diff --git a/api/server/controllers/agents/v1.js b/api/server/controllers/agents/v1.js
index 817e9e837c..a089f2d9c1 100644
--- a/api/server/controllers/agents/v1.js
+++ b/api/server/controllers/agents/v1.js
@@ -9,6 +9,7 @@ const {
   refreshListAvatars,
   collectEdgeAgentIds,
   mergeAgentOcrConversion,
+  sanitizeModelParameters,
   MAX_AVATAR_REFRESH_AGENTS,
   collectToolResourceFileIds,
   convertOcrToContextInPlace,
@@ -348,7 +349,10 @@ const createAgentHandler = async (req, res) => {
     const { tools = [], ...agentData } = removeNullishValues(validatedData);
 
     if (agentData.model_parameters && typeof agentData.model_parameters === 'object') {
-      agentData.model_parameters = removeNullishValues(agentData.model_parameters, true);
+      agentData.model_parameters = removeNullishValues(
+        sanitizeModelParameters(agentData.model_parameters),
+        true,
+      );
     }
 
     const { id: userId, role: userRole } = req.user;
@@ -604,7 +608,10 @@ const updateAgentHandler = async (req, res) => {
     const updateData = removeNullishValues(rest);
 
     if (updateData.model_parameters && typeof updateData.model_parameters === 'object') {
-      updateData.model_parameters = removeNullishValues(updateData.model_parameters, true);
+      updateData.model_parameters = removeNullishValues(
+        sanitizeModelParameters(updateData.model_parameters),
+        true,
+      );
     }
 
     if (avatarField === null) {
diff --git a/api/server/controllers/agents/v1.spec.js b/api/server/controllers/agents/v1.spec.js
index 8111193101..76d9796b74 100644
--- a/api/server/controllers/agents/v1.spec.js
+++ b/api/server/controllers/agents/v1.spec.js
@@ -500,6 +500,38 @@ describe('Agent Controllers - Mass Assignment Protection', () => {
       expect(agentInDb.model_parameters.maxContextTokens).toBeUndefined();
     });
 
+    test('should drop non-numeric strings and coerce numeric strings in model_parameters', async () => {
+      // Regression test for #12920: a stray placeholder string ("System") persisted
+      // into max_tokens was forwarded to the provider, causing a 400
+      const dataWithCorruptModelParams = {
+        provider: 'openai',
+        model: 'gpt-4',
+        name: 'Agent with Corrupt Model Params',
+        model_parameters: {
+          max_tokens: 'System',
+          maxContextTokens: '256000',
+          fileTokenLimit: 256000,
+          useResponsesApi: true,
+        },
+      };
+
+      mockReq.body = dataWithCorruptModelParams;
+
+      await createAgentHandler(mockReq, mockRes);
+
+      expect(mockRes.status).toHaveBeenCalledWith(201);
+
+      const createdAgent = mockRes.json.mock.calls[0][0];
+      expect(createdAgent.model_parameters.max_tokens).toBeUndefined();
+      expect(createdAgent.model_parameters.maxContextTokens).toBe(256000);
+      expect(createdAgent.model_parameters.fileTokenLimit).toBe(256000);
+      expect(createdAgent.model_parameters.useResponsesApi).toBe(true);
+
+      const agentInDb = await Agent.findOne({ id: createdAgent.id });
+      expect(agentInDb.model_parameters.max_tokens).toBeUndefined();
+      expect(agentInDb.model_parameters.maxContextTokens).toBe(256000);
+    });
+
     test('should handle invalid avatar format', async () => {
       const dataWithInvalidAvatar = {
         provider: 'openai',
@@ -697,6 +729,32 @@ describe('Agent Controllers - Mass Assignment Protection', () => {
       expect(agentInDb.name).toBe('Updated Agent');
     });
 
