diff --git a/src/Bonsai.ML.HiddenMarkovModels/ModelParameters.cs b/src/Bonsai.ML.HiddenMarkovModels/ModelParameters.cs
index 4ccfe7e2..a94bae28 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/ModelParameters.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/ModelParameters.cs
@@ -3,8 +3,8 @@
 using System.ComponentModel;
 using System.Linq;
 using System.Reactive.Linq;
+using System.Text;
 using Newtonsoft.Json;
-using Newtonsoft.Json.Converters;
 using System.Xml.Serialization;
 using Python.Runtime;
 using Bonsai.ML.HiddenMarkovModels.Observations;
@@ -15,7 +15,7 @@ namespace Bonsai.ML.HiddenMarkovModels
     [Combinator]
     [Description("")]
     [WorkflowElementCategory(ElementCategory.Source)]
-    public class ModelParameters
+    public class ModelParameters : PythonStringBuilder
     {
 
         private int numStates;
@@ -29,7 +29,7 @@ public class ModelParameters
         [JsonProperty("num_states")]
         [Description("The number of discrete latent states of the HMM model")]
         [Category("InitialParameters")]
-        public int NumStates { get => numStates; set => numStates = value; }
+        public int NumStates { get => numStates; set { numStates = value; UpdateString(); } }
 
         /// <summary>
         /// The dimensionality of the observations into the HMM model.
@@ -37,7 +37,7 @@ public class ModelParameters
         [JsonProperty("dimensions")]
         [Description("The dimensionality of the observations into the HMM model")]
         [Category("InitialParameters")]
-        public int Dimensions { get => dimensions; set => dimensions = value; }
+        public int Dimensions { get => dimensions; set { dimensions = value; UpdateString(); } }
 
         /// <summary>
         /// The type of distribution that the HMM will use to model the emission of data observations.
@@ -46,7 +46,7 @@ public class ModelParameters
         [JsonConverter(typeof(ObservationsTypeJsonConverter))]
         [Description("The type of distribution that the HMM will use to model the emission of data observations.")]
         [Category("InitialParameters")]
-        public ObservationsType ObservationsType { get => observationsType; set => observationsType = value; }
+        public ObservationsType ObservationsType { get => observationsType; set { observationsType = value; UpdateString(); } }
 
         /// <summary>
         /// The state parameters of the HMM model.
@@ -54,7 +54,16 @@ public class ModelParameters
         [XmlIgnore]
         [Description("The state parameters of the HMM model.")]
         [Category("ModelState")]
-        public StateParameters StateParameters { get => stateParameters; set => stateParameters = value; }
+        public StateParameters StateParameters
+        {
+            get => stateParameters;
+            set
+            {
+                stateParameters = value;
+                ObservationsType = stateParameters.Observations.ObservationsType;
+                UpdateString();
+            }
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ModelParameters"/> class.
@@ -98,17 +107,17 @@ public IObservable<ModelParameters> Process(IObservable<PyObject> source)
             var stateParametersObservable = new StateParameters().Process(sharedSource);
             return sharedSource.Select(pyObject =>
             {
-                var numStatesPyObj = pyObject.GetAttr<int>("num_states");
-                var dimensionsPyObj = pyObject.GetAttr<int>("dimensions");
+                NumStates = pyObject.GetAttr<int>("num_states");
+                Dimensions = pyObject.GetAttr<int>("dimensions");
                 var observationsTypeStrPyObj = pyObject.GetAttr<string>("observation_type");
 
-                var observationsTypePyObj = GetFromString(observationsTypeStrPyObj);
+                ObservationsType = GetFromString(observationsTypeStrPyObj);
 
                 return new ModelParameters()
                 {
-                    NumStates = numStatesPyObj,
-                    Dimensions = dimensionsPyObj,
-                    ObservationsType = observationsTypePyObj,
+                    NumStates = NumStates,
+                    Dimensions = Dimensions,
+                    ObservationsType = ObservationsType,
                 };
             }).Zip(stateParametersObservable, (modelParameters, stateParameters) =>
             {
@@ -117,12 +126,21 @@ public IObservable<ModelParameters> Process(IObservable<PyObject> source)
             });
         }
 
