diff --git a/cli/src/codex/appServerTypes.ts b/cli/src/codex/appServerTypes.ts
index e6cb42c5..ffebf0e6 100644
--- a/cli/src/codex/appServerTypes.ts
+++ b/cli/src/codex/appServerTypes.ts
@@ -153,7 +153,9 @@ export type SandboxPolicy =
         excludeSlashTmp?: boolean;
     };
 
-export type ReasoningEffort = 'none' | 'minimal' | 'low' | 'medium' | 'high' | 'xhigh';
+// The app server reports supported effort identifiers per model. Keep this
+// open so newly introduced server values can flow through without a CLI update.
+export type ReasoningEffort = string;
 export type ReasoningSummary = 'auto' | 'none' | 'brief' | 'detailed';
 
 export type CollaborationMode = {
diff --git a/cli/src/codex/runCodex.test.ts b/cli/src/codex/runCodex.test.ts
index 8b2ab0a2..5fc99c80 100644
--- a/cli/src/codex/runCodex.test.ts
+++ b/cli/src/codex/runCodex.test.ts
@@ -111,6 +111,7 @@ vi.mock('./utils/codexCliOverrides', () => ({
 }))
 
 import { runCodex as runCodexImpl } from './runCodex'
+import { RPC_METHODS } from '@hapi/protocol/rpcMethods'
 
 describe('runCodex', () => {
     beforeEach(() => {
@@ -242,4 +243,20 @@ describe('runCodex', () => {
             replayTranscriptHistoryOnStart: true
         }))
     })
+
+    it('accepts and normalizes model-reported reasoning efforts from session config', async () => {
+        await runCodexImpl({ workingDirectory: '/tmp/project' })
+
+        const registration = harness.session.rpcHandlerManager.registerHandler.mock.calls.find(
+            ([method]) => method === RPC_METHODS.SetSessionConfig
+        )
+        const handler = registration?.[1] as ((payload: unknown) => Promise<unknown>) | undefined
+        expect(handler).toBeTypeOf('function')
+
+        await handler?.({ modelReasoningEffort: 'max' })
+        await handler?.({ modelReasoningEffort: ' EXTREME ' })
+
+        expect(mockCodexSession.setModelReasoningEffort).toHaveBeenNthCalledWith(2, 'max')
+        expect(mockCodexSession.setModelReasoningEffort).toHaveBeenNthCalledWith(3, 'extreme')
+    })
 })
diff --git a/cli/src/codex/runCodex.ts b/cli/src/codex/runCodex.ts
index fe3a0f70..04b8a9df 100644
--- a/cli/src/codex/runCodex.ts
+++ b/cli/src/codex/runCodex.ts
@@ -19,11 +19,10 @@ import type { ReasoningEffort } from './appServerTypes';
 import { parseCodexSpecialCommand } from './codexSpecialCommands';
 import { listSlashCommands } from '@/modules/common/slashCommands';
 import { resolveCodexSlashCommand } from './utils/slashCommands';
+import { parseReasoningEffortValue } from './utils/reasoningEffort';
 
 export { emitReadyIfIdle } from './utils/emitReadyIfIdle';
 
-const REASONING_EFFORTS = new Set<ReasoningEffort>(['none', 'minimal', 'low', 'medium', 'high', 'xhigh'])
-
 export async function runCodex(opts: {
     startedBy?: 'runner' | 'terminal';
     codexArgs?: string[];
@@ -304,16 +303,6 @@ export async function runCodex(opts: {
         return parsed.data;
     };
 
-    const resolveModelReasoningEffort = (value: unknown): ReasoningEffort | undefined => {
-        if (value === null) {
-            return undefined;
-        }
-        if (typeof value !== 'string' || !REASONING_EFFORTS.has(value as ReasoningEffort)) {
-            throw new Error('Invalid model reasoning effort');
-        }
-        return value as ReasoningEffort;
-    };
-
     const resolveModel = (value: unknown): string => {
         if (typeof value !== 'string') {
             throw new Error('Invalid model');
@@ -363,7 +352,7 @@ export async function runCodex(opts: {
         }
 
         if (config.modelReasoningEffort !== undefined) {
-            currentModelReasoningEffort = resolveModelReasoningEffort(config.modelReasoningEffort);
+            currentModelReasoningEffort = parseReasoningEffortValue(config.modelReasoningEffort);
         }
 
         if (config.collaborationMode !== undefined) {
diff --git a/cli/src/codex/utils/appServerConfig.test.ts b/cli/src/codex/utils/appServerConfig.test.ts
index 378cec11..2142e18e 100644
--- a/cli/src/codex/utils/appServerConfig.test.ts
+++ b/cli/src/codex/utils/appServerConfig.test.ts
@@ -123,7 +123,7 @@ describe('appServerConfig', () => {
     it('passes model reasoning effort via thread config', () => {
         const params = buildThreadStartParams({
             cwd: '/workspace/project',
-            mode: { permissionMode: 'default', modelReasoningEffort: 'xhigh', collaborationMode: 'default' },
+            mode: { permissionMode: 'default', modelReasoningEffort: 'ultra', collaborationMode: 'default' },
             mcpServers
         });
 
