diff --git a/api/server/services/Files/images/encode.js b/api/server/services/Files/images/encode.js
index 2f075229aa..25110566ee 100644
--- a/api/server/services/Files/images/encode.js
+++ b/api/server/services/Files/images/encode.js
@@ -1,6 +1,6 @@
 const axios = require('axios');
 const { logger } = require('@librechat/data-schemas');
-const { logAxiosError, validateImage } = require('@librechat/api');
+const { logAxiosError, validateImage, runGuardedEncode } = require('@librechat/api');
 const {
   FileSources,
   VisionModes,
@@ -136,9 +136,12 @@ async function encodeAndFormat(req, files, params, mode) {
     if (blobStorageSources.has(source)) {
       try {
         const downloadStream = encodingMethods[source].getDownloadStream;
-        let stream = await downloadStream(req, file.filepath);
-        let base64Data = await streamToBase64(stream);
-        stream = null;
+        let base64Data = await runGuardedEncode(file.bytes ?? 0, async () => {
+          let stream = await downloadStream(req, file.filepath);
+          const data = await streamToBase64(stream);
+          stream = null;
+          return data;
+        });
         promises.push([file, base64Data]);
         base64Data = null;
         continue;
@@ -146,8 +149,11 @@ async function encodeAndFormat(req, files, params, mode) {
         logger.error('Error processing image from blob storage:', error);
       }
     } else if (source !== FileSources.local && base64Only.has(effectiveEndpoint)) {
-      const [_file, imageURL] = await preparePayload(req, file);
-      promises.push([_file, await fetchImageToBase64(imageURL)]);
+      const entry = await runGuardedEncode(file.bytes ?? 0, async () => {
+        const [_file, imageURL] = await preparePayload(req, file);
+        return [_file, await fetchImageToBase64(imageURL)];
+      });
+      promises.push(entry);
       continue;
     }
     promises.push(preparePayload(req, file));
diff --git a/api/server/services/Files/images/encode.spec.js b/api/server/services/Files/images/encode.spec.js
new file mode 100644
index 0000000000..700f930d32
--- /dev/null
+++ b/api/server/services/Files/images/encode.spec.js
@@ -0,0 +1,111 @@
+const { Readable } = require('stream');
+
+const mockRunGuardedEncode = jest.fn((_bytes, task) => task());
+
+jest.mock('axios');
+jest.mock('@librechat/api', () => ({
+  logAxiosError: jest.fn(({ message }) => message),
+  validateImage: jest.fn().mockResolvedValue({ isValid: true }),
+  runGuardedEncode: (...args) => mockRunGuardedEncode(...args),
+}));
+jest.mock('@librechat/data-schemas', () => ({
+  logger: { info: jest.fn(), warn: jest.fn(), error: jest.fn(), debug: jest.fn() },
+}));
+
+const mockPrepareImagePayload = jest.fn();
+const mockGetDownloadStream = jest.fn();
+jest.mock('~/server/services/Files/strategies', () => ({
+  getStrategyFunctions: jest.fn(() => ({
+    prepareImagePayload: mockPrepareImagePayload,
+    getDownloadStream: mockGetDownloadStream,
+  })),
+}));
+
+const axios = require('axios');
+const { FileSources } = require('librechat-data-provider');
+const { encodeAndFormat } = require('./encode');
+
+const makeReq = () => ({ body: {}, config: {} });
+
+beforeEach(() => {
+  jest.clearAllMocks();
+  mockRunGuardedEncode.mockImplementation((_bytes, task) => task());
+});
+
+describe('encodeAndFormat - request memory guard', () => {
+  it('gates blob-storage byte pulls and returns [file, base64]', async () => {
+    mockGetDownloadStream.mockResolvedValue(Readable.from([Buffer.from('blob-image-bytes')]));
+    const file = {
+      source: FileSources.s3,
+      height: 10,
+      width: 10,
+      type: 'image/png',
+      file_id: 'f-blob',
+      filepath: 'bucket/a.png',
+      filename: 'a.png',
+      bytes: 4321,
+    };
+
+    const result = await encodeAndFormat(makeReq(), [file], { endpoint: 'openai' });
+
+    expect(mockRunGuardedEncode).toHaveBeenCalledTimes(1);
+    expect(mockRunGuardedEncode.mock.calls[0][0]).toBe(4321);
+
+    const expectedBase64 = Buffer.from('blob-image-bytes').toString('base64');
+    expect(result.image_urls).toHaveLength(1);
+    expect(result.image_urls[0].image_url.url).toBe(`data:image/png;base64,${expectedBase64}`);
+  });
+
+  it('gates base64Only URL fetches and returns [file, base64]', async () => {
+    mockPrepareImagePayload.mockResolvedValue([
+      { source: FileSources.vectordb, type: 'image/png' },
+      'https://images.example/x.png',
+    ]);
+    axios.get.mockResolvedValue({ data: Buffer.from('url-image-bytes') });
+
+    const file = {
+      source: FileSources.vectordb,
+      height: 10,
+      width: 10,
+      type: 'image/png',
+      file_id: 'f-url',
+      filepath: 'remote/x.png',
+      filename: 'x.png',
+      bytes: 9876,
+    };
+
+    const result = await encodeAndFormat(makeReq(), [file], { endpoint: 'anthropic' });
+
+    expect(mockRunGuardedEncode).toHaveBeenCalledTimes(1);
+    expect(mockRunGuardedEncode.mock.calls[0][0]).toBe(9876);
+
+    const expectedBase64 = Buffer.from('url-image-bytes').toString('base64');
+    expect(result.image_urls).toHaveLength(1);
+    expect(result.image_urls[0].source.data).toBe(expectedBase64);
+  });
+
+  it('does not gate the non-buffering local prepare path', async () => {
+    const localBase64 = Buffer.from('local-image').toString('base64');
+    mockPrepareImagePayload.mockResolvedValue([
+      { source: FileSources.local, type: 'image/png' },
+      localBase64,
+    ]);
+
+    const file = {
+      source: FileSources.local,
+      height: 10,
+      width: 10,
+      type: 'image/png',
+      file_id: 'f-local',
+      filepath: 'local/p.png',
+      filename: 'p.png',
+      bytes: 555,
+    };
+
+    const result = await encodeAndFormat(makeReq(), [file], { endpoint: 'openai' });
+
+    expect(mockRunGuardedEncode).not.toHaveBeenCalled();
+    expect(result.image_urls).toHaveLength(1);
+    expect(result.image_urls[0].image_url.url).toBe(`data:image/png;base64,${localBase64}`);
+  });
+});
diff --git a/packages/api/src/files/encode/audio.ts b/packages/api/src/files/encode/audio.ts
index d29163d868..89f4f31df8 100644
--- a/packages/api/src/files/encode/audio.ts
+++ b/packages/api/src/files/encode/audio.ts
@@ -4,6 +4,7 @@ import type { IMongoFile } from '@librechat/data-schemas';
 import type { ServerRequest, StrategyFunctions, AudioResult } from '~/types';
 import { getFileStream, getConfiguredFileSizeLimit } from './utils';
 import { validateAudio } from '~/files/validation';
+import { runGuardedEncode } from './memoryGuard';
 
