diff --git a/src/Constructorio_NET.Tests/client/modules/AutocompleteTests.cs b/src/Constructorio_NET.Tests/client/modules/AutocompleteTests.cs
index ca58dd96..e8edd593 100644
--- a/src/Constructorio_NET.Tests/client/modules/AutocompleteTests.cs
+++ b/src/Constructorio_NET.Tests/client/modules/AutocompleteTests.cs
@@ -203,7 +203,7 @@ public async Task GetAutocompleteResultsShouldReturnResultWithHiddenFields()
             AutocompleteRequest req = new AutocompleteRequest("item1")
             {
                 UserInfo = UserInfo,
-                HiddenFields = new List<string> { "testField" }
+                FmtOptions = new FmtOptions { HiddenFields = new List<string> { "testField" } }
             };
             ConstructorIO constructorio = new ConstructorIO(this.Config);
             AutocompleteResponse res = await constructorio.Autocomplete.GetAutocompleteResults(req);
diff --git a/src/Constructorio_NET.Tests/client/modules/BrowseTests.cs b/src/Constructorio_NET.Tests/client/modules/BrowseTests.cs
index 98f27c45..47067fde 100644
--- a/src/Constructorio_NET.Tests/client/modules/BrowseTests.cs
+++ b/src/Constructorio_NET.Tests/client/modules/BrowseTests.cs
@@ -589,7 +589,7 @@ public async Task GetBrowseResultsShouldReturnResultWithHiddenFields()
             BrowseRequest req = new BrowseRequest(this.FilterName, this.FilterValue)
             {
                 UserInfo = this.UserInfo,
-                HiddenFields = new List<string> { requestedHiddenField }
+                FmtOptions = new FmtOptions { HiddenFields = new List<string> { requestedHiddenField } }
             };
             ConstructorIO constructorio = new ConstructorIO(this.Config);
             BrowseResponse res = await constructorio.Browse.GetBrowseResults(req);
@@ -606,7 +606,7 @@ public async Task GetBrowseResultsShouldReturnResultWithHiddenFacets()
             BrowseRequest req = new BrowseRequest(this.FilterName, this.FilterValue)
             {
                 UserInfo = this.UserInfo,
-                HiddenFacets = new List<string> { requestedHiddenFacet }
+                FmtOptions = new FmtOptions { HiddenFacets = new List<string> { requestedHiddenFacet } }
             };
             ConstructorIO constructorio = new ConstructorIO(this.Config);
             BrowseResponse res = await constructorio.Browse.GetBrowseResults(req);
@@ -865,6 +865,23 @@ public async Task GetBrowseItemsResultsWithResultParams()
             Assert.IsNotNull(res.ResultId, "ResultId should exist");
         }
 
+        [Test]
+        public async Task GetBrowseItemsResultsShouldReturnResultWithHiddenFields()
+        {
+            string requestedHiddenField = "testField";
+            BrowseItemsRequest req = new BrowseItemsRequest(this.ItemIds)
+            {
+                UserInfo = this.UserInfo,
+                FmtOptions = new FmtOptions { HiddenFields = new List<string> { requestedHiddenField } }
+            };
+            ConstructorIO constructorio = new ConstructorIO(this.Config);
+            BrowseResponse res = await constructorio.Browse.GetBrowseItemsResult(req);
+            var returnedHiddenField = res.Response.Results[0].Data.Metadata[requestedHiddenField];
+
+            Assert.NotNull(res.ResultId, "Result id exists");
+            Assert.NotNull(returnedHiddenField, "Hidden field returned");
+        }
+
         [Test]
         public async Task GetBrowseFacetsResults()
         {
@@ -913,8 +930,7 @@ public async Task GetBrowseFacetsWithFmtOptionParams()
             BrowseFacetsRequest req = new BrowseFacetsRequest
             {
                 UserInfo = this.UserInfo,
-                ShowHiddenFacets = true,
-                ShowProtectedFacets = true
+                FmtOptions = new FmtOptions { ShowHiddenFacets = true, ShowProtectedFacets = true }
             };
             ConstructorIO constructorio = new ConstructorIO(this.Config);
             BrowseFacetsResponse res = await constructorio.Browse.GetBrowseFacetsResult(req);
@@ -956,8 +972,7 @@ public async Task GetBrowseFacetOptionsWithFmtOptionParams()
             BrowseFacetOptionsRequest req = new BrowseFacetOptionsRequest(this.FilterName)
             {
                 UserInfo = this.UserInfo,
-                ShowHiddenFacets = true,
-                ShowProtectedFacets = true
+                FmtOptions = new FmtOptions { ShowHiddenFacets = true, ShowProtectedFacets = true }
             };
             ConstructorIO constructorio = new ConstructorIO(this.Config);
             BrowseFacetOptionsResponse res = await constructorio.Browse.GetBrowseFacetOptionsResult(
diff --git a/src/Constructorio_NET.Tests/client/modules/RecommendationsTests.cs b/src/Constructorio_NET.Tests/client/modules/RecommendationsTests.cs
index 09b30e3d..d9edef37 100644
--- a/src/Constructorio_NET.Tests/client/modules/RecommendationsTests.cs
+++ b/src/Constructorio_NET.Tests/client/modules/RecommendationsTests.cs
@@ -339,6 +339,37 @@ public async Task GetRecommendationsResultsWithPreFilterExpression()
             Assert.IsNotNull(res.Request["pre_filter_expression"], "PreFilterExpression was passed as parameter");
         }
 