@@ -133,7 +133,7 @@ describe('appServerConfig', () => {
                 args: ['mcp']
             },
             developer_instructions: codexSystemPrompt,
-            model_reasoning_effort: 'xhigh'
+            model_reasoning_effort: 'ultra'
         });
     });
 
diff --git a/cli/src/codex/utils/reasoningEffort.test.ts b/cli/src/codex/utils/reasoningEffort.test.ts
new file mode 100644
index 00000000..d7cf304b
--- /dev/null
+++ b/cli/src/codex/utils/reasoningEffort.test.ts
@@ -0,0 +1,17 @@
+import { describe, expect, it } from 'vitest';
+import { parseReasoningEffortValue } from './reasoningEffort';
+
+describe('parseReasoningEffortValue', () => {
+    it('normalizes non-empty model-reported values', () => {
+        expect(parseReasoningEffortValue(' EXTREME ')).toBe('extreme');
+    });
+
+    it('maps null to the default effort', () => {
+        expect(parseReasoningEffortValue(null)).toBeUndefined();
+    });
+
+    it('rejects empty and non-string values', () => {
+        expect(() => parseReasoningEffortValue('   ')).toThrow('Invalid model reasoning effort');
+        expect(() => parseReasoningEffortValue(42)).toThrow('Invalid model reasoning effort');
+    });
+});
diff --git a/cli/src/codex/utils/reasoningEffort.ts b/cli/src/codex/utils/reasoningEffort.ts
new file mode 100644
index 00000000..6e744239
--- /dev/null
+++ b/cli/src/codex/utils/reasoningEffort.ts
@@ -0,0 +1,16 @@
+import type { ReasoningEffort } from '../appServerTypes';
+
+export function parseReasoningEffortValue(value: unknown): ReasoningEffort | undefined {
+    if (value === null) {
+        return undefined;
+    }
+    if (typeof value !== 'string') {
+        throw new Error('Invalid model reasoning effort');
+    }
+
+    const effort = value.trim().toLowerCase();
+    if (!effort) {
+        throw new Error('Invalid model reasoning effort');
+    }
+    return effort;
+}
diff --git a/cli/src/codex/utils/slashCommands.test.ts b/cli/src/codex/utils/slashCommands.test.ts
index aac27c18..c07fc5e1 100644
--- a/cli/src/codex/utils/slashCommands.test.ts
+++ b/cli/src/codex/utils/slashCommands.test.ts
@@ -41,6 +41,12 @@ describe('resolveCodexSlashCommand', () => {
         expect(resolveCodexSlashCommand('/reasoning low', state)).toMatchObject({
             updates: { modelReasoningEffort: 'low' }
         });
+        expect(resolveCodexSlashCommand('/reasoning max', state)).toMatchObject({
+            updates: { modelReasoningEffort: 'max' }
+        });
+        expect(resolveCodexSlashCommand('/reasoning EXTREME', state)).toMatchObject({
+            updates: { modelReasoningEffort: 'extreme' }
+        });
         expect(resolveCodexSlashCommand('/permissions yolo', state)).toMatchObject({
             updates: { permissionMode: 'yolo' }
         });
diff --git a/cli/src/codex/utils/slashCommands.ts b/cli/src/codex/utils/slashCommands.ts
index 62c714a7..7c481fe1 100644
--- a/cli/src/codex/utils/slashCommands.ts
+++ b/cli/src/codex/utils/slashCommands.ts
@@ -3,8 +3,8 @@ import type { CodexPermissionMode } from '@hapi/protocol/types';
 import type { ReasoningEffort } from '../appServerTypes';
 import type { EnhancedMode } from '../loop';
 import type { SlashCommand } from '@/modules/common/slashCommands';
+import { parseReasoningEffortValue } from './reasoningEffort';
 
