diff --git a/src/shared/middleware/bodySizeGuard.ts b/src/shared/middleware/bodySizeGuard.ts
index af1167458b..fcf2afdb16 100644
--- a/src/shared/middleware/bodySizeGuard.ts
+++ b/src/shared/middleware/bodySizeGuard.ts
@@ -28,6 +28,9 @@ export const MAX_BODY_BYTES_AUDIO = 100 * 1024 * 1024;
 /** Larger limit for file uploads: 500 MB */
 export const MAX_BODY_BYTES_FILE = 500 * 1024 * 1024;
 
+/** Larger limit for LLM request payloads: 50 MB */
+export const MAX_BODY_BYTES_LLM_API = 50 * 1024 * 1024;
+
 /** Configured limit — reads from env or falls back to 10 MB */
 export const MAX_BODY_BYTES = parseRequestBodyLimitBytes(process.env.MAX_BODY_SIZE_BYTES);
 
@@ -35,6 +38,8 @@ type BodySizeRule = { prefix: string; limit: number };
 
 const ROUTE_LIMITS: BodySizeRule[] = [
   { prefix: "/api/db-backups/import", limit: MAX_BODY_BYTES_IMPORT },
+  { prefix: "/api/v1/chat/completions", limit: MAX_BODY_BYTES_LLM_API },
+  { prefix: "/api/v1/responses", limit: MAX_BODY_BYTES_LLM_API },
   { prefix: "/api/v1/audio/transcriptions", limit: MAX_BODY_BYTES_AUDIO },
   { prefix: "/api/v1/files", limit: MAX_BODY_BYTES_FILE },
 ];
diff --git a/src/shared/utils/inputSanitizer.ts b/src/shared/utils/inputSanitizer.ts
index fdfe8af507..bdc927f5d8 100644
--- a/src/shared/utils/inputSanitizer.ts
+++ b/src/shared/utils/inputSanitizer.ts
@@ -62,8 +62,8 @@ const INJECTION_PATTERNS = [
  * latency/GC source. Injection directives sit near the top of a prompt, so
  * scanning hundreds of KB of pasted code / RAG context buys only CPU. We bound
  * the scan to the first 16 KB (generous: real directives are far shorter) before
- * the regex loop. The 10 MB body-size cap that protects ingestion lives
- * elsewhere; this constant only bounds the regex scan. Refs #3932 / #4041.
+ * the regex loop. The body-size caps that protect ingestion live elsewhere;
+ * this constant only bounds the regex scan. Refs #3932 / #4041.
  */
 export const MAX_INJECTION_SCAN_BYTES = 16 * 1024;
 
diff --git a/tests/unit/body-size-guard.test.ts b/tests/unit/body-size-guard.test.ts
index bcb90126ab..1f4d8ae03b 100644
--- a/tests/unit/body-size-guard.test.ts
+++ b/tests/unit/body-size-guard.test.ts
@@ -4,6 +4,7 @@ import * as bodySizeGuard from "../../src/shared/middleware/bodySizeGuard.ts";
 import {
   MAX_BODY_BYTES_AUDIO,
   MAX_BODY_BYTES_FILE,
+  MAX_BODY_BYTES_LLM_API,
   getBodySizeLimit,
   checkBodySize,
 } from "../../src/shared/middleware/bodySizeGuard.ts";
@@ -23,6 +24,14 @@ test("body size guard uses maxBodySizeMb from settings for regular API routes",
 });
 
 test("body size guard keeps dedicated upload limits as lower bounds", () => {
+  assert.equal(
+    getBodySizeLimit("/api/v1/responses", { maxBodySizeMb: 10 }),
+    MAX_BODY_BYTES_LLM_API
+  );
+  assert.equal(
+    getBodySizeLimit("/api/v1/chat/completions", { maxBodySizeMb: 10 }),
+    MAX_BODY_BYTES_LLM_API
+  );
   assert.equal(
     getBodySizeLimit("/api/v1/audio/transcriptions", { maxBodySizeMb: 1 }),
     MAX_BODY_BYTES_AUDIO
@@ -49,6 +58,32 @@ test("checkBodySize reports the configured request limit in 413 responses", asyn
   assert.match(body.error.message, /100 MB/);
 });
 
+test("/api/v1/responses route guard allows 15 MB agent payloads by default", () => {
+  const fifteenMb = 15 * 1024 * 1024;
+  const request = new Request("http://localhost/api/v1/responses", {
+    method: "POST",
+    headers: { "content-length": String(fifteenMb) },
+  });
+
+  assert.equal(checkBodySize(request, getBodySizeLimit("/api/v1/responses")), null);
+});
+
+test("/api/v1/responses route guard rejects payloads above the LLM API floor", async () => {
+  const tooBig = MAX_BODY_BYTES_LLM_API + 1;
+  const request = new Request("http://localhost/api/v1/responses", {
+    method: "POST",
+    headers: { "content-length": String(tooBig) },
+  });
+
+  const response = checkBodySize(request, getBodySizeLimit("/api/v1/responses"));
+
+  assert.ok(response);
+  assert.equal(response.status, 413);
+  const body = await response.json();
+  assert.equal(body.error.code, "PAYLOAD_TOO_LARGE");
+  assert.match(body.error.message, /50 MB/);
+});
+
 test("/api/v1/files route has 512 MB dedicated limit floor", () => {
   const limit = getBodySizeLimit("/api/v1/files", { maxBodySizeMb: 1 });
   assert.equal(limit, MAX_BODY_BYTES_FILE);