diff --git a/include/ircd/m/sync.h b/include/ircd/m/sync.h
index c63e62a13..379d1569e 100644
--- a/include/ircd/m/sync.h
+++ b/include/ircd/m/sync.h
@@ -51,6 +51,7 @@ struct ircd::m::sync::item
 	handle _linear;
 	json::strung feature;
 	json::object opts;
+	bool phased;
 
   public:
 	string_view name() const;
@@ -77,6 +78,10 @@ struct ircd::m::sync::data
 	/// index is one beyond the vm::current_sequence and used for next_batch.
 	m::events::range range;
 
+	/// Whether to enable phased sync mode. The range.first will be <= 0
+	/// in this case, and only handlers with the phased feature
+	bool phased {false};
+
 	/// Statistics tracking. If null, stats won't be accumulated for the sync.
 	sync::stats *stats {nullptr};
 
diff --git a/ircd/m.cc b/ircd/m.cc
index 2fb18b9db..61f23561b 100644
--- a/ircd/m.cc
+++ b/ircd/m.cc
@@ -569,7 +569,7 @@ ircd::m::sync::loghead(const data &data)
 
 	return fmt::sprintf
 	{
-		headbuf, "%s %s %lu:%lu|%lu chunk:%zu sent:%s of %s in %s",
+		headbuf, "%s %s %ld:%lu|%lu chunk:%zu sent:%s of %s in %s",
 		remstr,
 		string_view{data.user.user_id},
 		data.range.first,
@@ -697,6 +697,10 @@ ircd::m::sync::item::item(std::string name,
 {
 	this->feature
 }
+,phased
+{
+	opts.get<bool>("phased", false)
+}
 {
 	log::debug
 	{
@@ -722,9 +726,22 @@ bool
 ircd::m::sync::item::polylog(data &data)
 try
 {
+	// Skip the item if disabled by configuration
 	if(!enable)
 		return false;
 
+	// Skip the item for phased-sync ranges if it's not phased-sync aware.
+	if(!phased && data.phased && int64_t(data.range.first) < 0L)
+	{
+		assert(data.phased);
+		return false;
+	}
+
+	// Skip the item for the initial-sync pass if it's phased-sync aware;
+	// it will be called for the first time at the next phase.
+	if(phased && data.phased && data.range.first == 0UL)
+		return false;
+
 	#ifdef RB_DEBUG
 	sync::stats stats
 	{
diff --git a/modules/client/sync.cc b/modules/client/sync.cc
index c72e6a6b3..56b0d1fcf 100644
--- a/modules/client/sync.cc
+++ b/modules/client/sync.cc
@@ -98,6 +98,13 @@ ircd::m::sync::linear_delta_max
 	{ "help",     linear_delta_max_help                },
 };
 
+decltype(ircd::m::sync::polylog_phased)
+ircd::m::sync::polylog_phased
+{
+	{ "name",     "ircd.client.sync.polylog.phased" },
+	{ "default",  true                              },
+};
+
 decltype(ircd::m::sync::polylog_only)
 ircd::m::sync::polylog_only
 {
@@ -145,18 +152,34 @@ ircd::m::sync::handle_get(client &client,
 		args.since, std::min(args.next_batch, m::vm::sequence::retired + 1)
 	};
 
-	// When the range indexes are the same, the client is polling for the next
-	// event which doesn't exist yet. There is no reason for the since parameter
-	// to be greater than that.
-	if(range.first > range.second)
+	// The phased initial sync feature uses negative since tokens.
+	const bool phased_range
+	{
+		int64_t(range.first) < 0L
+	};
+
+	// Check if the admin disabled phased sync.
+	if(!polylog_phased && phased_range)
 		throw m::NOT_FOUND
 		{
-			"Since parameter '%lu' is too far in the future."
-			" Cannot be greater than '%lu'.",
+			"Since parameter '%ld' must be >= 0.",
 			range.first,
-			range.second
 		};
 
+	// When the range indexes are the same, the client is polling for the next
+	// event which doesn't exist yet. There is no reason for the since parameter
+	// to be greater than that, unless it's a negative integer and phased
+	// sync is enabled
+	if(!polylog_phased || !phased_range)
+		if(range.first > range.second)
+			throw m::NOT_FOUND
+			{
+				"Since parameter '%lu' is too far in the future."
+				" Cannot be greater than '%lu'.",
+				range.first,
+				range.second
+			};
+
 	// Keep state for statistics of this sync here on the stack.
 	stats stats;
 	data data
@@ -169,6 +192,18 @@ ircd::m::sync::handle_get(client &client,
 		args.filter_id
 	};
 
+	const bool initial_sync
+	{
+		range.first == 0UL
+	};
+
+	// Conditions for phased sync for this client
+	data.phased =
+	{
+		(polylog_phased && args.phased) &&
+		(phased_range || initial_sync)
+	};
+
 	// Start the chunked encoded response.
 	resource::response::chunked response
 	{
@@ -190,11 +225,13 @@ ircd::m::sync::handle_get(client &client,
 
 	const bool should_longpoll
 	{
+		!data.phased &&
 		range.first > vm::sequence::retired
 	};
 
 	const bool should_linear
 	{
+		!data.phased &&
 		!should_longpoll &&
 		!bool(polylog_only) &&
 		range.second - range.first <= size_t(linear_delta_max)
@@ -213,8 +250,9 @@ ircd::m::sync::handle_get(client &client,
 	if(shortpolled)
 		return {};
 
