v1.64

Readme.txt

@@ -9,6 +9,29 @@ Welcome to the Steamworks SDK.  For documentation please see our partner
 website at: http://partner.steamgames.com
 
 
+----------------------------------------------------------------
+v1.64 11th March 2026
+----------------------------------------------------------------
+
+General:
+* androidarm64 libs now statically link libc++
+* androidarm64 libs now use 16KB max page size (from 4KB)
+* linuxarm64 libs now use 4KB max page size (from 64KB)
+
+ISteamApps:
+* Added last update timestamp to GetBetaInfo()
+
+ISteamUGC:
+* Added MarkDownloadedItemAsUnused()
+* Added GetDownloadedItems(), GetNumDownloadedItems()
+
+ISteamRemotePlay:
+* Added BSessionRemotePlayTogether()
+* Added GetSessionGuestID()
+* Added GetSmallSessionAvatar(), GetMediumSessionAvatar(), GetLargeSessionAvatar()
+* Added SteamRemotePlaySessionAvatarLoaded_t callback
+
+
 ----------------------------------------------------------------
 v1.63 18th November 2025
 ----------------------------------------------------------------

public/steam/isteamapps.h

@@ -116,13 +116,13 @@ public:
 	virtual int  GetNumBetas( int *pnAvailable, int *pnPrivate ) = 0; //
 
 	// return beta branch details, name, description, current BuildID and state flags (EBetaBranchFlags)
-	virtual bool GetBetaInfo( int iBetaIndex, uint32 *punFlags, uint32 *punBuildID, char *pchBetaName, int cchBetaName, char *pchDescription, int cchDescription ) = 0; // iterate through
+	virtual bool GetBetaInfo( int iBetaIndex, uint32 *punFlags, uint32 *punBuildID, char *pchBetaName, int cchBetaName, char *pchDescription, int cchDescription, uint32 *punLastUpdated ) = 0; // iterate through
 
 	// select this beta branch for this app as active, might need the game to restart so Steam can update to that branch
 	virtual bool SetActiveBeta( const char *pchBetaName ) = 0;
 };
 
-#define STEAMAPPS_INTERFACE_VERSION "STEAMAPPS_INTERFACE_VERSION008"
+#define STEAMAPPS_INTERFACE_VERSION "STEAMAPPS_INTERFACE_VERSION009"
 
 // Global interface accessor
 inline ISteamApps *SteamApps();

public/steam/isteamparentalsettings.h

@@ -13,6 +13,8 @@
 #include "steam_api_common.h"
 
 // Feature types for parental settings
+// These end up in a 32-bit bitfield so we're
+// limited on how many we can have.
 enum EParentalFeature
 {
 	k_EFeatureInvalid = 0,
@@ -31,6 +33,7 @@ enum EParentalFeature
 	k_EFeatureSiteLicense = 13,
 	k_EFeatureKioskMode_Deprecated = 14,
 	k_EFeatureBlockAlways = 15,
+	k_EFeatureDesktop = 16,
 	k_EFeatureMax
 };
 

public/steam/isteamremoteplay.h

@@ -282,9 +282,28 @@ public:
 	// Get the currently connected Steam Remote Play session ID at the specified index. Returns zero if index is out of bounds.
 	virtual RemotePlaySessionID_t GetSessionID( int iSessionIndex ) = 0;
 
+	// Return true if the session has joined using a Remote Play Together invitation
+	virtual bool BSessionRemotePlayTogether( RemotePlaySessionID_t unSessionID ) = 0;
+
 	// Get the SteamID of the connected user
 	virtual CSteamID GetSessionSteamID( RemotePlaySessionID_t unSessionID ) = 0;
 