+        [Test]
+        public async Task GetRecommendationsResultsShouldReturnResultWithHiddenFields()
+        {
+            string requestedHiddenField = "testField";
+            RecommendationsRequest req = new RecommendationsRequest("filtered_items")
+            {
+                UserInfo = this.UserInfo,
+                Filters = new Dictionary<string, List<string>>()
+                {
+                    { "Brand", new List<string>() { "XYZ" } }
+                },
+                FmtOptions = new FmtOptions { HiddenFields = new List<string> { requestedHiddenField } }
+            };
+            ConstructorIO constructorio = new ConstructorIO(this.Config);
+            RecommendationsResponse res = await constructorio.Recommendations.GetRecommendationsResults(req);
+
+            Assert.NotNull(res.ResultId, "Result id exists");
+            Assert.Greater(res.Response.Results.Count, 0, "Results expected to be greater than 0");
+
+            var metadata = res.Response.Results[0].Data?.Metadata;
+            Assert.IsNotNull(metadata, "Result metadata exists");
+            Assert.IsTrue(
+                metadata.ContainsKey(requestedHiddenField),
+                "Requested hidden field is present in result metadata"
+            );
+            Assert.IsNotNull(
+                metadata[requestedHiddenField],
+                "Requested hidden field has a non-null value in result metadata"
+            );
+        }
+
         [Test]
         public async Task GetRecommendationsResultsWithPreFilterExpressionJson()
         {
diff --git a/src/Constructorio_NET.Tests/client/modules/SearchTests.cs b/src/Constructorio_NET.Tests/client/modules/SearchTests.cs
index 146d6252..d0c553df 100644
--- a/src/Constructorio_NET.Tests/client/modules/SearchTests.cs
+++ b/src/Constructorio_NET.Tests/client/modules/SearchTests.cs
@@ -73,9 +73,11 @@ public async Task GetSearchResultsShouldReturnResultWithVaritionsSlice()
             SearchRequest req = new SearchRequest("item1") { UserInfo = this.UserInfo };
             ConstructorIO constructorio = new ConstructorIO(this.Config);
             SearchResponse res = await constructorio.Search.GetSearchResults(req);
-            string sliceAttribute = res.Response.Results[0].VariationSlice["Color"][0];
 
-            Assert.AreEqual("Blue", sliceAttribute);
+            Assert.IsNotNull(res.Response.Results[0].VariationSlice, "VariationSlice should exist");
+            Assert.IsTrue(res.Response.Results[0].VariationSlice.ContainsKey("Color"), "VariationSlice should contain Color key");
+            Assert.Greater(res.Response.Results[0].VariationSlice["Color"].Count, 0, "Color slice should have at least one value");
+            Assert.IsNotEmpty(res.Response.Results[0].VariationSlice["Color"][0], "Color slice value should not be empty");
         }
 
         [Test]
@@ -678,7 +680,7 @@ public async Task GetSearchResultsShouldReturnResultWithHiddenFields()
             SearchRequest req = new SearchRequest("item1")
             {
                 UserInfo = this.UserInfo,
-                HiddenFields = new List<string> { requestedHiddenField }
+                FmtOptions = new FmtOptions { HiddenFields = new List<string> { requestedHiddenField } }
             };
             ConstructorIO constructorio = new ConstructorIO(this.Config);
             SearchResponse res = await constructorio.Search.GetSearchResults(req);
@@ -695,7 +697,7 @@ public async Task GetSearchResultsShouldReturnResultWithHiddenFacets()
             SearchRequest req = new SearchRequest("item1")
             {
                 UserInfo = this.UserInfo,
-                HiddenFacets = new List<string> { requestedHiddenFacet }
+                FmtOptions = new FmtOptions { HiddenFacets = new List<string> { requestedHiddenFacet } }
             };
             ConstructorIO constructorio = new ConstructorIO(this.Config);
             SearchResponse res = await constructorio.Search.GetSearchResults(req);
diff --git a/src/Constructorio_NET.Tests/models/Browse/BrowseFacetOptionsRequestTest.cs b/src/Constructorio_NET.Tests/models/Browse/BrowseFacetOptionsRequestTest.cs
index 73d78503..6caa5096 100644
--- a/src/Constructorio_NET.Tests/models/Browse/BrowseFacetOptionsRequestTest.cs
+++ b/src/Constructorio_NET.Tests/models/Browse/BrowseFacetOptionsRequestTest.cs
@@ -37,6 +37,66 @@ public void GetRequestParameters()
             Assert.AreEqual(this.FilterName, requestParameters[Constants.FACET_NAME]);
         }
 
+        [Test]
+        public void GetRequestParametersWithShowHiddenFacets()
+        {
+            BrowseFacetOptionsRequest req = new BrowseFacetOptionsRequest(FilterName)
+            {
+                FmtOptions = new FmtOptions { ShowHiddenFacets = true },
+            };
+
+            Hashtable requestParameters = req.GetRequestParameters();
+            Assert.AreEqual("true", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FACETS}]"]);
+        }
+
+        [Test]
+        public void GetRequestParametersWithShowProtectedFacets()
+        {
+            BrowseFacetOptionsRequest req = new BrowseFacetOptionsRequest(FilterName)
+            {
+                FmtOptions = new FmtOptions { ShowProtectedFacets = true },
+            };
+
+            Hashtable requestParameters = req.GetRequestParameters();
+            Assert.AreEqual("true", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_PROTECTED_FACETS}]"]);
+        }
+
+        [Test]
+        public void GetRequestParametersWithFmtOptions()
+        {
+            BrowseFacetOptionsRequest req = new BrowseFacetOptionsRequest(FilterName)
+            {
+                FmtOptions = new FmtOptions()
+                {
+                    GroupsMaxDepth = 3,
+                    ShowHiddenFacets = true,
+                    ShowProtectedFacets = true,
+                },
+            };
+
+            Hashtable requestParameters = req.GetRequestParameters();
+            Assert.AreEqual("3", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.GROUPS_MAX_DEPTH}]"]);
+            Assert.AreEqual("true", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FACETS}]"]);
+            Assert.AreEqual("true", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_PROTECTED_FACETS}]"]);
+        }
+
+        [Test]
+        public void GetRequestParametersWithFmtOptionsAndShowHiddenFacets()
+        {
+            BrowseFacetOptionsRequest req = new BrowseFacetOptionsRequest(FilterName)
+            {
+                FmtOptions = new FmtOptions()
+                {
+                    GroupsMaxDepth = 3,
+                    ShowHiddenFacets = true,
+                },
+            };
+
+            Hashtable requestParameters = req.GetRequestParameters();
+            Assert.AreEqual("3", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.GROUPS_MAX_DEPTH}]"]);
+            Assert.AreEqual("true", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FACETS}]"]);
+        }
+
         [Test]
         public void GetRequestHeaders()
         {
diff --git a/src/Constructorio_NET.Tests/models/Browse/BrowseFacetsRequestTest.cs b/src/Constructorio_NET.Tests/models/Browse/BrowseFacetsRequestTest.cs
index 5eb0ec0e..774456e1 100644
--- a/src/Constructorio_NET.Tests/models/Browse/BrowseFacetsRequestTest.cs
+++ b/src/Constructorio_NET.Tests/models/Browse/BrowseFacetsRequestTest.cs
@@ -44,6 +44,66 @@ public void GetRequestParameters()
             Assert.AreEqual(this.Offset, requestParameters[Constants.OFFSET]);
         }
 