+    test('should sanitize corrupt numeric model_parameters on update', async () => {
+      mockReq.user.id = existingAgentAuthorId.toString();
+      mockReq.params.id = existingAgentId;
+      mockReq.body = {
+        name: 'Healed Agent',
+        model_parameters: {
+          max_tokens: 'System',
+          maxContextTokens: 256000,
+          temperature: '0.7',
+        },
+      };
+
+      await updateAgentHandler(mockReq, mockRes);
+
+      expect(mockRes.json).toHaveBeenCalled();
+
+      const updatedAgent = mockRes.json.mock.calls[0][0];
+      expect(updatedAgent.model_parameters.max_tokens).toBeUndefined();
+      expect(updatedAgent.model_parameters.maxContextTokens).toBe(256000);
+      expect(updatedAgent.model_parameters.temperature).toBe(0.7);
+
+      const agentInDb = await Agent.findOne({ id: existingAgentId });
+      expect(agentInDb.model_parameters.max_tokens).toBeUndefined();
+      expect(agentInDb.model_parameters.maxContextTokens).toBe(256000);
+    });
+
     test('should reject update with unauthorized fields (mass assignment protection)', async () => {
       mockReq.user.id = existingAgentAuthorId.toString();
       mockReq.params.id = existingAgentId;
diff --git a/client/src/components/SidePanel/Parameters/DynamicInput.tsx b/client/src/components/SidePanel/Parameters/DynamicInput.tsx
index cdc6f3a452..19d43cfaf3 100644
--- a/client/src/components/SidePanel/Parameters/DynamicInput.tsx
+++ b/client/src/components/SidePanel/Parameters/DynamicInput.tsx
@@ -1,4 +1,4 @@
-import { OptionTypes } from 'librechat-data-provider';
+import { OptionTypes, SettingTypes } from 'librechat-data-provider';
 import { Label, Input, HoverCard, HoverCardTrigger } from '@librechat/client';
 import type { DynamicSettingProps } from 'librechat-data-provider';
 import { useLocalize, useDebouncedInput, useParameterEffects, TranslationKeys } from '~/hooks';
@@ -8,6 +8,8 @@ import OptionHover from './OptionHover';
 import { ESide } from '~/common';
 
 function DynamicInput({
+  type,
+  range,
   label = '',
   settingKey,
   defaultValue,
@@ -15,8 +17,6 @@ function DynamicInput({
   columnSpan,
   setOption,
   optionType,
-  type,
-  range,
   placeholder = '',
   readonly = false,
   showDefault = false,
@@ -45,7 +45,7 @@ function DynamicInput({
   });
 
   const handleInputChange = (e: React.ChangeEvent<HTMLInputElement>) => {
-    if (type === 'number') {
+    if (type === SettingTypes.Number) {
       // Integer params: strip thousands separators so "120,000" / "120.000"
       // become 120000 instead of being truncated to 120 downstream by parseInt.
       // Keep a leading minus for fields whose range permits negatives (e.g.
@@ -58,7 +58,7 @@ function DynamicInput({
       setInputValue(sanitized, sanitized !== '-');
       return;
     }
-    setInputValue(e, !isNaN(Number(e.target.value)));
+    setInputValue(e, type === SettingTypes.String ? false : !isNaN(Number(e.target.value)));
   };
 
