diff --git a/ui/src/components/cliproxy/provider-model-selector.tsx b/ui/src/components/cliproxy/provider-model-selector.tsx
index 37ba59c8..405c9f19 100644
--- a/ui/src/components/cliproxy/provider-model-selector.tsx
+++ b/ui/src/components/cliproxy/provider-model-selector.tsx
@@ -21,19 +21,13 @@ import { Skeleton } from '@/components/ui/skeleton';
 import type { CliproxyProviderRoutingHints } from '@/lib/api-client';
 import type { CodexEffort, CodexServiceTier } from '@/lib/codex-effort';
 import {
-  applyCodexEffortSuffix,
   getCodexEffortDisplay,
   getCodexEffortVariants,
-  getSelectableCodexEfforts,
   parseCodexEffort,
   parseCodexServiceTier,
-  stripCodexEffortSuffix,
 } from '@/lib/codex-effort';
-import {
-  findCatalogModel,
-  getResolvedCatalogModels,
-  getSupplementalCatalogModels,
-} from '@/lib/model-catalogs';
+import { getResolvedCatalogModels, getSupplementalCatalogModels } from '@/lib/model-catalogs';
+import { getReasoningAdapter } from '@/lib/reasoning-control';
 import { cn } from '@/lib/utils';
 
 /** Model entry from catalog */
@@ -61,6 +55,8 @@ export interface ModelEntry {
   codexEfforts?: CodexEffort[];
   /** Additional Codex service-tier suffixes supported by this model in the dashboard UI. */
   codexServiceTiers?: CodexServiceTier[];
+  /** Reasoning-level suffixes this model supports via paren syntax in the dashboard UI. */
+  reasoningLevels?: string[];
 }
 
 /** Provider catalog */
@@ -575,22 +571,21 @@ export function FlexibleModelSelector({
       }
     : null;
   const hasAvailableModels = recommendedOptions.length + allModelOptions.length > 0;
-  const currentEffort = isCodexProvider ? parseCodexEffort(value) : undefined;
-  const baseModelId = isCodexProvider
-    ? stripCodexEffortSuffix(normalizeModelValue(value, routing))
-    : '';
-  const selectedCatalogModel =
-    isCodexProvider && baseModelId && catalog
-      ? findCatalogModel(catalog.provider, baseModelId, catalog)
-      : undefined;
-  const selectableEfforts = getSelectableCodexEfforts(
-    selectedCatalogModel?.codexMaxEffort,
-    selectedCatalogModel?.codexEfforts
-  );
-  const effortOptions =
-    currentEffort && !selectableEfforts.includes(currentEffort)
-      ? [...selectableEfforts, currentEffort]
-      : selectableEfforts;
+  const reasoningAdapter = getReasoningAdapter(catalog?.provider);
+  const currentReasoningLevel = reasoningAdapter?.parse(value);
+  const selectableReasoningLevels =
+    reasoningAdapter && catalog
+      ? reasoningAdapter.getOptions(
+          reasoningAdapter.strip(normalizeModelValue(value, routing)),
+          catalog
+        )
+      : null;
+  const reasoningOptions =
+    selectableReasoningLevels &&
+    currentReasoningLevel &&
+    !selectableReasoningLevels.includes(currentReasoningLevel)
+      ? [...selectableReasoningLevels, currentReasoningLevel]
+      : selectableReasoningLevels;
 
   return (
     <div className="space-y-1.5">
@@ -683,16 +678,11 @@ export function FlexibleModelSelector({
             ...allModelOptions,
           ]}
         />
-        {isCodexProvider && (
+        {reasoningAdapter && reasoningOptions && (
           <Select
-            value={currentEffort ?? 'auto'}
-            onValueChange={(effort) =>
-              onChange(
-                applyCodexEffortSuffix(
-                  value,
-                  effort === 'auto' ? undefined : (effort as CodexEffort)
-                )
-              )
+            value={currentReasoningLevel ?? 'auto'}
+            onValueChange={(level) =>
