diff --git a/src/Serval.Translation/Controllers/TranslationEnginesController.cs b/src/Serval.Translation/Controllers/TranslationEnginesController.cs
index 7001b331..3a09a127 100644
--- a/src/Serval.Translation/Controllers/TranslationEnginesController.cs
+++ b/src/Serval.Translation/Controllers/TranslationEnginesController.cs
@@ -1,4 +1,5 @@
 using System.Net.Sockets;
+using Serval.Translation.Utils;
 
 namespace Serval.Translation.Controllers;
 
@@ -1075,11 +1076,9 @@ private static Build Map(Engine engine, TranslationBuildConfigDto source)
         }
         try
         {
-            var jsonSerializerOptions = new JsonSerializerOptions();
-            jsonSerializerOptions.Converters.Add(new ObjectToInferredTypesConverter());
-            build.Options = JsonSerializer.Deserialize<IDictionary<string, object>>(
+            build.Options = Newtonsoft.Json.JsonConvert.DeserializeObject<IDictionary<string, object>>(
                 source.Options?.ToString() ?? "{}",
-                jsonSerializerOptions
+                new DictionaryJsonConverter()
             );
         }
         catch (Exception e)
diff --git a/src/Serval.Translation/Utils/DictionaryJsonConverter.cs b/src/Serval.Translation/Utils/DictionaryJsonConverter.cs
new file mode 100644
index 00000000..226878d0
--- /dev/null
+++ b/src/Serval.Translation/Utils/DictionaryJsonConverter.cs
@@ -0,0 +1,167 @@
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Serval.Translation.Utils;
+
+// Credit to anish-patel post in https://stackoverflow.com/questions/11561597/deserialize-json-recursively-to-idictionarystring-object
+public class DictionaryJsonConverter : JsonConverter
+{
+    public override void WriteJson(JsonWriter writer, object? value, Newtonsoft.Json.JsonSerializer serializer)
+    {
+        WriteValue(writer, value);
+    }
+
+    private void WriteValue(JsonWriter writer, object? value)
+    {
+        if (value is null)
+        {
+            writer.WriteNull();
+            return;
+        }
+        var t = JToken.FromObject(value);
+        switch (t.Type)
+        {
+            case JTokenType.Object:
+                WriteObject(writer, value);
+                break;
+            case JTokenType.Array:
+                WriteArray(writer, value);
+                break;
+            default:
+                writer.WriteValue(value);
+                break;
+        }
+    }
+
+    private void WriteObject(JsonWriter writer, object value)
+    {
+        writer.WriteStartObject();
+        var obj =
+            value as IDictionary<string, object>
+            ?? throw new JsonSerializationException("Object must implement IDictionary<string, object>");
+        foreach (var kvp in obj)
+        {
+            writer.WritePropertyName(kvp.Key);
+            WriteValue(writer, kvp.Value);
+        }
+        writer.WriteEndObject();
+    }
+
+    private void WriteArray(JsonWriter writer, object value)
+    {
+        writer.WriteStartArray();
+        var array =
+            value as IEnumerable<object>
+            ?? throw new JsonSerializationException(
+                "Unexpected type when converting IDictionary<string, object> to Array."
+            );
+        foreach (var o in array)
+        {
+            WriteValue(writer, o);
+        }
+        writer.WriteEndArray();
+    }
+
+    public override object ReadJson(
+        JsonReader reader,
+        Type objectType,
+        object? existingValue,
+        Newtonsoft.Json.JsonSerializer serializer
+    )
+    {
+        return ReadValue(reader);
+    }
+
+    private object ReadValue(JsonReader reader)
+    {
+        while (reader.TokenType == JsonToken.Comment)
+        {
+            if (!reader.Read())
+                throw new JsonSerializationException("Unexpected Token when converting IDictionary<string, object>");
+        }
+
+        return reader.TokenType switch
+        {
+            JsonToken.StartObject => ReadObject(reader),
+            JsonToken.StartArray => ReadArray(reader),
+            JsonToken.Integer
+            or JsonToken.Float
+            or JsonToken.String
+            or JsonToken.Boolean
+            or JsonToken.Undefined
+            or JsonToken.Null
+            or JsonToken.Date
+            or JsonToken.Bytes
+                => reader.Value
+                    ?? throw new JsonSerializationException(
+                        "Unexpected token when converting to " + reader.TokenType.ToString()
+                    ),
+            _
+                => throw new JsonSerializationException(
+                    string.Format("Unexpected token when converting IDictionary<string, object>: {0}", reader.TokenType)
+                ),
+        };
+    }
+
+    private object ReadArray(JsonReader reader)
+    {
+        IList<object> list = [];