-        public override string ToString()
+        protected override string BuildString()
         {
-            return $"num_states={numStates}," +
-                $"dimensions={dimensions}," +
-                $"observation_type=\"{GetString(observationsType)}\"," +
-                $"{(stateParameters == null ? "" : stateParameters)}";
+            StringBuilder.Clear();
+            StringBuilder.Append($"num_states={numStates},")
+                .Append($"dimensions={dimensions},");
+
+            if (stateParameters == null)
+            {
+                StringBuilder.Append($"observation_type=\"{GetString(observationsType)}\"");
+            }
+            else
+            {
+                StringBuilder.Append($"{stateParameters}");
+            }
+            return StringBuilder.ToString();
         }
     }
 }
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/AutoRegressiveObservations.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/AutoRegressiveObservations.cs
index 2701cf13..cbc39344 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/AutoRegressiveObservations.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/AutoRegressiveObservations.cs
@@ -1,8 +1,5 @@
-using System;
-using Python.Runtime;
-using System.Reactive.Linq;
 using System.ComponentModel;
-using System.Xml.Serialization;
+using System.Collections.Generic;
 using Newtonsoft.Json;
 
 namespace Bonsai.ML.HiddenMarkovModels.Observations
@@ -11,12 +8,14 @@ namespace Bonsai.ML.HiddenMarkovModels.Observations
     public class AutoRegressiveObservations : ObservationsModel
     {
 
+        private int lags = 1;
+
         /// <summary>
         /// The lags of the observations for each state.
         /// </summary>
         [JsonProperty]
         [Description("The lags of the observations for each state.")]
-        public int Lags { get; set; } = 1;
+        public int Lags { get => lags; set {lags = value; UpdateString(); } }
 
         /// <summary>
         /// The As of the observations for each state.
@@ -50,32 +49,28 @@ public class AutoRegressiveObservations : ObservationsModel
         [JsonProperty]
         public override object[] Params
         {
-            get { return [ As, Bs, Vs, SqrtSigmas ]; }
+            get =>[ As, Bs, Vs, SqrtSigmas ];
             set
             {
                 As = (double[,,])value[0];
                 Bs = (double[,])value[1];
                 Vs = (double[,,])value[2];
                 SqrtSigmas = (double[,,])value[3];
+                UpdateString();
             }
         }
 
-        public AutoRegressiveObservations (params object[] args)
-        {
-            Lags = (int)args[0];
-        }
-
         /// <inheritdoc/>
-        public override string ToString()
+        [JsonProperty]
+        public override Dictionary<string, object> Kwargs => new Dictionary<string, object>
         {
-            if (As is null || Bs is null || Vs is null || SqrtSigmas is null) 
-                return $"observation_params=None,observation_kwargs={{'lags':{Lags}}}";
+            ["lags"] = Lags,
+        };
 
-            return $"observation_params=({NumpyHelper.NumpyParser.ParseArray(As)}," +
-                $"{NumpyHelper.NumpyParser.ParseArray(Bs)}," +
-                $"{NumpyHelper.NumpyParser.ParseArray(Vs)}," +
-                $"{NumpyHelper.NumpyParser.ParseArray(SqrtSigmas)})," +
-                $"observation_kwargs={{'lags':{Lags}}}";
+        public AutoRegressiveObservations (params object[] args)
+        {
+            Lags = (int)args[0];
+            UpdateString();
         }
     }
 }
\ No newline at end of file
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/AutoRegressiveObservationsModel.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/AutoRegressiveObservationsModel.cs
index 15f0779e..4ea95582 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/AutoRegressiveObservationsModel.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/AutoRegressiveObservationsModel.cs
@@ -11,7 +11,7 @@ namespace Bonsai.ML.HiddenMarkovModels.Observations
     [Description("")]
     [WorkflowElementCategory(ElementCategory.Source)]
     [JsonObject(MemberSerialization.OptIn)]
-    public class AutoRegressiveObservationsModel : ObservationsModelBuilder<AutoRegressiveObservations>
+    public class AutoRegressiveObservationsModel
     {
         /// <summary>
         /// The lags of the observations for each state.
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/BernoulliObservations.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/BernoulliObservations.cs
index 2fa48384..e2b33035 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/BernoulliObservations.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/BernoulliObservations.cs
@@ -1,9 +1,6 @@
-using System;
-using Python.Runtime;
-using System.Reactive.Linq;
 using System.ComponentModel;
-using System.Xml.Serialization;
 using Newtonsoft.Json;
+using static Bonsai.ML.HiddenMarkovModels.Observations.ObservationsLookup;
 
