diff --git a/.github/workflows/linux-macOS-CI.yml b/.github/workflows/linux-macOS-CI.yml
index 6dbd7d80..b7babcfb 100644
--- a/.github/workflows/linux-macOS-CI.yml
+++ b/.github/workflows/linux-macOS-CI.yml
@@ -27,10 +27,12 @@ jobs:
             3.1.x
             5.0.x
             6.0.x
+            8.0.x
       - name: Restore
         run: dotnet restore src
       - name: Test
         run: |
           dotnet test src/ConfigCat.Client.Tests/ConfigCat.Client.Tests.csproj -c Release -f netcoreapp3.1 --no-restore
           dotnet test src/ConfigCat.Client.Tests/ConfigCat.Client.Tests.csproj -c Release -f net5.0 --no-restore
-          dotnet test src/ConfigCat.Client.Tests/ConfigCat.Client.Tests.csproj -c Release -f net6.0 --no-restore
\ No newline at end of file
+          dotnet test src/ConfigCat.Client.Tests/ConfigCat.Client.Tests.csproj -c Release -f net6.0 --no-restore
+          dotnet test src/ConfigCat.Client.Tests/ConfigCat.Client.Tests.csproj -c Release -f net8.0 --no-restore
\ No newline at end of file
diff --git a/.github/workflows/sonar-analysis.yml b/.github/workflows/sonar-analysis.yml
index 5b9f2387..730614cf 100644
--- a/.github/workflows/sonar-analysis.yml
+++ b/.github/workflows/sonar-analysis.yml
@@ -18,9 +18,10 @@ jobs:
     runs-on: windows-2022
     steps:
       - name: Set up JDK 11
-        uses: actions/setup-java@v1
+        uses: actions/setup-java@v3
         with:
-          java-version: 1.11
+          java-version: 17
+          distribution: zulu
       - uses: actions/checkout@v2
         with:
           fetch-depth: 0
@@ -51,4 +52,4 @@ jobs:
         run: |
           .\.sonar\scanner\dotnet-sonarscanner begin /k:"net-sdk" /d:sonar.host.url="https://sonarcloud.io" /o:"configcat" /d:sonar.login="${{ secrets.SONAR_TOKEN }}" /d:sonar.cs.opencover.reportsPaths="**/TestResults/**/coverage.opencover.xml" -d:sonar.cs.vstest.reportsPaths="**/TestResults/*.trx" /v:"${{ github.run_number }}" /d:sonar.exclusions="ConfigCatClient/Versioning/*" /d:sonar.coverage.exclusions="ConfigCatClient/Versioning/*"
           dotnet test src\ConfigCat.Client.Tests\ConfigCat.Client.Tests.csproj -c Release --logger trx --collect:"XPlat Code Coverage" -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.Format=opencover
-          .\.sonar\scanner\dotnet-sonarscanner end /d:sonar.login="${{ secrets.SONAR_TOKEN }}"
\ No newline at end of file
+          .\.sonar\scanner\dotnet-sonarscanner end /d:sonar.login="${{ secrets.SONAR_TOKEN }}"
diff --git a/appveyor.yml b/appveyor.yml
index ecf0a59c..84b48a45 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -1,5 +1,5 @@
 environment:
-  build_version: 8.2.0
+  build_version: 9.0.0
 version: $(build_version)-{build}
 image: Visual Studio 2022
 configuration: Release
@@ -16,11 +16,14 @@ dotnet_csproj:
   file_version: $(build_version)
   informational_version: $(build_version)
 install:
-- cmd: dotnet tool install -g InheritDocTool
-build_script: 
+- ps: |
+    dotnet tool install -g InheritDocTool
+    Invoke-WebRequest 'https://dot.net/v1/dotnet-install.ps1' -OutFile dotnet-install.ps1
+    ./dotnet-install.ps1 -Channel 8.0
+build_script:
 - cmd: echo __BUILD__
 - dotnet restore src/ConfigCatClient.sln
-- dotnet build -c %configuration% /p:ContinuousIntegrationBuild=true src/ConfigCatClient.sln 
+- dotnet build -c %configuration% /p:ContinuousIntegrationBuild=true src/ConfigCatClient.sln
 after_build:
 - cmd: echo __PACK__
 - inheritdoc -o
@@ -31,9 +34,10 @@ test_script:
 - dotnet test src\ConfigCat.Client.Tests\ConfigCat.Client.Tests.csproj -f netcoreapp3.1 -c %configuration% --no-build
 - dotnet test src\ConfigCat.Client.Tests\ConfigCat.Client.Tests.csproj -f net5.0 -c %configuration% --no-build
 - dotnet test src\ConfigCat.Client.Tests\ConfigCat.Client.Tests.csproj -f net6.0 -c %configuration% --no-build
+- dotnet test src\ConfigCat.Client.Tests\ConfigCat.Client.Tests.csproj -f net8.0 -c %configuration% --no-build
 artifacts:
 - path: artifacts\ConfigCat.Client.*.*nupkg
-  name: NuGet 
+  name: NuGet
 notifications:
 - provider: Email
   to:
diff --git a/samples/ASP.NETCore/WebApplication/Controllers/HomeController.cs b/samples/ASP.NETCore/WebApplication/Controllers/HomeController.cs
index e3ebccae..2aee4bf6 100644
--- a/samples/ASP.NETCore/WebApplication/Controllers/HomeController.cs
+++ b/samples/ASP.NETCore/WebApplication/Controllers/HomeController.cs
@@ -1,4 +1,4 @@
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.Diagnostics;
 using ConfigCat.Client;
 using Microsoft.AspNetCore.Mvc;
@@ -23,7 +23,7 @@ public IActionResult Index()
         {
             Email = "configcat@example.com",
             Country = "Canada",
-            Custom = new Dictionary<string, string>
+            Custom =
             {
                 {"SubscriptionType", "Pro"},
                 {"Version", "1.0.0"}
diff --git a/samples/ASP.NETCore/WebApplication/WebApplication.csproj b/samples/ASP.NETCore/WebApplication/WebApplication.csproj
index a08f56de..1eaeb5ac 100644
--- a/samples/ASP.NETCore/WebApplication/WebApplication.csproj
+++ b/samples/ASP.NETCore/WebApplication/WebApplication.csproj
@@ -8,7 +8,7 @@
   <ItemGroup>
     <ProjectReference Include="..\..\..\src\ConfigCatClient\ConfigCatClient.csproj" />
     <!-- Use PackageReference instead of the ProjectReference above in your application. -->
-    <!--<PackageReference Include="ConfigCat.Client" Version="8.1.0" />-->
+    <!--<PackageReference Include="ConfigCat.Client" Version="9.0.0" />-->
     <PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="6.0.*" />
     <PackageReference Include="Microsoft.Web.LibraryManager.Build" Version="2.1.175" />
   </ItemGroup>
diff --git a/samples/ConsoleApp/ConsoleApp.csproj b/samples/ConsoleApp/ConsoleApp.csproj
index f5928dab..9213c559 100644
--- a/samples/ConsoleApp/ConsoleApp.csproj
+++ b/samples/ConsoleApp/ConsoleApp.csproj
@@ -9,7 +9,7 @@
   <ItemGroup>
     <ProjectReference Include="..\..\src\ConfigCatClient\ConfigCatClient.csproj" />  
     <!-- Use PackageReference instead of the ProjectReference above in your application. -->
-    <!--<PackageReference Include="ConfigCat.Client" Version="8.1.0" />-->
+    <!--<PackageReference Include="ConfigCat.Client" Version="9.0.0" />-->
   </ItemGroup>
 