+
+        while (reader.Read())
+        {
+            switch (reader.TokenType)
+            {
+                case JsonToken.Comment:
+                    break;
+                default:
+                    var v = ReadValue(reader);
+
+                    list.Add(v);
+                    break;
+                case JsonToken.EndArray:
+                    return list;
+            }
+        }
+
+        throw new JsonSerializationException("Unexpected end when reading IDictionary<string, object>");
+    }
+
+    private object ReadObject(JsonReader reader)
+    {
+        var obj = new Dictionary<string, object>();
+
+        while (reader.Read())
+        {
+            switch (reader.TokenType)
+            {
+                case JsonToken.PropertyName:
+                    var propertyName =
+                        reader.Value!.ToString()
+                        ?? throw new JsonSerializationException(
+                            "Unexpected Token when converting IDictionary<string, object>"
+                        );
+
+                    if (!reader.Read())
+                    {
+                        throw new JsonSerializationException("Unexpected end when reading IDictionary<string, object>");
+                    }
+
+                    var v = ReadValue(reader);
+
+                    obj[propertyName] = v;
+                    break;
+                case JsonToken.Comment:
+                    break;
+                case JsonToken.EndObject:
+                    return obj;
+            }
+        }
+
+        throw new JsonSerializationException("Unexpected end when reading IDictionary<string, object>");
+    }
+
+    public override bool CanConvert(Type objectType)
+    {
+        return typeof(IDictionary<string, object>).IsAssignableFrom(objectType);
+    }
+}
diff --git a/tests/Serval.ApiServer.IntegrationTests/TranslationEngineTests.cs b/tests/Serval.ApiServer.IntegrationTests/TranslationEngineTests.cs
index bc0f4cee..3e208868 100644
--- a/tests/Serval.ApiServer.IntegrationTests/TranslationEngineTests.cs
+++ b/tests/Serval.ApiServer.IntegrationTests/TranslationEngineTests.cs
@@ -64,7 +64,7 @@ public async Task SetUp()
             TargetLanguage = "en",
             Type = "Echo",
             Owner = "client1",
-            Corpora = new List<Translation.Models.Corpus>()
+            Corpora = []
         };
         var e1 = new Engine
         {
@@ -74,7 +74,7 @@ public async Task SetUp()
             TargetLanguage = "en",
             Type = "Echo",
             Owner = "client1",
-            Corpora = new List<Translation.Models.Corpus>()
+            Corpora = []
         };
         var e2 = new Engine
         {
@@ -84,7 +84,7 @@ public async Task SetUp()
             TargetLanguage = "en",
             Type = "Echo",
             Owner = "client2",
-            Corpora = new List<Translation.Models.Corpus>()
+            Corpora = []
         };
         var be0 = new Engine
         {
@@ -94,7 +94,7 @@ public async Task SetUp()
             TargetLanguage = "es",
             Type = "SMTTransfer",
             Owner = "client1",
-            Corpora = new List<Translation.Models.Corpus>()
+            Corpora = []
         };
         var ce0 = new Engine
         {
@@ -104,7 +104,7 @@ public async Task SetUp()
             TargetLanguage = "es",
             Type = "Nmt",
             Owner = "client1",
-            Corpora = new List<Translation.Models.Corpus>()
+            Corpora = []
         };
 
         await _env.Engines.InsertAllAsync(new[] { e0, e1, e2, be0, ce0 });
@@ -740,7 +740,7 @@ public async Task GetAllPretranslationsAsync_Exists()
             CorpusRef = addedCorpus.Id,
             TextId = "all",
             EngineRef = ECHO_ENGINE1_ID,
-            Refs = new List<string> { "ref1", "ref2" },
+            Refs = ["ref1", "ref2"],
             Translation = "translation",
             ModelRevision = 1
         };
@@ -799,7 +799,7 @@ public async Task GetAllPretranslationsAsync_TextIdExists()
             CorpusRef = addedCorpus.Id,
             TextId = "all",
             EngineRef = ECHO_ENGINE1_ID,
-            Refs = new List<string> { "ref1", "ref2" },
+            Refs = ["ref1", "ref2"],
             Translation = "translation",
             ModelRevision = 1
         };
@@ -825,7 +825,7 @@ public async Task GetAllPretranslationsAsync_TextIdDoesNotExist()
             CorpusRef = addedCorpus.Id,
             TextId = "all",
             EngineRef = ECHO_ENGINE1_ID,
-            Refs = new List<string> { "ref1", "ref2" },
+            Refs = ["ref1", "ref2"],
             Translation = "translation",
             ModelRevision = 1
         };
@@ -964,22 +964,19 @@ public async Task StartBuildForEngineByIdAsync(IEnumerable<string> scope, int ex
