :: TestTree
 testsPParams =
   testGroup
     "Test the protocol parameters."
-    [ testCase "Overlay Schedule when d is zero" $
-        testOverlayScheduleZero,
-      testCase "generate overlay schedule without genesis nodes" $
-        testNoGenesisOverlay,
-      testCase "VRF checks when the activeSlotCoeff is one" $
+    [ testCase "VRF checks when the activeSlotCoeff is one" $
         testVRFCheckWithActiveSlotCoeffOne
     ]