+              onChange(reasoningAdapter.apply(value, level === 'auto' ? undefined : level))
             }
             disabled={disabled || !value}
           >
@@ -704,9 +694,9 @@ export function FlexibleModelSelector({
             </SelectTrigger>
             <SelectContent>
               <SelectItem value="auto">{t('providerModelSelector.effortAuto')}</SelectItem>
-              {effortOptions.map((effort) => (
-                <SelectItem key={effort} value={effort}>
-                  {effort}
+              {reasoningOptions.map((level) => (
+                <SelectItem key={level} value={level}>
+                  {level}
                 </SelectItem>
               ))}
             </SelectContent>
diff --git a/ui/src/lib/model-catalogs.ts b/ui/src/lib/model-catalogs.ts
index 34c82ca4..ea566f9f 100644
--- a/ui/src/lib/model-catalogs.ts
+++ b/ui/src/lib/model-catalogs.ts
@@ -402,11 +402,13 @@ export const MODEL_CATALOGS: Record<string, ProviderCatalog> = {
         id: 'grok-4.5',
         name: 'Grok 4.5',
         description: 'Frontier model for coding, engineering, and agentic workflows',
+        reasoningLevels: ['low', 'medium', 'high'],
       },
       {
         id: 'grok-4.3',
         name: 'Grok 4.3',
         description: 'General-purpose Grok model with a one-million-token context window',
+        reasoningLevels: ['none', 'low', 'medium', 'high'],
       },
       {
         id: 'grok-4.20-0309-reasoning',
@@ -1147,6 +1149,7 @@ export function buildUiCatalog(
           ? undefined
           : (model.extendedContext ?? staticModel?.extendedContext),
       presetMapping: staticModel?.presetMapping,
+      reasoningLevels: model.reasoningLevels ?? staticModel?.reasoningLevels,
     };
   });
 
diff --git a/ui/src/lib/reasoning-control.ts b/ui/src/lib/reasoning-control.ts
new file mode 100644
index 00000000..9bf6489d
--- /dev/null
+++ b/ui/src/lib/reasoning-control.ts
@@ -0,0 +1,63 @@
+import type { ProviderCatalog } from '@/components/cliproxy/provider-model-selector';
+import {
+  applyCodexEffortSuffix,
+  getSelectableCodexEfforts,
+  parseCodexEffort,
+  stripCodexEffortSuffix,
+  type CodexEffort,
+} from '@/lib/codex-effort';
+import { findCatalogModel } from '@/lib/model-catalogs';
+
+export interface ReasoningAdapter {
+  parse(value: string | undefined): string | undefined;
+  strip(value: string | undefined): string;
+  apply(value: string | undefined, level?: string): string;
+  getOptions(baseId: string, catalog: ProviderCatalog): string[] | null;
+}
+
+const XAI_LEVEL_SUFFIX_REGEX = /\(([a-z]+)\)$/i;
+
+export function parseXaiReasoningLevel(modelId: string | undefined): string | undefined {
+  const match = modelId?.trim().match(XAI_LEVEL_SUFFIX_REGEX);
+  return match?.[1]?.toLowerCase();
+}
+
+export function stripXaiReasoningSuffix(modelId: string | undefined): string {
+  return modelId?.trim().replace(XAI_LEVEL_SUFFIX_REGEX, '') ?? '';
+}
+
+export function applyXaiReasoningSuffix(modelId: string | undefined, level?: string): string {
+  const baseModelId = stripXaiReasoningSuffix(modelId);
+  if (!baseModelId || !level) return baseModelId;
+  return `${baseModelId}(${level})`;
+}
+
+const codexAdapter: ReasoningAdapter = {
+  parse: (value) => parseCodexEffort(value),
+  strip: (value) => stripCodexEffortSuffix(value),
+  apply: (value, level) => applyCodexEffortSuffix(value, level as CodexEffort | undefined),
+  getOptions: (baseId, catalog) => {
+    const model = baseId ? findCatalogModel(catalog.provider, baseId, catalog) : undefined;
+    return getSelectableCodexEfforts(model?.codexMaxEffort, model?.codexEfforts);
