diff --git a/textile/features.textile b/textile/features.textile
index 131f7be8..171dbd43 100644
--- a/textile/features.textile
+++ b/textile/features.textile
@@ -1914,6 +1914,7 @@ h4. ConnectionDetails
 ** @(CD2g)@ @serverId@ string is a unique identifier for the front-end server that the client has connected to. This server ID is only used for the purposes of debugging
 ** @(CD2h)@ @maxIdleInterval@ is the maximum length of time in milliseconds that the server will allow no activity to occur in the server->client direction. After such a period of inactivity, the server will send a @HEARTBEAT@ or transport-level ping to the client. If the value is 0, the server will allow arbitrarily-long levels of inactivity.
 ** @(CD2i)@ @objectsGCGracePeriod@ integer - the length of time, in milliseconds, that the client library must wait before releasing resources for tombstoned objects and map entries (see "RTO10":../objects-features#RTO10)
+** @(CD2j)@ @siteCode@ string - the identifier for the regional site that the connection is connected to. This is used when applying operations on ACK to perform the @siteTimeserials@ check (see "RTO3d":../objects-features#RTO3d, "RTO20a":../objects-features#RTO20a)
 h4. ChannelProperties
 * @(CP1)@ properties of a channel and its state
 * @(CP2)@ The attributes of @ChannelProperties@ consist of:
@@ -2658,6 +2659,7 @@ class ConnectionDetails: // CD*, internal
   serverId: String // CD2g
   maxIdleInterval: Duration // CD2h
   objectsGCGracePeriod: Int // CD2i
+  siteCode: String // CD2j
 
 class Message: // TM*
   constructor(name: String?, data: Data?) // TM4
diff --git a/textile/objects-features.textile b/textile/objects-features.textile
index abffa805..0862a132 100644
--- a/textile/objects-features.textile
+++ b/textile/objects-features.textile
@@ -102,6 +102,13 @@ h3(#realtime-objects). RealtimeObjects
 ** @(RTO3a)@ @ObjectsPool@ is a @Dict<String, LiveObject>@ - a map of @LiveObject@s keyed by "@objectId@":../features#OST2a string
 ** @(RTO3b)@ It must always contain a @LiveMap@ object with id @root@
 *** @(RTO3b1)@ Upon initialization of the @ObjectsPool@, create a new @LiveMap@ (per "RTLM4":#RTLM4) with @objectId@ set to @root@ and add it to the @ObjectsPool@
+** @(RTO3c)@ An internal @appliedOnAckSerials@ set should be used to maintain a sliding window of serials for operations that have been applied on ACK but for which the echo has not yet been received
+*** @(RTO3c1)@ @appliedOnAckSerials@ is a @Set<String>@ - a set of "@serial@":../features#OM2h strings
+*** @(RTO3c2)@ It is empty upon @RealtimeObjects@ initialization
+** @(RTO3d)@ The @RealtimeObjects@ instance must store the @siteCode@ of the site that the connection is connected to
+*** @(RTO3d1)@ The @siteCode@ is obtained from the @ConnectionDetails@ received in a @CONNECTED@ @ProtocolMessage@, per "RTN24":../features#RTN24
+*** @(RTO3d2)@ The @siteCode@ value is updated whenever a new @CONNECTED@ @ProtocolMessage@ is received
+*** @(RTO3d3)@ The @siteCode@ is used when applying operations on ACK to perform the @siteTimeserials@ check as described in "RTO20a":#RTO20a
 * @(RTO4)@ When a channel @ATTACHED@ @ProtocolMessage@ is received, the @ProtocolMessage@ may contain a @HAS_OBJECTS@ bit flag indicating that it will perform an objects sync, see "TR3":../features#TR3 . Note that this does not imply that objects are definitely present on the channel, only that there may be; the @OBJECT_SYNC@ message may be empty
 ** @(RTO4c)@ Upon receipt of an @ATTACHED@ @ProtocolMessage@, the "RTO17":#RTO17 sync state must transition to @SYNCING@ if not already @SYNCING@. This must occur before performing any "RTO4b":#RTO4b actions.