 </Project>
diff --git a/src/ConfigCat.Client.Tests/ConfigCat.Client.Tests.csproj b/src/ConfigCat.Client.Tests/ConfigCat.Client.Tests.csproj
index 784def52..c3933b03 100644
--- a/src/ConfigCat.Client.Tests/ConfigCat.Client.Tests.csproj
+++ b/src/ConfigCat.Client.Tests/ConfigCat.Client.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net45;net461;netcoreapp3.1;net5.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net45;net461;netcoreapp3.1;net5.0;net6.0;net8.0</TargetFrameworks>
     <IsPackable>false</IsPackable>
     <AssemblyName>ConfigCatClientTests</AssemblyName>
     <SignAssembly>true</SignAssembly>
diff --git a/src/ConfigCat.Client.Tests/Helpers/LoggingHelper.cs b/src/ConfigCat.Client.Tests/Helpers/LoggingHelper.cs
index 1ed18ede..a2b5a4ba 100644
--- a/src/ConfigCat.Client.Tests/Helpers/LoggingHelper.cs
+++ b/src/ConfigCat.Client.Tests/Helpers/LoggingHelper.cs
@@ -1,6 +1,6 @@
-using Moq;
-using System.Collections.Generic;
 using System;
+using System.Collections.Generic;
+using Moq;
 