+	// Get the guest ID of the connected user if they are a Remote Play Together guest
+	// This returns 0 if the sessionID isn't valid or the session isn't a Remote Play Together guest
+	virtual uint32 GetSessionGuestID( RemotePlaySessionID_t unSessionID ) = 0;
+
+	// gets the small (32x32) avatar of the connected user, which is a handle to be used in IClientUtils::GetImageRGBA(), or 0 if the sessionID isn't valid
+	// returns -1 if this image has yet to be loaded, in this case wait for a RemotePlaySessionAvatarLoaded_t callback and then call this again
+	virtual int GetSmallSessionAvatar( RemotePlaySessionID_t unSessionID ) = 0;
+
+	// gets the medium (64x64) avatar of the connected user, which is a handle to be used in IClientUtils::GetImageRGBA(), or 0 if the sessionID isn't valid
+	// returns -1 if this image has yet to be loaded, in this case wait for a RemotePlaySessionAvatarLoaded_t callback and then call this again
+	virtual int GetMediumSessionAvatar( RemotePlaySessionID_t unSessionID ) = 0;
+
+	// gets the large (184x184) avatar of the connected user, which is a handle to be used in IClientUtils::GetImageRGBA(), or 0 if the sessionID isn't valid
+	// returns -1 if this image has yet to be loaded, in this case wait for a RemotePlaySessionAvatarLoaded_t callback and then call this again
+	virtual int GetLargeSessionAvatar( RemotePlaySessionID_t unSessionID ) = 0;
+
 	// Get the name of the session client device
 	// This returns NULL if the sessionID is not valid
 	virtual const char *GetSessionClientName( RemotePlaySessionID_t unSessionID ) = 0;
@@ -337,8 +356,8 @@ public:
 	// nHeight - The height of the cursor, in pixels
 	// nHotX - The X coordinate of the cursor hot spot in pixels, offset from the left of the cursor
 	// nHotY - The Y coordinate of the cursor hot spot in pixels, offset from the top of the cursor
-	// pBGRA - A pointer to the cursor pixels, with the color channels in red, green, blue, alpha order
-	// nPitch - The distance between pixel rows in bytes, defaults to nWidth * 4 
+	// pBGRA - A pointer to the cursor pixels, with 8-bit color channels in red, green, blue, alpha order
+	// nPitch - The distance between pixel rows in bytes, defaults to nWidth * 4
 	virtual RemotePlayCursorID_t CreateMouseCursor( int nWidth, int nHeight, int nHotX, int nHotY, const void *pBGRA, int nPitch = 0 ) = 0;
 
 	// Set the mouse cursor for a remote player
@@ -348,7 +367,7 @@ public:
 	virtual void SetMouseCursor( RemotePlaySessionID_t unSessionID, RemotePlayCursorID_t unCursorID ) = 0;
 };
 
-#define STEAMREMOTEPLAY_INTERFACE_VERSION "STEAMREMOTEPLAY_INTERFACE_VERSION003"
+#define STEAMREMOTEPLAY_INTERFACE_VERSION "STEAMREMOTEPLAY_INTERFACE_VERSION004"
 
 // Global interface accessor
 inline ISteamRemotePlay *SteamRemotePlay();
@@ -366,17 +385,25 @@ STEAM_DEFINE_USER_INTERFACE_ACCESSOR( ISteamRemotePlay *, SteamRemotePlay, STEAM
 
 STEAM_CALLBACK_BEGIN( SteamRemotePlaySessionConnected_t, k_iSteamRemotePlayCallbacks + 1 )
 	STEAM_CALLBACK_MEMBER( 0, RemotePlaySessionID_t, m_unSessionID )
-STEAM_CALLBACK_END( 0 )
+STEAM_CALLBACK_END( 1 )
 
 
 STEAM_CALLBACK_BEGIN( SteamRemotePlaySessionDisconnected_t, k_iSteamRemotePlayCallbacks + 2 )
 	STEAM_CALLBACK_MEMBER( 0, RemotePlaySessionID_t, m_unSessionID )
-STEAM_CALLBACK_END( 0 )
+STEAM_CALLBACK_END( 1 )
 