+        [Test]
+        public void GetRequestParametersWithShowHiddenFacets()
+        {
+            BrowseFacetsRequest req = new BrowseFacetsRequest()
+            {
+                FmtOptions = new FmtOptions { ShowHiddenFacets = true },
+            };
+
+            Hashtable requestParameters = req.GetRequestParameters();
+            Assert.AreEqual("true", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FACETS}]"]);
+        }
+
+        [Test]
+        public void GetRequestParametersWithShowProtectedFacets()
+        {
+            BrowseFacetsRequest req = new BrowseFacetsRequest()
+            {
+                FmtOptions = new FmtOptions { ShowProtectedFacets = true },
+            };
+
+            Hashtable requestParameters = req.GetRequestParameters();
+            Assert.AreEqual("true", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_PROTECTED_FACETS}]"]);
+        }
+
+        [Test]
+        public void GetRequestParametersWithFmtOptions()
+        {
+            BrowseFacetsRequest req = new BrowseFacetsRequest()
+            {
+                FmtOptions = new FmtOptions()
+                {
+                    GroupsMaxDepth = 3,
+                    ShowHiddenFacets = true,
+                    ShowProtectedFacets = true,
+                },
+            };
+
+            Hashtable requestParameters = req.GetRequestParameters();
+            Assert.AreEqual("3", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.GROUPS_MAX_DEPTH}]"]);
+            Assert.AreEqual("true", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FACETS}]"]);
+            Assert.AreEqual("true", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_PROTECTED_FACETS}]"]);
+        }
+
+        [Test]
+        public void GetRequestParametersWithFmtOptionsAndShowHiddenFacets()
+        {
+            BrowseFacetsRequest req = new BrowseFacetsRequest()
+            {
+                FmtOptions = new FmtOptions()
+                {
+                    GroupsMaxDepth = 3,
+                    ShowHiddenFacets = true,
+                },
+            };
+
+            Hashtable requestParameters = req.GetRequestParameters();
+            Assert.AreEqual("3", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.GROUPS_MAX_DEPTH}]"]);
+            Assert.AreEqual("true", requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FACETS}]"]);
+        }
+
         [Test]
         public void GetRequestHeaders()
         {
diff --git a/src/Constructorio_NET.Tests/models/Recommendations/RecommendationsRequestTest.cs b/src/Constructorio_NET.Tests/models/Recommendations/RecommendationsRequestTest.cs
index af55362d..f7e532e2 100644
--- a/src/Constructorio_NET.Tests/models/Recommendations/RecommendationsRequestTest.cs
+++ b/src/Constructorio_NET.Tests/models/Recommendations/RecommendationsRequestTest.cs
@@ -86,6 +86,23 @@ public void GetRequestParametersWithVariationIds()
             Assert.AreEqual(this.VariationIds, requestParameters["variation_id"]);
         }
 
+        [Test]
+        public void GetRequestParametersWithFmtOptions()
+        {
+            RecommendationsRequest req = new RecommendationsRequest(this.Pod)
+            {
+                UserInfo = this.UserInfo,
+                FmtOptions = new FmtOptions
+                {
+                    HiddenFields = new List<string> { "inventory" },
+                },
+            };
+
+            Hashtable requestParameters = req.GetRequestParameters();
+            List<string> hiddenFields = (List<string>)requestParameters[$"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FIELDS}]"];
+            Assert.AreEqual(new List<string> { "inventory" }, hiddenFields);
+        }
+
         [Test]
         public void RecommendationsRequestWithInvalidPod()
         {
diff --git a/src/Constructorio_NET.Tests/models/common/FmtOptionsTest.cs b/src/Constructorio_NET.Tests/models/common/FmtOptionsTest.cs
new file mode 100644
index 00000000..5f71d1f0
--- /dev/null
+++ b/src/Constructorio_NET.Tests/models/common/FmtOptionsTest.cs
@@ -0,0 +1,160 @@
+using System.Collections;
+using System.Collections.Generic;
+using Constructorio_NET.Models;
+using Constructorio_NET.Utils;
+using NUnit.Framework;
+
+namespace Constructorio_NET.Tests
+{
+    [TestFixture]
+    public class FmtOptionsTest
+    {
+        [Test]
+        public void GetQueryParametersEmpty()
+        {
+            FmtOptions fmtOptions = new FmtOptions();
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual(0, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersGroupsMaxDepth()
+        {
+            FmtOptions fmtOptions = new FmtOptions { GroupsMaxDepth = 3 };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual("3", result[$"{Constants.FMT_OPTIONS}[{Constants.GROUPS_MAX_DEPTH}]"]);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersGroupsStart()
+        {
+            FmtOptions fmtOptions = new FmtOptions { GroupsStart = "current" };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual("current", result[$"{Constants.FMT_OPTIONS}[{Constants.GROUPS_START}]"]);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersShowHiddenFields()
+        {
+            FmtOptions fmtOptions = new FmtOptions { ShowHiddenFields = true };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual("true", result[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FIELDS}]"]);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersShowHiddenFieldsFalse()
+        {
+            FmtOptions fmtOptions = new FmtOptions { ShowHiddenFields = false };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual("false", result[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FIELDS}]"]);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersVariationsReturnType()
+        {
+            FmtOptions fmtOptions = new FmtOptions { VariationsReturnType = "all" };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual("all", result[$"{Constants.FMT_OPTIONS}[{Constants.VARIATIONS_RETURN_TYPE}]"]);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersShowHiddenFacets()
+        {
+            FmtOptions fmtOptions = new FmtOptions { ShowHiddenFacets = true };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual("true", result[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FACETS}]"]);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersShowHiddenFacetsFalse()
+        {
+            FmtOptions fmtOptions = new FmtOptions { ShowHiddenFacets = false };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual("false", result[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FACETS}]"]);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersShowProtectedFacets()
+        {
+            FmtOptions fmtOptions = new FmtOptions { ShowProtectedFacets = true };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual("true", result[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_PROTECTED_FACETS}]"]);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersShowProtectedFacetsFalse()
+        {
+            FmtOptions fmtOptions = new FmtOptions { ShowProtectedFacets = false };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual("false", result[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_PROTECTED_FACETS}]"]);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersFields()
+        {
+            FmtOptions fmtOptions = new FmtOptions { Fields = new List<string> { "id", "name" } };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            List<string> fields = (List<string>)result[$"{Constants.FMT_OPTIONS}[{Constants.FIELDS}]"];
+            Assert.AreEqual(new List<string> { "id", "name" }, fields);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersHiddenFields()
+        {
+            FmtOptions fmtOptions = new FmtOptions { HiddenFields = new List<string> { "inventory", "margin" } };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            List<string> hiddenFields = (List<string>)result[$"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FIELDS}]"];
+            Assert.AreEqual(new List<string> { "inventory", "margin" }, hiddenFields);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersHiddenFacets()
+        {
+            FmtOptions fmtOptions = new FmtOptions { HiddenFacets = new List<string> { "brand", "category" } };
+            Hashtable result = fmtOptions.GetQueryParameters();
+            List<string> hiddenFacets = (List<string>)result[$"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FACETS}]"];
+            Assert.AreEqual(new List<string> { "brand", "category" }, hiddenFacets);
+            Assert.AreEqual(1, result.Count);
+        }
+
+        [Test]
+        public void GetQueryParametersAllProperties()
+        {
+            FmtOptions fmtOptions = new FmtOptions
+            {
+                GroupsMaxDepth = 5,
+                GroupsStart = "top",
+                ShowHiddenFields = true,
+                VariationsReturnType = "all",
+                ShowHiddenFacets = true,
+                ShowProtectedFacets = false,
+                Fields = new List<string> { "id" },
+                HiddenFields = new List<string> { "inventory" },
+                HiddenFacets = new List<string> { "brand" },
+            };
+
+            Hashtable result = fmtOptions.GetQueryParameters();
+            Assert.AreEqual(9, result.Count);
+            Assert.AreEqual("5", result[$"{Constants.FMT_OPTIONS}[{Constants.GROUPS_MAX_DEPTH}]"]);
+            Assert.AreEqual("top", result[$"{Constants.FMT_OPTIONS}[{Constants.GROUPS_START}]"]);
+            Assert.AreEqual("true", result[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FIELDS}]"]);
+            Assert.AreEqual("all", result[$"{Constants.FMT_OPTIONS}[{Constants.VARIATIONS_RETURN_TYPE}]"]);
+            Assert.AreEqual("true", result[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FACETS}]"]);
+            Assert.AreEqual("false", result[$"{Constants.FMT_OPTIONS}[{Constants.SHOW_PROTECTED_FACETS}]"]);
+            Assert.AreEqual(new List<string> { "id" }, result[$"{Constants.FMT_OPTIONS}[{Constants.FIELDS}]"]);
+            Assert.AreEqual(new List<string> { "inventory" }, result[$"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FIELDS}]"]);
+            Assert.AreEqual(new List<string> { "brand" }, result[$"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FACETS}]"]);
+        }
+    }
+}
diff --git a/src/Constructorio_NET.Tests/utils/HelpersTest.cs b/src/Constructorio_NET.Tests/utils/HelpersTest.cs
index ba3ea796..ab05ef12 100644
--- a/src/Constructorio_NET.Tests/utils/HelpersTest.cs
+++ b/src/Constructorio_NET.Tests/utils/HelpersTest.cs
@@ -166,7 +166,7 @@ public void MakeUrlSearchWithHiddenFields()
             List<string> hiddenFields = new List<string>() { "inventory", "margin" };
             Hashtable queryParams = new Hashtable()
             {
-                { Constants.HIDDEN_FIELDS, hiddenFields }
+                { $"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FIELDS}]", hiddenFields }
             };
 
