diff --git a/packages/types/src/model.ts b/packages/types/src/model.ts
index bcdf5681e13..6c7d0a4b4b6 100644
--- a/packages/types/src/model.ts
+++ b/packages/types/src/model.ts
@@ -22,7 +22,7 @@ export type ReasoningEffortWithMinimal = z.infer<typeof reasoningEffortWithMinim
  * Extended Reasoning Effort (includes "none" and "minimal")
  * Note: "disable" is a UI/control value, not a value sent as effort
  */
-export const reasoningEffortsExtended = ["none", "minimal", "low", "medium", "high"] as const
+export const reasoningEffortsExtended = ["none", "minimal", "low", "medium", "high", "xhigh"] as const
 
 export const reasoningEffortExtendedSchema = z.enum(reasoningEffortsExtended)
 
@@ -31,7 +31,7 @@ export type ReasoningEffortExtended = z.infer<typeof reasoningEffortExtendedSche
 /**
  * Reasoning Effort user setting (includes "disable")
  */
-export const reasoningEffortSettingValues = ["disable", "none", "minimal", "low", "medium", "high"] as const
+export const reasoningEffortSettingValues = ["disable", "none", "minimal", "low", "medium", "high", "xhigh"] as const
 export const reasoningEffortSettingSchema = z.enum(reasoningEffortSettingValues)
 
 /**
@@ -88,7 +88,7 @@ export const modelInfoSchema = z.object({
 	defaultTemperature: z.number().optional(),
 	requiredReasoningBudget: z.boolean().optional(),
 	supportsReasoningEffort: z
-		.union([z.boolean(), z.array(z.enum(["disable", "none", "minimal", "low", "medium", "high"]))])
+		.union([z.boolean(), z.array(z.enum(["disable", "none", "minimal", "low", "medium", "high", "xhigh"]))])
 		.optional(),
 	requiredReasoningEffort: z.boolean().optional(),
 	preserveReasoning: z.boolean().optional(),
diff --git a/packages/types/src/providers/openai.ts b/packages/types/src/providers/openai.ts
index a896e5b6ac5..722b57677cc 100644
--- a/packages/types/src/providers/openai.ts
+++ b/packages/types/src/providers/openai.ts
@@ -15,7 +15,7 @@ export const openAiNativeModels = {
 		supportsImages: true,
 		supportsPromptCache: true,
 		promptCacheRetention: "24h",
-		supportsReasoningEffort: ["low", "medium", "high"],
+		supportsReasoningEffort: ["low", "medium", "high", "xhigh"],
 		reasoningEffort: "medium",
 		inputPrice: 1.25,
 		outputPrice: 10.0,
diff --git a/src/api/providers/__tests__/openai-native.spec.ts b/src/api/providers/__tests__/openai-native.spec.ts
index 73c79aebd9a..0482b8893b8 100644
--- a/src/api/providers/__tests__/openai-native.spec.ts
+++ b/src/api/providers/__tests__/openai-native.spec.ts
@@ -464,6 +464,46 @@ describe("OpenAiNativeHandler", () => {
 			)
 		})
 
+		it("should support xhigh reasoning effort for GPT-5.1 Codex Max", async () => {
+			// Mock fetch for Responses API
+			const mockFetch = vitest.fn().mockResolvedValue({
+				ok: true,
+				body: new ReadableStream({
+					start(controller) {
+						controller.enqueue(
+							new TextEncoder().encode(
+								'data: {"type":"response.output_item.added","item":{"type":"text","text":"XHigh effort"}}\n\n',
+							),
+						)
+						controller.enqueue(new TextEncoder().encode("data: [DONE]\n\n"))