         {
             case 201:
                 TranslationCorpus addedCorpus = await client.AddCorpusAsync(engineId, TestCorpusConfig);
-                ptcc = new PretranslateCorpusConfig
-                {
-                    CorpusId = addedCorpus.Id,
-                    TextIds = new List<string> { "all" }
-                };
-                tcc = new()
-                {
-                    CorpusId = addedCorpus.Id,
-                    TextIds = new List<string> { "all" }
-                };
+                ptcc = new PretranslateCorpusConfig { CorpusId = addedCorpus.Id, TextIds = ["all"] };
+                tcc = new() { CorpusId = addedCorpus.Id, TextIds = ["all"] };
                 tbc = new TranslationBuildConfig
                 {
-                    Pretranslate = new List<PretranslateCorpusConfig> { ptcc },
-                    TrainOn = new List<TrainingCorpusConfig> { tcc },
-                    Options =
-                        "{\"max_steps\":10, \"use_key_terms\":false, \"some_double\":10.5, \"some_string\":\"string\"}"
+                    Pretranslate = [ptcc],
+                    TrainOn = [tcc],
+                    Options = """
+                        {"max_steps":10,
+                        "use_key_terms":false,
+                        "some_double":10.5,
+                        "some_nested": {"more_nested": {"other_double":10.5}},
+                        "some_string":"string"}
+                        """
                 };
                 TranslationBuild resultAfterStart;
                 Assert.ThrowsAsync<ServalApiException>(async () =>
@@ -996,12 +993,8 @@ public async Task StartBuildForEngineByIdAsync(IEnumerable<string> scope, int ex
             case 400:
             case 403:
             case 404:
-                ptcc = new PretranslateCorpusConfig
-                {
-                    CorpusId = "cccccccccccccccccccccccc",
-                    TextIds = new List<string> { "all" }
-                };
-                tbc = new TranslationBuildConfig { Pretranslate = new List<PretranslateCorpusConfig> { ptcc } };
+                ptcc = new PretranslateCorpusConfig { CorpusId = "cccccccccccccccccccccccc", TextIds = ["all"] };
+                tbc = new TranslationBuildConfig { Pretranslate = [ptcc] };
                 var ex = Assert.ThrowsAsync<ServalApiException>(async () =>
                 {
                     await client.StartBuildAsync(engineId, tbc);
@@ -1112,12 +1105,8 @@ public async Task TryToQueueMultipleBuildsPerSingleUser()
         var engineId = NMT_ENGINE1_ID;
         var expectedStatusCode = 409;
         TranslationCorpus addedCorpus = await client.AddCorpusAsync(engineId, TestCorpusConfigNonEcho);
-        var ptcc = new PretranslateCorpusConfig
-        {
-            CorpusId = addedCorpus.Id,
-            TextIds = new List<string> { "all" }
-        };
-        var tbc = new TranslationBuildConfig { Pretranslate = new List<PretranslateCorpusConfig> { ptcc } };
+        var ptcc = new PretranslateCorpusConfig { CorpusId = addedCorpus.Id, TextIds = ["all"] };
+        var tbc = new TranslationBuildConfig { Pretranslate = [ptcc] };
         TranslationBuild build = await client.StartBuildAsync(engineId, tbc);
         var ex = Assert.ThrowsAsync<ServalApiException>(async () =>
         {
@@ -1174,7 +1163,7 @@ private static AsyncUnaryCall<TResponse> CreateAsyncUnaryCall<TResponse>(StatusC
             Task.FromException<TResponse>(new RpcException(status)),
             Task.FromResult(new Metadata()),
             () => status,
-            () => new Metadata(),
+            () => [],
             () => { }
         );
     }
@@ -1185,7 +1174,7 @@ private static AsyncUnaryCall<TResponse> CreateAsyncUnaryCall<TResponse>(TRespon
             Task.FromResult(response),
             Task.FromResult(new Metadata()),
             () => Status.DefaultSuccess,
-            () => new Metadata(),
+            () => [],
             () => { }
         );
     }
diff --git a/tests/Serval.E2ETests/ServalApiTests.cs b/tests/Serval.E2ETests/ServalApiTests.cs
index 10e88f7d..c28c6bcd 100644
--- a/tests/Serval.E2ETests/ServalApiTests.cs
+++ b/tests/Serval.E2ETests/ServalApiTests.cs
@@ -116,6 +116,7 @@ public async Task NmtBatch()
             new TrainingCorpusConfig { CorpusId = cId1, TextIds = new string[] { "1JN.txt" } }
         };
         var cId2 = await _helperClient.AddTextCorpusToEngine(engineId, new string[] { "3JN.txt" }, "es", "en", true);
+        _helperClient.TranslationBuildConfig.Options = """{"train_params":{"save_strategy": "yes"}}""";
         await _helperClient.BuildEngine(engineId);
         await Task.Delay(1000);
         IList<Pretranslation> lTrans = await _helperClient.translationEnginesClient.GetAllPretranslationsAsync(