-const REASONING_EFFORTS = new Set<ReasoningEffort>(['none', 'minimal', 'low', 'medium', 'high', 'xhigh']);
 export const MAX_CODEX_GOAL_OBJECTIVE_CHARS = 4_000;
 
 const UNSUPPORTED_CODEX_BUILTIN_COMMANDS = new Set([
@@ -186,16 +186,11 @@ export function resolveCodexSlashCommand(
                 updates: { modelReasoningEffort: null }
             };
         }
-        if (!REASONING_EFFORTS.has(rest as ReasoningEffort)) {
-            return {
-                kind: 'handled',
-                message: `Unknown Codex reasoning effort: ${rest}`
-            };
-        }
+        const effort = parseReasoningEffortValue(rest);
         return {
             kind: 'handled',
-            message: `Codex reasoning effort set to ${rest}`,
-            updates: { modelReasoningEffort: rest as ReasoningEffort }
+            message: `Codex reasoning effort set to ${effort}`,
+            updates: { modelReasoningEffort: effort }
         };
     }
 
@@ -259,7 +254,7 @@ export function resolveCodexSlashCommand(
                 '- `/compact` — compact current Codex thread context',
                 '- `/status` — show current Codex session config',
                 '- `/model [name|auto]` — show or set model',
-                '- `/reasoning [low|medium|high|xhigh|default]` — show or set reasoning effort',
+                '- `/reasoning [level|default]` — show or set reasoning effort',
                 '- `/fast [on|off|status]` — toggle Fast mode (GPT-5.5 / GPT-5.4, ChatGPT login)',
                 '- `/permissions [default|read-only|safe-yolo|yolo]` — show or set permission mode',
                 '',
diff --git a/cli/src/commands/codex.test.ts b/cli/src/commands/codex.test.ts
index 1e5fba1c..058b2420 100644
--- a/cli/src/commands/codex.test.ts
+++ b/cli/src/commands/codex.test.ts
@@ -121,6 +121,20 @@ describe('codexCommand', () => {
         }
     })
 
+    it('accepts and normalizes a dynamic model reasoning effort', async () => {
+        await codexCommand.run(createCommandContext([
+            '--started-by',
+            'runner',
+            '--model-reasoning-effort',
+            ' EXTREME '
+        ]))
+
+        expect(runCodexMock).toHaveBeenCalledWith({
+            startedBy: 'runner',
+            modelReasoningEffort: 'extreme'
+        })
+    })
+
     it('prints the upgrade error and exits when the local version check fails', async () => {
         const consoleErrorSpy = vi.spyOn(console, 'error').mockImplementation(() => {})
         const exitSpy = vi.spyOn(process, 'exit').mockImplementation(((code?: number) => {
diff --git a/cli/src/commands/codex.ts b/cli/src/commands/codex.ts
index 579bf5cb..a57cce5c 100644
--- a/cli/src/commands/codex.ts
+++ b/cli/src/commands/codex.ts
@@ -7,20 +7,7 @@ import { CODEX_PERMISSION_MODES } from '@hapi/protocol/modes'
 import type { CodexPermissionMode } from '@hapi/protocol/types'
 import type { ReasoningEffort } from '@/codex/appServerTypes'
 import { assertCodexLocalSupported } from '@/codex/utils/codexVersion'
-
-function parseReasoningEffort(value: string): ReasoningEffort {
-    switch (value) {
-        case 'none':
-        case 'minimal':
-        case 'low':
-        case 'medium':
-        case 'high':
-        case 'xhigh':
-            return value
-        default:
-            throw new Error('Invalid --model-reasoning-effort value')
-    }
-}
+import { parseReasoningEffortValue } from '@/codex/utils/reasoningEffort'
 
 // Mirror the web /service-tier endpoint's enum so the internal resume spawn
 // path can never seed/persist an unsupported tier string.
@@ -86,7 +73,7 @@ export const codexCommand: CommandDefinition = {
                     if (!effort) {
                         throw new Error('Missing --model-reasoning-effort value')
                     }
-                    options.modelReasoningEffort = parseReasoningEffort(effort)
+                    options.modelReasoningEffort = parseReasoningEffortValue(effort)
                 } else if (arg === '--service-tier') {
                     const tier = commandArgs[++i]
                     if (!tier) {
diff --git a/hub/src/web/server.ts b/hub/src/web/server.ts
index b0cf0592..e3c1a96a 100644
--- a/hub/src/web/server.ts
+++ b/hub/src/web/server.ts
@@ -191,10 +191,18 @@ function findWebappDistDir(): { distDir: string; indexHtmlPath: string } {
 }
 