 
 STEAM_CALLBACK_BEGIN( SteamRemotePlayTogetherGuestInvite_t, k_iSteamRemotePlayCallbacks + 3 )
 	STEAM_CALLBACK_MEMBER_ARRAY( 0, char, m_szConnectURL, 1024 )
-STEAM_CALLBACK_END( 0 )
+STEAM_CALLBACK_END( 1 )
+
+
+STEAM_CALLBACK_BEGIN( SteamRemotePlaySessionAvatarLoaded_t, k_iSteamRemotePlayCallbacks + 4 )
+	STEAM_CALLBACK_MEMBER( 0, RemotePlaySessionID_t, m_unSessionID ) // sessionID the avatar has been loaded for
+	STEAM_CALLBACK_MEMBER( 1, int, m_iImage ) // the image index of the now loaded image
+	STEAM_CALLBACK_MEMBER( 2, int, m_iWide ) // width of the loaded image
+	STEAM_CALLBACK_MEMBER( 3, int, m_iTall ) // height of the loaded image
+STEAM_CALLBACK_END( 4 )
 
 
 #pragma pack( pop )

public/steam/isteamugc.h

@@ -400,6 +400,15 @@ public:
 
 	// Set the local load order for these items. If there are any items not in the given list, they will sort by the time subscribed.
 	virtual bool SetSubscriptionsLoadOrder( PublishedFileId_t *pvecPublishedFileIDs, uint32 unNumPublishedFileIDs ) = 0;
+
+	// Tells the client to no longer try to keep the item in its local cache, unless it was subscribed to by other users on this machine
+	virtual bool MarkDownloadedItemAsUnused( PublishedFileId_t nPublishedFileID ) = 0;
+
+	// Returns the number of items actually downloaded locally
+	virtual uint32 GetNumDownloadedItems() = 0;
+
+	// Returns the ids of the items downloaded
+	virtual uint32 GetDownloadedItems( PublishedFileId_t *pvecPublishedFileIDs, uint32 cMaxEntries ) = 0;
 };
 
 #define STEAMUGC_INTERFACE_VERSION "STEAMUGC_INTERFACE_VERSION021"

public/steam/isteamuserstats.h

@@ -354,7 +354,7 @@ struct UserAchievementStored_t
 	enum { k_iCallback = k_iSteamUserStatsCallbacks + 3 };
 
 	uint64		m_nGameID;				// Game this is for
-	bool		m_bGroupAchievement;	// if this is a "group" achievement
+	bool		m_bGroupAchievement;	// unused. if this is a "group" achievement
 	char		m_rgchAchievementName[k_cchStatNameMax];		// name of the achievement
 	uint32		m_nCurProgress;			// current progress towards the achievement
 	uint32		m_nMaxProgress;			// "out of" this many