             string url = MakeUrl(this.Options, paths, queryParams);
@@ -182,7 +182,7 @@ public void MakeUrlSearchWithHiddenFacets()
             List<string> hiddenFacets = new List<string>() { "inventory", "margin" };
             Hashtable queryParams = new Hashtable()
             {
-                { Constants.HIDDEN_FACETS, hiddenFacets }
+                { $"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FACETS}]", hiddenFacets }
             };
 
             string url = MakeUrl(this.Options, paths, queryParams);
@@ -195,15 +195,11 @@ public void MakeUrlSearchWithHiddenFacets()
         public void MakeUrlSearchWithFmtOptions()
         {
             List<string> paths = new List<string> { "search", this.Query };
-            Dictionary<string, string> fmtOptions = new Dictionary<string, string>()
-            {
-                { "groups_max_depth", "3" },
-                { "groups_start", "current" }
-            };
             Hashtable queryParams = new Hashtable()
             {
                 { Constants.SECTION, "Search Suggestions" },
-                { Constants.FMT_OPTIONS, fmtOptions }
+                { $"{Constants.FMT_OPTIONS}[{Constants.GROUPS_MAX_DEPTH}]", "3" },
+                { $"{Constants.FMT_OPTIONS}[{Constants.GROUPS_START}]", "current" },
             };
 
             string url = MakeUrl(this.Options, paths, queryParams);
@@ -214,6 +210,77 @@ public void MakeUrlSearchWithFmtOptions()
             Assert.That(regexMatched1 && regexMatched2, "url should be properly formed");
         }
 