 ** @(RTO4a)@ If the @HAS_OBJECTS@ flag is 1, the server will shortly perform an @OBJECT_SYNC@ sequence as described in "RTO5":#RTO5
@@ -111,6 +118,8 @@ h3(#realtime-objects). RealtimeObjects
 **** @(RTO4b2a)@ Emit a @LiveMapUpdate@ object for the @LiveMap@ with ID @root@, with @LiveMapUpdate.update@ consisting of entries for the keys that were removed, each set to @removed@
 *** @(RTO4b3)@ The @SyncObjectsPool@ list must be cleared
 *** @(RTO4b5)@ The @BufferedObjectOperations@ list must be cleared
+*** @(RTO4b6)@ The @appliedOnAckSerials@ set must be cleared
+*** @(RTO4b7)@ The @BufferedAcks@ list must be cleared (see "RTO21":#RTO21)
 *** @(RTO4b4)@ Perform the actions for objects sync completion as described in "RTO5c":#RTO5c
 * @(RTO5)@ The realtime system reserves the right to initiate an objects sync of the objects on a channel at any point once a channel is attached. A server initiated objects sync provides Ably with a means to send a complete list of objects present on the channel at any point
 ** @(RTO5d)@ If an @OBJECT_SYNC@ @ProtocolMessage@ is received and "@ObjectMessage.object@":../features#TR4r is null or omitted, the client library should skip processing that @ProtocolMessage@
@@ -120,6 +129,8 @@ h3(#realtime-objects). RealtimeObjects
 *** @(RTO5a2)@ If a new sequence id is sent from Ably, the client library must treat it as the start of a new objects sync sequence, and any previous in-flight sync must be discarded:
 **** @(RTO5a2a)@ The @SyncObjectsPool@ list must be cleared
 **** @(RTO5a2b)@ The @BufferedObjectOperations@ list must be cleared
+**** @(RTO5a2c)@ The @appliedOnAckSerials@ set must be cleared
+**** @(RTO5a2d)@ The @BufferedAcks@ list must be cleared (see "RTO21":#RTO21)
 *** @(RTO5a3)@ If the sequence id matches the previously received sequence id, the client library should continue the sync process
 *** @(RTO5a4)@ The objects sync sequence for that sequence identifier is considered complete once the cursor is empty; that is when the @channelSerial@ looks like @<sequence id>:@
 *** @(RTO5a5)@ An @OBJECT_SYNC@ may also be sent with no @channelSerial@ attribute. In this case, the sync data is entirely contained within the @ProtocolMessage@
@@ -138,9 +149,11 @@ h3(#realtime-objects). RealtimeObjects
 **** @(RTO5c2a)@ The object with ID @root@ must not be removed from @ObjectsPool@, as per "RTO3b":#RTO3b
 *** @(RTO5c7)@ For each previously existing object that was updated as a result of "RTO5c1a":#RTO5c1a, emit the corresponding stored @LiveObjectUpdate@ object from "RTO5c1a2":#RTO5c1a2
 *** @(RTO5c6)@ @ObjectMessages@ stored in the @BufferedObjectOperations@ list are applied as described in "RTO9":#RTO9
+*** @(RTO5c9)@ Apply buffered ACKs stored in the @BufferedAcks@ list as described in "RTO21c":#RTO21c
 *** @(RTO5c3)@ Clear any stored sync sequence identifiers and cursor values
 *** @(RTO5c4)@ The @SyncObjectsPool@ must be cleared
 *** @(RTO5c5)@ The @BufferedObjectOperations@ list must be cleared
+*** @(RTO5c10)@ The @BufferedAcks@ list must be cleared
 *** @(RTO5c8)@ The "RTO17":#RTO17 sync state must transition to @SYNCED@
 * @(RTO6)@ Certain object operations may require creating a zero-value object if one does not already exist in the internal @ObjectsPool@ for the given @objectId@. This can be done as follows:
 ** @(RTO6a)@ If an object with @objectId@ exists in @ObjectsPool@, do not create a new object
@@ -157,6 +170,9 @@ h3(#realtime-objects). RealtimeObjects
 * @(RTO9)@ @OBJECT@ messages can be applied to @RealtimeObjects@ in the following way:
 ** @(RTO9a)@ For each @ObjectMessage@ in the provided list:
 *** @(RTO9a1)@ If @ObjectMessage.operation@ is null or omitted, log a warning indicating that an unsupported object operation message has been received, and discard the current @ObjectMessage@ without taking any action
+*** @(RTO9a0)@ If the @appliedOnAckSerials@ set contains @ObjectMessage.serial@, this operation has already been applied on ACK:
+**** @(RTO9a0a)@ Remove @ObjectMessage.serial@ from the @appliedOnAckSerials@ set
+**** @(RTO9a0b)@ Do not proceed with applying this operation. This handles the case where the operation has already been applied on ACK
 *** @(RTO9a2)@ The @ObjectMessage.operation.action@ field (see "@ObjectOperationAction@":../features#OOP2) determines the type of operation to apply:
 **** @(RTO9a2a)@ If @ObjectMessage.operation.action@ is one of the following: @MAP_CREATE@, @MAP_SET@, @MAP_REMOVE@, @COUNTER_CREATE@, @COUNTER_INC@, or @OBJECT_DELETE@, then:
 ***** @(RTO9a2a1)@ If it does not already exist, create a zero-value @LiveObject@ in the internal @ObjectsPool@ per "RTO6":#RTO6 using the @objectId@ from @ObjectMessage.operation.objectId@
@@ -222,6 +238,34 @@ h3(#realtime-objects). RealtimeObjects
 *** @(RTO18f1)@ The subscription object includes an @off@ function
 *** @(RTO18f2)@ Calling @off@ deregisters the listener previously registered by the user via the corresponding @on@ call
 * @(RTO19)@ @RealtimeObjects#off@ function - deregisters an event listener previously registered via @RealtimeObjects#on@ ("RTO18":#RTO18)
+* @(RTO20)@ Applying operations on ACK - when the client library receives an @ACK@ @ProtocolMessage@ for an operation that it published, it should apply that operation to the local objects immediately, before receiving the echo of that operation over the Realtime connection. This ensures that when the promise returned by an operation method (such as @LiveMap#set@) resolves, the operation has already been applied to the local objects
+** @(RTO20a)@ When an @ACK@ @ProtocolMessage@ is received for a published @ObjectMessage@:
+*** @(RTO20a1)@ Extract the operation's @serial@ from the @ProtocolMessage.msgSerial@ field (see "RTL17":../features#RTL17)
+*** @(RTO20a2)@ If the "RTO17":#RTO17 sync state is not @SYNCED@, buffer the ACK as described in "RTO21":#RTO21 instead of applying it immediately
+*** @(RTO20a3)@ Perform the standard @siteTimeserials@ check using this @serial@ and the @siteCode@ stored in @RealtimeObjects@ per "RTO3d":#RTO3d:
+**** @(RTO20a3a)@ For each @ObjectMessage@ that was published in the original @OBJECT@ @ProtocolMessage@, get the target @LiveObject@ from the @ObjectsPool@ using @ObjectMessage.operation.objectId@
+**** @(RTO20a3b)@ For each target @LiveObject@, check if the operation can be applied using "@LiveObject.canApplyOperation@":#RTLO4a, passing in a synthetic @ObjectMessage@ with @ObjectMessage.serial@ set to the @serial@ from "RTO20a1":#RTO20a1, and @ObjectMessage.siteCode@ set to the @siteCode@ from "RTO3d":#RTO3d
+**** @(RTO20a3c)@ If the check disallows the application of the operation for any of the target objects, do not proceed with applying any of the operations on ACK. This handles the case where the operation has already been applied due to receiving the echo before the ACK
+*** @(RTO20a4)@ For each @ObjectMessage@ that was published in the original @OBJECT@ @ProtocolMessage@:
+**** @(RTO20a4a)@ Apply the operation to the target @LiveObject@ per "RTO9a2a":#RTO9a2a