+  },
+};
+
+const xaiAdapter: ReasoningAdapter = {
+  parse: parseXaiReasoningLevel,
+  strip: stripXaiReasoningSuffix,
+  apply: applyXaiReasoningSuffix,
+  getOptions: (baseId, catalog) => {
+    if (!baseId) return null;
+    const levels = findCatalogModel(catalog.provider, baseId, catalog)?.reasoningLevels;
+    return levels?.length ? [...levels] : null;
+  },
+};
+
+const REASONING_ADAPTERS: Record<string, ReasoningAdapter> = {
+  codex: codexAdapter,
+  xai: xaiAdapter,
+};
+
+export function getReasoningAdapter(provider: string | undefined): ReasoningAdapter | undefined {
+  return provider ? REASONING_ADAPTERS[provider.toLowerCase()] : undefined;
+}
diff --git a/ui/tests/unit/ui/lib/reasoning-control.test.ts b/ui/tests/unit/ui/lib/reasoning-control.test.ts
new file mode 100644
index 00000000..a31f815f
--- /dev/null
+++ b/ui/tests/unit/ui/lib/reasoning-control.test.ts
@@ -0,0 +1,168 @@
+import { describe, expect, it } from 'vitest';
+import type { ProviderCatalog } from '@/components/cliproxy/provider-model-selector';
+import {
+  applyXaiReasoningSuffix,
+  getReasoningAdapter,
+  parseXaiReasoningLevel,
+  stripXaiReasoningSuffix,
+} from '@/lib/reasoning-control';
+
+const xaiCatalog: ProviderCatalog = {
+  provider: 'xai',
+  displayName: 'xAI (Grok)',
+  defaultModel: 'grok-build-0.1',
+  models: [
+    { id: 'grok-build-0.1', name: 'Grok Build 0.1' },
+    { id: 'grok-4.5', name: 'Grok 4.5', reasoningLevels: ['low', 'medium', 'high'] },
+    { id: 'grok-4.3', name: 'Grok 4.3', reasoningLevels: ['none', 'low', 'medium', 'high'] },
+  ],
+};
+
+const codexCatalog: ProviderCatalog = {
+  provider: 'codex',
+  displayName: 'Codex',
+  defaultModel: 'gpt-5.3-codex',
+  models: [
+    { id: 'gpt-5.3-codex', name: 'GPT-5.3 Codex', codexMaxEffort: 'xhigh' },
+    { id: 'gpt-5.4-mini', name: 'GPT-5.4 Mini', codexMaxEffort: 'high' },
+    {
+      id: 'gpt-5.6-sol',
+      name: 'GPT-5.6 Sol',
+      codexEfforts: ['low', 'medium', 'high', 'xhigh'],
+    },
+  ],
+};
+
+describe('xai paren codec', () => {
+  it('parses paren level suffixes', () => {
+    expect(parseXaiReasoningLevel('grok-4.5(high)')).toBe('high');
+    expect(parseXaiReasoningLevel('grok-4.3(none)')).toBe('none');
+    expect(parseXaiReasoningLevel('grok-4.5(HIGH)')).toBe('high');
+  });
+
+  it('returns undefined for unsuffixed or non-level values', () => {
+    expect(parseXaiReasoningLevel('grok-4.5')).toBeUndefined();
+    expect(parseXaiReasoningLevel('grok-4(1m)')).toBeUndefined();
+    expect(parseXaiReasoningLevel(undefined)).toBeUndefined();
+  });
+
+  it('only matches the suffix at end-of-string', () => {
+    expect(parseXaiReasoningLevel('grok(high)-fast')).toBeUndefined();
+    expect(stripXaiReasoningSuffix('grok(high)-fast')).toBe('grok(high)-fast');
+  });
+
+  it('strips paren suffixes for catalog lookup', () => {
+    expect(stripXaiReasoningSuffix('grok-4.5(high)')).toBe('grok-4.5');
+    expect(stripXaiReasoningSuffix('grok-4.5')).toBe('grok-4.5');
+    expect(stripXaiReasoningSuffix(undefined)).toBe('');
+  });
+
+  it('applies and replaces paren suffixes', () => {
+    expect(applyXaiReasoningSuffix('grok-4.5', 'high')).toBe('grok-4.5(high)');
+    expect(applyXaiReasoningSuffix('grok-4.5(high)', 'low')).toBe('grok-4.5(low)');
+    expect(applyXaiReasoningSuffix('grok-4.3', 'none')).toBe('grok-4.3(none)');
+  });
+
+  it('strips the suffix when no level is given', () => {
+    expect(applyXaiReasoningSuffix('grok-4.5(high)', undefined)).toBe('grok-4.5');
+    expect(applyXaiReasoningSuffix('grok-4.3(none)', undefined)).toBe('grok-4.3');