 function serveEmbeddedAsset(asset: EmbeddedWebAsset): Response {
+    const headers: Record<string, string> = {
+        'Content-Type': asset.mimeType
+    }
+
+    if (asset.path === '/sw.js') {
+        headers['Cache-Control'] = 'no-store, no-cache, must-revalidate'
+        headers['CDN-Cache-Control'] = 'no-store'
+        headers['Cloudflare-CDN-Cache-Control'] = 'no-store'
+    }
+
     return new Response(Bun.file(asset.sourcePath), {
-        headers: {
-            'Content-Type': asset.mimeType
-        }
+        headers
     })
 }
 
diff --git a/web/src/components/AssistantChat/HappyComposer.tsx b/web/src/components/AssistantChat/HappyComposer.tsx
index 70b1f086..d5033cc4 100644
--- a/web/src/components/AssistantChat/HappyComposer.tsx
+++ b/web/src/components/AssistantChat/HappyComposer.tsx
@@ -471,7 +471,7 @@ export function HappyComposer(props: {
             ? getCodexComposerReasoningEffortOptions(
                 modelReasoningEffort,
                 agentFlavor,
-                agentFlavor === 'opencode' ? availableModelReasoningEffortOptions : undefined
+                availableModelReasoningEffortOptions
             )
             : [],
         [agentFlavor, modelReasoningEffort, availableModelReasoningEffortOptions]
diff --git a/web/src/components/AssistantChat/codexReasoningEffortOptions.test.ts b/web/src/components/AssistantChat/codexReasoningEffortOptions.test.ts
index 1b531f34..901e2c71 100644
--- a/web/src/components/AssistantChat/codexReasoningEffortOptions.test.ts
+++ b/web/src/components/AssistantChat/codexReasoningEffortOptions.test.ts
@@ -23,6 +23,39 @@ describe('getCodexComposerReasoningEffortOptions', () => {
         ])
     })
 
+    it('uses arbitrary model-reported efforts for Codex', () => {
+        expect(getCodexComposerReasoningEffortOptions('extreme', 'codex', [
+            { value: 'low' },
+            { value: 'medium' },
+            { value: 'high' },
+            { value: 'xhigh' },
+            { value: 'max' },
+            { value: 'ultra' },
+            { value: 'extreme' }
+        ])).toEqual([
+            { value: null, label: 'Default' },
+            { value: 'low', label: 'Low' },
+            { value: 'medium', label: 'Medium' },
+            { value: 'high', label: 'High' },
+            { value: 'xhigh', label: 'XHigh' },
+            { value: 'max', label: 'Max' },
+            { value: 'ultra', label: 'Ultra' },
+            { value: 'extreme', label: 'Extreme' }
+        ])
+    })
+
+    it('keeps an unsupported current Codex effort visible', () => {
+        expect(getCodexComposerReasoningEffortOptions('ultra', 'codex', [
+            { value: 'low' },
+            { value: 'max' }
+        ])).toEqual([
+            { value: null, label: 'Default' },
+            { value: 'ultra', label: 'Ultra' },
+            { value: 'low', label: 'Low' },
+            { value: 'max', label: 'Max' }
+        ])
+    })
+
     it('returns no options for OpenCode until dynamic options are available', () => {
         expect(getCodexComposerReasoningEffortOptions(null, 'opencode')).toEqual([])
         expect(getCodexComposerReasoningEffortOptions(null, 'opencode', [])).toEqual([])
diff --git a/web/src/components/AssistantChat/codexReasoningEffortOptions.ts b/web/src/components/AssistantChat/codexReasoningEffortOptions.ts
index b2dfc9d0..692a51ee 100644
--- a/web/src/components/AssistantChat/codexReasoningEffortOptions.ts
+++ b/web/src/components/AssistantChat/codexReasoningEffortOptions.ts
@@ -14,7 +14,8 @@ const CODEX_REASONING_EFFORT_LABELS: Record<string, string> = {
     medium: 'Medium',
     high: 'High',
     xhigh: 'XHigh',
-    max: 'Max'
+    max: 'Max',
+    ultra: 'Ultra'
 }
 
 function normalizeCodexComposerReasoningEffort(effort?: string | null): string | null {
@@ -31,7 +32,7 @@ function formatCodexReasoningEffortLabel(effort: string): string {
         ?? `${effort.charAt(0).toUpperCase()}${effort.slice(1)}`
 }
 