+**** @(RTO20a4b)@ Note that the @siteTimeserials@ for the object must not be updated when applying on ACK, as they will be updated when the echo is received
+*** @(RTO20a5)@ Insert the operation's @serial@ into the @appliedOnAckSerials@ set
+*** @(RTO20a6)@ Resolve the promise or callback associated with the publish operation, indicating success to the caller
+* @(RTO21)@ Buffering ACKs during SYNCING state - when the @RealtimeObjects@ sync state is @SYNCING@, ACKs for published operations must be buffered and applied after the sync completes. This is necessary because applying operations on ACK during a sync could result in those operations being applied to stale object state
+** @(RTO21a)@ An internal @BufferedAcks@ list should be used to store ACKs that are received while the sync state is @SYNCING@
+*** @(RTO21a1)@ @BufferedAcks@ is an array of @BufferedAck@ instances
+*** @(RTO21a2)@ Each @BufferedAck@ contains:
+**** @(RTO21a2a)@ @serial@ - the @serial@ value from the ACK @ProtocolMessage@
+**** @(RTO21a2b)@ @objectMessages@ - the array of @ObjectMessage@ instances that were published in the original operation
+*** @(RTO21a3)@ @BufferedAcks@ is empty upon @RealtimeObjects@ initialization
+** @(RTO21b)@ When an ACK is received and the sync state is @SYNCING@ (per "RTO20a2":#RTO20a2):
+*** @(RTO21b1)@ Create a @BufferedAck@ instance with the @serial@ and @objectMessages@ from the ACK
+*** @(RTO21b2)@ Add the @BufferedAck@ to the @BufferedAcks@ list
+*** @(RTO21b3)@ Resolve the promise or callback associated with the publish operation, indicating success to the caller. This resolution must have no impact on the buffering of the ACK; the operation is not applied to local objects until after the sync completes
+** @(RTO21c)@ Applying buffered ACKs - when the sync completes (per "RTO5c9":#RTO5c9), apply all buffered ACKs:
+*** @(RTO21c1)@ For each @BufferedAck@ in the @BufferedAcks@ list:
+**** @(RTO21c1a)@ Apply the ACK as described in "RTO20a":#RTO20a, skipping the check in "RTO20a2":#RTO20a2 (since the sync state is now @SYNCED@)
+**** @(RTO21c1b)@ Skip the promise resolution step in "RTO20a6":#RTO20a6, as the promise was already resolved when the ACK was buffered
 
 h3(#liveobject). LiveObject
 
@@ -317,11 +361,13 @@ h3(#livecounter). LiveCounter
 *** @(RTLC6e1)@ Return a @LiveCounterUpdate@ object with @LiveCounterUpdate.noop@ set to @true@, indicating that no update was made to the object
 ** @(RTLC6f)@ If @ObjectState.tombstone@ is @true@, tombstone the current @LiveCounter@ using "@LiveObject.tombstone@":#RTLO4e, passing in the outer @ObjectMessage@ for the @ObjectState@. Finish processing the @ObjectState@
 *** @(RTLC6f1)@ Return a @LiveCounterUpdate@ object with @LiveCounterUpdate.update.amount@ set to the negative @data@ value that this @LiveCounter@ had before being tombstoned
+** @(RTLC6g)@ Store the current @data@ value as @previousData@ for use in "RTLC6h":#RTLC6h
 ** @(RTLC6b)@ Set the private flag @createOperationIsMerged@ to @false@
 ** @(RTLC6c)@ Set @data@ to the value of @ObjectState.counter.count@, or to 0 if it does not exist
-** @(RTLC6d)@ If @ObjectState.createOp@ is present, merge the initial value into the @LiveCounter@ as described in "RTLC10":#RTLC10, passing in the @ObjectState.createOp@ instance
+** @(RTLC6d)@ If @ObjectState.createOp@ is present, merge the initial value into the @LiveCounter@ as described in "RTLC10":#RTLC10, passing in the @ObjectState.createOp@ instance. Discard the @LiveCounterUpdate@ object returned by the merge operation