+        [Test]
+        public void MakeUrlSearchWithFmtOptionsFieldsArray()
+        {
+            List<string> paths = new List<string> { "search", this.Query };
+            Hashtable queryParams = new Hashtable()
+            {
+                { $"{Constants.FMT_OPTIONS}[{Constants.FIELDS}]", new List<string> { "id", "variation_id", "name" } }
+            };
+
+            string url = MakeUrl(this.Options, paths, queryParams);
+            bool hasField0 = Regex.Match(url, "&fmt_options%5Bfields%5D=id").Success;
+            bool hasField1 = Regex.Match(url, "&fmt_options%5Bfields%5D=variation_id").Success;
+            bool hasField2 = Regex.Match(url, "&fmt_options%5Bfields%5D=name").Success;
+            Assert.That(hasField0 && hasField1 && hasField2, "url should have repeated fields keys");
+        }
+
+        [Test]
+        public void MakeUrlSearchWithFmtOptionsHiddenFieldsArray()
+        {
+            List<string> paths = new List<string> { "search", this.Query };
+            Hashtable queryParams = new Hashtable()
+            {
+                { $"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FIELDS}]", new List<string> { "inventory", "margin" } }
+            };
+
+            string url = MakeUrl(this.Options, paths, queryParams);
+            bool hasField0 = Regex.Match(url, "&fmt_options%5Bhidden_fields%5D=inventory").Success;
+            bool hasField1 = Regex.Match(url, "&fmt_options%5Bhidden_fields%5D=margin").Success;
+            Assert.That(hasField0 && hasField1, "url should have repeated hidden_fields keys");
+        }
+
+        [Test]
+        public void MakeUrlSearchWithFmtOptionsHiddenFacetsArray()
+        {
+            List<string> paths = new List<string> { "search", this.Query };
+            Hashtable queryParams = new Hashtable()
+            {
+                { $"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FACETS}]", new List<string> { "brand", "category" } }
+            };
+
+            string url = MakeUrl(this.Options, paths, queryParams);
+            bool hasFacet0 = Regex.Match(url, "&fmt_options%5Bhidden_facets%5D=brand").Success;
+            bool hasFacet1 = Regex.Match(url, "&fmt_options%5Bhidden_facets%5D=category").Success;
+            Assert.That(hasFacet0 && hasFacet1, "url should have repeated hidden_facets keys");
+        }
+
+        [Test]
+        public void MakeUrlSearchWithFmtOptionsAllProperties()
+        {
+            List<string> paths = new List<string> { "search", this.Query };
+            Hashtable queryParams = new Hashtable()
+            {
+                { $"{Constants.FMT_OPTIONS}[{Constants.GROUPS_MAX_DEPTH}]", "5" },
+                { $"{Constants.FMT_OPTIONS}[{Constants.GROUPS_START}]", "top" },
+                { $"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FIELDS}]", "true" },
+                { $"{Constants.FMT_OPTIONS}[{Constants.VARIATIONS_RETURN_TYPE}]", "all" },
+                { $"{Constants.FMT_OPTIONS}[{Constants.FIELDS}]", new List<string> { "id" } },
+                { $"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FIELDS}]", new List<string> { "inventory" } },
+                { $"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FACETS}]", new List<string> { "brand" } },
+            };
+
+            string url = MakeUrl(this.Options, paths, queryParams);
+            Assert.That(Regex.Match(url, "&fmt_options%5Bgroups_max_depth%5D=5").Success, "should have groups_max_depth");
+            Assert.That(Regex.Match(url, "&fmt_options%5Bgroups_start%5D=top").Success, "should have groups_start");
+            Assert.That(Regex.Match(url, "&fmt_options%5Bshow_hidden_fields%5D=true").Success, "should have show_hidden_fields");
+            Assert.That(Regex.Match(url, "&fmt_options%5Bvariations_return_type%5D=all").Success, "should have variations_return_type");
+            Assert.That(Regex.Match(url, "&fmt_options%5Bfields%5D=id").Success, "should have fields array");
+            Assert.That(Regex.Match(url, "&fmt_options%5Bhidden_fields%5D=inventory").Success, "should have hidden_fields array");
+            Assert.That(Regex.Match(url, "&fmt_options%5Bhidden_facets%5D=brand").Success, "should have hidden_facets array");
+        }
+
         [Test]
         public void MakeUrlSearchWithFiltersPerSection()
         {
diff --git a/src/constructor.io/models/Autocomplete/AutocompleteRequest.cs b/src/constructor.io/models/Autocomplete/AutocompleteRequest.cs
index fb5ce35a..a10f00f9 100644
--- a/src/constructor.io/models/Autocomplete/AutocompleteRequest.cs
+++ b/src/constructor.io/models/Autocomplete/AutocompleteRequest.cs
@@ -32,9 +32,9 @@ public class AutocompleteRequest : IFilterable, IUserDetails
         public Dictionary<string, Dictionary<string, List<string>>> FiltersPerSection { get; set; }
 
         /// <summary>
-        /// Gets or sets hidden metadata fields to return.
+        /// Gets or sets the format options used to refine result groups.
         /// </summary>
-        public List<string> HiddenFields { get; set; }
+        public FmtOptions FmtOptions { get; set; }
 
         /// <summary>
         /// Gets or sets user test cells.
@@ -126,9 +126,12 @@ public Hashtable GetRequestParameters()
                 }
             }
 
-            if (this.HiddenFields != null)
+            if (this.FmtOptions != null)
             {
-                parameters.Add(Constants.HIDDEN_FIELDS, this.HiddenFields);
+                foreach (DictionaryEntry entry in this.FmtOptions.GetQueryParameters())
+                {
+                    parameters.Add(entry.Key, entry.Value);
+                }
             }
 
             return parameters;
diff --git a/src/constructor.io/models/Browse/BrowseFacetOptionsRequest.cs b/src/constructor.io/models/Browse/BrowseFacetOptionsRequest.cs
index b4bc0cae..7e809d9d 100644
--- a/src/constructor.io/models/Browse/BrowseFacetOptionsRequest.cs
+++ b/src/constructor.io/models/Browse/BrowseFacetOptionsRequest.cs
@@ -11,10 +11,8 @@ namespace Constructorio_NET.Models
     public class BrowseFacetOptionsRequest
     {
         public string FacetName { get; set; }
-        public bool ShowHiddenFacets { get; set; }
-        public bool ShowProtectedFacets { get; set; }
+        public FmtOptions FmtOptions { get; set; }
         public UserInfo UserInfo { get; set; }
-        private Dictionary<string, string> FmtOptions { get; set; }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="BrowseFacetOptionsRequest"/> class.
@@ -22,7 +20,6 @@ public class BrowseFacetOptionsRequest
         /// <param name="facetName">Facet to use for the request.</param>
         public BrowseFacetOptionsRequest(string facetName)
         {
-            FmtOptions = new Dictionary<string, string>();
             this.FacetName = facetName;
         }
 
@@ -39,19 +36,12 @@ public Hashtable GetRequestParameters()
                 parameters.Add(Constants.FACET_NAME, this.FacetName);
             }
 