-	if(longpoll_enable && longpoll::poll(data, args))
-		return {};
+	if(longpoll_enable && (!data.phased || initial_sync))
+		if(longpoll::poll(data, args))
+			return {};
 
 	const auto &next_batch
 	{
@@ -335,23 +373,34 @@ try
 	});
 
 	if(ret)
+	{
+		const int64_t next_batch
+		{
+			data.phased?
+				int64_t(data.range.first) - 1L:
+				int64_t(data.range.second)
+		};
+
 		json::stack::member
 		{
 			*data.out, "next_batch", json::value
 			{
-				lex_cast(data.range.second), json::STRING
+				lex_cast(next_batch), json::STRING
 			}
 		};
+	}
 
 	if(!ret)
 		checkpoint.decommit();
 
-	if(stats_info) log::info
+	if(!data.phased && stats_info) log::info
 	{
-		log, "request %s polylog commit:%b complete @%lu",
+		log, "request %s polylog commit:%b complete @%ld",
 		loghead(data),
 		ret,
-		data.range.second
+		data.phased?
+			data.range.first:
+			data.range.second
 	};
 
 	return ret;
diff --git a/modules/client/sync.h b/modules/client/sync.h
index a55b81005..6fb2b7ee9 100644
--- a/modules/client/sync.h
+++ b/modules/client/sync.h
@@ -24,6 +24,7 @@ namespace ircd::m::sync
 	extern conf::item<size_t> linear_buffer_size;
 	extern conf::item<size_t> linear_delta_max;
 	extern conf::item<bool> longpoll_enable;
+	extern conf::item<bool> polylog_phased;
 	extern conf::item<bool> polylog_only;
 
 	static const_buffer flush(data &, resource::response::chunked &, const const_buffer &);
@@ -143,5 +144,10 @@ struct ircd::m::sync::args
 		request.query.get("set_presence", true)
 	};
 
+	bool phased
+	{
+		request.query.get("phased", true)
+	};
+
 	args(const resource::request &request);
 };
diff --git a/modules/client/sync/rooms.cc b/modules/client/sync/rooms.cc
index c80155337..58dbf274f 100644
--- a/modules/client/sync/rooms.cc
+++ b/modules/client/sync/rooms.cc
@@ -19,7 +19,7 @@ namespace ircd::m::sync
 	static bool should_ignore(const data &);
 
 	static bool _rooms_polylog_room(data &, const m::room &);
-	static bool _rooms_polylog(data &, const string_view &membership);
+	static bool _rooms_polylog(data &, const string_view &membership, int64_t &phase);
 	static bool rooms_polylog(data &);
 
 	static bool _rooms_linear(data &, const string_view &membership);
@@ -31,9 +31,10 @@ namespace ircd::m::sync
 decltype(ircd::m::sync::rooms)
 ircd::m::sync::rooms
 {
-	"rooms",
-	rooms_polylog,
-	rooms_linear
+	"rooms", rooms_polylog, rooms_linear,
+	{
+		{ "phased", true }
+	}
 };
 
 bool
@@ -92,16 +93,31 @@ bool
 ircd::m::sync::rooms_polylog(data &data)
 {
 	bool ret{false};
-	ret |= _rooms_polylog(data, "invite");
-	ret |= _rooms_polylog(data, "join");
-	ret |= _rooms_polylog(data, "leave");
-	ret |= _rooms_polylog(data, "ban");
+	int64_t phase(0);
+
+	ret |= _rooms_polylog(data, "join", phase);
+	if(data.phased && ret)
+		return ret;
+
+	ret |= _rooms_polylog(data, "invite", phase);
+	if(data.phased && ret)
+		return ret;
+
+	ret |= _rooms_polylog(data, "leave", phase);
+	if(data.phased && ret)
+		return ret;
+
+	ret |= _rooms_polylog(data, "ban", phase);
+	if(data.phased && ret)
+		return ret;
+
 	return ret;
 }
 
 bool
 ircd::m::sync::_rooms_polylog(data &data,
-                              const string_view &membership)
+                              const string_view &membership,
+                              int64_t &phase)
 {
 	const scope_restore theirs
 	{
@@ -114,9 +130,23 @@ ircd::m::sync::_rooms_polylog(data &data,
 	};
 
 	bool ret{false};
-	data.user_rooms.for_each(membership, [&data, &ret]
+	const user::rooms::closure_bool closure{[&data, &ret, &phase]
 	(const m::room &room, const string_view &membership_)
 	{
+		assert(!data.phased || int64_t(data.range.first) < 0L);
+
+		if(data.phased)
+		{
+			if(phase >= int64_t(data.range.first))
+			{
+				--phase;
+				return true;
+			}
+
+			if(phase < int64_t(data.range.first) && ret)
+				return false;
+		}
+
 		#if defined(RB_DEBUG)
 		sync::stats stats
 		{
@@ -129,7 +159,20 @@ ircd::m::sync::_rooms_polylog(data &data,
 			stats.timer = timer{};
 		#endif
 
-		ret |= _rooms_polylog_room(data, room);
+		{
+			const scope_restore range
+			{
+				data.range.first, data.phased? 0UL : data.range.first
+			};
+
+			ret |= _rooms_polylog_room(data, room);
+		}
+
+		if(data.phased && !ret)
+		{
+			--data.range.first;
+			return true;
+		}
 
 		#if defined(RB_DEBUG)
 		thread_local char tmbuf[32];
@@ -141,7 +184,14 @@ ircd::m::sync::_rooms_polylog(data &data,
 			ircd::pretty(tmbuf, stats.timer.at<milliseconds>(), true)
 		};
 		#endif
-	});
+
+		return true;
+	}};
+
+	const bool done
+	{
+		data.user_rooms.for_each(membership, closure)
+	};
 
 	return ret;
 }