assets/skills/claude-code/claude-api/csharp/claude-api/files-api.md

# Files API — C#

## Files API (Beta)

Files live under `client.Beta.Files` (namespace `Anthropic.Models.Beta.Files`). `BinaryContent` implicit-converts from `Stream` and `byte[]`.

```csharp
using Anthropic.Models.Beta.Files;
using Anthropic.Models.Beta.Messages;

FileMetadata meta = await client.Beta.Files.Upload(
    new FileUploadParams { File = File.OpenRead("doc.pdf") });

// Referencing the uploaded file requires Beta message types:
new BetaRequestDocumentBlock {
    Source = new BetaFileDocumentSource { FileID = meta.ID },
}
```

The non-beta `DocumentBlockParamSource` union has no file-ID variant — file references need `client.Beta.Messages.Create()`.

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