diff --git a/binaries/data/mods/public/gui/gamesetup/Persistence/PersistentMatchSettings.js b/binaries/data/mods/public/gui/gamesetup/Persistence/PersistentMatchSettings.js
index d45fc7c00e..97419ad196 100644
--- a/binaries/data/mods/public/gui/gamesetup/Persistence/PersistentMatchSettings.js
+++ b/binaries/data/mods/public/gui/gamesetup/Persistence/PersistentMatchSettings.js
@@ -24,7 +24,8 @@ class PersistentMatchSettings
 			Engine.FileExists(this.filename) &&
 			Engine.ReadJSONFile(this.filename);
 
-		const persistedSettings = data?.engine_info?.engine_version == this.engineInfo.engine_version &&
+		const persistedSettings = data?.engine_info?.engine_serialization_version &&
+			data.engine_info.engine_serialization_version == this.engineInfo.engine_serialization_version &&
 			hasSameMods(data?.engine_info?.mods, this.engineInfo.mods) &&
 			data.attributes || {};
 
diff --git a/binaries/data/mods/public/gui/loadgame/SavegameList.js b/binaries/data/mods/public/gui/loadgame/SavegameList.js
index d39cc181aa..8c28d35f15 100644
--- a/binaries/data/mods/public/gui/loadgame/SavegameList.js
+++ b/binaries/data/mods/public/gui/loadgame/SavegameList.js
@@ -174,8 +174,8 @@ class SavegameList
 	isCompatibleSavegame(metadata, engineInfo)
 	{
 		return engineInfo &&
-			metadata.engine_version &&
-			metadata.engine_version == engineInfo.engine_version &&
+			metadata.engine_serialization_version &&
+			metadata.engine_serialization_version == engineInfo.engine_serialization_version &&
 			hasSameMods(metadata.mods, engineInfo.mods);
 	}
 
diff --git a/binaries/data/mods/public/gui/loadgame/SavegameLoader.js b/binaries/data/mods/public/gui/loadgame/SavegameLoader.js
index c8de3ee389..154df3ca1f 100644
--- a/binaries/data/mods/public/gui/loadgame/SavegameLoader.js
+++ b/binaries/data/mods/public/gui/loadgame/SavegameLoader.js
@@ -24,9 +24,9 @@ class SavegameLoader
 		// Check compatibility before really loading it
 		const engineInfo = Engine.GetEngineInfo();
 		const sameMods = hasSameMods(metadata.mods, engineInfo.mods);
-		const sameEngineVersion = metadata.engine_version && metadata.engine_version == engineInfo.engine_version;
+		const compatibleEngineVersions = metadata.engine_serialization_version && metadata.engine_serialization_version == engineInfo.engine_serialization_version;
 
-		if (sameEngineVersion && sameMods)
+		if (compatibleEngineVersions && sameMods)
 		{
 			this.closePageCallback(gameId);
 			return;
@@ -35,14 +35,17 @@ class SavegameLoader
 		// Version not compatible ... ask for confirmation
 		let message = "";
 
-		if (!sameEngineVersion)
-			if (metadata.engine_version)
-				message += sprintf(translate("This savegame needs 0 A.D. version %(requiredVersion)s, while you are running version %(currentVersion)s."), {
-					"requiredVersion": metadata.engine_version,
-					"currentVersion": engineInfo.engine_version
+		if (!compatibleEngineVersions)
+		{
+			if (metadata.engine_serialization_version)
+				message += sprintf(translate("This savegame needs 0 A.D. version %(requiredCompatibleVersion)s or compatible. You are running version %(currentVersion)s, compatible down to %(compatibleVersion)s."), {
+					"requiredCompatibleVersion": metadata.engine_serialization_version,
+					"currentVersion": engineInfo.engine_version,
+					"compatibleVersion": engineInfo.engine_serialization_version,
 				}) + "\n";
 			else
 				message += translate("This savegame needs an older version of 0 A.D.") + "\n";
+		}
 
