diff --git a/src/agents/tools/pdf-native-providers.test.ts b/src/agents/tools/pdf-native-providers.test.ts
index 98a8b5e5052..b7eecd23935 100644
--- a/src/agents/tools/pdf-native-providers.test.ts
+++ b/src/agents/tools/pdf-native-providers.test.ts
@@ -112,6 +112,65 @@ describe("native PDF provider API calls", () => {
     ).rejects.toThrow("Anthropic PDF request failed");
   });
 
+  it("bounds large Anthropic API error bodies", async () => {
+    let canceled = false;
+    const body = new ReadableStream<Uint8Array>({
+      start(controller) {
+        controller.enqueue(new TextEncoder().encode(`${"x".repeat(9_000)}tail-marker`));
+      },
+      cancel() {
+        canceled = true;
+      },
+    });
+    mockFetchResponse(
+      new Response(body, {
+        status: 400,
+        statusText: "Bad Request",
+      }),
+    );
+
+    const error = await pdfNativeProviders
+      .anthropicAnalyzePdf(makeAnthropicAnalyzeParams())
+      .catch((caught: unknown) => caught as Error);
+
+    expect(error).toBeInstanceOf(Error);
+    expect(error.message).toContain("Anthropic PDF request failed");
+    expect(error.message).not.toContain("tail-marker");
+    expect(error.message.length).toBeLessThan(500);
+    expect(canceled).toBe(true);
+  });
+
+  it("cancels Anthropic API error bodies that exactly fill the byte cap", async () => {
+    let canceled = false;
+    const body = new ReadableStream<Uint8Array>({
+      start(controller) {
+        controller.enqueue(new TextEncoder().encode("x".repeat(8 * 1024)));
+      },
+      cancel() {
+        canceled = true;
+      },
+    });
+    mockFetchResponse(
+      new Response(body, {
+        status: 400,
+        statusText: "Bad Request",
+      }),
+    );
+
+    const error = await Promise.race([
+      pdfNativeProviders
+        .anthropicAnalyzePdf(makeAnthropicAnalyzeParams())
+        .catch((caught: unknown) => caught as Error),
+      new Promise<Error>((_resolve, reject) => {
+        setTimeout(() => reject(new Error("timed out waiting for bounded error body")), 500);
+      }),
+    ]);
+
+    expect(error).toBeInstanceOf(Error);
+    expect(error.message).toContain("Anthropic PDF request failed");
+    expect(canceled).toBe(true);
+  });
+
   it("anthropicAnalyzePdf throws when response has no text", async () => {
     mockFetchResponse({
       ok: true,
diff --git a/src/agents/tools/pdf-native-providers.ts b/src/agents/tools/pdf-native-providers.ts
index fd46cc84beb..0500b485c42 100644
--- a/src/agents/tools/pdf-native-providers.ts
+++ b/src/agents/tools/pdf-native-providers.ts
@@ -13,6 +13,59 @@ type PdfInput = {
 };
 
 const NATIVE_PDF_PROVIDER_FETCH_TIMEOUT_MS = 120_000;
+const NATIVE_PDF_ERROR_BODY_MAX_BYTES = 8 * 1024;
+const NATIVE_PDF_ERROR_BODY_MAX_CHARS = 400;
+
+async function readErrorBodySnippet(res: Response): Promise<string> {
+  try {
+    const body = res.body;
+    if (!body || typeof body.getReader !== "function") {
+      return (await res.text()).slice(0, NATIVE_PDF_ERROR_BODY_MAX_CHARS);
+    }
+
+    const reader = body.getReader();
+    const chunks: Uint8Array[] = [];
+    let total = 0;
+    let truncated = false;
+    try {
+      while (true) {
+        const { done, value } = await reader.read();
+        if (done || !value?.byteLength) {
+          break;
+        }
+        const remaining = NATIVE_PDF_ERROR_BODY_MAX_BYTES - total;
+        if (remaining <= 0) {
+          truncated = true;
+          break;
+        }
+        if (value.byteLength > remaining) {
+          chunks.push(value.subarray(0, remaining));
+          total += remaining;
+          truncated = true;
+          break;
+        }
+        chunks.push(value);
+        total += value.byteLength;
+        if (total >= NATIVE_PDF_ERROR_BODY_MAX_BYTES) {
+          truncated = true;
+          break;
+        }
+      }
+    } finally {
+      if (truncated) {
+        await reader.cancel().catch(() => undefined);
+      }
+      try {
+        reader.releaseLock();
+      } catch {}
+    }
+    return new TextDecoder()
+      .decode(Buffer.concat(chunks, total))
+      .slice(0, NATIVE_PDF_ERROR_BODY_MAX_CHARS);
+  } catch {
+    return "";
+  }
+}
 
 // ---------------------------------------------------------------------------
 // Anthropic – native PDF via Messages API
@@ -80,9 +133,9 @@ export async function anthropicAnalyzePdf(params: {
   });
 
   if (!res.ok) {
-    const body = await res.text().catch(() => "");
+    const body = await readErrorBodySnippet(res);
     throw new Error(
-      `Anthropic PDF request failed (${res.status} ${res.statusText})${body ? `: ${body.slice(0, 400)}` : ""}`,
+      `Anthropic PDF request failed (${res.status} ${res.statusText})${body ? `: ${body}` : ""}`,
     );
   }
 
@@ -165,9 +218,9 @@ export async function geminiAnalyzePdf(params: {
   });
 
   if (!res.ok) {
-    const body = await res.text().catch(() => "");
+    const body = await readErrorBodySnippet(res);
     throw new Error(
-      `Gemini PDF request failed (${res.status} ${res.statusText})${body ? `: ${body.slice(0, 400)}` : ""}`,
+      `Gemini PDF request failed (${res.status} ${res.statusText})${body ? `: ${body}` : ""}`,
     );
   }