 /**
  * Encodes and formats audio files for different providers
@@ -30,7 +31,11 @@ export async function encodeAndFormatAudios(
   const result: AudioResult = { audios: [], files: [] };
 
   const results = await Promise.allSettled(
-    files.map((file) => getFileStream(req, file, encodingMethods, getStrategyFunctions)),
+    files.map((file) =>
+      runGuardedEncode(file.bytes ?? 0, () =>
+        getFileStream(req, file, encodingMethods, getStrategyFunctions),
+      ),
+    ),
   );
 
   for (const settledResult of results) {
diff --git a/packages/api/src/files/encode/document.spec.ts b/packages/api/src/files/encode/document.spec.ts
index 846b61eb88..3a955312c2 100644
--- a/packages/api/src/files/encode/document.spec.ts
+++ b/packages/api/src/files/encode/document.spec.ts
@@ -1013,4 +1013,39 @@ describe('encodeAndFormatDocuments - fileConfig integration', () => {
       expect(result.files).toHaveLength(0);
     });
   });
+
+  describe('concurrency guard', () => {
+    it('bounds parallel getFileStream calls and returns all documents unchanged', async () => {
+      const req = createMockRequest(50) as ServerRequest;
+      const files = Array.from({ length: 6 }, (_, i) =>
+        createMockDocFile(1, 'text/plain', `doc-${i}.txt`),
+      );
+
+      let active = 0;
+      let peak = 0;
+      mockedGetFileStream.mockImplementation(async (_req, file) => {
+        active++;
+        peak = Math.max(peak, active);
+        await new Promise((resolve) => setImmediate(resolve));
+        await new Promise((resolve) => setImmediate(resolve));
+        active--;
+        return {
+          file,
+          content: Buffer.from(`content-${file.filename}`).toString('base64'),
+          metadata: file,
+        };
+      });
+
+      const result = await encodeAndFormatDocuments(
+        req,
+        files,
+        { provider: Providers.OPENAI, useResponsesApi: true },
+        mockStrategyFunctions,
+      );
+
+      expect(peak).toBe(3);
+      expect(result.documents).toHaveLength(6);
+      expect(result.files).toHaveLength(6);
+    });
+  });
 });
diff --git a/packages/api/src/files/encode/document.ts b/packages/api/src/files/encode/document.ts
index 9f595fee1e..e83abe30db 100644
--- a/packages/api/src/files/encode/document.ts
+++ b/packages/api/src/files/encode/document.ts
@@ -15,6 +15,7 @@ import type {
 } from '~/types';
 import { validatePdf, validateBedrockDocument } from '~/files/validation';
 import { getFileStream, getConfiguredFileSizeLimit } from './utils';
+import { runGuardedEncode } from './memoryGuard';
 
 const ANTHROPIC_CITATION_TYPES = new Set([
   'application/pdf',
@@ -140,9 +141,11 @@ export async function encodeAndFormatDocuments(
   const configuredFileSizeLimit = getConfiguredFileSizeLimit(req, { provider, endpoint });
 
   const results = await Promise.allSettled(
-    processableFiles.map((file) => {
-      return getFileStream(req, file, encodingMethods, getStrategyFunctions);
-    }),
+    processableFiles.map((file) =>
+      runGuardedEncode(file.bytes ?? 0, () =>
+        getFileStream(req, file, encodingMethods, getStrategyFunctions),
+      ),
+    ),
   );
 