public/steam/steam_api.json

@@ -1547,6 +1547,16 @@
       ],
       "struct": "SteamRemotePlayTogetherGuestInvite_t"
     },
+    {
+      "callback_id": 5704,
+      "fields": [
+        { "fieldname":"m_unSessionID", "fieldtype":"RemotePlaySessionID_t" },
+        { "fieldname":"m_iImage", "fieldtype":"int" },
+        { "fieldname":"m_iWide", "fieldtype":"int" },
+        { "fieldname":"m_iTall", "fieldtype":"int" }
+      ],
+      "struct": "SteamRemotePlaySessionAvatarLoaded_t"
+    },
     {
       "callback_id": 1251,
       "fields": [
@@ -4049,7 +4059,8 @@
         { "name":"k_EFeatureSiteLicense", "value":"13" },
         { "name":"k_EFeatureKioskMode_Deprecated", "value":"14" },
         { "name":"k_EFeatureBlockAlways", "value":"15" },
-        { "name":"k_EFeatureMax", "value":"16" }
+        { "name":"k_EFeatureDesktop", "value":"16" },
+        { "name":"k_EFeatureMax", "value":"17" }
       ]
     },
     {
@@ -4407,6 +4418,7 @@
         { "name":"k_ESteamNetworkingConfig_LogLevel_P2PRendezvous", "value":"17" },
         { "name":"k_ESteamNetworkingConfig_LogLevel_SDRRelayPings", "value":"18" },
         { "name":"k_ESteamNetworkingConfig_ECN", "value":"999" },
+        { "name":"k_ESteamNetworkingConfig_SDRClient_EnableTOSProbes", "value":"998" },
         { "name":"k_ESteamNetworkingConfig_DELETED_EnumerateDevVars", "value":"35" },
         { "name":"k_ESteamNetworkingConfigValue__Force32Bit", "value":"2147483647" }
       ]
@@ -7882,7 +7894,7 @@
         {
           "kind": "user",
           "name": "SteamApps",
-          "name_flat": "SteamAPI_SteamApps_v008"
+          "name_flat": "SteamAPI_SteamApps_v009"
         }
       ],
       "classname": "ISteamApps",
@@ -8138,7 +8150,8 @@
             { "paramname":"pchBetaName", "paramtype":"char *" },
             { "paramname":"cchBetaName", "paramtype":"int" },
             { "paramname":"pchDescription", "paramtype":"char *" },
-            { "paramname":"cchDescription", "paramtype":"int" }
+            { "paramname":"cchDescription", "paramtype":"int" },
+            { "paramname":"punLastUpdated", "paramtype":"uint32 *" }
           ],
           "returntype": "bool"
         },
@@ -8151,7 +8164,7 @@
           "returntype": "bool"
         }
       ],
-      "version_string": "STEAMAPPS_INTERFACE_VERSION008"
+      "version_string": "STEAMAPPS_INTERFACE_VERSION009"
     },
     {
       "accessors": [
@@ -10577,6 +10590,29 @@
             { "paramname":"unNumPublishedFileIDs", "paramtype":"uint32" }
           ],
           "returntype": "bool"
+        },
+        {
+          "methodname": "MarkDownloadedItemAsUnused",
+          "methodname_flat": "SteamAPI_ISteamUGC_MarkDownloadedItemAsUnused",
+          "params": [
+            { "paramname":"nPublishedFileID", "paramtype":"PublishedFileId_t" }
+          ],
+          "returntype": "bool"
+        },
+        {
+          "methodname": "GetNumDownloadedItems",
+          "methodname_flat": "SteamAPI_ISteamUGC_GetNumDownloadedItems",
+          "params": [],
+          "returntype": "uint32"
+        },
+        {
+          "methodname": "GetDownloadedItems",
+          "methodname_flat": "SteamAPI_ISteamUGC_GetDownloadedItems",
+          "params": [
+            { "paramname":"pvecPublishedFileIDs", "paramtype":"PublishedFileId_t *" },
+            { "paramname":"cMaxEntries", "paramtype":"uint32" }
+          ],
+          "returntype": "uint32"
         }
       ],
       "version_string": "STEAMUGC_INTERFACE_VERSION021"
@@ -11795,7 +11831,7 @@
         {
           "kind": "user",
           "name": "SteamRemotePlay",
-          "name_flat": "SteamAPI_SteamRemotePlay_v003"
+          "name_flat": "SteamAPI_SteamRemotePlay_v004"
         }
       ],
       "classname": "ISteamRemotePlay",
@@ -11815,6 +11851,14 @@
           ],
           "returntype": "RemotePlaySessionID_t"
         },
+        {
+          "methodname": "BSessionRemotePlayTogether",
+          "methodname_flat": "SteamAPI_ISteamRemotePlay_BSessionRemotePlayTogether",
+          "params": [
+            { "paramname":"unSessionID", "paramtype":"RemotePlaySessionID_t" }
+          ],
+          "returntype": "bool"
+        },
         {
           "methodname": "GetSessionSteamID",
           "methodname_flat": "SteamAPI_ISteamRemotePlay_GetSessionSteamID",
@@ -11824,6 +11868,38 @@
           "returntype": "CSteamID",
           "returntype_flat": "uint64_steamid"
         },
+        {
+          "methodname": "GetSessionGuestID",
+          "methodname_flat": "SteamAPI_ISteamRemotePlay_GetSessionGuestID",
+          "params": [
+            { "paramname":"unSessionID", "paramtype":"RemotePlaySessionID_t" }
+          ],
+          "returntype": "uint32"
+        },
+        {
+          "methodname": "GetSmallSessionAvatar",
+          "methodname_flat": "SteamAPI_ISteamRemotePlay_GetSmallSessionAvatar",
+          "params": [
+            { "paramname":"unSessionID", "paramtype":"RemotePlaySessionID_t" }
+          ],
+          "returntype": "int"
+        },
+        {
+          "methodname": "GetMediumSessionAvatar",
+          "methodname_flat": "SteamAPI_ISteamRemotePlay_GetMediumSessionAvatar",
+          "params": [
+            { "paramname":"unSessionID", "paramtype":"RemotePlaySessionID_t" }
+          ],
+          "returntype": "int"
+        },
+        {
+          "methodname": "GetLargeSessionAvatar",
+          "methodname_flat": "SteamAPI_ISteamRemotePlay_GetLargeSessionAvatar",
+          "params": [
+            { "paramname":"unSessionID", "paramtype":"RemotePlaySessionID_t" }
+          ],
+          "returntype": "int"
+        },
         {
           "methodname": "GetSessionClientName",
           "methodname_flat": "SteamAPI_ISteamRemotePlay_GetSessionClientName",
@@ -11927,7 +12003,7 @@
           "returntype": "void"
         }
       ],
-      "version_string": "STEAMREMOTEPLAY_INTERFACE_VERSION003"
+      "version_string": "STEAMREMOTEPLAY_INTERFACE_VERSION004"
     },
     {
       "accessors": [
@@ -14008,7 +14084,8 @@
         { "fieldname":"m_cbPendingReliable", "fieldtype":"int" },
         { "fieldname":"m_cbSentUnackedReliable", "fieldtype":"int" },
         { "fieldname":"m_usecQueueTime", "fieldtype":"SteamNetworkingMicroseconds" },
-        { "fieldname":"reserved", "fieldtype":"uint32 [16]" }
+        { "fieldname":"m_usecMaxJitter", "fieldtype":"int32" },
+        { "fieldname":"reserved", "fieldtype":"uint32 [15]" }
       ],
       "struct": "SteamNetConnectionRealTimeStatus_t"
     },

