diff --git a/cli/src/api/apiMachine.ts b/cli/src/api/apiMachine.ts
index 24fbf89d..110044f4 100644
--- a/cli/src/api/apiMachine.ts
+++ b/cli/src/api/apiMachine.ts
@@ -102,7 +102,7 @@ export class ApiMachineClient {
 
     setRPCHandlers({ spawnSession, stopSession, requestShutdown }: MachineRpcHandlers): void {
         this.rpcHandlerManager.registerHandler('spawn-happy-session', async (params: any) => {
-            const { directory, sessionId, resumeSessionId, machineId, approvedNewDirectoryCreation, agent, model, yolo, token, sessionType, worktreeName } = params || {}
+            const { directory, sessionId, resumeSessionId, machineId, approvedNewDirectoryCreation, agent, model, modelReasoningEffort, yolo, token, sessionType, worktreeName } = params || {}
 
             if (!directory) {
                 throw new Error('Directory is required')
@@ -116,6 +116,7 @@ export class ApiMachineClient {
                 approvedNewDirectoryCreation,
                 agent,
                 model,
+                modelReasoningEffort,
                 yolo,
                 token,
                 sessionType,
diff --git a/cli/src/codex/loop.ts b/cli/src/codex/loop.ts
index bff31774..5860d0c0 100644
--- a/cli/src/codex/loop.ts
+++ b/cli/src/codex/loop.ts
@@ -14,6 +14,7 @@ export interface EnhancedMode {
     permissionMode: PermissionMode;
     model?: string;
     collaborationMode: CodexCollaborationMode;
+    modelReasoningEffort?: string;
 }
 
 interface LoopOptions {
diff --git a/cli/src/codex/runCodex.ts b/cli/src/codex/runCodex.ts
index 55fd1c56..3708159e 100644
--- a/cli/src/codex/runCodex.ts
+++ b/cli/src/codex/runCodex.ts
@@ -21,6 +21,7 @@ export async function runCodex(opts: {
     permissionMode?: PermissionMode;
     resumeSessionId?: string;
     model?: string;
+    modelReasoningEffort?: string;
 }): Promise<void> {
     const workingDirectory = getInvokedCwd();
     const startedBy = opts.startedBy ?? 'terminal';
@@ -45,6 +46,7 @@ export async function runCodex(opts: {
     const messageQueue = new MessageQueue2<EnhancedMode>((mode) => hashObject({
         permissionMode: mode.permissionMode,
         model: mode.model,
+        modelReasoningEffort: mode.modelReasoningEffort,
         collaborationMode: mode.collaborationMode
     }));
 
@@ -53,6 +55,7 @@ export async function runCodex(opts: {
 
     let currentPermissionMode: PermissionMode = opts.permissionMode ?? 'default';
     let currentModel = opts.model;
+    const currentModelReasoningEffort = opts.modelReasoningEffort;
     let currentCollaborationMode: EnhancedMode['collaborationMode'] = 'default';
 
     const lifecycle = createRunnerLifecycle({
@@ -105,6 +108,7 @@ export async function runCodex(opts: {
         const enhancedMode: EnhancedMode = {
             permissionMode: messagePermissionMode ?? 'default',
             model: currentModel,
+            modelReasoningEffort: currentModelReasoningEffort,
             collaborationMode: currentCollaborationMode
         };
         const formattedText = formatMessageWithAttachments(message.content.text, message.content.attachments);
diff --git a/cli/src/codex/utils/appServerConfig.test.ts b/cli/src/codex/utils/appServerConfig.test.ts
index 7930728d..de651439 100644
--- a/cli/src/codex/utils/appServerConfig.test.ts
+++ b/cli/src/codex/utils/appServerConfig.test.ts
@@ -64,6 +64,22 @@ describe('appServerConfig', () => {
         });
     });
 