-            if (this.ShowHiddenFacets)
+            if (this.FmtOptions != null)
             {
-                this.FmtOptions.Add(Constants.SHOW_HIDDEN_FACETS, this.ShowHiddenFacets.ToString());
-            }
-
-            if (this.ShowProtectedFacets)
-            {
-                this.FmtOptions.Add(Constants.SHOW_PROTECTED_FACETS, this.ShowProtectedFacets.ToString());
-            }
-
-            if (this.FmtOptions != null && this.FmtOptions.Count != 0)
-            {
-                parameters.Add(Constants.FMT_OPTIONS, this.FmtOptions);
+                foreach (DictionaryEntry entry in this.FmtOptions.GetQueryParameters())
+                {
+                    parameters.Add(entry.Key, entry.Value);
+                }
             }
 
             return parameters;
diff --git a/src/constructor.io/models/Browse/BrowseFacetsRequest.cs b/src/constructor.io/models/Browse/BrowseFacetsRequest.cs
index 58b5056c..443922d1 100644
--- a/src/constructor.io/models/Browse/BrowseFacetsRequest.cs
+++ b/src/constructor.io/models/Browse/BrowseFacetsRequest.cs
@@ -13,18 +13,8 @@ public class BrowseFacetsRequest
         public int Page { get; set; }
         public int ResultsPerPage { get; set; }
         public int Offset { get; set; }
-        public bool ShowHiddenFacets { get; set; }
-        public bool ShowProtectedFacets { get; set; }
+        public FmtOptions FmtOptions { get; set; }
         public UserInfo UserInfo { get; set; }
-        private Dictionary<string, string> FmtOptions { get; set; }
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="BrowseFacetsRequest"/> class.
-        /// </summary>
-        public BrowseFacetsRequest()
-        {
-            FmtOptions = new Dictionary<string, string>();
-        }
 
         /// <summary>
         /// Get request parameters.
@@ -49,19 +39,12 @@ public Hashtable GetRequestParameters()
                 parameters.Add(Constants.RESULTS_PER_PAGE, this.ResultsPerPage);
             }
 
-            if (this.ShowHiddenFacets)
+            if (this.FmtOptions != null)
             {
-                this.FmtOptions.Add(Constants.SHOW_HIDDEN_FACETS, this.ShowHiddenFacets.ToString());
-            }
-
-            if (this.ShowProtectedFacets)
-            {
-                this.FmtOptions.Add(Constants.SHOW_PROTECTED_FACETS, this.ShowProtectedFacets.ToString());
-            }
-
-            if (this.FmtOptions != null && this.FmtOptions.Count != 0)
-            {
-                parameters.Add(Constants.FMT_OPTIONS, this.FmtOptions);
+                foreach (DictionaryEntry entry in this.FmtOptions.GetQueryParameters())
+                {
+                    parameters.Add(entry.Key, entry.Value);
+                }
             }
 
             return parameters;
diff --git a/src/constructor.io/models/Browse/BrowseItemsRequest.cs b/src/constructor.io/models/Browse/BrowseItemsRequest.cs
index 60179f6b..41d1b249 100644
--- a/src/constructor.io/models/Browse/BrowseItemsRequest.cs
+++ b/src/constructor.io/models/Browse/BrowseItemsRequest.cs
@@ -13,9 +13,7 @@ public class BrowseItemsRequest
     {
         public List<string> ItemIds { get; set; }
         public Dictionary<string, List<string>> Filters { get; set; }
-        public Dictionary<string, string> FmtOptions { get; set; }
-        public List<string> HiddenFields { get; set; }
-        public List<string> HiddenFacets { get; set; }
+        public FmtOptions FmtOptions { get; set; }
         public int Offset { get; set; }
         public int Page { get; set; }
         public int ResultsPerPage { get; set; }
@@ -83,17 +81,10 @@ public Hashtable GetRequestParameters()
 
             if (this.FmtOptions != null)
             {
-                parameters.Add(Constants.FMT_OPTIONS, this.FmtOptions);
-            }
-
-            if (this.HiddenFields != null)
-            {
-                parameters.Add(Constants.HIDDEN_FIELDS, this.HiddenFields);
-            }
-
-            if (this.HiddenFacets != null)
-            {
-                parameters.Add(Constants.HIDDEN_FACETS, this.HiddenFacets);
+                foreach (DictionaryEntry entry in this.FmtOptions.GetQueryParameters())
+                {
+                    parameters.Add(entry.Key, entry.Value);
+                }
             }
 
             if (this.Offset != 0)
diff --git a/src/constructor.io/models/Browse/BrowseRequest.cs b/src/constructor.io/models/Browse/BrowseRequest.cs
index 19b32d14..5e3037dd 100644
--- a/src/constructor.io/models/Browse/BrowseRequest.cs
+++ b/src/constructor.io/models/Browse/BrowseRequest.cs
@@ -25,23 +25,13 @@ public class BrowseRequest : IPlpRequest
         /// <summary>
         /// Gets or sets the format options used to refine result groups.
         /// </summary>
-        public Dictionary<string, string> FmtOptions { get; set; }
+        public FmtOptions FmtOptions { get; set; }
 
         /// <summary>
         /// Gets or sets the filtering expression used to scope search results.
         /// </summary>
         public PreFilterExpression PreFilterExpression { get; set; }
 
-        /// <summary>
-        /// Gets or sets hidden metadata fields to return.
-        /// </summary>
-        public List<string> HiddenFields { get; set; }
-
-        /// <summary>
-        /// Gets or sets hidden facets fields to return.
-        /// </summary>
-        public List<string> HiddenFacets { get; set; }
-
         /// <summary>
         /// Gets or sets the number of results to skip from the beginning.
         /// Can't be used together with <see cref="Page"/>.
@@ -145,25 +135,18 @@ public Hashtable GetRequestParameters()
                 parameters.Add(Constants.FILTERS, this.Filters);
             }
 
-            if (this.FmtOptions != null)
-            {
-                parameters.Add(Constants.FMT_OPTIONS, this.FmtOptions);
-            }
-
             if (this.PreFilterExpression != null)
             {
                 string preFilterJson = this.PreFilterExpression.GetExpression();
                 parameters.Add(Constants.PRE_FILTER_EXPRESSION, preFilterJson);
             }
 
-            if (this.HiddenFields != null)
-            {
-                parameters.Add(Constants.HIDDEN_FIELDS, this.HiddenFields);
-            }
-
-            if (this.HiddenFacets != null)
+            if (this.FmtOptions != null)
             {
-                parameters.Add(Constants.HIDDEN_FACETS, this.HiddenFacets);
+                foreach (DictionaryEntry entry in this.FmtOptions.GetQueryParameters())
+                {
+                    parameters.Add(entry.Key, entry.Value);
+                }
             }
 
             if (this.Offset != 0)
diff --git a/src/constructor.io/models/Recommendations/RecommendationsRequest.cs b/src/constructor.io/models/Recommendations/RecommendationsRequest.cs
index 71eef298..04a9eace 100644
--- a/src/constructor.io/models/Recommendations/RecommendationsRequest.cs
+++ b/src/constructor.io/models/Recommendations/RecommendationsRequest.cs
@@ -80,6 +80,11 @@ public RecommendationsRequest(string podId)
         /// </summary>
         public PreFilterExpression PreFilterExpression { get; set; }
 