   for (const settledResult of results) {
diff --git a/packages/api/src/files/encode/index.ts b/packages/api/src/files/encode/index.ts
index a0708596f3..ca4949cbf0 100644
--- a/packages/api/src/files/encode/index.ts
+++ b/packages/api/src/files/encode/index.ts
@@ -1,3 +1,4 @@
 export * from './audio';
 export * from './document';
 export * from './video';
+export * from './memoryGuard';
diff --git a/packages/api/src/files/encode/memoryGuard.spec.ts b/packages/api/src/files/encode/memoryGuard.spec.ts
new file mode 100644
index 0000000000..68b673f25e
--- /dev/null
+++ b/packages/api/src/files/encode/memoryGuard.spec.ts
@@ -0,0 +1,149 @@
+import { InFlightBytesSemaphore, runGuardedEncode } from './memoryGuard';
+
+const tick = (): Promise<void> => new Promise((resolve) => setImmediate(resolve));
+
+function deferred<T = void>(): {
+  promise: Promise<T>;
+  resolve: (value: T) => void;
+  reject: (error: unknown) => void;
+} {
+  let resolve!: (value: T) => void;
+  let reject!: (error: unknown) => void;
+  const promise = new Promise<T>((res, rej) => {
+    resolve = res;
+    reject = rej;
+  });
+  return { promise, resolve, reject };
+}
+
+describe('memoryGuard', () => {
+  describe('runGuardedEncode concurrency cap', () => {
+    it('never runs more than 3 tasks at once and completes all', async () => {
+      let active = 0;
+      let peak = 0;
+      const gates = [deferred(), deferred(), deferred(), deferred(), deferred()];
+
+      const calls = gates.map((gate, i) =>
+        runGuardedEncode(1, async () => {
+          active++;
+          peak = Math.max(peak, active);
+          await gate.promise;
+          active--;
+          return i;
+        }),
+      );
+
+      await tick();
+      expect(active).toBe(3);
+
+      for (const gate of gates) {
+        gate.resolve();
+        await tick();
+      }
+
+      await expect(Promise.all(calls)).resolves.toEqual([0, 1, 2, 3, 4]);
+      expect(peak).toBe(3);
+    });
+  });
+
+  describe('runGuardedEncode release on throw', () => {
+    it('frees the slot when a task rejects', async () => {
+      await expect(
+        runGuardedEncode(1, async () => {
+          throw new Error('boom');
+        }),
+      ).rejects.toThrow('boom');
+
+      await expect(runGuardedEncode(1, async () => 'ok')).resolves.toBe('ok');
+    });
+  });
+
+  describe('InFlightBytesSemaphore', () => {
+    it('does not admit a later reservation ahead of an earlier queued one that still fits', async () => {
+      const sem = new InFlightBytesSemaphore(100);
+      const order: string[] = [];
+
+      const releaseActive = await sem.acquire(60);
+
+      void sem.acquire(60).then(() => order.push('first'));
+      void sem.acquire(10).then(() => order.push('second'));
+
+      await tick();
+      expect(order).toEqual([]);
+
+      releaseActive();
+      await tick();
+      expect(order).toEqual(['first', 'second']);
+    });
+
+    it('admits queued waiters in FIFO order as budget frees', async () => {
+      const sem = new InFlightBytesSemaphore(100);
+      const order: string[] = [];
+      const releases: Record<string, () => void> = {};
+
+      const releaseA = await sem.acquire(100);
+
+      for (const label of ['B', 'C', 'D']) {
+        void sem.acquire(60).then((release) => {
+          order.push(label);
+          releases[label] = release;
+        });
+      }
+
+      await tick();
+      expect(order).toEqual([]);
+
+      releaseA();
+      await tick();
+      expect(order).toEqual(['B']);
+