+    it('passes model reasoning effort via thread config', () => {
+        const params = buildThreadStartParams({
+            mode: { permissionMode: 'default', modelReasoningEffort: 'xhigh', collaborationMode: 'default' },
+            mcpServers
+        });
+
+        expect(params.config).toEqual({
+            'mcp_servers.hapi': {
+                command: 'node',
+                args: ['mcp']
+            },
+            developer_instructions: codexSystemPrompt,
+            model_reasoning_effort: 'xhigh'
+        });
+    });
+
     it('builds turn params with mode defaults', () => {
         const params = buildTurnStartParams({
             threadId: 'thread-1',
diff --git a/cli/src/codex/utils/appServerConfig.ts b/cli/src/codex/utils/appServerConfig.ts
index 00eb1165..439966ee 100644
--- a/cli/src/codex/utils/appServerConfig.ts
+++ b/cli/src/codex/utils/appServerConfig.ts
@@ -84,7 +84,8 @@ export function buildThreadStartParams(args: {
     } = resolveInstructions(args);
     const configWithInstructions = {
         ...config,
-        developer_instructions: resolvedDeveloperInstructions
+        developer_instructions: resolvedDeveloperInstructions,
+        ...(args.mode.modelReasoningEffort ? { model_reasoning_effort: args.mode.modelReasoningEffort } : {})
     };
 
     const params: ThreadStartParams = {
diff --git a/cli/src/commands/codex.ts b/cli/src/commands/codex.ts
index 15ec84f9..0848c85f 100644
--- a/cli/src/commands/codex.ts
+++ b/cli/src/commands/codex.ts
@@ -18,6 +18,7 @@ export const codexCommand: CommandDefinition = {
                 permissionMode?: CodexPermissionMode
                 resumeSessionId?: string
                 model?: string
+                modelReasoningEffort?: string
             } = {}
             const unknownArgs: string[] = []
 
@@ -44,6 +45,12 @@ export const codexCommand: CommandDefinition = {
                     }
                     options.model = model
                     unknownArgs.push('--model', model)
+                } else if (arg === '--model-reasoning-effort') {
+                    const effort = commandArgs[++i]
+                    if (!effort) {
+                        throw new Error('Missing --model-reasoning-effort value')
+                    }
+                    options.modelReasoningEffort = effort
                 } else {
                     unknownArgs.push(arg)
                 }
diff --git a/cli/src/modules/common/rpcTypes.ts b/cli/src/modules/common/rpcTypes.ts
index 15a3602c..c3a8d034 100644
--- a/cli/src/modules/common/rpcTypes.ts
+++ b/cli/src/modules/common/rpcTypes.ts
@@ -6,6 +6,7 @@ export interface SpawnSessionOptions {
     approvedNewDirectoryCreation?: boolean
     agent?: 'claude' | 'codex' | 'cursor' | 'gemini' | 'opencode'
     model?: string
+    modelReasoningEffort?: string
     yolo?: boolean
     token?: string
     sessionType?: 'simple' | 'worktree'
diff --git a/cli/src/runner/run.ts b/cli/src/runner/run.ts
index 058d2743..a87eda69 100644
--- a/cli/src/runner/run.ts
+++ b/cli/src/runner/run.ts
@@ -361,6 +361,9 @@ export async function startRunner(): Promise<void> {
         if (options.model && agent !== 'opencode') {
           args.push('--model', options.model);
         }
+        if (options.modelReasoningEffort && agent === 'codex') {
+          args.push('--model-reasoning-effort', options.modelReasoningEffort);
+        }
         if (yolo) {
           args.push('--yolo');
         }
diff --git a/hub/src/sync/rpcGateway.ts b/hub/src/sync/rpcGateway.ts
index ca508636..a2fce60f 100644
--- a/hub/src/sync/rpcGateway.ts
+++ b/hub/src/sync/rpcGateway.ts
@@ -109,6 +109,7 @@ export class RpcGateway {
         directory: string,
         agent: 'claude' | 'codex' | 'cursor' | 'gemini' | 'opencode' = 'claude',
         model?: string,
+        modelReasoningEffort?: string,
         yolo?: boolean,
         sessionType?: 'simple' | 'worktree',
         worktreeName?: string,
@@ -118,7 +119,7 @@ export class RpcGateway {
             const result = await this.machineRpc(
                 machineId,
                 'spawn-happy-session',
-                { type: 'spawn-in-directory', directory, agent, model, yolo, sessionType, worktreeName, resumeSessionId }
+                { type: 'spawn-in-directory', directory, agent, model, modelReasoningEffort, yolo, sessionType, worktreeName, resumeSessionId }
             )
             if (result && typeof result === 'object') {
                 const obj = result as Record<string, unknown>
diff --git a/hub/src/sync/syncEngine.ts b/hub/src/sync/syncEngine.ts
index 063e441a..6e159d6d 100644
--- a/hub/src/sync/syncEngine.ts
+++ b/hub/src/sync/syncEngine.ts
@@ -310,12 +310,13 @@ export class SyncEngine {
         directory: string,
         agent: 'claude' | 'codex' | 'cursor' | 'gemini' | 'opencode' = 'claude',
         model?: string,
+        modelReasoningEffort?: string,
         yolo?: boolean,
         sessionType?: 'simple' | 'worktree',
         worktreeName?: string,
         resumeSessionId?: string
     ): Promise<{ type: 'success'; sessionId: string } | { type: 'error'; message: string }> {
-        return await this.rpcGateway.spawnSession(machineId, directory, agent, model, yolo, sessionType, worktreeName, resumeSessionId)
+        return await this.rpcGateway.spawnSession(machineId, directory, agent, model, modelReasoningEffort, yolo, sessionType, worktreeName, resumeSessionId)
     }
 