 namespace Bonsai.ML.HiddenMarkovModels.Observations
 {
@@ -25,16 +22,11 @@ public class BernoulliObservations : ObservationsModel
          public override object[] Params
         {
             get { return [ LogitPs ]; }
-            set { LogitPs = (double[,])value[0]; }
-        }
-
-        /// <inheritdoc/>
-        public override string ToString()
-        {
-            if (LogitPs is null) 
-                return $"observation_params=None";
-
-            return $"observation_params=({NumpyHelper.NumpyParser.ParseArray(LogitPs)},)";
+            set 
+            { 
+                LogitPs = (double[,])value[0];
+                UpdateString();
+            }
         }
     }
 }
\ No newline at end of file
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/BernoulliObservationsModel.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/BernoulliObservationsModel.cs
index 450da47a..529cce89 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/BernoulliObservationsModel.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/BernoulliObservationsModel.cs
@@ -11,7 +11,7 @@ namespace Bonsai.ML.HiddenMarkovModels.Observations
     [Description("")]
     [WorkflowElementCategory(ElementCategory.Source)]
     [JsonObject(MemberSerialization.OptIn)]
-    public class BernoulliObservationsModel : ObservationsModelBuilder<BernoulliObservations>
+    public class BernoulliObservationsModel
     {
         /// <summary>
         /// The logit P of the observations for each state.
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/ExponentialObservations.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/ExponentialObservations.cs
index 38e33ac5..536575a2 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/ExponentialObservations.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/ExponentialObservations.cs
@@ -1,9 +1,7 @@
-using System;
-using Python.Runtime;
-using System.Reactive.Linq;
 using System.ComponentModel;
-using System.Xml.Serialization;
+using System.Text;
 using Newtonsoft.Json;
+using static Bonsai.ML.HiddenMarkovModels.Observations.ObservationsLookup;
 
 namespace Bonsai.ML.HiddenMarkovModels.Observations
 {
@@ -29,16 +27,8 @@ public override object[] Params
             set
             {
                 LogLambdas = (double[,])value[0];
+                UpdateString();
             }
         }
-
-        /// <inheritdoc/>
-        public override string ToString()
-        {
-            if (LogLambdas is null) 
-                return $"observation_params=None";
-
-            return $"observation_params=({NumpyHelper.NumpyParser.ParseArray(LogLambdas)},)";
-        }
     }
 }
\ No newline at end of file
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/ExponentialObservationsModel.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/ExponentialObservationsModel.cs
index decd52f7..7cbece9d 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/ExponentialObservationsModel.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/ExponentialObservationsModel.cs
@@ -9,9 +9,9 @@ namespace Bonsai.ML.HiddenMarkovModels.Observations
 {
     [Combinator]
     [Description("")]
-    [WorkflowElementCategory(ElementCategory.Transform)]
+    [WorkflowElementCategory(ElementCategory.Source)]
     [JsonObject(MemberSerialization.OptIn)]
-    public class ExponentialObservationsModel : ObservationsModelBuilder<ExponentialObservations>
+    public class ExponentialObservationsModel
     {
 
         /// <summary>
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/GaussianObservations.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/GaussianObservations.cs
index 3478c4bc..2bd81948 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/GaussianObservations.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/GaussianObservations.cs
@@ -32,22 +32,13 @@ public class GaussianObservations : ObservationsModel
         [JsonProperty]
         public override object[] Params
         {
-            get { return [ Mus, SqrtSigmas ]; }
+            get => [ Mus, SqrtSigmas ];
             set
             {
                 Mus = (double[,])value[0];
                 SqrtSigmas = (double[,,])value[1];
+                UpdateString();
             }
         }
-
-        /// <inheritdoc/>
-        public override string ToString()
-        {
-            if (Mus is null || SqrtSigmas is null) 
-                return $"observation_params=None";
-
-            return $"observation_params=({NumpyHelper.NumpyParser.ParseArray(Mus)}," +
-                $"{NumpyHelper.NumpyParser.ParseArray(SqrtSigmas)})";
-        }
     }
 }
\ No newline at end of file
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/GaussianObservationsModel.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/GaussianObservationsModel.cs
index 804b68f8..3aba98af 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/GaussianObservationsModel.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/GaussianObservationsModel.cs
@@ -10,9 +10,9 @@ namespace Bonsai.ML.HiddenMarkovModels.Observations
 {
     [Combinator]
     [Description("")]
-    [WorkflowElementCategory(ElementCategory.Transform)]
+    [WorkflowElementCategory(ElementCategory.Source)]
     [JsonObject(MemberSerialization.OptIn)]
-    public class GaussianObservationsModel : ObservationsModelBuilder<GaussianObservations>
+    public class GaussianObservationsModel
     {
 