+        /// <summary>
+        /// Gets or sets format options to control result formatting.
+        /// </summary>
+        public FmtOptions FmtOptions { get; set; }
+
         /// <summary>
         /// Get request parameters.
         /// </summary>
@@ -158,6 +163,14 @@ public Hashtable GetRequestParameters()
                 parameters.Add(Constants.PRE_FILTER_EXPRESSION, preFilterJson);
             }
 
+            if (this.FmtOptions != null)
+            {
+                foreach (DictionaryEntry entry in this.FmtOptions.GetQueryParameters())
+                {
+                    parameters.Add(entry.Key, entry.Value);
+                }
+            }
+
             return parameters;
         }
 
diff --git a/src/constructor.io/models/Search/SearchRequest.cs b/src/constructor.io/models/Search/SearchRequest.cs
index a2c98f9e..baa3bb1d 100644
--- a/src/constructor.io/models/Search/SearchRequest.cs
+++ b/src/constructor.io/models/Search/SearchRequest.cs
@@ -25,23 +25,13 @@ public class SearchRequest : IPlpRequest
         /// <summary>
         /// Gets or sets the format options used to refine result groups.
         /// </summary>
-        public Dictionary<string, string> FmtOptions { get; set; }
+        public FmtOptions FmtOptions { get; set; }
 
         /// <summary>
         /// Gets or sets the filtering expression used to scope search results.
         /// </summary>
         public PreFilterExpression PreFilterExpression { get; set; }
 
-        /// <summary>
-        /// Gets or sets hidden metadata fields to return.
-        /// </summary>
-        public List<string> HiddenFields { get; set; }
-
-        /// <summary>
-        /// Gets or sets hidden facets fields to return.
-        /// </summary>
-        public List<string> HiddenFacets { get; set; }
-
         /// <summary>
         /// Gets or sets the number of results to skip from the beginning.
         /// Can't be used together with <see cref="Page"/>.
@@ -142,17 +132,10 @@ public Hashtable GetRequestParameters()
 
             if (this.FmtOptions != null)
             {
-                parameters.Add(Constants.FMT_OPTIONS, this.FmtOptions);
-            }
-
-            if (this.HiddenFields != null)
-            {
-                parameters.Add(Constants.HIDDEN_FIELDS, this.HiddenFields);
-            }
-
-            if (this.HiddenFacets != null)
-            {
-                parameters.Add(Constants.HIDDEN_FACETS, this.HiddenFacets);
+                foreach (DictionaryEntry entry in this.FmtOptions.GetQueryParameters())
+                {
+                    parameters.Add(entry.Key, entry.Value);
+                }
             }
 
             if (this.Offset != 0)
diff --git a/src/constructor.io/models/common/FmtOptions.cs b/src/constructor.io/models/common/FmtOptions.cs
new file mode 100644
index 00000000..0ce5a6c6
--- /dev/null
+++ b/src/constructor.io/models/common/FmtOptions.cs
@@ -0,0 +1,116 @@
+using System.Collections;
+using System.Collections.Generic;
+using Constructorio_NET.Utils;
+
+namespace Constructorio_NET.Models
+{
+    /// <summary>
+    /// Format options used to refine result groups and control response fields.
+    /// </summary>
+    public class FmtOptions
+    {
+        /// <summary>
+        /// Gets or sets the maximum depth of result groups to return.
+        /// </summary>
+        public int? GroupsMaxDepth { get; set; }
+
+        /// <summary>
+        /// Gets or sets the starting point for groups.
+        /// Valid values: "current", "top", or "group_id:{id}".
+        /// </summary>
+        public string? GroupsStart { get; set; }
+
+        /// <summary>
+        /// Gets or sets the list of fields to return in results.
+        /// </summary>
+        public List<string>? Fields { get; set; }
+
+        /// <summary>
+        /// Gets or sets hidden metadata fields to return.
+        /// </summary>
+        public List<string>? HiddenFields { get; set; }
+
+        /// <summary>
+        /// Gets or sets hidden facet fields to return.
+        /// </summary>
+        public List<string>? HiddenFacets { get; set; }
+
+        /// <summary>
+        /// Gets or sets whether to show hidden fields.
+        /// </summary>
+        public bool? ShowHiddenFields { get; set; }
+
+        /// <summary>
+        /// Gets or sets the variations return type.
+        /// Valid values: "default", "all", "matched".
+        /// </summary>
+        public string? VariationsReturnType { get; set; }
+
+        /// <summary>
+        /// Gets or sets whether to show hidden facets.
+        /// </summary>
+        public bool? ShowHiddenFacets { get; set; }
+
+        /// <summary>
+        /// Gets or sets whether to show protected facets.
+        /// </summary>
+        public bool? ShowProtectedFacets { get; set; }
+
+        /// <summary>
+        /// Returns a Hashtable of pre-formatted query parameters with keys like "fmt_options[property_name]".
+        /// Values are either string or List&lt;string&gt;.
+        /// </summary>
+        /// <returns>Hashtable of query parameters.</returns>
+        public Hashtable GetQueryParameters()
+        {
+            Hashtable parameters = new Hashtable();
+
+            if (this.GroupsMaxDepth.HasValue)
+            {
+                parameters.Add($"{Constants.FMT_OPTIONS}[{Constants.GROUPS_MAX_DEPTH}]", this.GroupsMaxDepth.Value.ToString());
+            }
+
+            if (!string.IsNullOrEmpty(this.GroupsStart))
+            {
+                parameters.Add($"{Constants.FMT_OPTIONS}[{Constants.GROUPS_START}]", this.GroupsStart);
+            }
+
+            if (this.ShowHiddenFields.HasValue)
+            {
+                parameters.Add($"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FIELDS}]", this.ShowHiddenFields.Value.ToString().ToLower());
+            }
+
+            if (!string.IsNullOrEmpty(this.VariationsReturnType))
+            {
+                parameters.Add($"{Constants.FMT_OPTIONS}[{Constants.VARIATIONS_RETURN_TYPE}]", this.VariationsReturnType);
+            }
+
+            if (this.ShowHiddenFacets.HasValue)
+            {
+                parameters.Add($"{Constants.FMT_OPTIONS}[{Constants.SHOW_HIDDEN_FACETS}]", this.ShowHiddenFacets.Value.ToString().ToLower());
+            }
+
+            if (this.ShowProtectedFacets.HasValue)
+            {
+                parameters.Add($"{Constants.FMT_OPTIONS}[{Constants.SHOW_PROTECTED_FACETS}]", this.ShowProtectedFacets.Value.ToString().ToLower());
+            }
+
+            if (this.Fields != null)
+            {
+                parameters.Add($"{Constants.FMT_OPTIONS}[{Constants.FIELDS}]", this.Fields);
+            }
+
+            if (this.HiddenFields != null)
+            {
+                parameters.Add($"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FIELDS}]", this.HiddenFields);
+            }
+
+            if (this.HiddenFacets != null)
+            {
+                parameters.Add($"{Constants.FMT_OPTIONS}[{Constants.HIDDEN_FACETS}]", this.HiddenFacets);
+            }
+
+            return parameters;
+        }
+    }
+}
diff --git a/src/constructor.io/models/common/IPlpRequest.cs b/src/constructor.io/models/common/IPlpRequest.cs
index c9bb8eb1..e895de41 100644
--- a/src/constructor.io/models/common/IPlpRequest.cs
+++ b/src/constructor.io/models/common/IPlpRequest.cs
@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Constructorio_NET.Models
 {
     public interface IPlpRequest : IFilterable, IPageable, ISortable, IUserDetails
@@ -7,17 +5,7 @@ public interface IPlpRequest : IFilterable, IPageable, ISortable, IUserDetails
         /// <summary>
         /// Gets or sets the format options used to refine result groups.
         /// </summary>
-        Dictionary<string, string> FmtOptions { get; set; }
-
-        /// <summary>
-        /// Gets or sets hidden facets fields to return.
-        /// </summary>
-        List<string> HiddenFacets { get; set; }
-
-        /// <summary>
-        /// Gets or sets hidden metadata fields to return.
-        /// </summary>
-        List<string> HiddenFields { get; set; }
+        FmtOptions FmtOptions { get; set; }
 