 		if (!sameMods)
 		{
diff --git a/binaries/data/mods/public/gui/replaymenu/replay_actions.js b/binaries/data/mods/public/gui/replaymenu/replay_actions.js
index be3a701b4d..b81dec4d3d 100644
--- a/binaries/data/mods/public/gui/replaymenu/replay_actions.js
+++ b/binaries/data/mods/public/gui/replaymenu/replay_actions.js
@@ -84,7 +84,7 @@ function reallyStartVisualReplay(replayDirectory)
 function displayReplayCompatibilityError(replay)
 {
 	var errMsg;
-	if (replayHasSameEngineVersion(replay))
+	if (replayHasCompatibleEngineVersion(replay))
 	{
 		const gameMods = replay.attribs.mods || [];
 		errMsg = translate("This replay needs a different sequence of mods:") + "\n" +
@@ -93,8 +93,9 @@ function displayReplayCompatibilityError(replay)
 	else
 	{
 		errMsg = translate("This replay is not compatible with your version of the game!") + "\n";
-		errMsg += sprintf(translate("Your version: %(version)s"), { "version": g_EngineInfo.engine_version }) + "\n";
-		errMsg += sprintf(translate("Required version: %(version)s"), { "version": replay.attribs.engine_version });
+		errMsg += sprintf(translate("Your version: %(version)s, compatible down to %(compatibleVersion)s"), { "version": g_EngineInfo.engine_version, "compatibleVersion": g_EngineInfo.engine_serialization_version }) + "\n";
+		if (replay.attribs.engine_serialization_version)
+			errMsg += sprintf(translate("Replay version: %(version)s"), { "version": replay.attribs.engine_serialization_version });
 	}
 
 	messageBox(500, 200, errMsg, translate("Incompatible replay"));
diff --git a/binaries/data/mods/public/gui/replaymenu/replay_menu.js b/binaries/data/mods/public/gui/replaymenu/replay_menu.js
index f13193c2cd..ad14071eb4 100644
--- a/binaries/data/mods/public/gui/replaymenu/replay_menu.js
+++ b/binaries/data/mods/public/gui/replaymenu/replay_menu.js
@@ -360,13 +360,13 @@ function getReplayDuration(replay)
  */
 function isReplayCompatible(replay)
 {
-	return replayHasSameEngineVersion(replay) && hasSameMods(replay.attribs.mods, g_EngineInfo.mods);
+	return replayHasCompatibleEngineVersion(replay) && hasSameMods(replay.attribs.mods, g_EngineInfo.mods);
 }
 
 /**
  * True if we can start the given replay with the currently loaded mods.
  */
-function replayHasSameEngineVersion(replay)
+function replayHasCompatibleEngineVersion(replay)
 {
-	return replay.attribs.engine_version && replay.attribs.engine_version == g_EngineInfo.engine_version;
+	return replay.attribs.engine_serialization_version && replay.attribs.engine_serialization_version == g_EngineInfo.engine_serialization_version;
 }
diff --git a/source/lib/build_version.h b/source/lib/build_version.h
index 304359034c..b38463674d 100644
--- a/source/lib/build_version.h
+++ b/source/lib/build_version.h
@@ -23,8 +23,46 @@
 #ifndef INCLUDED_BUILDVERSION
 #define INCLUDED_BUILDVERSION
 
