diff --git a/ClickHouse.Driver.Tests/ADO/DataSourceTests.cs b/ClickHouse.Driver.Tests/ADO/DataSourceTests.cs
index 27086d992..5ba5eee0c 100644
--- a/ClickHouse.Driver.Tests/ADO/DataSourceTests.cs
+++ b/ClickHouse.Driver.Tests/ADO/DataSourceTests.cs
@@ -1,4 +1,6 @@
 #if NET7_0_OR_GREATER
+using System.Data;
+using System.Threading.Tasks;
 using ClickHouse.Driver.ADO;
 using NUnit.Framework;
 
@@ -14,5 +16,16 @@ public void CanCreateConnection()
         using var connection = dataSource.CreateConnection();
         Assert.That(connectionString, Is.EqualTo(connection.ConnectionString));
     }
+
+    [Test]
+    public async Task OpenConnectionAsync_WithoutCancellationToken_ReturnsOpenClickHouseConnection()
+    {
+        using var dataSource = new ClickHouseDataSource(TestUtilities.GetTestClickHouseClientSettings());
+        await using ClickHouseConnection connection = await dataSource.OpenConnectionAsync();
+        Assert.That(connection.State, Is.EqualTo(ConnectionState.Open));
+
+        using var command = connection.CreateCommand("SELECT 1");
+        Assert.That(await command.ExecuteScalarAsync(), Is.EqualTo(1));
+    }
 }
 #endif
diff --git a/ClickHouse.Driver/ADO/ClickHouseDataSource.cs b/ClickHouse.Driver/ADO/ClickHouseDataSource.cs
index 998c1b3a9..8489cffe0 100644
--- a/ClickHouse.Driver/ADO/ClickHouseDataSource.cs
+++ b/ClickHouse.Driver/ADO/ClickHouseDataSource.cs
@@ -144,7 +144,7 @@ protected override DbConnection CreateDbConnection()
 
     IClickHouseConnection IClickHouseDataSource.OpenConnection() => OpenConnection();
 
-    public new async Task<ClickHouseConnection> OpenConnectionAsync(CancellationToken cancellationToken)
+    public new async Task<ClickHouseConnection> OpenConnectionAsync(CancellationToken cancellationToken = default)
     {
         var cn = await OpenDbConnectionAsync(cancellationToken).ConfigureAwait(false);
         return (ClickHouseConnection)cn;
diff --git a/ClickHouse.Driver/PublicAPI/PublicAPI.Unshipped.txt b/ClickHouse.Driver/PublicAPI/PublicAPI.Unshipped.txt
index 156f29ee6..519045bec 100644
--- a/ClickHouse.Driver/PublicAPI/PublicAPI.Unshipped.txt
+++ b/ClickHouse.Driver/PublicAPI/PublicAPI.Unshipped.txt
@@ -91,7 +91,7 @@ ClickHouse.Driver.ADO.ClickHouseDataSource.CreateConnection() -> ClickHouse.Driv
 ClickHouse.Driver.ADO.ClickHouseDataSource.LoggerFactory.get -> Microsoft.Extensions.Logging.ILoggerFactory
 ClickHouse.Driver.ADO.ClickHouseDataSource.LoggerFactory.set -> void
 ClickHouse.Driver.ADO.ClickHouseDataSource.OpenConnection() -> ClickHouse.Driver.ADO.ClickHouseConnection
-ClickHouse.Driver.ADO.ClickHouseDataSource.OpenConnectionAsync(System.Threading.CancellationToken cancellationToken) -> System.Threading.Tasks.Task<ClickHouse.Driver.ADO.ClickHouseConnection>
+ClickHouse.Driver.ADO.ClickHouseDataSource.OpenConnectionAsync(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.Task<ClickHouse.Driver.ADO.ClickHouseConnection>
 ClickHouse.Driver.ADO.ClickHouseDataSource.Settings.get -> ClickHouse.Driver.ADO.ClickHouseClientSettings
 ClickHouse.Driver.ADO.ClickHouseDefaults
 ClickHouse.Driver.ADO.Feature.Dynamic = 2048 -> ClickHouse.Driver.ADO.Feature
diff --git a/ClickHouse.Driver/PublicAPI/net8.0/PublicAPI.Shipped.txt b/ClickHouse.Driver/PublicAPI/net8.0/PublicAPI.Shipped.txt
index a36e88a58..dc4c5aaae 100644
--- a/ClickHouse.Driver/PublicAPI/net8.0/PublicAPI.Shipped.txt
+++ b/ClickHouse.Driver/PublicAPI/net8.0/PublicAPI.Shipped.txt
@@ -5,7 +5,7 @@ ClickHouse.Driver.ADO.ClickHouseDataSource.CreateConnection() -> ClickHouse.Driv
 ClickHouse.Driver.ADO.ClickHouseDataSource.Logger.get -> Microsoft.Extensions.Logging.ILogger
 ClickHouse.Driver.ADO.ClickHouseDataSource.Logger.set -> void
 ClickHouse.Driver.ADO.ClickHouseDataSource.OpenConnection() -> ClickHouse.Driver.ADO.ClickHouseConnection
-ClickHouse.Driver.ADO.ClickHouseDataSource.OpenConnectionAsync(System.Threading.CancellationToken cancellationToken) -> System.Threading.Tasks.Task<ClickHouse.Driver.ADO.ClickHouseConnection>
+ClickHouse.Driver.ADO.ClickHouseDataSource.OpenConnectionAsync(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.Task<ClickHouse.Driver.ADO.ClickHouseConnection>
 ClickHouse.Driver.ADO.Readers.ClickHouseDataReader.GetTuple(int ordinal) -> System.Runtime.CompilerServices.ITuple
 ClickHouse.Driver.IClickHouseDataSource
 ClickHouse.Driver.IClickHouseDataSource.ConnectionString.get -> string
diff --git a/changelog.d/686-datasource-openconnectionasync.fixes.md b/changelog.d/686-datasource-openconnectionasync.fixes.md
new file mode 100644
index 000000000..c0e4c0a92
--- /dev/null
+++ b/changelog.d/686-datasource-openconnectionasync.fixes.md
@@ -0,0 +1,7 @@
+* Fixed `ClickHouseDataSource.OpenConnectionAsync()` without a cancellation token being typed as
+  `DbConnection` instead of `ClickHouseConnection`
+  ([#686](https://github.com/ClickHouse/clickhouse-cs/issues/686)). The documented ADO.NET examples
+  now compile.
+  - The call now returns `Task<ClickHouseConnection>` instead of `ValueTask<DbConnection>`. Code
+    that stores it as a `ValueTask<DbConnection>`, or calls `.AsTask()` or `.Preserve()` on it, no
+    longer compiles: await the call directly, or call it through `DbDataSource` to keep the old type.