C# Feature - await using

await using

await using disposes resources asynchronously when they implement IAsyncDisposable. It is the async counterpart to using.

Introduced In

This feature was introduced in C# 8.0 (2019).

Why This Feature Exists

Some resources need asynchronous cleanup, such as flushing buffers, completing network writes, or closing remote connections. A synchronous Dispose() call cannot express that work well. await using keeps disposal aligned with async control flow.

When To Use It

Use it for types that implement IAsyncDisposable.
Use it in async methods that work with streams, transactions, writers, or SDK types that expose async cleanup.
Prefer it over explicit try/finally plus DisposeAsync() when the scope is straightforward.

Before

var stream = new AsyncFileWriter(path);

try
{
  await stream.WriteAsync(payload);
}
finally
{
  await stream.DisposeAsync();
}

After

await using var stream = new AsyncFileWriter(path);
await stream.WriteAsync(payload);

Practical Example

await using var transaction = await connection.BeginTransactionAsync();

await command.ExecuteNonQueryAsync();
await transaction.CommitAsync();

Common Pitfalls

await using only works for IAsyncDisposable; it is not interchangeable with IDisposable.
Disposal happens at the end of the current scope, so keep the scope as small as practical.
If both sync and async disposal exist, prefer the async form inside async codepaths.

Version Notes

C# 8 introduced await using together with async disposal support.