diff --git a/coderd/x/chatd/chatprompt/chatprompt.go b/coderd/x/chatd/chatprompt/chatprompt.go
index 126edf8dba8ab..ac86b11e96b17 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 8f66da7cecfc8..895fe02aeaa87 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 1d9b43c4ff4f1..891a01f880c3a 100644
--- a/coderd/x/chatd/chatprovider/chatprovider_test.go
+++ b/coderd/x/chatd/chatprovider/chatprovider_test.go
@@ -1308,10 +1308,11 @@ 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) {
@@ -1330,6 +1331,7 @@ 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"`
@@ -1346,6 +1348,11 @@ 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)
 			}
@@ -1369,7 +1376,11 @@ 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 241ab475c02d8..bfd4d2b0f748c 100644
--- a/go.mod
+++ b/go.mod
@@ -94,8 +94,12 @@ 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.
-// See: https://github.com/coder/fantasy/commits/7d46e640327a
-replace charm.land/fantasy => github.com/coder/fantasy v0.0.0-20260602023814-7d46e640327a
+// 11) coder/fantasy#38 @b2b2fc6d524c, 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.
+// See: https://github.com/coder/fantasy/commits/b2b2fc6d524c
+replace charm.land/fantasy => github.com/coder/fantasy v0.0.0-20260604065934-b2b2fc6d524c
 
 // coder/coder uses a fork of charmbracelet's fork of the Anthropic Go SDK
 // with performance improvements and Bedrock header cleanup.
diff --git a/go.sum b/go.sum
index 61bfd608f8bed..58ffd01501505 100644
--- a/go.sum
+++ b/go.sum
@@ -324,8 +324,8 @@ github.com/coder/bubbletea v1.2.2-0.20241212190825-007a1cdb2c41 h1:SBN/DA63+ZHwu
 github.com/coder/bubbletea v1.2.2-0.20241212190825-007a1cdb2c41/go.mod h1:I9ULxr64UaOSUv7hcb3nX4kowodJCVS7vt7VVJk/kW4=
 github.com/coder/clistat v1.2.1 h1:P9/10njXMyj5cWzIU5wkRsSy5LVQH49+tcGMsAgWX0w=
 github.com/coder/clistat v1.2.1/go.mod h1:m7SC0uj88eEERgvF8Kn6+w6XF21BeSr+15f7GoLAw0A=
-github.com/coder/fantasy v0.0.0-20260602023814-7d46e640327a h1:ffQixHAwjJLHgFfe4rtrAsFNRGhEyWnBSpInnLIxDPo=
-github.com/coder/fantasy v0.0.0-20260602023814-7d46e640327a/go.mod h1:wZ0e3lEPqrM0XiIdAUQLvMKCLYhc3gi96MRX2wjbX44=
+github.com/coder/fantasy v0.0.0-20260604065934-b2b2fc6d524c h1:POkVNoDnbNv3CfeFInwai0yMkjGkdqjgqIcG/SlnuLg=
+github.com/coder/fantasy v0.0.0-20260604065934-b2b2fc6d524c/go.mod h1:wZ0e3lEPqrM0XiIdAUQLvMKCLYhc3gi96MRX2wjbX44=
 github.com/coder/flog v1.1.0 h1:kbAes1ai8fIS5OeV+QAnKBQE22ty1jRF/mcAwHpLBa4=
 github.com/coder/flog v1.1.0/go.mod h1:UQlQvrkJBvnRGo69Le8E24Tcl5SJleAAR7gYEHzAmdQ=
 github.com/coder/go-httpstat v0.0.0-20230801153223-321c88088322 h1:m0lPZjlQ7vdVpRBPKfYIFlmgevoTkBxB10wv6l2gOaU=