+						controller.close()
+					},
+				}),
+			})
+			global.fetch = mockFetch as any
+
+			// Mock SDK to fail
+			mockResponsesCreate.mockRejectedValue(new Error("SDK not available"))
+
+			handler = new OpenAiNativeHandler({
+				...mockOptions,
+				apiModelId: "gpt-5.1-codex-max",
+				reasoningEffort: "xhigh",
+			})
+
+			const stream = handler.createMessage(systemPrompt, messages)
+			for await (const _chunk of stream) {
+				// drain
+			}
+
+			expect(mockFetch).toHaveBeenCalledWith(
+				"https://api.openai.com/v1/responses",
+				expect.objectContaining({
+					body: expect.stringContaining('"effort":"xhigh"'),
+				}),
+			)
+		})
+
 		it("should omit reasoning when selection is 'disable'", async () => {
 			// Mock fetch for Responses API
 			const mockFetch = vitest.fn().mockResolvedValue({
diff --git a/webview-ui/src/i18n/locales/ca/settings.json b/webview-ui/src/i18n/locales/ca/settings.json
index 1d2124b6fba..87f1112a532 100644
--- a/webview-ui/src/i18n/locales/ca/settings.json
+++ b/webview-ui/src/i18n/locales/ca/settings.json
@@ -506,6 +506,7 @@
 			"none": "Cap",
 			"minimal": "Mínim (el més ràpid)",
 			"high": "Alt",
+			"xhigh": "Molt alt",
 			"medium": "Mitjà",
 			"low": "Baix"
 		},
diff --git a/webview-ui/src/i18n/locales/de/settings.json b/webview-ui/src/i18n/locales/de/settings.json
index 53799baca6a..b1463e58ac8 100644
--- a/webview-ui/src/i18n/locales/de/settings.json
+++ b/webview-ui/src/i18n/locales/de/settings.json
@@ -506,6 +506,7 @@
 			"none": "Keine",
 			"minimal": "Minimal (schnellste)",
 			"high": "Hoch",
+			"xhigh": "Sehr hoch",
 			"medium": "Mittel",
 			"low": "Niedrig"
 		},
diff --git a/webview-ui/src/i18n/locales/en/settings.json b/webview-ui/src/i18n/locales/en/settings.json
index 6dd07ca4110..89a3f7150da 100644
--- a/webview-ui/src/i18n/locales/en/settings.json
+++ b/webview-ui/src/i18n/locales/en/settings.json
@@ -512,7 +512,8 @@
 			"minimal": "Minimal (Fastest)",
 			"low": "Low",
 			"medium": "Medium",
-			"high": "High"
+			"high": "High",
+			"xhigh": "Extra High"
 		},
 		"verbosity": {
 			"label": "Output Verbosity",
diff --git a/webview-ui/src/i18n/locales/es/settings.json b/webview-ui/src/i18n/locales/es/settings.json
index 25a7ee2128f..3cf4c9a5b54 100644
--- a/webview-ui/src/i18n/locales/es/settings.json
+++ b/webview-ui/src/i18n/locales/es/settings.json
@@ -506,6 +506,7 @@
 			"none": "Ninguno",
 			"minimal": "Mínimo (el más rápido)",
 			"high": "Alto",
+			"xhigh": "Muy alto",
 			"medium": "Medio",
 			"low": "Bajo"
 		},
diff --git a/webview-ui/src/i18n/locales/fr/settings.json b/webview-ui/src/i18n/locales/fr/settings.json
index f53715ec1e4..b03b2d9bf32 100644
--- a/webview-ui/src/i18n/locales/fr/settings.json
+++ b/webview-ui/src/i18n/locales/fr/settings.json
@@ -506,6 +506,7 @@
 			"none": "Aucun",
 			"minimal": "Minimal (le plus rapide)",
 			"high": "Élevé",
+			"xhigh": "Très élevé",
 			"medium": "Moyen",
 			"low": "Faible"
 		},
diff --git a/webview-ui/src/i18n/locales/hi/settings.json b/webview-ui/src/i18n/locales/hi/settings.json