 namespace ConfigCat.Client;
 
diff --git a/src/ConfigCat.Client.Tests/UserTests.cs b/src/ConfigCat.Client.Tests/UserTests.cs
index c0b9f222..dbae79db 100644
--- a/src/ConfigCat.Client.Tests/UserTests.cs
+++ b/src/ConfigCat.Client.Tests/UserTests.cs
@@ -1,5 +1,3 @@
-using System;
-using System.Globalization;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
 namespace ConfigCat.Client.Tests;
diff --git a/src/ConfigCatClient/ConfigCatClient.cs b/src/ConfigCatClient/ConfigCatClient.cs
index 876389ed..0974ebc0 100644
--- a/src/ConfigCatClient/ConfigCatClient.cs
+++ b/src/ConfigCatClient/ConfigCatClient.cs
@@ -192,26 +192,22 @@ private void Dispose(bool disposing)
 
         if (disposing)
         {
-            if (this.configService is IDisposable disposable)
-            {
-                disposable.Dispose();
-            }
-
-            this.overrideDataSource?.Dispose();
+            (this.configService as IDisposable)?.Dispose();
+            (this.overrideDataSource as IDisposable)?.Dispose();
         }
         else
         {
             // Execution gets here when consumer forgets to dispose the client instance.
             // In this case we need to make sure that background work is stopped,
             // otherwise it would go on endlessly, that is, we'd end up with a memory leak.
-            var autoPollConfigService = this.configService as AutoPollConfigService;
-            var localFileDataSource = this.overrideDataSource as LocalFileDataSource;
-            if (autoPollConfigService is not null || localFileDataSource is not null)
+            var configService = this.configService as IDisposable;
+            var localFileDataSource = this.overrideDataSource as IDisposable;
+            if (configService is not null || localFileDataSource is not null)
             {
                 Task.Run(() =>
                 {
-                    autoPollConfigService?.StopScheduler();
-                    localFileDataSource?.StopWatch();
+                    configService?.Dispose();
+                    localFileDataSource?.Dispose();
                 });
             }
         }
diff --git a/src/ConfigCatClient/Evaluation/EvaluateLogHelper.cs b/src/ConfigCatClient/Evaluation/EvaluateLogHelper.cs
index 584cad75..a39d2880 100644
--- a/src/ConfigCatClient/Evaluation/EvaluateLogHelper.cs
+++ b/src/ConfigCatClient/Evaluation/EvaluateLogHelper.cs
@@ -1,5 +1,5 @@
-using ConfigCat.Client.Utils;
 using System.Globalization;
+using ConfigCat.Client.Utils;
 
 namespace ConfigCat.Client.Evaluation;
 
diff --git a/src/ConfigCatClient/Evaluation/EvaluationDetails.cs b/src/ConfigCatClient/Evaluation/EvaluationDetails.cs
index 5cee4682..2349e348 100644
--- a/src/ConfigCatClient/Evaluation/EvaluationDetails.cs
+++ b/src/ConfigCatClient/Evaluation/EvaluationDetails.cs
@@ -6,7 +6,7 @@ namespace ConfigCat.Client;
 /// <summary>
 /// The evaluated value and additional information about the evaluation of a feature flag or setting.
 /// </summary>
-public abstract record class EvaluationDetails
+public abstract class EvaluationDetails
 {
     internal static EvaluationDetails<TValue> FromEvaluateResult<TValue>(string key, TValue value, in EvaluateResult evaluateResult,
         DateTime? fetchTime, User? user)
@@ -106,7 +106,7 @@ private protected EvaluationDetails(string key)
 }
 