-function buildOpencodeComposerReasoningEffortOptions(
+function buildDynamicReasoningEffortOptions(
     currentEffort: string | null,
     dynamicOptions: ComposerReasoningEffortSourceOption[]
 ): CodexComposerReasoningEffortOption[] {
@@ -66,7 +67,11 @@ export function getCodexComposerReasoningEffortOptions(
         if (!dynamicOptions || dynamicOptions.length === 0) {
             return []
         }
-        return buildOpencodeComposerReasoningEffortOptions(normalizedCurrentEffort, dynamicOptions)
+        return buildDynamicReasoningEffortOptions(normalizedCurrentEffort, dynamicOptions)
+    }
+
+    if (dynamicOptions && dynamicOptions.length > 0) {
+        return buildDynamicReasoningEffortOptions(normalizedCurrentEffort, dynamicOptions)
     }
 
     const options: CodexComposerReasoningEffortOption[] = [
diff --git a/web/src/components/NewSession/ReasoningEffortSelector.tsx b/web/src/components/NewSession/ReasoningEffortSelector.tsx
index 23d55f14..36f042c8 100644
--- a/web/src/components/NewSession/ReasoningEffortSelector.tsx
+++ b/web/src/components/NewSession/ReasoningEffortSelector.tsx
@@ -1,10 +1,12 @@
 import type { AgentType, CodexReasoningEffort } from './types'
 import { CODEX_REASONING_EFFORT_OPTIONS } from './types'
 import { useTranslation } from '@/lib/use-translation'
+import { getCodexComposerReasoningEffortOptions } from '@/components/AssistantChat/codexReasoningEffortOptions'
 
 export function ReasoningEffortSelector(props: {
     agent: AgentType
     value: CodexReasoningEffort
+    availableOptions?: Array<{ value: string; name?: string }>
     isDisabled: boolean
     onChange: (value: CodexReasoningEffort) => void
 }) {
@@ -14,6 +16,15 @@ export function ReasoningEffortSelector(props: {
         return null
     }
 
+    const options = props.agent === 'codex' && props.availableOptions?.length
+        ? getCodexComposerReasoningEffortOptions(null, props.agent, props.availableOptions).map((option) => ({
+            value: option.value ?? 'default',
+            label: option.label
+        }))
+        : CODEX_REASONING_EFFORT_OPTIONS.filter(
+            (option) => props.agent === 'opencode' ? option.value !== 'xhigh' : option.value !== 'max'
+        )
+
     return (
         <div className="flex flex-col gap-1.5 px-3 py-3">
             <label className="text-xs font-medium text-[var(--app-hint)]">
@@ -26,7 +37,7 @@ export function ReasoningEffortSelector(props: {
                 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.filter((option) => props.agent === 'opencode' ? option.value !== 'xhigh' : option.value !== 'max').map((option) => (
+                {options.map((option) => (
                     <option key={option.value} value={option.value}>
                         {option.label}
                     </option>
diff --git a/web/src/components/NewSession/index.tsx b/web/src/components/NewSession/index.tsx
index f19e311a..24557f76 100644
--- a/web/src/components/NewSession/index.tsx
+++ b/web/src/components/NewSession/index.tsx
@@ -12,6 +12,7 @@ import { useActiveSuggestions, type Suggestion } from '@/hooks/useActiveSuggesti
 import { useDirectorySuggestions } from '@/hooks/useDirectorySuggestions'
 import { useRecentPaths } from '@/hooks/useRecentPaths'
 import { useTranslation } from '@/lib/use-translation'
+import { getCodexModelReasoningEfforts } from '@/lib/codexModelCapabilities'
 import {
     buildNewSessionCursorPickerState,
     isCursorEffortWireAllowed,
@@ -199,6 +200,26 @@ export function NewSession(props: {
         }
         return options
     }, [codexModelsState.models, model])
+    const codexSupportedReasoningEfforts = useMemo(
+        () => getCodexModelReasoningEfforts(codexModelsState.models, model),
+        [codexModelsState.models, model]
+    )
+    const codexReasoningEffortOptions = useMemo(
+        () => codexSupportedReasoningEfforts?.map((value) => ({ value })),
+        [codexSupportedReasoningEfforts]
+    )
+
+    useEffect(() => {
+        if (
+            agent !== 'codex'
+            || modelReasoningEffort === 'default'
+            || !codexSupportedReasoningEfforts
+            || codexSupportedReasoningEfforts.includes(modelReasoningEffort)
+        ) {
+            return
+        }
+        setModelReasoningEffort('default')
+    }, [agent, codexSupportedReasoningEfforts, modelReasoningEffort])
     const cursorModelsState = useCursorModelsForMachine({
         api: props.api,
         machineId,
@@ -719,7 +740,8 @@ export function NewSession(props: {
             <ReasoningEffortSelector
                 agent={agent}
                 value={modelReasoningEffort}
-                isDisabled={isFormDisabled}
+                availableOptions={agent === 'codex' ? codexReasoningEffortOptions : undefined}
+                isDisabled={isFormDisabled || (agent === 'codex' && codexModelsState.isLoading)}
                 onChange={setModelReasoningEffort}
             />
             <YoloToggle
diff --git a/web/src/components/NewSession/types.ts b/web/src/components/NewSession/types.ts
index 0da14396..a0ee044c 100644
--- a/web/src/components/NewSession/types.ts
+++ b/web/src/components/NewSession/types.ts
@@ -10,7 +10,8 @@ import type { AgentFlavor, ClaudeEffortLevel } from '@hapi/protocol'
 