public/steam/steam_api_flat.h

@@ -453,9 +453,9 @@ S_API bool SteamAPI_ISteamUserStats_GetAchievementProgressLimitsFloat( ISteamUse
 // ISteamApps
 
 // A versioned accessor is exported by the library
-S_API ISteamApps *SteamAPI_SteamApps_v008();
+S_API ISteamApps *SteamAPI_SteamApps_v009();
 // Inline, unversioned accessor to get the current version.  Essentially the same as SteamApps(), but using this ensures that you are using a matching library.
-inline ISteamApps *SteamAPI_SteamApps() { return SteamAPI_SteamApps_v008(); }
+inline ISteamApps *SteamAPI_SteamApps() { return SteamAPI_SteamApps_v009(); }
 S_API bool SteamAPI_ISteamApps_BIsSubscribed( ISteamApps* self );
 S_API bool SteamAPI_ISteamApps_BIsLowViolence( ISteamApps* self );
 S_API bool SteamAPI_ISteamApps_BIsCybercafe( ISteamApps* self );
@@ -487,7 +487,7 @@ S_API bool SteamAPI_ISteamApps_BIsSubscribedFromFamilySharing( ISteamApps* self
 S_API bool SteamAPI_ISteamApps_BIsTimedTrial( ISteamApps* self, uint32 * punSecondsAllowed, uint32 * punSecondsPlayed );
 S_API bool SteamAPI_ISteamApps_SetDlcContext( ISteamApps* self, AppId_t nAppID );
 S_API int SteamAPI_ISteamApps_GetNumBetas( ISteamApps* self, int * pnAvailable, int * pnPrivate );
-S_API bool SteamAPI_ISteamApps_GetBetaInfo( ISteamApps* self, int iBetaIndex, uint32 * punFlags, uint32 * punBuildID, char * pchBetaName, int cchBetaName, char * pchDescription, int cchDescription );
+S_API bool SteamAPI_ISteamApps_GetBetaInfo( ISteamApps* self, int iBetaIndex, uint32 * punFlags, uint32 * punBuildID, char * pchBetaName, int cchBetaName, char * pchDescription, int cchDescription, uint32 * punLastUpdated );
 S_API bool SteamAPI_ISteamApps_SetActiveBeta( ISteamApps* self, const char * pchBetaName );
 
