diff --git a/provider/anthropicprovider/agent.go b/provider/anthropicprovider/agent.go
index d4aff6d7..73079ad4 100644
--- a/provider/anthropicprovider/agent.go
+++ b/provider/anthropicprovider/agent.go
@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"iter"
 	"maps"
+	"mime"
 	"reflect"
 	"slices"
 	"strings"
@@ -482,6 +483,17 @@ func (a *client) buildMessageParams(messages []*message.Message, opts []agent.Op
 	return params, nil
 }
 
+// isPDFMediaType reports whether mediaType denotes a PDF document. Media types
+// may carry parameters (e.g. "application/pdf; charset=binary") and arbitrary
+// casing, so the base type is parsed and compared case-insensitively.
+func isPDFMediaType(mediaType string) bool {
+	base, _, err := mime.ParseMediaType(mediaType)
+	if err != nil {
+		base = strings.ToLower(strings.TrimSpace(mediaType))
+	}
+	return base == "application/pdf"
+}
+
 // buildWebSearchTool maps a hosted WebSearch tool to the Anthropic
 // web_search_20250305 tool request, populating the optional MaxUses,
 // AllowedDomains, BlockedDomains and UserLocation fields from the tool's
@@ -632,13 +644,32 @@ func buildMessageParam(msg *message.Message) (anthropic.MessageParam, error) {
 			}
 			content = append(content, anthropic.NewToolResultBlock(c.CallID, resStr, c.Error != nil))
 		case *message.DataContent:
-			if c.TopLevelMediaType() == "image" {
+			switch {
+			case c.TopLevelMediaType() == "image":
 				mediaType := c.MediaType
 				if mediaType == "" {
 					mediaType = "image/jpeg"
 				}
 				content = append(content, anthropic.NewImageBlockBase64(mediaType, c.Data))
+			case isPDFMediaType(c.MediaType):
+				content = append(content, anthropic.NewDocumentBlock(anthropic.Base64PDFSourceParam{
+					Data: c.Data,
+				}))
+			}
+		case *message.URIContent:
+			switch {
+			case c.TopLevelMediaType() == "image":
+				content = append(content, anthropic.NewImageBlock(anthropic.URLImageSourceParam{URL: c.URI}))
+			case isPDFMediaType(c.MediaType):
+				content = append(content, anthropic.NewDocumentBlock(anthropic.URLPDFSourceParam{URL: c.URI}))
 			}
+		case *message.HostedFileContent:
+			// The stable Anthropic Messages API used here (anthropic.MessageNewParams)
+			// has no file-id image/document source in anthropic-sdk-go v1.58.1; only
+			// the Beta API exposes BetaFileImageSourceParam/BetaFileDocumentSourceParam.
+			// A hosted file reference therefore cannot be forwarded yet, so surface an
+			// explicit error rather than silently dropping it.
+			return anthropic.MessageParam{}, fmt.Errorf("anthropic: hosted file references (file id %q) are not supported by the Messages API; use DataContent or URIContent instead", c.FileID)
 		}
 	}
 
diff --git a/provider/anthropicprovider/agent_test.go b/provider/anthropicprovider/agent_test.go
index 049c8614..8ba976ed 100644
--- a/provider/anthropicprovider/agent_test.go
+++ b/provider/anthropicprovider/agent_test.go
@@ -847,6 +847,172 @@ func TestToolUseEmptyArgumentsSerializeAsObject(t *testing.T) {
 	}
 }
 