 export type AgentType = AgentFlavor
 export type SessionType = 'simple' | 'worktree'
-export type CodexReasoningEffort = 'default' | 'low' | 'medium' | 'high' | 'xhigh' | 'max'
+// Codex reports supported efforts dynamically; keep this open for new server values.
+export type CodexReasoningEffort = string
 export type ClaudeEffort = 'auto' | ClaudeEffortLevel
 
 function modelPresetOptions<TModel extends string>(
diff --git a/web/src/components/SessionChat.test.ts b/web/src/components/SessionChat.test.ts
index 2e92dab6..85f0eb0f 100644
--- a/web/src/components/SessionChat.test.ts
+++ b/web/src/components/SessionChat.test.ts
@@ -1,5 +1,6 @@
-import { describe, expect, it } from 'vitest'
+import { describe, expect, it, vi } from 'vitest'
 import {
+    applyModelChangeWithReasoningRollback,
     buildGoalStateMessages,
     isScratchlistHotkeyBlockedTarget,
     isScratchlistToggleHotkey,
@@ -9,6 +10,42 @@ import {
 import type { PendingSchedule } from '@/components/AssistantChat/ScheduleTimePicker'
 import type { AttachmentMetadata, DecryptedMessage } from '@/types/api'
 
+describe('applyModelChangeWithReasoningRollback', () => {
+    it('restores the previous effort when the model switch fails after clearing it', async () => {
+        const modelError = new Error('model switch failed')
+        const setModel = vi.fn(async () => { throw modelError })
+        const setModelReasoningEffort = vi.fn(async () => {})
+
+        await expect(applyModelChangeWithReasoningRollback({
+            model: 'gpt-next',
+            previousModelReasoningEffort: 'extreme',
+            shouldClearReasoningEffort: true,
+            setModel,
+            setModelReasoningEffort
+        })).rejects.toBe(modelError)
+
+        expect(setModelReasoningEffort.mock.calls).toEqual([[null], ['extreme']])
+        expect(setModel).toHaveBeenCalledWith('gpt-next')
+    })
+
+    it('keeps the cleared effort when the model switch succeeds', async () => {
+        const setModel = vi.fn(async () => {})
+        const setModelReasoningEffort = vi.fn(async () => {})
+
+        await applyModelChangeWithReasoningRollback({
+            model: 'gpt-next',
+            previousModelReasoningEffort: 'extreme',
+            shouldClearReasoningEffort: true,
+            setModel,
+            setModelReasoningEffort
+        })
+
+        expect(setModelReasoningEffort).toHaveBeenCalledOnce()
+        expect(setModelReasoningEffort).toHaveBeenCalledWith(null)
+        expect(setModel).toHaveBeenCalledWith('gpt-next')
+    })
+})
+
 function userMessage(props: {
     id: string
     createdAt: number
diff --git a/web/src/components/SessionChat.tsx b/web/src/components/SessionChat.tsx
index 57eedc3b..2b1765fe 100644
--- a/web/src/components/SessionChat.tsx
+++ b/web/src/components/SessionChat.tsx
@@ -21,6 +21,10 @@ import { buildConversationOutline } from '@/chat/outline'
 import { buildVisibleChatBlocks, isToolGroupBlock, type ToolGroupBlock } from '@/chat/toolGroups'
 import { isQueuedForInvocation, mergeMessages } from '@/lib/messages'
 import { inactiveSessionCanResume } from '@/lib/sessionResume'
+import {
+    getCodexModelReasoningEfforts,
+    supportsCodexReasoningEffort
+} from '@/lib/codexModelCapabilities'
 import { HappyComposer, type ComposerSendError } from '@/components/AssistantChat/HappyComposer'
 import { codexModelAdvertisesFastTier } from '@/components/AssistantChat/codexFastMode'
 import type { PendingSchedule } from '@/components/AssistantChat/ScheduleTimePicker'
@@ -64,6 +68,33 @@ import { useVoiceOptional } from '@/lib/voice-context'
 import { VoiceBackendSession, registerSessionStore, registerVoiceHooksStore, voiceHooks } from '@/realtime'
 import { isRemoteTerminalSupported } from '@/utils/terminalSupport'
 