         /// <summary>
         /// Gets or sets the filtering expression used to scope search results.
diff --git a/src/constructor.io/utils/Constants.cs b/src/constructor.io/utils/Constants.cs
index 69ed876e..cc6e43a9 100644
--- a/src/constructor.io/utils/Constants.cs
+++ b/src/constructor.io/utils/Constants.cs
@@ -9,8 +9,11 @@ public static class Constants
         public const string FACET_NAME = "facet_name";
         public const string FILTERS = "filters";
         public const string FILTERS_PER_SECTION = "filters_per_section";
+        public const string FIELDS = "fields";
         public const string FMT_OPTIONS = "fmt_options";
         public const string FORCE = "force";
+        public const string GROUPS_MAX_DEPTH = "groups_max_depth";
+        public const string GROUPS_START = "groups_start";
         public const string HIDDEN_FIELDS = "hidden_fields";
         public const string HIDDEN_FACETS = "hidden_facets";
         public const string ITEM_IDS = "ids";
@@ -19,6 +22,7 @@ public static class Constants
         public const string RESULTS_PER_PAGE = "num_results_per_page";
         public const string SECURITY_TOKEN = "x-cnstrc-token";
         public const string SHOW_HIDDEN_FACETS = "show_hidden_facets";
+        public const string SHOW_HIDDEN_FIELDS = "show_hidden_fields";
         public const string SHOW_PROTECTED_FACETS = "show_protected_facets";
         public const string USER_SEGMENTS = "us";
         public const string SECTION = "section";
@@ -33,6 +37,7 @@ public static class Constants
         public const string USER_ID = "ui";
         public const string USER_IP = "X-Forwarded-For";
         public const string VARIATIONS_MAP = "variations_map";
+        public const string VARIATIONS_RETURN_TYPE = "variations_return_type";
         public const string START_DATE = "start_date";
         public const string END_DATE = "end_date";
         public const string STATUS = "status";
diff --git a/src/constructor.io/utils/Helpers.cs b/src/constructor.io/utils/Helpers.cs
index 5b15bc4b..56f85bb8 100644
--- a/src/constructor.io/utils/Helpers.cs
+++ b/src/constructor.io/utils/Helpers.cs
@@ -177,47 +177,6 @@ protected static string MakeUrl(Hashtable options, List<string> paths, Hashtable
                     }
                 }
 
-                // Add format options to query string
-                if (queryParams.Contains(Constants.FMT_OPTIONS))
-                {
-                    Dictionary<string, string> fmtOptions = (Dictionary<string, string>)queryParams[Constants.FMT_OPTIONS];
-                    queryParams.Remove(Constants.FMT_OPTIONS);
-
-                    foreach (var fmtOption in fmtOptions)
-                    {
-                        url.Append("&" + Constants.FMT_OPTIONS + UrlEscapedStartSquareBracket)
-                            .Append(OurEscapeDataString(fmtOption.Key))
-                            .Append(UrlEscapedEndSquareBracket + "=")
-                            .Append(OurEscapeDataString(fmtOption.Value));
-                    }
-                }
-
-                // Add hidden fields as fmt_options
-                if (queryParams.Contains(Constants.HIDDEN_FIELDS))
-                {
-                    List<string> hiddenFields = (List<string>)queryParams[Constants.HIDDEN_FIELDS];
-                    queryParams.Remove(Constants.HIDDEN_FIELDS);
-
-                    foreach (var hiddenField in hiddenFields)
-                    {
-                        url.Append("&" + Constants.FMT_OPTIONS + UrlEscapedStartSquareBracket + Constants.HIDDEN_FIELDS + UrlEscapedEndSquareBracket + "=")
-                            .Append(OurEscapeDataString(hiddenField));
-                    }
-                }
-
-                // Add hidden facets as fmt_options
-                if (queryParams.Contains(Constants.HIDDEN_FACETS))
-                {
-                    List<string> hiddenFacets = (List<string>)queryParams[Constants.HIDDEN_FACETS];
-                    queryParams.Remove(Constants.HIDDEN_FACETS);
-
-                    foreach (var hiddenFacet in hiddenFacets)
-                    {
-                        url.Append("&" + Constants.FMT_OPTIONS + UrlEscapedStartSquareBracket + Constants.HIDDEN_FACETS + UrlEscapedEndSquareBracket + "=")
-                            .Append(OurEscapeDataString(hiddenFacet));
-                    }
-                }
-
                 // Add quiz answers to query string
                 if (queryParams.Contains(Constants.ANSWERS))
                 {