   const placeholderText = placeholderCode
diff --git a/client/src/components/SidePanel/Parameters/__tests__/DynamicInput.spec.tsx b/client/src/components/SidePanel/Parameters/__tests__/DynamicInput.spec.tsx
new file mode 100644
index 0000000000..5cd348ab90
--- /dev/null
+++ b/client/src/components/SidePanel/Parameters/__tests__/DynamicInput.spec.tsx
@@ -0,0 +1,155 @@
+import React from 'react';
+import userEvent from '@testing-library/user-event';
+import { render, screen, act, fireEvent } from '@testing-library/react';
+import type { TSetOption, SettingRange } from 'librechat-data-provider';
+import DynamicInput from '../DynamicInput';
+import { ChatContext } from '~/Providers';
+
+type ChatContextValue = React.ContextType<typeof ChatContext>;
+
+const chatContextValue = { preset: null } as unknown as ChatContextValue;
+
+function setup({
+  type,
+  range,
+  settingKey,
+}: {
+  type: 'number' | 'string';
+  range?: SettingRange;
+  settingKey: string;
+}) {
+  const commit = jest.fn();
+  const setOption = jest.fn(() => commit) as unknown as TSetOption;
+  render(
+    <ChatContext.Provider value={chatContextValue}>
+      <DynamicInput
+        settingKey={settingKey}
+        type={type}
+        range={range}
+        setOption={setOption}
+        conversation={{}}
+      />
+    </ChatContext.Provider>,
+  );
+  return { input: screen.getByRole('textbox'), commit };
+}
+
+describe('DynamicInput', () => {
+  beforeEach(() => {
+    jest.useFakeTimers();
+  });
+
+  afterEach(() => {
+    jest.useRealTimers();
+  });
+
+  it('strips typed non-numeric text for number settings', async () => {
+    const user = userEvent.setup({ advanceTimers: jest.advanceTimersByTime });
+    const { input, commit } = setup({ type: 'number', settingKey: 'max_tokens' });
+
+    await user.type(input, 'System');
+
+    expect(input).toHaveValue('');
+    act(() => {
+      jest.advanceTimersByTime(500);
+    });
+    expect(commit).toHaveBeenLastCalledWith('');
+  });
+
+  it('strips pasted or autofilled non-numeric text for number settings', () => {
+    const { input, commit } = setup({ type: 'number', settingKey: 'max_tokens' });
+
+    fireEvent.change(input, { target: { value: 'System' } });
+
+    expect(input).toHaveValue('');
+    act(() => {
+      jest.advanceTimersByTime(500);
+    });
+    expect(commit).toHaveBeenLastCalledWith('');
+  });
+
+  it('commits numeric input as a number for number settings', async () => {
+    const user = userEvent.setup({ advanceTimers: jest.advanceTimersByTime });
+    const { input, commit } = setup({ type: 'number', settingKey: 'max_tokens' });
+
+    await user.type(input, '4096');
+
+    expect(input).toHaveValue('4096');
+    act(() => {
+      jest.advanceTimersByTime(500);
+    });
+    expect(commit).toHaveBeenLastCalledWith(4096);
+  });
+
+  it('strips thousands separators from pasted values', () => {
+    const { input, commit } = setup({ type: 'number', settingKey: 'maxContextTokens' });
+
+    fireEvent.change(input, { target: { value: '120,000' } });
+
+    expect(input).toHaveValue('120000');
+    act(() => {
+      jest.advanceTimersByTime(500);
+    });
+    expect(commit).toHaveBeenLastCalledWith(120000);
+  });
+
+  it('allows typing negative numbers when the range permits (e.g. thinkingBudget -1)', async () => {
+    const user = userEvent.setup({ advanceTimers: jest.advanceTimersByTime });
+    const { input, commit } = setup({
+      type: 'number',
+      range: { min: -1, max: 24576, step: 1 },
+      settingKey: 'thinkingBudget',
+    });
+
+    await user.type(input, '-1');
+
+    expect(input).toHaveValue('-1');
+    act(() => {
+      jest.advanceTimersByTime(500);
+    });
+    expect(commit).toHaveBeenLastCalledWith(-1);
+  });
+
+  it('drops the minus sign when the range does not permit negatives', async () => {
+    const user = userEvent.setup({ advanceTimers: jest.advanceTimersByTime });
+    const { input, commit } = setup({ type: 'number', settingKey: 'max_tokens' });
+
+    await user.type(input, '-1');
+
+    expect(input).toHaveValue('1');
+    act(() => {
+      jest.advanceTimersByTime(500);
+    });
+    expect(commit).toHaveBeenLastCalledWith(1);
+  });
+