+    expect(applyXaiReasoningSuffix(undefined, 'high')).toBe('');
+  });
+
+  it('round-trips through parse and apply', () => {
+    const stored = applyXaiReasoningSuffix('grok-4.5', 'high');
+    expect(parseXaiReasoningLevel(stored)).toBe('high');
+    expect(applyXaiReasoningSuffix(stored, parseXaiReasoningLevel(stored))).toBe(stored);
+  });
+});
+
+describe('getReasoningAdapter', () => {
+  it('returns adapters for codex and xai only', () => {
+    expect(getReasoningAdapter('codex')).toBeDefined();
+    expect(getReasoningAdapter('xai')).toBeDefined();
+    expect(getReasoningAdapter('XAI')).toBeDefined();
+    expect(getReasoningAdapter('gemini')).toBeUndefined();
+    expect(getReasoningAdapter(undefined)).toBeUndefined();
+  });
+});
+
+function requireAdapter(provider: string) {
+  const adapter = getReasoningAdapter(provider);
+  if (!adapter) throw new Error(`missing reasoning adapter for ${provider}`);
+  return adapter;
+}
+
+describe('xai adapter', () => {
+  const adapter = requireAdapter('xai');
+
+  it('returns per-model levels from catalog metadata', () => {
+    expect(adapter.getOptions('grok-4.5', xaiCatalog)).toEqual(['low', 'medium', 'high']);
+    expect(adapter.getOptions('grok-4.3', xaiCatalog)).toEqual(['none', 'low', 'medium', 'high']);
+  });
+
+  it('hides the control for models without levels metadata', () => {
+    expect(adapter.getOptions('grok-build-0.1', xaiCatalog)).toBeNull();
+    expect(adapter.getOptions('grok-unknown-model', xaiCatalog)).toBeNull();
+    expect(adapter.getOptions('', xaiCatalog)).toBeNull();
+  });
+
+  it('writes and clears suffixed values through apply', () => {
+    expect(adapter.apply('grok-4.5', 'high')).toBe('grok-4.5(high)');
+    expect(adapter.apply('grok-4.5(high)', undefined)).toBe('grok-4.5');
+    expect(adapter.apply('grok-4.3', 'none')).toBe('grok-4.3(none)');
+  });
+
+  it('pre-selects stored suffixed values', () => {
+    expect(adapter.parse('grok-4.5(high)')).toBe('high');
+    expect(adapter.strip('grok-4.5(high)')).toBe('grok-4.5');
+  });
+});
+
+describe('codex adapter', () => {
+  const adapter = requireAdapter('codex');
+
+  it('delegates parse and strip to codex-effort helpers', () => {
+    expect(adapter.parse('gpt-5.3-codex-high')).toBe('high');
+    expect(adapter.parse('gpt-5.4-high-fast')).toBe('high');
+    expect(adapter.parse('gpt-5.3-codex')).toBeUndefined();
+    expect(adapter.strip('gpt-5.4-fast-high')).toBe('gpt-5.4');
+  });
+
+  it('applies dash suffixes preserving fast tier and routing prefix', () => {
+    expect(adapter.apply('gpt-5.4-high-fast', 'low')).toBe('gpt-5.4-low-fast');
+    expect(adapter.apply('gpt-5.4-high-fast', undefined)).toBe('gpt-5.4-fast');
+    expect(adapter.apply('codex/gpt-5.6-sol', 'high')).toBe('codex/gpt-5.6-sol-high');
+  });
+
+  it('returns catalog-driven effort options', () => {
+    expect(adapter.getOptions('gpt-5.4-mini', codexCatalog)).toEqual([
+      'minimal',
+      'low',
+      'medium',
+      'high',
+    ]);
+    expect(adapter.getOptions('gpt-5.6-sol', codexCatalog)).toEqual([
+      'low',
+      'medium',
+      'high',
+      'xhigh',
+    ]);
+  });
+
+  it('falls back to all five efforts for custom or unselected models', () => {
+    expect(adapter.getOptions('my-org/custom-model', codexCatalog)).toEqual([
+      'minimal',
+      'low',
+      'medium',
+      'high',
+      'xhigh',
+    ]);
+    expect(adapter.getOptions('', codexCatalog)).toEqual([
+      'minimal',
+      'low',
+      'medium',
+      'high',
+      'xhigh',
+    ]);
+  });
+});