 *** @(RTLC6d1)@ This clause has been replaced by "RTLC10a":#RTLC10a
 *** @(RTLC6d2)@ This clause has been replaced by "RTLC10b":#RTLC10b
+** @(RTLC6h)@ Calculate the diff between @previousData@ from "RTLC6g":#RTLC6g and the current @data@ per "RTLC14":#RTLC14, and return the resulting @LiveCounterUpdate@ object
 * @(RTLC7)@ An @ObjectOperation@ from @ObjectMessage.operation@ can be applied to a @LiveCounter@ by performing the following actions in order:
 ** @(RTLC7a)@ A client library may choose to implement this logic as a convenience method named @applyOperation@, which accepts an @ObjectMessage@ instance with an existing @ObjectMessage.operation@ object, with @ObjectMessage.operation.objectId@ matching the Object ID of this @LiveCounter@. This @ObjectMessage@ represents the operation to be applied to this @LiveCounter@
 ** @(RTLC7b)@ If @ObjectMessage.operation@ cannot be applied based on the result of "@LiveObject.canApplyOperation@":#RTLO4a, log a debug or trace message indicating that the operation cannot be applied because its serial value is not newer than the object's, and discard the @ObjectMessage@ without taking any further action
@@ -354,6 +400,11 @@ h3(#livecounter). LiveCounter
 ** @(RTLC10b)@ Set the private flag @createOperationIsMerged@ to @true@
 ** @(RTLC10c)@ If @ObjectOperation.counter.count@ exists, return a @LiveCounterUpdate@ object with @LiveCounterUpdate.update.amount@ set to @ObjectOperation.counter.count@
 ** @(RTLC10d)@ If @ObjectOperation.counter.count@ does not exist, return a @LiveCounterUpdate@ object with @LiveCounterUpdate.noop@ set to @true@
+* @(RTLC14)@ The diff between two @LiveCounter@ data values can be calculated in the following way:
+** @(RTLC14a)@ Expects the following arguments:
+*** @(RTLC14a1)@ @previousData@ @Number@ - the previous @data@ value
+*** @(RTLC14a2)@ @newData@ @Number@ - the new @data@ value
+** @(RTLC14b)@ Return a @LiveCounterUpdate@ object with @LiveCounterUpdate.update.amount@ set to @newData - previousData@
 
 h3(#livemap). LiveMap
 
@@ -446,17 +497,19 @@ h3(#livemap). LiveMap
 *** @(RTLM6e1)@ Return a @LiveMapUpdate@ object with @LiveMapUpdate.noop@ set to @true@, indicating that no update was made to the object
 ** @(RTLM6f)@ If @ObjectState.tombstone@ is @true@, tombstone the current @LiveMap@ using "@LiveObject.tombstone@":#RTLO4e, passing in the outer @ObjectMessage@ for the @ObjectState@. Finish processing the @ObjectState@
 *** @(RTLM6f1)@ Return a @LiveMapUpdate@ object with @LiveMapUpdate.update@ consisting of entries for the keys that were removed as a result of the object being tombstoned, each set to @removed@
+** @(RTLM6g)@ Store the current @data@ value as @previousData@ for use in "RTLM6h":#RTLM6h
 ** @(RTLM6b)@ Set the private flag @createOperationIsMerged@ to @false@
 ** @(RTLM6c)@ Set @data@ to @ObjectState.map.entries@, or to an empty map if it does not exist
 *** @(RTLM6c1)@ For each @ObjectsMapEntry@ with @ObjectsMapEntry.tombstone@ equal to @true@, additionally set the @ObjectsMapEntry.tombstonedAt@ field as follows:
 **** @(RTLM6c1a)@ Set it equal to @ObjectsMapEntry.serialTimestamp@ if it exists
 **** @(RTLM6c1b)@ Otherwise, set it to the current time using the local clock
 ***** @(RTLM6c1b1)@ Log a debug or trace message indicating that @ObjectsMapEntry.serialTimestamp@ was not provided and the local clock is being used instead for the tombstone timestamp
-** @(RTLM6d)@ If @ObjectState.createOp@ is present, merge the initial value into the @LiveMap@ as described in "RTLM17":#RTLM17, passing in the @ObjectState.createOp@ instance