     async resumeSession(sessionId: string, namespace: string): Promise<ResumeSessionResult> {
diff --git a/hub/src/web/routes/machines.ts b/hub/src/web/routes/machines.ts
index 626c5f95..cbc410af 100644
--- a/hub/src/web/routes/machines.ts
+++ b/hub/src/web/routes/machines.ts
@@ -8,6 +8,7 @@ const spawnBodySchema = z.object({
     directory: z.string().min(1),
     agent: z.enum(['claude', 'codex', 'cursor', 'gemini', 'opencode']).optional(),
     model: z.string().optional(),
+    modelReasoningEffort: z.string().optional(),
     yolo: z.boolean().optional(),
     sessionType: z.enum(['simple', 'worktree']).optional(),
     worktreeName: z.string().optional()
@@ -54,6 +55,7 @@ export function createMachinesRoutes(getSyncEngine: () => SyncEngine | null): Ho
             parsed.data.directory,
             parsed.data.agent,
             parsed.data.model,
+            parsed.data.modelReasoningEffort,
             parsed.data.yolo,
             parsed.data.sessionType,
             parsed.data.worktreeName
diff --git a/web/src/api/client.ts b/web/src/api/client.ts
index 065c6597..9c54ab07 100644
--- a/web/src/api/client.ts
+++ b/web/src/api/client.ts
@@ -381,13 +381,14 @@ export class ApiClient {
         directory: string,
         agent?: 'claude' | 'codex' | 'cursor' | 'gemini' | 'opencode',
         model?: string,
+        modelReasoningEffort?: string,
         yolo?: boolean,
         sessionType?: 'simple' | 'worktree',
         worktreeName?: string
     ): Promise<SpawnResponse> {
         return await this.request<SpawnResponse>(`/api/machines/${encodeURIComponent(machineId)}/spawn`, {
             method: 'POST',
-            body: JSON.stringify({ directory, agent, model, yolo, sessionType, worktreeName })
+            body: JSON.stringify({ directory, agent, model, modelReasoningEffort, yolo, sessionType, worktreeName })
         })
     }
 