+type SessionModelSelection = { provider: string; modelId: string } | string | null
+
+export async function applyModelChangeWithReasoningRollback(args: {
+    model: SessionModelSelection
+    previousModelReasoningEffort: string | null
+    shouldClearReasoningEffort: boolean
+    setModel: (model: SessionModelSelection) => Promise<void>
+    setModelReasoningEffort: (effort: string | null) => Promise<void>
+}): Promise<void> {
+    let clearedReasoningEffort = false
+
+    try {
+        if (args.shouldClearReasoningEffort) {
+            await args.setModelReasoningEffort(null)
+            clearedReasoningEffort = true
+        }
+        await args.setModel(args.model)
+    } catch (error) {
+        if (clearedReasoningEffort && args.previousModelReasoningEffort) {
+            await args.setModelReasoningEffort(args.previousModelReasoningEffort).catch((restoreError) => {
+                console.error('Failed to restore model reasoning effort:', restoreError)
+            })
+        }
+        throw error
+    }
+}
+
 /**
  * Returns whether a PendingSchedule should trigger an auto-clear timer.
  *
@@ -516,6 +547,16 @@ function SessionChatInner(props: SessionChatProps) {
         }
         return options
     }, [agentFlavor, codexModelsState.models])
+    const codexSupportedReasoningEfforts = useMemo(
+        () => agentFlavor === 'codex'
+            ? getCodexModelReasoningEfforts(codexModelsState.models, props.session.model)
+            : undefined,
+        [agentFlavor, codexModelsState.models, props.session.model]
+    )
+    const codexReasoningEffortOptions = useMemo(
+        () => codexSupportedReasoningEfforts?.map((value) => ({ value })),
+        [codexSupportedReasoningEfforts]
+    )
     const opencodeModelsState = useOpencodeModels({
         api: props.api,
         sessionId: props.session.id,
@@ -909,16 +950,39 @@ function SessionChatInner(props: SessionChatProps) {
     }, [setCollaborationMode, props.onRefresh, haptic])
 
     // Model mode change handler
-    const handleModelChange = useCallback(async (model: { provider: string; modelId: string } | string | null) => {
+    const handleModelChange = useCallback(async (model: SessionModelSelection) => {
+        const previousModelReasoningEffort = props.session.modelReasoningEffort
+        const shouldClearReasoningEffort = agentFlavor === 'codex'
+            && Boolean(previousModelReasoningEffort)
+            && supportsCodexReasoningEffort(
+                codexModelsState.models,
+                model,
+                previousModelReasoningEffort
+            ) === false
+
         try {
-            await setModel(model)
+            await applyModelChangeWithReasoningRollback({
+                model,
+                previousModelReasoningEffort,
+                shouldClearReasoningEffort,
+                setModel,
+                setModelReasoningEffort
+            })
             haptic.notification('success')
             props.onRefresh()
         } catch (e) {
             haptic.notification('error')
             console.error('Failed to set model:', e)
         }
-    }, [setModel, props.onRefresh, haptic])
+    }, [
+        agentFlavor,
+        codexModelsState.models,
+        props.session.modelReasoningEffort,
+        setModelReasoningEffort,
+        setModel,
+        props.onRefresh,
+        haptic
+    ])
 