 // ISteamNetworking
@@ -796,6 +796,9 @@ S_API SteamAPICall_t SteamAPI_ISteamUGC_GetWorkshopEULAStatus( ISteamUGC* self )
 S_API uint32 SteamAPI_ISteamUGC_GetUserContentDescriptorPreferences( ISteamUGC* self, EUGCContentDescriptorID * pvecDescriptors, uint32 cMaxEntries );
 S_API bool SteamAPI_ISteamUGC_SetItemsDisabledLocally( ISteamUGC* self, PublishedFileId_t * pvecPublishedFileIDs, uint32 unNumPublishedFileIDs, bool bDisabledLocally );
 S_API bool SteamAPI_ISteamUGC_SetSubscriptionsLoadOrder( ISteamUGC* self, PublishedFileId_t * pvecPublishedFileIDs, uint32 unNumPublishedFileIDs );
+S_API bool SteamAPI_ISteamUGC_MarkDownloadedItemAsUnused( ISteamUGC* self, PublishedFileId_t nPublishedFileID );
+S_API uint32 SteamAPI_ISteamUGC_GetNumDownloadedItems( ISteamUGC* self );
+S_API uint32 SteamAPI_ISteamUGC_GetDownloadedItems( ISteamUGC* self, PublishedFileId_t * pvecPublishedFileIDs, uint32 cMaxEntries );
 
 // ISteamHTMLSurface
 
@@ -943,12 +946,17 @@ S_API bool SteamAPI_ISteamParentalSettings_BIsFeatureInBlockList( ISteamParental
 // ISteamRemotePlay
 
 // A versioned accessor is exported by the library
-S_API ISteamRemotePlay *SteamAPI_SteamRemotePlay_v003();
+S_API ISteamRemotePlay *SteamAPI_SteamRemotePlay_v004();
 // Inline, unversioned accessor to get the current version.  Essentially the same as SteamRemotePlay(), but using this ensures that you are using a matching library.
-inline ISteamRemotePlay *SteamAPI_SteamRemotePlay() { return SteamAPI_SteamRemotePlay_v003(); }
+inline ISteamRemotePlay *SteamAPI_SteamRemotePlay() { return SteamAPI_SteamRemotePlay_v004(); }
 S_API uint32 SteamAPI_ISteamRemotePlay_GetSessionCount( ISteamRemotePlay* self );
 S_API RemotePlaySessionID_t SteamAPI_ISteamRemotePlay_GetSessionID( ISteamRemotePlay* self, int iSessionIndex );
+S_API bool SteamAPI_ISteamRemotePlay_BSessionRemotePlayTogether( ISteamRemotePlay* self, RemotePlaySessionID_t unSessionID );
 S_API uint64_steamid SteamAPI_ISteamRemotePlay_GetSessionSteamID( ISteamRemotePlay* self, RemotePlaySessionID_t unSessionID );
+S_API uint32 SteamAPI_ISteamRemotePlay_GetSessionGuestID( ISteamRemotePlay* self, RemotePlaySessionID_t unSessionID );
+S_API int SteamAPI_ISteamRemotePlay_GetSmallSessionAvatar( ISteamRemotePlay* self, RemotePlaySessionID_t unSessionID );
+S_API int SteamAPI_ISteamRemotePlay_GetMediumSessionAvatar( ISteamRemotePlay* self, RemotePlaySessionID_t unSessionID );
+S_API int SteamAPI_ISteamRemotePlay_GetLargeSessionAvatar( ISteamRemotePlay* self, RemotePlaySessionID_t unSessionID );
 S_API const char * SteamAPI_ISteamRemotePlay_GetSessionClientName( ISteamRemotePlay* self, RemotePlaySessionID_t unSessionID );
 S_API ESteamDeviceFormFactor SteamAPI_ISteamRemotePlay_GetSessionClientFormFactor( ISteamRemotePlay* self, RemotePlaySessionID_t unSessionID );
 S_API bool SteamAPI_ISteamRemotePlay_BGetSessionClientResolution( ISteamRemotePlay* self, RemotePlaySessionID_t unSessionID, int * pnResolutionX, int * pnResolutionY );