diff --git a/web/src/components/NewSession/ReasoningEffortSelector.tsx b/web/src/components/NewSession/ReasoningEffortSelector.tsx
new file mode 100644
index 00000000..aea9f435
--- /dev/null
+++ b/web/src/components/NewSession/ReasoningEffortSelector.tsx
@@ -0,0 +1,37 @@
+import type { AgentType, CodexReasoningEffort } from './types'
+import { CODEX_REASONING_EFFORT_OPTIONS } from './types'
+import { useTranslation } from '@/lib/use-translation'
+
+export function ReasoningEffortSelector(props: {
+    agent: AgentType
+    value: CodexReasoningEffort
+    isDisabled: boolean
+    onChange: (value: CodexReasoningEffort) => void
+}) {
+    const { t } = useTranslation()
+
+    if (props.agent !== 'codex') {
+        return null
+    }
+
+    return (
+        <div className="flex flex-col gap-1.5 px-3 py-3">
+            <label className="text-xs font-medium text-[var(--app-hint)]">
+                {t('newSession.reasoningEffort')}{' '}
+                <span className="font-normal">({t('newSession.model.optional')})</span>
+            </label>
+            <select
+                value={props.value}
+                onChange={(e) => props.onChange(e.target.value as CodexReasoningEffort)}
+                disabled={props.isDisabled}
+                className="w-full px-3 py-2 text-sm rounded-lg border border-[var(--app-divider)] bg-[var(--app-bg)] text-[var(--app-text)] focus:outline-none focus:ring-2 focus:ring-[var(--app-link)] disabled:opacity-50"
+            >
+                {CODEX_REASONING_EFFORT_OPTIONS.map((option) => (
+                    <option key={option.value} value={option.value}>
+                        {option.label}
+                    </option>
+                ))}
+            </select>
+        </div>
+    )
+}
diff --git a/web/src/components/NewSession/index.tsx b/web/src/components/NewSession/index.tsx
index 60efd325..407999cf 100644
--- a/web/src/components/NewSession/index.tsx
+++ b/web/src/components/NewSession/index.tsx
@@ -7,12 +7,13 @@ import { useSessions } from '@/hooks/queries/useSessions'
 import { useActiveSuggestions, type Suggestion } from '@/hooks/useActiveSuggestions'
 import { useDirectorySuggestions } from '@/hooks/useDirectorySuggestions'
 import { useRecentPaths } from '@/hooks/useRecentPaths'
-import type { AgentType, SessionType } from './types'
+import type { AgentType, CodexReasoningEffort, SessionType } from './types'
 import { ActionButtons } from './ActionButtons'
 import { AgentSelector } from './AgentSelector'
 import { DirectorySection } from './DirectorySection'
 import { MachineSelector } from './MachineSelector'
 import { ModelSelector } from './ModelSelector'
+import { ReasoningEffortSelector } from './ReasoningEffortSelector'
 import {
     loadPreferredAgent,
     loadPreferredYoloMode,
@@ -43,6 +44,7 @@ export function NewSession(props: {
     const [pathExistence, setPathExistence] = useState<Record<string, boolean>>({})
     const [agent, setAgent] = useState<AgentType>(loadPreferredAgent)
     const [model, setModel] = useState('auto')
+    const [modelReasoningEffort, setModelReasoningEffort] = useState<CodexReasoningEffort>('default')
     const [yoloMode, setYoloMode] = useState(loadPreferredYoloMode)
     const [sessionType, setSessionType] = useState<SessionType>('simple')
     const [worktreeName, setWorktreeName] = useState('')
@@ -220,11 +222,15 @@ export function NewSession(props: {
         setError(null)
         try {
             const resolvedModel = model !== 'auto' && agent !== 'opencode' ? model : undefined
+            const resolvedModelReasoningEffort = agent === 'codex' && modelReasoningEffort !== 'default'
+                ? modelReasoningEffort
+                : undefined
             const result = await spawnSession({
                 machineId,
                 directory: directory.trim(),
                 agent,
                 model: resolvedModel,
+                modelReasoningEffort: resolvedModelReasoningEffort,
                 yolo: yoloMode,
                 sessionType,
                 worktreeName: sessionType === 'worktree' ? (worktreeName.trim() || undefined) : undefined
@@ -294,6 +300,12 @@ export function NewSession(props: {
                 isDisabled={isFormDisabled}
                 onModelChange={setModel}
             />
+            <ReasoningEffortSelector
+                agent={agent}
+                value={modelReasoningEffort}
+                isDisabled={isFormDisabled}
+                onChange={setModelReasoningEffort}
+            />
             <YoloToggle
                 yoloMode={yoloMode}
                 isDisabled={isFormDisabled}
diff --git a/web/src/components/NewSession/types.ts b/web/src/components/NewSession/types.ts
index 71f308e4..f2dbb3ae 100644
--- a/web/src/components/NewSession/types.ts
+++ b/web/src/components/NewSession/types.ts
@@ -1,5 +1,6 @@
 export type AgentType = 'claude' | 'codex' | 'cursor' | 'gemini' | 'opencode'
 export type SessionType = 'simple' | 'worktree'
+export type CodexReasoningEffort = 'default' | 'low' | 'medium' | 'high' | 'xhigh'
 