-#define PYROGENESIS_VERSION "0.28.0"
-#define PYROGENESIS_VERSION_WORD 0,28,0,0
+/*
+ * The version of the game is built as MAJOR.MINOR.PATCH, where
+ * - MAJOR is 0
+ * - MINOR is incremented for each main release
+ * - PATCH is incremented whenever we release a bugfix patch release
+ *
+ * TODO: This does not respect semver.
+ */
+#define PS_VERSION_MAJOR 0
+#define PS_VERSION_MINOR 28
+#define PS_VERSION_PATCH 0
+
+/*
+ * When a patch version is released, it should stay simulation-compatible with
+ * all the previous patch releases of the same main release. This allows players
+ * to keep replaying their games and playing online against other versions of the
+ * same main release.
+ *
+ * The "compatible patch version" is the earliest patch version with which the
+ * current version is compatible. It should ideally stay at 0 all the time.
+ * If the compatible patch version is bumped:
+ * - a new lobby room must be opened
+ * - the version of the public '0ad' mod must be bumped
+ * - incompatible replays and savegames will be rotated as new folders are created
+ *
+ * This does not describe compatibility with the modding API. Modders are advised
+ * to rely on the actual engine version.
+ */
+#define PS_SERIALIZATION_COMPATIBLE_PATCH 0
+
+#define STR(ver) #ver
+#define DOTCONCAT(v1, v2, v3) STR(v1) "." STR(v2) "." STR(v3)
+
+// See definition of PS_VERSION_* for details
+#define PS_VERSION DOTCONCAT(PS_VERSION_MAJOR, PS_VERSION_MINOR, PS_VERSION_PATCH)
+// Used in Windows .rc file
+#define PS_VERSION_WORD PS_VERSION_MAJOR,PS_VERSION_MINOR,PS_VERSION_PATCH,0
+// See definition of PS_SERIALIZATION_COMPATIBLE_PATCH for details
+#define PS_SERIALIZATION_VERSION DOTCONCAT(PS_VERSION_MAJOR, PS_VERSION_MINOR, PS_SERIALIZATION_COMPATIBLE_PATCH)
+
 extern wchar_t build_version[];
 
 #endif // INCLUDED_BUILDVERSION
diff --git a/source/lib/sysdep/os/win/pyrogenesis.rc b/source/lib/sysdep/os/win/pyrogenesis.rc
index deb27f234a..7da833fb96 100644
--- a/source/lib/sysdep/os/win/pyrogenesis.rc
+++ b/source/lib/sysdep/os/win/pyrogenesis.rc
@@ -9,8 +9,8 @@
 #endif
 
 VS_VERSION_INFO VERSIONINFO
-FILEVERSION     PYROGENESIS_VERSION_WORD
-PRODUCTVERSION  PYROGENESIS_VERSION_WORD
+FILEVERSION     PS_VERSION_WORD
+PRODUCTVERSION  PS_VERSION_WORD
 FILEFLAGSMASK   VS_FFI_FILEFLAGSMASK
 FILEFLAGS       VER_DEBUG
 FILEOS          VOS_NT_WINDOWS32
@@ -23,12 +23,12 @@ BEGIN
         BEGIN
             VALUE "CompanyName", "Wildfire Games"
             VALUE "FileDescription", "Pyrogenesis engine"
-            VALUE "FileVersion", PYROGENESIS_VERSION
+            VALUE "FileVersion", PS_VERSION
             VALUE "InternalName", "pyrogenesis.rc"
             VALUE "LegalCopyright", "Copyright (C) 2025 Wildfire Games"
             VALUE "OriginalFilename", "pyrogenesis.rc"
             VALUE "ProductName", "Pyrogenesis"
-            VALUE "ProductVersion", PYROGENESIS_VERSION
+            VALUE "ProductVersion", PS_VERSION
         END
     END
     BLOCK "VarFileInfo"
diff --git a/source/lobby/XmppClient.cpp b/source/lobby/XmppClient.cpp
index 8f39534750..646b86b942 100644
--- a/source/lobby/XmppClient.cpp
+++ b/source/lobby/XmppClient.cpp
@@ -130,7 +130,7 @@ XmppClient::XmppClient(const ScriptInterface* scriptInterface, const std::string
 
 	m_client->registerConnectionListener(this);
 	m_client->setPresence(gloox::Presence::Available, -1);
-	m_client->disco()->setVersion("Pyrogenesis", PYROGENESIS_VERSION);
+	m_client->disco()->setVersion("Pyrogenesis", PS_SERIALIZATION_VERSION);
 	m_client->disco()->setIdentity("client", "bot");
 	m_client->setCompression(false);
 