public/steam/steamnetworkingtypes.h

@@ -797,8 +797,17 @@ struct SteamNetConnectionRealTimeStatus_t
 	/// Nagle delay is ignored for the purposes of this calculation.
 	SteamNetworkingMicroseconds m_usecQueueTime;
 
+	/// Highest packet jitter experienced, since the last time this information
+	/// was returned.  (The high water mark is cleared each time you fetch the info.)
+	/// 
+	/// - The units are microseconds, although the measurement precision is usually
+	///   not nearly this precise.
+	/// - A negative value means "no data available".
+	/// - Not all connections are able to measure jitter.
+	int32 m_usecMaxJitter;
+
 	// Internal stuff, room to change API easily
-	uint32 reserved[16];
+	uint32 reserved[15];
 };
 
 /// Quick status of a particular lane
@@ -1688,12 +1697,24 @@ enum ESteamNetworkingConfigValue
 	k_ESteamNetworkingConfig_LogLevel_P2PRendezvous = 17, // [connection int32] P2P rendezvous messages
 	k_ESteamNetworkingConfig_LogLevel_SDRRelayPings = 18, // [global int32] Ping relays
 
-	// Experimental.  Set the ECN header field on all outbound UDP packets
-	// -1 = the default, and means "don't set anything".
-	// 0..3 = set that value.  (Even though 0 is the default UDP ECN value, a 0 here means "explicitly set a 0".)
+//
+// Experimental values.  These are subject to be deleted or change at any time,
+// do not set them, except as a result of an explicit and advanced user opt-in,
+// and do not write anything that depends on them existing, or have any particular
+// behaviour.
+//
+	// [global int32] ECN value to send in every packet.
+	// -1 = The default, and means "auto".  We will set ECN=1, if it appears that the local internet connection appears to understand it and there may be some benefit.
+	// 0..2 = use that value.
 	k_ESteamNetworkingConfig_ECN = 999,
 
-	// Deleted, do not use
+	// [global int32] If true, send and request different TOS values in probes to relays
+	// to try to deduce if there is any bleaching or mutating of the TOS field in either direction
+	k_ESteamNetworkingConfig_SDRClient_EnableTOSProbes = 998,
+
+//
+// Deleted, do not use
+//
 	k_ESteamNetworkingConfig_DELETED_EnumerateDevVars = 35,
 
 	k_ESteamNetworkingConfigValue__Force32Bit = 0x7fffffff

public/steam/steamtypes.h

@@ -86,7 +86,7 @@ typedef uint32 DepotId_t;
 const DepotId_t k_uDepotIdInvalid = 0x0;
 
 // RTime32.  Seconds elapsed since Jan 1 1970, i.e. unix timestamp.
-// It's the same as time_t, but it is always 32-bit and unsigned.  
+// It's the same as time_t, but it is always 32-bit and unsigned.
 typedef uint32 RTime32;
 
 // handle to a Steam API call