         /// <summary>
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/ObservationsModel.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/ObservationsModel.cs
index e5e058fb..f145a26c 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/ObservationsModel.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/ObservationsModel.cs
@@ -1,12 +1,14 @@
-using Newtonsoft.Json;
 using System;
+using System.Collections.Generic;
+using System.Text;
+using static Bonsai.ML.HiddenMarkovModels.Observations.ObservationsLookup;
 
 namespace Bonsai.ML.HiddenMarkovModels.Observations
 {
     /// <summary>
     /// An abstract class for creating an observations model.
     /// </summary>
-    public abstract class ObservationsModel
+    public abstract class ObservationsModel : PythonStringBuilder
     {
         /// <summary>
         /// The type of observations model.
@@ -21,6 +23,46 @@ public abstract class ObservationsModel
         /// <summary>
         /// The keyword arguments that are used to construct the observations models.
         /// </summary>
-        public virtual object[] Kwargs => Array.Empty<object>();
+        public virtual Dictionary<string, object> Kwargs => new();
+
+        protected override string BuildString()
+        {
+            StringBuilder.Clear();
+            StringBuilder.Append($"observation_type=\"{GetString(ObservationsType)}\"");
+
+            if (Params != null && Params.Length > 0) 
+            {
+                var paramsStringBuilder = new StringBuilder();
+                paramsStringBuilder.Append(",observation_params=(");
+
+                foreach (var param in Params) {
+                    if (param is null) {
+                        paramsStringBuilder.Clear();
+                        break;
+                    }
+                    var arrString = param is Array array ? NumpyHelper.NumpyParser.ParseArray(array) : param.ToString();
+                    paramsStringBuilder.Append($"{arrString},");
+                }
+
+                if (paramsStringBuilder.Length > 0) {
+                    paramsStringBuilder.Remove(paramsStringBuilder.Length - 1, 1);
+                    paramsStringBuilder.Append(")");
+                    StringBuilder.Append(paramsStringBuilder);
+                }
+                
+            }
+
+            if (Kwargs is not null && Kwargs.Count > 0)
+            {
+                StringBuilder.Append(",observation_kwargs={");
+                foreach (var kp in Kwargs) {
+                    StringBuilder.Append($"\"{kp.Key}\":{(kp.Value is Array ? NumpyHelper.NumpyParser.ParseArray((Array)kp.Value) : kp.Value)},");
+                }
+                StringBuilder.Remove(StringBuilder.Length - 1, 1);
+                StringBuilder.Append("}");   
+            }
+
+            return StringBuilder.ToString();
+        }
     }
 }
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/ObservationsModelBuilder.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/ObservationsModelBuilder.cs
deleted file mode 100644
index 0b239960..00000000
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/ObservationsModelBuilder.cs
+++ /dev/null
@@ -1,6 +0,0 @@
-namespace Bonsai.ML.HiddenMarkovModels.Observations
-{
-    public abstract class ObservationsModelBuilder<T> where T : ObservationsModel
-    {
-    }
-}
\ No newline at end of file
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/PoissonObservations.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/PoissonObservations.cs
index 02a79e4b..e0597ea7 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/PoissonObservations.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/PoissonObservations.cs
@@ -29,37 +29,8 @@ public override object[] Params
             set
             {
                 LogLambdas = (double[,])value[0];
+                UpdateString();
             }
         }
-
-        public IObservable<PoissonObservations> Process()
-        {
-            return Observable.Return(
-                new PoissonObservations {
-                    LogLambdas = LogLambdas
-                });
-        }
-
-        public IObservable<PoissonObservations> Process(IObservable<PyObject> source)
-        {
-            return Observable.Select(source, pyObject =>
-            {
-                var logLambdasPyObj = (double[,])pyObject.GetArrayAttr("log_lambdas");
-
-                return new PoissonObservations
-                {
-                    LogLambdas = logLambdasPyObj
-                };
-            });
-        }
-
-        /// <inheritdoc/>
-        public override string ToString()
-        {
-            if (LogLambdas is null) 
-                return $"observation_params=None";
-
-            return $"observation_params=({NumpyHelper.NumpyParser.ParseArray(LogLambdas)},)";
-        }
     }
 }
\ No newline at end of file
diff --git a/src/Bonsai.ML.HiddenMarkovModels/Observations/PoissonObservationsModel.cs b/src/Bonsai.ML.HiddenMarkovModels/Observations/PoissonObservationsModel.cs
index 1af8f77a..0d7ebf6f 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/Observations/PoissonObservationsModel.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/Observations/PoissonObservationsModel.cs
@@ -9,8 +9,9 @@ namespace Bonsai.ML.HiddenMarkovModels.Observations
 {
     [Combinator]
     [Description("")]
-    [WorkflowElementCategory(ElementCategory.Transform)]
-    public class PoissonObservationsModel : ObservationsModelBuilder<PoissonObservations>
+    [WorkflowElementCategory(ElementCategory.Source)]
+    [JsonObject(MemberSerialization.OptIn)]
+    public class PoissonObservationsModel
     {
 