+** @(RTLM6d)@ If @ObjectState.createOp@ is present, merge the initial value into the @LiveMap@ as described in "RTLM17":#RTLM17, passing in the @ObjectState.createOp@ instance. Discard the @LiveMapUpdate@ object returned by the merge operation
 *** @(RTLM6d1)@ This clause has been replaced by "RTLM17a":#RTLM17a
 **** @(RTLM6d1a)@ This clause has been replaced by "RTLM17a1":#RTLM17a1
 **** @(RTLM6d1b)@ This clause has been replaced by "RTLM17a2":#RTLM17a2
 *** @(RTLM6d2)@ This clause has been replaced by "RTLM17b":#RTLM17b
+** @(RTLM6h)@ Calculate the diff between @previousData@ from "RTLM6g":#RTLM6g and the current @data@ per "RTLM22":#RTLM22, and return the resulting @LiveMapUpdate@ object
 * @(RTLM15)@ An @ObjectOperation@ from @ObjectMessage.operation@ can be applied to a @LiveMap@ by performing the following actions in order:
 ** @(RTLM15a)@ A client library may choose to implement this logic as a convenience method named @applyOperation@, which accepts an @ObjectMessage@ instance with an existing @ObjectMessage.operation@ object, with @ObjectMessage.operation.objectId@ matching the Object ID of this @LiveMap@. This @ObjectMessage@ represents the operation to be applied to this @LiveMap@
 ** @(RTLM15b)@ If @ObjectMessage.operation@ cannot be applied based on the result of "@LiveObject.canApplyOperation@":#RTLO4a, log a debug or trace message indicating that the operation cannot be applied because its serial value is not newer than the object's, and discard the @ObjectMessage@ without taking any further action
@@ -536,6 +589,14 @@ h3(#livemap). LiveMap
 * @(RTLM19)@ The @LiveMap@ can be checked to determine whether it should release resources for its tombstoned @ObjectsMapEntry@ entries as follows:
 ** @(RTLM19a)@ For each @ObjectsMapEntry@ in the internal @data@:
 *** @(RTLM19a1)@ If @ObjectsMapEntry.tombstone@ is @true@, and the difference between the current time and @ObjectsMapEntry.tombstonedAt@ is greater than or equal to the "grace period":#RTO10b, remove the entry from the internal @data@ map and release resources for the corresponding @ObjectsMapEntry@ entity to allow it to be garbage collected
+* @(RTLM22)@ The diff between two @LiveMap@ data values can be calculated in the following way:
+** @(RTLM22a)@ Expects the following arguments:
+*** @(RTLM22a1)@ @previousData@ @Dict<String, ObjectsMapEntry>@ - the previous @data@ value
+*** @(RTLM22a2)@ @newData@ @Dict<String, ObjectsMapEntry>@ - the new @data@ value
+** @(RTLM22b)@ Return a @LiveMapUpdate@ object where @LiveMapUpdate.update@ is calculated by considering only the non-tombstoned entries from @previousData@ and @newData@. An entry is non-tombstoned if its @ObjectsMapEntry.tombstone@ field is @false@. The update is populated as follows:
+*** @(RTLM22b1)@ For each key that exists in the non-tombstoned entries of @previousData@ but does not exist in the non-tombstoned entries of @newData@, add the key to @LiveMapUpdate.update@ with the value @removed@
+*** @(RTLM22b2)@ For each key that exists in the non-tombstoned entries of @newData@ but does not exist in the non-tombstoned entries of @previousData@, add the key to @LiveMapUpdate.update@ with the value @updated@
+*** @(RTLM22b3)@ For each key that exists in the non-tombstoned entries of both @previousData@ and @newData@, perform a deep comparison of the entry data from @previousData@ and @newData@. If the data values differ, add the key to @LiveMapUpdate.update@ with the value @updated@
 
 h2(#idl). Interface Definition