+// A URIContent image URL and a DataContent application/pdf must be forwarded to
+// Anthropic as an image block with a URL source and a document block. Before the
+// fix these inputs fell through the content switch and were silently dropped,
+// diverging from the OpenAI chat provider which maps all three multimodal inputs.
+func TestBuildMessageParam_ImageURLAndPDFAreForwarded(t *testing.T) {
+	bodyCh := make(chan []byte, 1)
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, err := io.ReadAll(r.Body)
+		if err != nil {
+			t.Errorf("read request body: %v", err)
+			http.Error(w, "internal error", http.StatusInternalServerError)
+			return
+		}
+		bodyCh <- body
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = io.WriteString(w, minimalMessageResponse("ok"))
+	}))
+	defer server.Close()
+
+	a := newTestClient(t, server)
+
+	msgs := []*message.Message{
+		{Role: message.RoleUser, Contents: message.Contents{
+			&message.URIContent{URI: "https://example.com/cat.png", MediaType: "image/png"},
+			&message.DataContent{Data: "JVBERi0xLjQK", MediaType: "application/pdf"},
+		}},
+	}
+	if _, err := a.Run(t.Context(), msgs).Collect(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	var req map[string]any
+	if err := json.Unmarshal(<-bodyCh, &req); err != nil {
+		t.Fatalf("unmarshal request body: %v", err)
+	}
+	messages, ok := req["messages"].([]any)
+	if !ok {
+		t.Fatalf("request messages = %#v, want a JSON array", req["messages"])
+	}
+
+	var imageURL, documentBase64 bool
+	for _, m := range messages {
+		msg, ok := m.(map[string]any)
+		if !ok {
+			continue
+		}
+		blocks, ok := msg["content"].([]any)
+		if !ok {
+			continue
+		}
+		for _, b := range blocks {
+			block, ok := b.(map[string]any)
+			if !ok {
+				continue
+			}
+			source, _ := block["source"].(map[string]any)
+			switch block["type"] {
+			case "image":
+				if source["type"] == "url" && source["url"] == "https://example.com/cat.png" {
+					imageURL = true
+				}
+			case "document":
+				if source["type"] == "base64" && source["media_type"] == "application/pdf" && source["data"] == "JVBERi0xLjQK" {
+					documentBase64 = true
+				}
+			}
+		}
+	}
+	if !imageURL {
+		t.Error("image block with a URL source not found in request")
+	}
+	if !documentBase64 {
+		t.Error("document block with a base64 application/pdf source not found in request")
+	}
+}
+
+// A PDF media type that carries parameters or non-canonical casing (e.g.
+// "application/PDF; charset=binary") must still be recognized and forwarded as a
+// document block, not dropped.
+func TestBuildMessageParam_PDFMediaTypeWithParametersIsForwarded(t *testing.T) {
+	bodyCh := make(chan []byte, 1)
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, err := io.ReadAll(r.Body)
+		if err != nil {
+			t.Errorf("read request body: %v", err)
+			http.Error(w, "internal error", http.StatusInternalServerError)
+			return
+		}
+		bodyCh <- body
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = io.WriteString(w, minimalMessageResponse("ok"))
+	}))
+	defer server.Close()
+
+	a := newTestClient(t, server)
+
+	msgs := []*message.Message{
+		{Role: message.RoleUser, Contents: message.Contents{
+			&message.DataContent{Data: "JVBERi0xLjQK", MediaType: "application/PDF; charset=binary"},
+		}},
+	}
+	if _, err := a.Run(t.Context(), msgs).Collect(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	var req map[string]any
+	if err := json.Unmarshal(<-bodyCh, &req); err != nil {
+		t.Fatalf("unmarshal request body: %v", err)
+	}
+	messages, ok := req["messages"].([]any)
+	if !ok {
+		t.Fatalf("request messages = %#v, want a JSON array", req["messages"])
+	}
+
+	var documentBase64 bool
+	for _, m := range messages {
+		msg, ok := m.(map[string]any)
+		if !ok {
+			continue
+		}
+		blocks, ok := msg["content"].([]any)
+		if !ok {
+			continue
+		}
+		for _, b := range blocks {
+			block, ok := b.(map[string]any)
+			if !ok {
+				continue
+			}
+			source, _ := block["source"].(map[string]any)
+			if block["type"] == "document" && source["type"] == "base64" && source["data"] == "JVBERi0xLjQK" {
+				documentBase64 = true
+			}
+		}
+	}
+	if !documentBase64 {
+		t.Error("document block for a PDF media type with parameters not found in request")
+	}
+}
+
+// A HostedFileContent cannot be represented by the stable Messages API, so the
+// request must fail with an explicit error rather than silently dropping it.
+func TestBuildMessageParam_HostedFileContentReturnsError(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		t.Error("request should not be sent when a hosted file reference is present")
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = io.WriteString(w, minimalMessageResponse("ok"))
+	}))
+	defer server.Close()
+
+	a := newTestClient(t, server)
+
+	msgs := []*message.Message{
+		{Role: message.RoleUser, Contents: message.Contents{
+			&message.HostedFileContent{FileID: "file_123"},
+		}},
+	}
+	_, err := a.Run(t.Context(), msgs).Collect()
+	if err == nil {
+		t.Fatal("expected an error for a hosted file reference, got nil")
+	}
+	if !strings.Contains(err.Error(), "file_123") {
+		t.Errorf("error = %v, want it to mention the offending file id", err)
+	}
+}
+
 // A hosted WebSearch tool must be mapped to the Anthropic web_search_20250305
 // tool request, with MaxUses/AllowedDomains/UserLocation carried across from
 // AdditionalProperties. This mirrors the OpenAI providers and the Python