diff --git a/src/Serval.Translation/Controllers/TranslationEnginesController.cs b/src/Serval.Translation/Controllers/TranslationEnginesController.cs
index 7001b331..015e740e 100644
--- a/src/Serval.Translation/Controllers/TranslationEnginesController.cs
+++ b/src/Serval.Translation/Controllers/TranslationEnginesController.cs
@@ -1,4 +1,5 @@
 using System.Net.Sockets;
+using MongoDB.Bson;
 
 namespace Serval.Translation.Controllers;
 
@@ -1075,12 +1076,7 @@ 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>>(
-                source.Options?.ToString() ?? "{}",
-                jsonSerializerOptions
-            );
+            build.OptionsDocument = BsonDocument.Parse(source.Options?.ToString() ?? "{}");
         }
         catch (Exception e)
         {
@@ -1089,7 +1085,7 @@ private static Build Map(Engine engine, TranslationBuildConfigDto source)
         return build;
     }
 
-    private QueueDto Map(Queue source) => new() { Size = source.Size, EngineType = source.EngineType };
+    private static QueueDto Map(Queue source) => new() { Size = source.Size, EngineType = source.EngineType };
 
     private TranslationEngineDto Map(Engine source)
     {
@@ -1110,6 +1106,11 @@ private TranslationEngineDto Map(Engine source)
 
     private TranslationBuildDto Map(Build source)
     {
+        string options;
+        if (source.OptionsDocument is not null)
+            options = source.OptionsDocument.ToString();
+        else
+            options = JsonSerializer.Serialize(source.Options);
         return new TranslationBuildDto
         {
             Id = source.Id,
@@ -1129,7 +1130,7 @@ private TranslationBuildDto Map(Build source)
             QueueDepth = source.QueueDepth,
             State = source.State,
             DateFinished = source.DateFinished,
-            Options = source.Options
+            Options = options
         };
     }
 
diff --git a/src/Serval.Translation/Models/Build.cs b/src/Serval.Translation/Models/Build.cs
index 0a4f6a8c..ee5af4d6 100644
--- a/src/Serval.Translation/Models/Build.cs
+++ b/src/Serval.Translation/Models/Build.cs
@@ -15,4 +15,5 @@ public class Build : IEntity
     public JobState State { get; set; } = JobState.Pending;
     public DateTime? DateFinished { get; set; }
     public IDictionary<string, object>? Options { get; set; }
+    public BsonDocument? OptionsDocument { get; set; }
 }
diff --git a/src/Serval.Translation/Services/EngineService.cs b/src/Serval.Translation/Services/EngineService.cs
index f15e9cda..135b2899 100644
--- a/src/Serval.Translation/Services/EngineService.cs
+++ b/src/Serval.Translation/Services/EngineService.cs
@@ -185,12 +185,17 @@ public async Task<bool> StartBuildAsync(Build build, CancellationToken cancellat
             Dictionary<string, PretranslateCorpus>? pretranslate = build.Pretranslate?.ToDictionary(c => c.CorpusRef);
             Dictionary<string, TrainingCorpus>? trainOn = build.TrainOn?.ToDictionary(c => c.CorpusRef);
             var client = _grpcClientFactory.CreateClient<TranslationEngineApi.TranslationEngineApiClient>(engine.Type);
+            string options;
+            if (build.OptionsDocument is not null)
+                options = build.OptionsDocument.ToString();
+            else
+                options = JsonSerializer.Serialize(build.Options);
             var request = new StartBuildRequest
             {
                 EngineType = engine.Type,
                 EngineId = engine.Id,
                 BuildId = build.Id,
-                Options = JsonSerializer.Serialize(build.Options),
+                Options = options,
                 Corpora =
                 {
                     engine.Corpora.Select(c =>
diff --git a/src/Serval.Translation/Usings.cs b/src/Serval.Translation/Usings.cs
index 79e2783d..2f18b032 100644
--- a/src/Serval.Translation/Usings.cs
+++ b/src/Serval.Translation/Usings.cs
@@ -13,6 +13,7 @@
 global using Microsoft.Extensions.Configuration;
 global using Microsoft.Extensions.Logging;
 global using Microsoft.Extensions.Options;
+global using MongoDB.Bson;
 global using NSwag.Annotations;
 global using Serval.Shared.Configuration;
 global using Serval.Shared.Contracts;
diff --git a/tests/Serval.ApiServer.IntegrationTests/TranslationEngineTests.cs b/tests/Serval.ApiServer.IntegrationTests/TranslationEngineTests.cs
index bc0f4cee..29779cd4 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 +964,21 @@ 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":{
+                            "other_double":10.5
+                         },
+                         "some_string":"string"}
+                        """
                 };
                 TranslationBuild resultAfterStart;
                 Assert.ThrowsAsync<ServalApiException>(async () =>
@@ -996,12 +995,8 @@ 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 +1107,8 @@ 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 +1165,7 @@ private static AsyncUnaryCall<TResponse> CreateAsyncUnaryCall<TResponse>(StatusC
             Task.FromException<TResponse>(new RpcException(status)),
             Task.FromResult(new Metadata()),
             () => status,
-            () => new Metadata(),
+            () => [],
             () => { }
         );
     }
@@ -1185,7 +1176,7 @@ private static AsyncUnaryCall<TResponse> CreateAsyncUnaryCall<TResponse>(TRespon
             Task.FromResult(response),
             Task.FromResult(new Metadata()),
             () => Status.DefaultSuccess,
-            () => new Metadata(),
+            () => [],
             () => { }
         );
     }