Adding a capabilities flag and bumping the communication to 1.5.0

com.unity.ml-agents/Runtime/Academy.cs

         ///         <term>1.4.0</term>
         ///         <description>Support training analytics sent from python trainer to the editor.</description>
         ///     </item>
+        ///     <item>
+        ///         <term>1.5.0</term>
+        ///         <description>Support variable length observation training.</description>
+        ///     </item>
-        const string k_ApiVersion = "1.4.0";
+        const string k_ApiVersion = "1.5.0";
 
         /// <summary>
         /// Unity package version of com.unity.ml-agents.

com.unity.ml-agents/Runtime/Communicator/GrpcExtensions.cs

                 {
                     observationProto.DimensionProperties.Add((int)dimensionProperties[i]);
                 }
+                // Checking trainer compatibility with variable length observations
+                if (dimensionProperties.Length == 2)
+                {
+                    if (dimensionProperties[0] == DimensionProperty.VariableSize &&
+                    dimensionProperties[1] == DimensionProperty.None)
+                    {
+                        var trainerCanHandleVarLenObs = Academy.Instance.TrainerCapabilities == null || Academy.Instance.TrainerCapabilities.VariableLengthObservation;
+                        Debug.Log(trainerCanHandleVarLenObs);
+                        if (!trainerCanHandleVarLenObs)
+                        {
+                            throw new UnityAgentsException("Variable Length Observations are not supported by the trainer");
+                        }
+                    }
+                }
             }
             observationProto.Shape.AddRange(shape);
 
                 CompressedChannelMapping = proto.CompressedChannelMapping,
                 HybridActions = proto.HybridActions,
                 TrainingAnalytics = proto.TrainingAnalytics,
+                VariableLengthObservation = proto.VariableLengthObservation,
             };
         }
 
                 CompressedChannelMapping = rlCaps.CompressedChannelMapping,
                 HybridActions = rlCaps.HybridActions,
                 TrainingAnalytics = rlCaps.TrainingAnalytics,
+                VariableLengthObservation = rlCaps.VariableLengthObservation,
             };
         }
 

com.unity.ml-agents/Runtime/Communicator/UnityRLCapabilities.cs

         public bool CompressedChannelMapping;
         public bool HybridActions;
         public bool TrainingAnalytics;
+        public bool VariableLengthObservation;
 
         /// <summary>
         /// A class holding the capabilities flags for Reinforcement Learning across C# and the Trainer codebase.  This
             bool concatenatedPngObservations = true,
             bool compressedChannelMapping = true,
             bool hybridActions = true,
-            bool trainingAnalytics = true)
+            bool trainingAnalytics = true,
+            bool variableLengthObservation = true)
         {
             BaseRLCapabilities = baseRlCapabilities;
             ConcatenatedPngObservations = concatenatedPngObservations;
+            VariableLengthObservation = variableLengthObservation;
         }
 
         /// <summary>

ml-agents-envs/mlagents_envs/environment.py

     #  * 1.2.0 - support compression mapping for stacked compressed observations.
     #  * 1.3.0 - support action spaces with both continuous and discrete actions.
     #  * 1.4.0 - support training analytics sent from python trainer to the editor.
-    API_VERSION = "1.4.0"
+    #  * 1.5.0 - support variable length observation training.
+    API_VERSION = "1.5.0"
 
     # Default port that the editor listens on. If an environment executable
     # isn't specified, this port will be used.
         capabilities.compressedChannelMapping = True
         capabilities.hybridActions = True
         capabilities.trainingAnalytics = True
+        capabilities.variableLengthObservation = True
         return capabilities
 
     @staticmethod

protobuf-definitions/proto/mlagents_envs/communicator_objects/capabilities.proto

 
     // support for training analytics
     bool trainingAnalytics = 5;
+
+    // Support for variable length observations of rank 2
+    bool variableLengthObservation = 6;
 }