         /// <summary>
@@ -39,14 +40,5 @@ public IObservable<PoissonObservations> Process(IObservable<PyObject> source)
                 };
             });
         }
-
-        /// <inheritdoc/>
-        public override string ToString()
-        {
-            if (LogLambdas is null) 
-                return $"observation_params=None";
-
-            return $"observation_params=({NumpyHelper.NumpyParser.ParseArray(LogLambdas)},)";
-        }
     }
 }
\ No newline at end of file
diff --git a/src/Bonsai.ML.HiddenMarkovModels/StateParameters.cs b/src/Bonsai.ML.HiddenMarkovModels/StateParameters.cs
index 940ea355..190c4136 100644
--- a/src/Bonsai.ML.HiddenMarkovModels/StateParameters.cs
+++ b/src/Bonsai.ML.HiddenMarkovModels/StateParameters.cs
@@ -19,7 +19,7 @@ namespace Bonsai.ML.HiddenMarkovModels
     [JsonConverter(typeof(StateParametersJsonConverter))]
     [Description("StateParameters of a Hidden Markov Model (HMM).")]
     [WorkflowElementCategory(ElementCategory.Source)]
-    public class StateParameters
+    public class StateParameters : PythonStringBuilder
     {
 
         private double[] initialStateDistribution = null;
@@ -36,7 +36,10 @@ public class StateParameters
         public double[] InitialStateDistribution
         {
             get => initialStateDistribution;
-            set => initialStateDistribution = value;
+            set {
+                initialStateDistribution = value;
+                UpdateString();
+            }
         }
 
         /// <summary>
@@ -49,7 +52,10 @@ public double[] InitialStateDistribution
         public double[,] LogTransitionProbabilities
         {
             get => logTransitionProbabilities;
-            set => logTransitionProbabilities = value;
+            set {
+                logTransitionProbabilities = value;
+                UpdateString();
+            }
         }
 
         /// <summary>
@@ -62,7 +68,10 @@ public double[] InitialStateDistribution
         public ObservationsModel Observations
         {
             get => observations;
-            set => observations = value;
+            set { 
+                observations = value;
+                UpdateString();
+            }
         }
 
         public IObservable<StateParameters> Process()
@@ -120,11 +129,25 @@ public IObservable<StateParameters> Process(IObservable<PyObject> source)
             });
         }
 
-        public override string ToString()
+        protected override string BuildString()
         {
-            return $"initial_state_distribution={(InitialStateDistribution == null ? "None" : NumpyHelper.NumpyParser.ParseArray(InitialStateDistribution))}," + 
-                $"log_transition_probabilities={(LogTransitionProbabilities == null ? "None" : NumpyHelper.NumpyParser.ParseArray(LogTransitionProbabilities))}," +
-                $"{(Observations == null ? "" : Observations)}";
+            StringBuilder.Clear();
+
+            if (InitialStateDistribution != null) {
+                StringBuilder.Append($"initial_state_distribution={NumpyHelper.NumpyParser.ParseArray(InitialStateDistribution)},");
+            }
+
+            if (LogTransitionProbabilities != null) {
+                StringBuilder.Append($"log_transition_probabilities={NumpyHelper.NumpyParser.ParseArray(LogTransitionProbabilities)},");
+            }
+
+            if (Observations != null) {
+                StringBuilder.Append($"{Observations},");
+            }
+
+            StringBuilder.Remove(StringBuilder.Length - 1, 1);
+
+            return StringBuilder.ToString();            
         }
     }
 }