 export const MODEL_OPTIONS: Record<AgentType, { value: string; label: string }[]> = {
     claude: [
@@ -27,3 +28,11 @@ export const MODEL_OPTIONS: Record<AgentType, { value: string; label: string }[]
     ],
     opencode: [],
 }
+
+export const CODEX_REASONING_EFFORT_OPTIONS: { value: CodexReasoningEffort; label: string }[] = [
+    { value: 'default', label: 'Default' },
+    { value: 'low', label: 'Low' },
+    { value: 'medium', label: 'Medium' },
+    { value: 'high', label: 'High' },
+    { value: 'xhigh', label: 'XHigh' },
+]
diff --git a/web/src/hooks/mutations/useSpawnSession.ts b/web/src/hooks/mutations/useSpawnSession.ts
index 7db0bcb7..82f0622b 100644
--- a/web/src/hooks/mutations/useSpawnSession.ts
+++ b/web/src/hooks/mutations/useSpawnSession.ts
@@ -8,6 +8,7 @@ type SpawnInput = {
     directory: string
     agent?: 'claude' | 'codex' | 'cursor' | 'gemini' | 'opencode'
     model?: string
+    modelReasoningEffort?: string
     yolo?: boolean
     sessionType?: 'simple' | 'worktree'
     worktreeName?: string
@@ -30,6 +31,7 @@ export function useSpawnSession(api: ApiClient | null): {
                 input.directory,
                 input.agent,
                 input.model,
+                input.modelReasoningEffort,
                 input.yolo,
                 input.sessionType,
                 input.worktreeName
diff --git a/web/src/lib/locales/en.ts b/web/src/lib/locales/en.ts
index 19cdb668..5f2b91aa 100644
--- a/web/src/lib/locales/en.ts
+++ b/web/src/lib/locales/en.ts
@@ -104,6 +104,7 @@ export default {
   'newSession.agent': 'Agent',
   'newSession.model': 'Model',
   'newSession.model.optional': 'optional',
+  'newSession.reasoningEffort': 'Reasoning effort',
   'newSession.yolo': 'YOLO mode',
   'newSession.yolo.title': 'Bypass approvals and sandbox',
   'newSession.yolo.desc': 'Uses dangerous agent flags when spawning.',
diff --git a/web/src/lib/locales/zh-CN.ts b/web/src/lib/locales/zh-CN.ts
index 8e596b80..bf511b38 100644
--- a/web/src/lib/locales/zh-CN.ts
+++ b/web/src/lib/locales/zh-CN.ts
@@ -106,6 +106,7 @@ export default {
   'newSession.agent': '代理',
   'newSession.model': '模型',
   'newSession.model.optional': '可选',
+  'newSession.reasoningEffort': '推理强度',
   'newSession.yolo': 'YOLO 模式',
   'newSession.yolo.title': '跳过审批和沙箱',
   'newSession.yolo.desc': '启动时使用危险的代理标志。',