diff --git a/coderd/x/chatd/chatprompt/chatprompt.go b/coderd/x/chatd/chatprompt/chatprompt.go
index 126edf8dba..ac86b11e96 100644
--- a/coderd/x/chatd/chatprompt/chatprompt.go
+++ b/coderd/x/chatd/chatprompt/chatprompt.go
@@ -1588,6 +1588,7 @@ func partsToMessageParts(
 				continue
 			}
 			result = append(result, fantasy.FilePart{
+				Filename:        name,
 				Data:            data,
 				MediaType:       mediaType,
 				ProviderOptions: opts,
diff --git a/coderd/x/chatd/chatprompt/chatprompt_test.go b/coderd/x/chatd/chatprompt/chatprompt_test.go
index 8f66da7cec..895fe02aea 100644
--- a/coderd/x/chatd/chatprompt/chatprompt_test.go
+++ b/coderd/x/chatd/chatprompt/chatprompt_test.go
@@ -502,6 +502,7 @@ func TestConvertMessagesWithFiles_MixedResolvedAndMissingFilePartsInSingleMessag
 
 	filePart, ok := fantasy.AsMessagePart[fantasy.FilePart](prompt[0].Content[0])
 	require.True(t, ok, "expected first part to stay a FilePart")
+	require.Equal(t, "resolved.png", filePart.Filename)
 	require.Equal(t, resolvedData, filePart.Data)
 	require.Equal(t, "image/png", filePart.MediaType)
 
diff --git a/coderd/x/chatd/chatprovider/chatprovider_test.go b/coderd/x/chatd/chatprovider/chatprovider_test.go
index 80911d89cd..261c6e9528 100644
--- a/coderd/x/chatd/chatprovider/chatprovider_test.go
+++ b/coderd/x/chatd/chatprovider/chatprovider_test.go
@@ -1401,10 +1401,11 @@ func TestModelFromConfig_ExtraHeaders(t *testing.T) {
 // path that lets a user-uploaded PDF actually reach Claude/Bedrock: a
 // fantasy.FilePart with MediaType "application/pdf" must be serialized as an
 // Anthropic "document" content block with a base64 source carrying the PDF
-// bytes. Older fantasy versions silently dropped PDF FileParts in the
-// Anthropic provider, so the user message ended up empty and the model never
-// saw the document. See coder/fantasy#37 (cherry-pick of upstream
-// charmbracelet/fantasy#197). The Generate call would fail outright on the
+// bytes and a sanitized filename as the document title. Older fantasy versions
+// silently dropped PDF FileParts in the Anthropic provider, so the user
+// message ended up empty and the model never saw the document. The underlying
+// PDF block support came from coder/fantasy#37, a cherry-pick of upstream
+// charmbracelet/fantasy#197. The Generate call would fail outright on the
 // regressed code path because the dropped FilePart leaves the request with
 // zero messages.
 func TestModelFromConfig_AnthropicPDFFilePartReachesProvider(t *testing.T) {
@@ -1423,6 +1424,7 @@ func TestModelFromConfig_AnthropicPDFFilePartReachesProvider(t *testing.T) {
 
 		var blocks []struct {
 			Type   string `json:"type"`
+			Title  string `json:"title"`
 			Source struct {
 				Type      string `json:"type"`
 				MediaType string `json:"media_type"`
@@ -1439,6 +1441,11 @@ func TestModelFromConfig_AnthropicPDFFilePartReachesProvider(t *testing.T) {
 			}
 			assert.Equal(t, "base64", block.Source.Type, "PDF document block must use a base64 source")
 			assert.Equal(t, wantData, block.Source.Data, "PDF bytes must round-trip base64 unchanged")
+			assert.Equal(t,
+				"quarterly report v1 pdf",
+				block.Title,
+				"PDF filename must reach Anthropic as a sanitized document title",
+			)
 			if block.Source.MediaType != "" {
 				assert.Equal(t, "application/pdf", block.Source.MediaType)
 			}
@@ -1462,7 +1469,11 @@ func TestModelFromConfig_AnthropicPDFFilePartReachesProvider(t *testing.T) {
 			{
 				Role: fantasy.MessageRoleUser,
 				Content: []fantasy.MessagePart{
-					fantasy.FilePart{Data: pdfData, MediaType: "application/pdf"},
+					fantasy.FilePart{
+						Filename:  "quarterly_report.v1.pdf",
+						Data:      pdfData,
+						MediaType: "application/pdf",
+					},
 				},
 			},
 		},
diff --git a/go.mod b/go.mod
index 95f96d276c..82bfbab673 100644
--- a/go.mod
+++ b/go.mod
@@ -94,7 +94,11 @@ replace github.com/spf13/afero => github.com/aslilac/afero v0.0.0-20250403163713
 //     emit a Base64 PDF document block for application/pdf FileParts on the
 //     Anthropic provider so user-uploaded PDFs actually reach Claude/Bedrock
 //     instead of being silently dropped.
-// 11) coder/fantasy#39, support Anthropic thinking_display natively.
+// 11) coder/fantasy#38, forward PDF and text filenames as a sanitized
+//     Anthropic document title so Claude can refer to attachments by
+//     name, and warn on unsupported FilePart media types instead of
+//     silently dropping them.
+// 12) coder/fantasy#39, support Anthropic thinking_display natively.
 // See: https://github.com/coder/fantasy/commits/a2a3f2171ec8
 replace charm.land/fantasy => github.com/coder/fantasy v0.0.0-20260604204802-a2a3f2171ec8