+      releases['B']();
+      await tick();
+      expect(order).toEqual(['B', 'C']);
+
+      releases['C']();
+      await tick();
+      expect(order).toEqual(['B', 'C', 'D']);
+    });
+
+    it('runs an oversize reservation alone without deadlocking', async () => {
+      const sem = new InFlightBytesSemaphore(100);
+
+      const releaseOversize = await sem.acquire(500);
+
+      let smallAdmitted = false;
+      void sem.acquire(10).then(() => {
+        smallAdmitted = true;
+      });
+
+      await tick();
+      expect(smallAdmitted).toBe(false);
+
+      releaseOversize();
+      await tick();
+      expect(smallAdmitted).toBe(true);
+    });
+
+    it('release is idempotent', async () => {
+      const sem = new InFlightBytesSemaphore(100);
+
+      const releaseFirst = await sem.acquire(100);
+      releaseFirst();
+      releaseFirst();
+
+      const releaseSecond = await sem.acquire(100);
+
+      let thirdAdmitted = false;
+      void sem.acquire(100).then(() => {
+        thirdAdmitted = true;
+      });
+
+      await tick();
+      expect(thirdAdmitted).toBe(false);
+
+      releaseSecond();
+      await tick();
+      expect(thirdAdmitted).toBe(true);
+    });
+  });
+});
diff --git a/packages/api/src/files/encode/memoryGuard.ts b/packages/api/src/files/encode/memoryGuard.ts
new file mode 100644
index 0000000000..227a6d4544
--- /dev/null
+++ b/packages/api/src/files/encode/memoryGuard.ts
@@ -0,0 +1,65 @@
+import { createConcurrencyLimiter } from '~/utils/promise';
+
+const ENCODE_CONCURRENCY = 3;
+const ENCODE_INFLIGHT_BYTES_MAX = 256 * 1024 * 1024;
+
+export class InFlightBytesSemaphore {
+  private inFlight = 0;
+  private readonly queue: Array<{ bytes: number; resolve: () => void }> = [];
+
+  constructor(private readonly ceiling: number) {}
+
+  acquire(bytes: number): Promise<() => void> {
+    const reserve = Math.max(0, bytes || 0);
+
+    if (this.queue.length === 0 && this.canAdmit(reserve)) {
+      return Promise.resolve(this.grant(reserve));
+    }
+
+    return new Promise<() => void>((resolve) => {
+      this.queue.push({ bytes: reserve, resolve: () => resolve(this.grant(reserve)) });
+    });
+  }
+
+  private canAdmit(reserve: number): boolean {
+    return this.inFlight === 0 || this.inFlight + reserve <= this.ceiling;
+  }
+
+  private grant(reserve: number): () => void {
+    this.inFlight += reserve;
+    let released = false;
+    return () => {
+      if (released) {
+        return;
+      }
+      released = true;
+      this.inFlight -= reserve;
+      this.drain();
+    };
+  }
+
+  private drain(): void {
+    while (this.queue.length > 0) {
+      const head = this.queue[0];
+      if (!this.canAdmit(head.bytes)) {
+        break;
+      }
+      this.queue.shift();
+      head.resolve();
+    }
+  }
+}
+
+const encodeLimit = createConcurrencyLimiter(ENCODE_CONCURRENCY);
+const inFlightBytes = new InFlightBytesSemaphore(ENCODE_INFLIGHT_BYTES_MAX);
+
+export function runGuardedEncode<T>(estimatedBytes: number, task: () => Promise<T>): Promise<T> {
+  return encodeLimit(async () => {
+    const release = await inFlightBytes.acquire(estimatedBytes);
+    try {
+      return await task();
+    } finally {
+      release();
+    }
+  });
+}
diff --git a/packages/api/src/files/encode/utils.ts b/packages/api/src/files/encode/utils.ts
index 9afa627cc7..899f3592a2 100644
--- a/packages/api/src/files/encode/utils.ts
+++ b/packages/api/src/files/encode/utils.ts
@@ -56,11 +56,13 @@ export async function getFileStream(
 