 /// <inheritdoc/>
-public sealed record class EvaluationDetails<TValue> : EvaluationDetails
+public sealed class EvaluationDetails<TValue> : EvaluationDetails
 {
     /// <summary>
     /// Initializes a new instance of the <see cref="EvaluationDetails{TValue}"/> class.
diff --git a/src/ConfigCatClient/Extensions/ObjectExtensions.cs b/src/ConfigCatClient/Extensions/ObjectExtensions.cs
index 00606d83..49800c2c 100644
--- a/src/ConfigCatClient/Extensions/ObjectExtensions.cs
+++ b/src/ConfigCatClient/Extensions/ObjectExtensions.cs
@@ -1,6 +1,5 @@
 using System.Diagnostics;
 using System.Globalization;
-using System.Runtime.CompilerServices;
 using ConfigCat.Client;
 
 #if USE_NEWTONSOFT_JSON
diff --git a/src/ConfigCatClient/Extensions/SerializationExtensions.cs b/src/ConfigCatClient/Extensions/SerializationExtensions.cs
index 684b3818..2f3d3e86 100644
--- a/src/ConfigCatClient/Extensions/SerializationExtensions.cs
+++ b/src/ConfigCatClient/Extensions/SerializationExtensions.cs
@@ -20,22 +20,24 @@ internal static class SerializationExtensions
     };
 #endif
 
-    public static T? Deserialize<T>(this string json) => json.AsSpan().Deserialize<T>();
+    public static T? Deserialize<T>(this string json) => json.AsMemory().Deserialize<T>();
 
-    public static T? Deserialize<T>(this ReadOnlySpan<char> json)
+    // NOTE: It would be better to use ReadOnlySpan<char>, however when the full string is wrapped in a span, json.ToString() result in a copy of the string.
+    // This is not the case with ReadOnlyMemory<char>, so we use that until support for .NET 4.5 support is dropped.
+    public static T? Deserialize<T>(this ReadOnlyMemory<char> json)
     {
 #if USE_NEWTONSOFT_JSON
         using var stringReader = new StringReader(json.ToString());
         using var reader = new JsonTextReader(stringReader);
         return Serializer.Deserialize<T>(reader);
 #else
-        return JsonSerializer.Deserialize<T>(json);
+        return JsonSerializer.Deserialize<T>(json.Span);
 #endif
     }
 
-    public static T? DeserializeOrDefault<T>(this string json) => json.AsSpan().DeserializeOrDefault<T>();
+    public static T? DeserializeOrDefault<T>(this string json) => json.AsMemory().DeserializeOrDefault<T>();
 
-    public static T? DeserializeOrDefault<T>(this ReadOnlySpan<char> json)
+    public static T? DeserializeOrDefault<T>(this ReadOnlyMemory<char> json)
     {
         try
         {
diff --git a/src/ConfigCatClient/Extensions/TaskExtensions.cs b/src/ConfigCatClient/Extensions/TaskExtensions.cs
index b28fd899..bc9adb85 100644
--- a/src/ConfigCatClient/Extensions/TaskExtensions.cs
+++ b/src/ConfigCatClient/Extensions/TaskExtensions.cs
@@ -61,7 +61,16 @@ static async Task<T> Awaited(Task task, CancellationToken cancellationToken)
             using (tokenRegistration)
             {
                 var completedTask = await Task.WhenAny(task, cancellationTask).ConfigureAwait(false);
-                return completedTask is Task<T> taskWithResult ? taskWithResult.GetAwaiter().GetResult() : default!;
+                if (completedTask is Task<T> taskWithResult)
+                {
+                    return taskWithResult.GetAwaiter().GetResult();
+                }
+                else
+                {
+                    // Although the task has no return value, the potential cancellation or exception still needs to be propagated.
+                    completedTask.GetAwaiter().GetResult();
+                    return default!;
+                }
             }
         }
     }
diff --git a/src/ConfigCatClient/FetchResult.cs b/src/ConfigCatClient/FetchResult.cs
index 6bdb73a4..4c92aff3 100644
--- a/src/ConfigCatClient/FetchResult.cs
+++ b/src/ConfigCatClient/FetchResult.cs
@@ -3,7 +3,7 @@
 
 namespace ConfigCat.Client;
 
-internal readonly record struct FetchResult
+internal readonly struct FetchResult
 {
     private static readonly object NotModifiedToken = new();
 
diff --git a/src/ConfigCatClient/Override/IOverrideDataSource.cs b/src/ConfigCatClient/Override/IOverrideDataSource.cs
index 31ea4f0e..d5a6a196 100644
--- a/src/ConfigCatClient/Override/IOverrideDataSource.cs
+++ b/src/ConfigCatClient/Override/IOverrideDataSource.cs
@@ -1,11 +1,10 @@
-using System;
 using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 
 namespace ConfigCat.Client.Override;
 