+  it('commits digit-only input as a string for string settings', async () => {
+    const user = userEvent.setup({ advanceTimers: jest.advanceTimersByTime });
+    const { input, commit } = setup({ type: 'string', settingKey: 'modelLabel' });
+
+    await user.type(input, '123');
+
+    expect(input).toHaveValue('123');
+    act(() => {
+      jest.advanceTimersByTime(500);
+    });
+    expect(commit).toHaveBeenLastCalledWith('123');
+  });
+
+  it('preserves the numeric sniffing fallback when no type is provided', () => {
+    const commit = jest.fn();
+    const setOption = jest.fn(() => commit) as unknown as TSetOption;
+    render(
+      <ChatContext.Provider value={chatContextValue}>
+        <DynamicInput settingKey="custom" setOption={setOption} conversation={{}} />
+      </ChatContext.Provider>,
+    );
+    const input = screen.getByRole('textbox');
+
+    fireEvent.change(input, { target: { value: '42' } });
+    act(() => {
+      jest.advanceTimersByTime(500);
+    });
+    expect(commit).toHaveBeenLastCalledWith(42);
+  });
+});
diff --git a/packages/api/src/agents/index.ts b/packages/api/src/agents/index.ts
index 28c70bb538..8865ef8762 100644
--- a/packages/api/src/agents/index.ts
+++ b/packages/api/src/agents/index.ts
@@ -14,6 +14,7 @@ export * from './legacy';
 export * from './memory';
 export * from './orphans';
 export * from './migration';
+export * from './parameters';
 export * from './openai';
 export * from './transactions';
 export * from './usage';
diff --git a/packages/api/src/agents/parameters.spec.ts b/packages/api/src/agents/parameters.spec.ts
new file mode 100644
index 0000000000..423ca5168a
--- /dev/null
+++ b/packages/api/src/agents/parameters.spec.ts
@@ -0,0 +1,90 @@
+import { sanitizeModelParameters } from './parameters';
+
+describe('sanitizeModelParameters', () => {
+  it('drops non-numeric strings from numeric keys', () => {
+    const result = sanitizeModelParameters({
+      max_tokens: 'System',
+      maxContextTokens: 256000,
+      fileTokenLimit: 256000,
+    });
+    expect(result).toEqual({ maxContextTokens: 256000, fileTokenLimit: 256000 });
+  });
+
+  it('coerces numeric strings to numbers', () => {
+    const result = sanitizeModelParameters({
+      max_tokens: '4096',
+      temperature: ' 0.7 ',
+      maxOutputTokens: '8192',
+    });
+    expect(result).toEqual({ max_tokens: 4096, temperature: 0.7, maxOutputTokens: 8192 });
+  });
+
+  it('preserves explicit zero and negative values', () => {
+    const result = sanitizeModelParameters({
+      max_tokens: 0,
+      frequency_penalty: -1.5,
+      presence_penalty: '-0.5',
+    });
+    expect(result).toEqual({ max_tokens: 0, frequency_penalty: -1.5, presence_penalty: -0.5 });
+  });
+
+  it('drops NaN, Infinity, empty strings, booleans, and objects from numeric keys', () => {
+    const result = sanitizeModelParameters({
+      max_tokens: NaN,
+      maxTokens: Infinity,
+      maxOutputTokens: '',
+      max_output_tokens: '   ',
+      maxContextTokens: true,
+      max_context_tokens: { value: 4096 },
+      topK: null,
+      topP: undefined,
+    });
+    expect(result).toEqual({});
+  });
+
+  it('passes non-numeric keys through untouched', () => {
+    const result = sanitizeModelParameters({
+      model: 'gemma4:26b',
+      region: 'us-east-1',
+      useResponsesApi: true,
+      promptCache: false,
+      customSetting: 'value',
+    });
+    expect(result).toEqual({
+      model: 'gemma4:26b',
+      region: 'us-east-1',
+      useResponsesApi: true,
+      promptCache: false,
+      customSetting: 'value',
+    });
+  });
+
+  it('handles all known numeric key variants', () => {
+    const keys = [
+      'temperature',
+      'top_p',
+      'topP',
+      'top_k',
+      'topK',
+      'frequency_penalty',
+      'frequencyPenalty',
+      'presence_penalty',
+      'presencePenalty',
+      'max_tokens',
+      'maxTokens',
+      'max_output_tokens',
+      'maxOutputTokens',
+      'max_context_tokens',
+      'maxContextTokens',
+      'fileTokenLimit',
+      'thinking_budget',
+      'thinkingBudget',
+    ];
+    const corrupt = Object.fromEntries(keys.map((key) => [key, 'System']));
+    expect(sanitizeModelParameters(corrupt)).toEqual({});