diff --git a/source/main.cpp b/source/main.cpp
index 184509f411..1fa5308112 100644
--- a/source/main.cpp
+++ b/source/main.cpp
@@ -561,7 +561,9 @@ static void RunGameOrAtlas(const std::span<const char* const> argv)
 
 	if (args.Has("version"))
 	{
-		debug_printf("Pyrogenesis %s\n", PYROGENESIS_VERSION);
+		debug_printf("Pyrogenesis %s\n", PS_VERSION);
+		if (std::strcmp(PS_VERSION, PS_SERIALIZATION_VERSION) != 0)
+			debug_printf("Compatible down to patch %s\n", PS_SERIALIZATION_VERSION);
 		return;
 	}
 
diff --git a/source/network/NetProtocol.h b/source/network/NetProtocol.h
index 54f1a967f2..96074c9964 100644
--- a/source/network/NetProtocol.h
+++ b/source/network/NetProtocol.h
@@ -44,7 +44,7 @@ Message CreateHandshake() {
 		handshake.m_Magic = PS_PROTOCOL_MAGIC;
 
 	handshake.m_ProtocolVersion = PS_PROTOCOL_VERSION;
-	handshake.m_EngineVersion = PYROGENESIS_VERSION;
+	handshake.m_EngineVersion = PS_SERIALIZATION_VERSION;
 
 	for (const Mod::ModData* mod : Mod::Instance().GetEnabledModsData())
 	{
diff --git a/source/network/scripting/JSInterface_Network.cpp b/source/network/scripting/JSInterface_Network.cpp
index c3247cf167..29b437681e 100644
--- a/source/network/scripting/JSInterface_Network.cpp
+++ b/source/network/scripting/JSInterface_Network.cpp
@@ -128,7 +128,7 @@ void StartNetworkHost(const CStrW& playerName, const u16 serverPort, const CStr&
 		 * TODO: it should be possible to implement SRP or something along those lines to completely protect from this,
 		 * but the cost/benefit ratio is probably not worth it.
 		 */
-		CStr hashedPass = HashCryptographically(password, hostJID + password + PYROGENESIS_VERSION);
+		CStr hashedPass = HashCryptographically(password, hostJID + password + PS_SERIALIZATION_VERSION);
 		g_NetServer->SetPassword(hashedPass);
 		g_NetClient->SetHostJID(hostJID);
 		g_NetClient->SetGamePassword(hashedPass);
@@ -176,7 +176,7 @@ void StartNetworkJoinLobby(const CStrW& playerName, const CStr& hostJID, const C
 	ENSURE(!g_NetServer);
 	ENSURE(!g_Game);
 
-	CStr hashedPass = HashCryptographically(password, hostJID + password + PYROGENESIS_VERSION);
+	CStr hashedPass = HashCryptographically(password, hostJID + password + PS_SERIALIZATION_VERSION);
 	g_Game = new CGame(true);
 	g_NetClient = new CNetClient(g_Game);
 	g_NetClient->SetUserName(playerName);
diff --git a/source/ps/CLogger.cpp b/source/ps/CLogger.cpp
index 79c640bd1e..5642da8b08 100644
--- a/source/ps/CLogger.cpp
+++ b/source/ps/CLogger.cpp
@@ -77,8 +77,8 @@ CLogger::CLogger(std::ostream& mainLog, std::ostream& interestingLog, const bool
 	m_InterestingLog{interestingLog},
 	m_UseDebugPrintf{useDebugPrintf}
 {
-	m_MainLog << html_header0 << PYROGENESIS_VERSION << ") Main log" << html_header1;
-	m_InterestingLog << html_header0 << PYROGENESIS_VERSION << ") Main log (warnings and errors only)" << html_header1;
+	m_MainLog << html_header0 << PS_VERSION << ") Main log" << html_header1;
+	m_InterestingLog << html_header0 << PS_VERSION << ") Main log (warnings and errors only)" << html_header1;
 }
 