-internal interface IOverrideDataSource : IDisposable
+internal interface IOverrideDataSource
 {
     Dictionary<string, Setting> GetOverrides();
 
diff --git a/src/ConfigCatClient/Override/LocalDictionaryDataSource.cs b/src/ConfigCatClient/Override/LocalDictionaryDataSource.cs
index 55af9791..fcdfe511 100644
--- a/src/ConfigCatClient/Override/LocalDictionaryDataSource.cs
+++ b/src/ConfigCatClient/Override/LocalDictionaryDataSource.cs
@@ -20,8 +20,6 @@ public LocalDictionaryDataSource(IDictionary<string, object> overrideValues, boo
         }
     }
 
-    public void Dispose() { /* no need to dispose anything */ }
-
     public Dictionary<string, Setting> GetOverrides() => GetSettingsFromSource();
 
     public Task<Dictionary<string, Setting>> GetOverridesAsync(CancellationToken cancellationToken = default) => Task.FromResult(GetSettingsFromSource());
diff --git a/src/ConfigCatClient/Override/LocalFileDataSource.cs b/src/ConfigCatClient/Override/LocalFileDataSource.cs
index 67579fd1..33f3bb6e 100644
--- a/src/ConfigCatClient/Override/LocalFileDataSource.cs
+++ b/src/ConfigCatClient/Override/LocalFileDataSource.cs
@@ -8,7 +8,7 @@
 
 namespace ConfigCat.Client.Override;
 
-internal sealed class LocalFileDataSource : IOverrideDataSource
+internal sealed class LocalFileDataSource : IOverrideDataSource, IDisposable
 {
     private const int WAIT_TIME_FOR_UNLOCK = 200; // ms
     private const int MAX_WAIT_ITERATIONS = 50; // ms
diff --git a/src/ConfigCatClient/ProjectConfig.cs b/src/ConfigCatClient/ProjectConfig.cs
index 87b22cf8..fb93389c 100644
--- a/src/ConfigCatClient/ProjectConfig.cs
+++ b/src/ConfigCatClient/ProjectConfig.cs
@@ -81,7 +81,7 @@ public static ProjectConfig Deserialize(string value)
         var httpETagSpan = value.AsSpan(index, endIndex - index);
 
         index = endIndex + 1;
-        var configJsonSpan = value.AsSpan(index);
+        var configJsonSpan = value.AsMemory(index);
 
         Config? config;
         string? configJson;
diff --git a/src/ConfigCatClient/RefreshResult.cs b/src/ConfigCatClient/RefreshResult.cs
index b400a4ca..4d0bcd73 100644
--- a/src/ConfigCatClient/RefreshResult.cs
+++ b/src/ConfigCatClient/RefreshResult.cs
@@ -6,7 +6,7 @@ namespace ConfigCat.Client;
 /// <summary>
 /// Contains the result of an <see cref="IConfigCatClient.ForceRefresh"/> or <see cref="IConfigCatClient.ForceRefreshAsync"/> operation.
 /// </summary>
-public readonly record struct RefreshResult
+public readonly struct RefreshResult
 {
     /// <summary>
     /// Creates an instance of the <see cref="RefreshResult"/> struct which indicates that the operation was successful.
diff --git a/src/ConfigCatClient/User.cs b/src/ConfigCatClient/User.cs
index 2291ba2c..f49ab126 100644
--- a/src/ConfigCatClient/User.cs
+++ b/src/ConfigCatClient/User.cs
@@ -43,7 +43,7 @@ public class User
     /// <remarks>
     /// The set of allowed attribute values depends on the comparison type of the condition which references the User Object attribute.<br/>
     /// <see cref="string"/> values are supported by all comparison types (in some cases they need to be provided in a specific format though).<br/>
-    /// Some of the comparison types work with other types of values, as descibed below.
+    /// Some of the comparison types work with other types of values, as described below.
     /// <para>
     /// Text-based comparisons (EQUALS, IS ONE OF, etc.)<br/>
     /// * accept <see cref="string"/> values,<br/>