     const handleCursorBaseModelChange = useCallback(async (baseKey: string | null) => {
         if (!cursorPicker) {
@@ -1243,9 +1307,11 @@ function SessionChatInner(props: SessionChatProps) {
                         piModels={agentFlavor === 'pi' ? (piModelsState.availableModels.length > 0 ? piModelsState.availableModels : piCachedModels) : undefined}
                         piSelectedModel={agentFlavor === 'pi' ? piSelectedModel : undefined}
                         availableModelReasoningEffortOptions={
-                            agentFlavor === 'opencode' && opencodeReasoningEffortState.options.length > 0
-                                ? opencodeReasoningEffortState.options
-                                : undefined
+                            agentFlavor === 'codex'
+                                ? codexReasoningEffortOptions
+                                : agentFlavor === 'opencode' && opencodeReasoningEffortState.options.length > 0
+                                    ? opencodeReasoningEffortState.options
+                                    : undefined
                         }
                         active={props.session.active}
                         allowSendWhenInactive
diff --git a/web/src/lib/codexModelCapabilities.test.ts b/web/src/lib/codexModelCapabilities.test.ts
new file mode 100644
index 00000000..fb19eafa
--- /dev/null
+++ b/web/src/lib/codexModelCapabilities.test.ts
@@ -0,0 +1,44 @@
+import { describe, expect, it } from 'vitest'
+import type { CodexModelSummary } from '@/types/api'
+import {
+    getCodexModelReasoningEfforts,
+    resolveCodexModel,
+    supportsCodexReasoningEffort
+} from './codexModelCapabilities'
+
+const models: CodexModelSummary[] = [
+    {
+        id: 'gpt-5.6-sol',
+        displayName: 'GPT-5.6-Sol',
+        isDefault: true,
+        supportedReasoningEfforts: ['low', 'medium', 'high', 'xhigh', 'max', 'ultra']
+    },
+    {
+        id: 'gpt-5.6-luna',
+        displayName: 'GPT-5.6-Luna',
+        isDefault: false,
+        supportedReasoningEfforts: ['LOW', 'medium', 'max', 'max', '  ']
+    }
+]
+
+describe('Codex model capabilities', () => {
+    it('resolves auto and missing model ids to the reported default model', () => {
+        expect(resolveCodexModel(models, 'auto')?.id).toBe('gpt-5.6-sol')
+        expect(resolveCodexModel(models, null)?.id).toBe('gpt-5.6-sol')
+        expect(resolveCodexModel(models, { modelId: 'gpt-5.6-luna' })?.id).toBe('gpt-5.6-luna')
+    })
+
+    it('returns normalized, de-duplicated efforts for the selected model', () => {
+        expect(getCodexModelReasoningEfforts(models, 'gpt-5.6-luna')).toEqual([
+            'low',
+            'medium',
+            'max'
+        ])
+    })
+
+    it('distinguishes unsupported efforts from unavailable capability data', () => {
+        expect(supportsCodexReasoningEffort(models, 'gpt-5.6-sol', 'ultra')).toBe(true)
+        expect(supportsCodexReasoningEffort(models, 'gpt-5.6-luna', 'ultra')).toBe(false)
+        expect(supportsCodexReasoningEffort(models, 'unknown', 'ultra')).toBeUndefined()
+    })
+})
diff --git a/web/src/lib/codexModelCapabilities.ts b/web/src/lib/codexModelCapabilities.ts
new file mode 100644
index 00000000..e622b9b1
--- /dev/null
+++ b/web/src/lib/codexModelCapabilities.ts
@@ -0,0 +1,44 @@
+import type { CodexModelSummary } from '@/types/api'
+
+type ModelSelection = string | { modelId: string } | null | undefined
+
+function normalizeEfforts(efforts: readonly string[] | undefined): string[] | undefined {
+    if (!efforts) return undefined
+
+    const normalized = [...new Set(
+        efforts
+            .map((effort) => effort.trim().toLowerCase())
+            .filter(Boolean)
+    )]
+    return normalized.length > 0 ? normalized : undefined
+}
+
+export function resolveCodexModel(
+    models: readonly CodexModelSummary[],
+    model: ModelSelection
+): CodexModelSummary | null {
+    const normalizedModelId = (typeof model === 'string' ? model : model?.modelId)?.trim()
+    if (!normalizedModelId || normalizedModelId === 'auto') {
+        return models.find((model) => model.isDefault) ?? models[0] ?? null
+    }
+
+    return models.find((model) => model.id === normalizedModelId) ?? null
+}
+
+export function getCodexModelReasoningEfforts(
+    models: readonly CodexModelSummary[],
+    model: ModelSelection
+): string[] | undefined {
+    return normalizeEfforts(resolveCodexModel(models, model)?.supportedReasoningEfforts)
+}
+
+export function supportsCodexReasoningEffort(
+    models: readonly CodexModelSummary[],
+    model: ModelSelection,
+    effort: string | null | undefined
+): boolean | undefined {
+    const supportedEfforts = getCodexModelReasoningEfforts(models, model)
+    if (!supportedEfforts) return undefined
+    if (!effort) return true
+    return supportedEfforts.includes(effort.trim().toLowerCase())
+}