 CLogger::~CLogger()
diff --git a/source/ps/Pyrogenesis.cpp b/source/ps/Pyrogenesis.cpp
index 15d2228151..e6255630b6 100644
--- a/source/ps/Pyrogenesis.cpp
+++ b/source/ps/Pyrogenesis.cpp
@@ -57,7 +57,7 @@ static void AppendAsciiFile(FILE* out, const OsPath& pathname)
 void psBundleLogs(FILE* f)
 {
 	fwprintf(f, L"Build Version: %ls\n\n", build_version);
-	fwprintf(f, L"Engine Version: %hs\n\n", PYROGENESIS_VERSION);
+	fwprintf(f, L"Engine Version: %hs\n\n", PS_VERSION);
 
 	fwprintf(f, L"System info:\n\n");
 	OsPath path1 = psLogDir()/"system_info.txt";
diff --git a/source/ps/Replay.cpp b/source/ps/Replay.cpp
index 6f49f6bc12..19aadb4088 100644
--- a/source/ps/Replay.cpp
+++ b/source/ps/Replay.cpp
@@ -80,7 +80,7 @@ void CReplayLogger::StartGame(JS::MutableHandleValue attribs)
 	Script::SetProperty(rq, attribs, "timestamp", (double)std::time(nullptr));
 
 	// Add engine version and currently loaded mods for sanity checks when replaying
-	Script::SetProperty(rq, attribs, "engine_version", PYROGENESIS_VERSION);
+	Script::SetProperty(rq, attribs, "engine_serialization_version", PS_SERIALIZATION_VERSION);
 	JS::RootedValue mods(rq.cx);
 	Script::ToJSVal(rq, &mods, g_Mods.GetEnabledModsData());
 	Script::SetProperty(rq, attribs, "mods", mods);
diff --git a/source/ps/SavedGame.cpp b/source/ps/SavedGame.cpp
index 793fb349ff..6e7ea7bc1b 100644
--- a/source/ps/SavedGame.cpp
+++ b/source/ps/SavedGame.cpp
@@ -112,7 +112,8 @@ Status SavedGames::Save(const CStrW& name, const CStrW& description, CSimulation
 	Script::CreateObject(
 		rq,
 		&metadata,
-		"engine_version", PYROGENESIS_VERSION,
+		"engine_version", PS_VERSION,
+		"engine_serialization_version", PS_SERIALIZATION_VERSION,
 		"time", static_cast<double>(now),
 		"playerID", g_Game->GetPlayerID(),
 		"mods", mods,
diff --git a/source/ps/VisualReplay.cpp b/source/ps/VisualReplay.cpp
index d1d3701e79..61c1a09e70 100644
--- a/source/ps/VisualReplay.cpp
+++ b/source/ps/VisualReplay.cpp
@@ -61,7 +61,7 @@ const u8 minimumReplayDuration = 3;
 
 OsPath VisualReplay::GetDirectoryPath()
 {
-	return Paths(g_CmdLineArgs).UserData() / "replays" / PYROGENESIS_VERSION;
+	return Paths(g_CmdLineArgs).UserData() / "replays" / PS_SERIALIZATION_VERSION;
 }
 
 OsPath VisualReplay::GetCacheFilePath()
diff --git a/source/ps/scripting/JSInterface_Mod.cpp b/source/ps/scripting/JSInterface_Mod.cpp
index 2d6443c949..9d1b713774 100644
--- a/source/ps/scripting/JSInterface_Mod.cpp
+++ b/source/ps/scripting/JSInterface_Mod.cpp
@@ -135,7 +135,8 @@ JS::Value GetEngineInfo(const ScriptInterface& scriptInterface)
 	Script::CreateObject(
 		 rq,
 		 &metainfo,
-		 "engine_version", PYROGENESIS_VERSION,
+		 "engine_version", PS_VERSION,
+		 "engine_serialization_version", PS_SERIALIZATION_VERSION,
 		 "mods", mods);
 
 	Script::DeepFreezeObject(rq, metainfo);