   const { getDownloadStream } = encodingMethods[source];
   const stream = await getDownloadStream(req, file.filepath);
-  const buffer = await getStream.buffer(stream);
+  let buffer: Buffer | null = await getStream.buffer(stream);
+  const content = buffer.toString('base64');
+  buffer = null;
 
   return {
     file,
-    content: buffer.toString('base64'),
+    content,
     metadata: {
       file_id: file.file_id,
       temp_file_id: file.temp_file_id,
diff --git a/packages/api/src/files/encode/video.ts b/packages/api/src/files/encode/video.ts
index b0d9bb8c2d..26c8d007d5 100644
--- a/packages/api/src/files/encode/video.ts
+++ b/packages/api/src/files/encode/video.ts
@@ -4,6 +4,7 @@ import type { IMongoFile } from '@librechat/data-schemas';
 import type { ServerRequest, StrategyFunctions, VideoResult } from '~/types';
 import { getFileStream, getConfiguredFileSizeLimit } from './utils';
 import { validateVideo } from '~/files/validation';
+import { runGuardedEncode } from './memoryGuard';
 
 /**
  * Encodes and formats video files for different providers
@@ -30,7 +31,11 @@ export async function encodeAndFormatVideos(
   const result: VideoResult = { videos: [], files: [] };
 
   const results = await Promise.allSettled(
-    files.map((file) => getFileStream(req, file, encodingMethods, getStrategyFunctions)),
+    files.map((file) =>
+      runGuardedEncode(file.bytes ?? 0, () =>
+        getFileStream(req, file, encodingMethods, getStrategyFunctions),
+      ),
+    ),
   );
 
   for (const settledResult of results) {