+
+    const valid = Object.fromEntries(keys.map((key, i) => [key, `${i + 1}`]));
+    const expected = Object.fromEntries(keys.map((key, i) => [key, i + 1]));
+    expect(sanitizeModelParameters(valid)).toEqual(expected);
+  });
+});
diff --git a/packages/api/src/agents/parameters.ts b/packages/api/src/agents/parameters.ts
new file mode 100644
index 0000000000..6179f91125
--- /dev/null
+++ b/packages/api/src/agents/parameters.ts
@@ -0,0 +1,55 @@
+const NUMERIC_PARAM_KEYS = new Set([
+  'temperature',
+  'top_p',
+  'topP',
+  'top_k',
+  'topK',
+  'frequency_penalty',
+  'frequencyPenalty',
+  'presence_penalty',
+  'presencePenalty',
+  'max_tokens',
+  'maxTokens',
+  'max_output_tokens',
+  'maxOutputTokens',
+  'max_context_tokens',
+  'maxContextTokens',
+  'fileTokenLimit',
+  'thinking_budget',
+  'thinkingBudget',
+]);
+
+function coerceFiniteNumber(value: unknown): number | undefined {
+  if (typeof value === 'number') {
+    return Number.isFinite(value) ? value : undefined;
+  }
+  if (typeof value !== 'string') {
+    return undefined;
+  }
+  const trimmed = value.trim();
+  if (trimmed === '') {
+    return undefined;
+  }
+  const parsed = Number(trimmed);
+  return Number.isFinite(parsed) ? parsed : undefined;
+}
+
+/**
+ * Coerces known numeric model parameter keys to finite numbers, dropping values
+ * that cannot be represented as one (e.g. a stray placeholder string captured by
+ * the UI). Explicit `0` and negative values are preserved; other keys pass through.
+ */
+export function sanitizeModelParameters(params: Record<string, unknown>): Record<string, unknown> {
+  const result: Record<string, unknown> = {};
+  for (const [key, value] of Object.entries(params)) {
+    if (!NUMERIC_PARAM_KEYS.has(key)) {
+      result[key] = value;
+      continue;
+    }
+    const coerced = coerceFiniteNumber(value);
+    if (coerced !== undefined) {
+      result[key] = coerced;
+    }
+  }
+  return result;
+}
diff --git a/packages/data-provider/src/parameterSettings.ts b/packages/data-provider/src/parameterSettings.ts
index 44389cb323..4f495307fd 100644
--- a/packages/data-provider/src/parameterSettings.ts
+++ b/packages/data-provider/src/parameterSettings.ts
@@ -112,7 +112,7 @@ export const librechat = {
     labelCode: true,
     type: 'number',
     component: 'input',
-    placeholder: 'com_nav_theme_system',
+    placeholder: 'com_endpoint_default',
     placeholderCode: true,
     description: 'com_endpoint_context_info',
     descriptionCode: true,
@@ -149,7 +149,7 @@ export const librechat = {
     labelCode: true,
     description: 'com_ui_file_token_limit_desc',
     descriptionCode: true,
-    placeholder: 'com_nav_theme_system',
+    placeholder: 'com_endpoint_default',
     placeholderCode: true,
     type: 'number',
     component: 'input',
@@ -222,7 +222,7 @@ const openAIParams: Record<string, SettingDefinition> = {
     component: 'input',
     description: 'com_endpoint_openai_max_tokens',
     descriptionCode: true,
-    placeholder: 'com_nav_theme_system',
+    placeholder: 'com_endpoint_default',
     placeholderCode: true,
     optionType: 'model',
     columnSpan: 2,
@@ -350,7 +350,7 @@ const anthropic: Record<string, SettingDefinition> = {
     component: 'input',
     description: 'com_endpoint_anthropic_maxoutputtokens',
     descriptionCode: true,
-    placeholder: 'com_nav_theme_system',
+    placeholder: 'com_endpoint_default',
     placeholderCode: true,
     range: {
       min: anthropicSettings.maxOutputTokens.min,
@@ -539,7 +539,7 @@ const bedrock: Record<string, SettingDefinition> = {
     component: 'input',
     description: 'com_endpoint_anthropic_maxoutputtokens',
     descriptionCode: true,
-    placeholder: 'com_nav_theme_system',
+    placeholder: 'com_endpoint_default',
     placeholderCode: true,
     optionType: 'model',
     columnSpan: 2,
@@ -684,7 +684,7 @@ const google: Record<string, SettingDefinition> = {
     component: 'input',
     description: 'com_endpoint_google_maxoutputtokens',
     descriptionCode: true,
-    placeholder: 'com_nav_theme_system',
+    placeholder: 'com_endpoint_default',
     placeholderCode: true,
     default: googleSettings.maxOutputTokens.default,
     range: {