index 3d6ab6969c4..0baba60d199 100644
--- a/webview-ui/src/i18n/locales/hi/settings.json
+++ b/webview-ui/src/i18n/locales/hi/settings.json
@@ -506,6 +506,7 @@
 			"none": "कोई नहीं",
 			"minimal": "न्यूनतम (सबसे तेज़)",
 			"high": "उच्च",
+			"xhigh": "बहुत उच्च",
 			"medium": "मध्यम",
 			"low": "निम्न"
 		},
diff --git a/webview-ui/src/i18n/locales/id/settings.json b/webview-ui/src/i18n/locales/id/settings.json
index c519f0dccb9..e0ba9f1b99c 100644
--- a/webview-ui/src/i18n/locales/id/settings.json
+++ b/webview-ui/src/i18n/locales/id/settings.json
@@ -510,6 +510,7 @@
 			"none": "Tidak Ada",
 			"minimal": "Minimal (Tercepat)",
 			"high": "Tinggi",
+			"xhigh": "Sangat tinggi",
 			"medium": "Sedang",
 			"low": "Rendah"
 		},
diff --git a/webview-ui/src/i18n/locales/it/settings.json b/webview-ui/src/i18n/locales/it/settings.json
index 568cf19d47c..83af1aa57ee 100644
--- a/webview-ui/src/i18n/locales/it/settings.json
+++ b/webview-ui/src/i18n/locales/it/settings.json
@@ -506,6 +506,7 @@
 			"none": "Nessuno",
 			"minimal": "Minimo (più veloce)",
 			"high": "Alto",
+			"xhigh": "Molto alto",
 			"medium": "Medio",
 			"low": "Basso"
 		},
diff --git a/webview-ui/src/i18n/locales/ja/settings.json b/webview-ui/src/i18n/locales/ja/settings.json
index 00b45386301..1a534c6bb5b 100644
--- a/webview-ui/src/i18n/locales/ja/settings.json
+++ b/webview-ui/src/i18n/locales/ja/settings.json
@@ -506,6 +506,7 @@
 			"none": "なし",
 			"minimal": "最小 (最速)",
 			"high": "高",
+			"xhigh": "非常に高い",
 			"medium": "中",
 			"low": "低"
 		},
diff --git a/webview-ui/src/i18n/locales/ko/settings.json b/webview-ui/src/i18n/locales/ko/settings.json
index fcbda4acebe..f5d40d7ecd2 100644
--- a/webview-ui/src/i18n/locales/ko/settings.json
+++ b/webview-ui/src/i18n/locales/ko/settings.json
@@ -506,6 +506,7 @@
 			"none": "없음",
 			"minimal": "최소 (가장 빠름)",
 			"high": "높음",
+			"xhigh": "매우 높음",
 			"medium": "중간",
 			"low": "낮음"
 		},
diff --git a/webview-ui/src/i18n/locales/nl/settings.json b/webview-ui/src/i18n/locales/nl/settings.json
index 404e35e0da1..d15bd799b82 100644
--- a/webview-ui/src/i18n/locales/nl/settings.json
+++ b/webview-ui/src/i18n/locales/nl/settings.json
@@ -506,6 +506,7 @@
 			"none": "Geen",
 			"minimal": "Minimaal (Snelst)",
 			"high": "Hoog",
+			"xhigh": "Zeer hoog",
 			"medium": "Middel",
 			"low": "Laag"
 		},
diff --git a/webview-ui/src/i18n/locales/pl/settings.json b/webview-ui/src/i18n/locales/pl/settings.json
index 08225847b92..80ee0a1949c 100644
--- a/webview-ui/src/i18n/locales/pl/settings.json
+++ b/webview-ui/src/i18n/locales/pl/settings.json
@@ -506,6 +506,7 @@
 			"none": "Brak",
 			"minimal": "Minimalny (najszybszy)",
 			"high": "Wysoki",
+			"xhigh": "Bardzo wysoki",
 			"medium": "Średni",
 			"low": "Niski"
 		},
diff --git a/webview-ui/src/i18n/locales/pt-BR/settings.json b/webview-ui/src/i18n/locales/pt-BR/settings.json
index a1f4155a879..74a9842574f 100644
--- a/webview-ui/src/i18n/locales/pt-BR/settings.json
+++ b/webview-ui/src/i18n/locales/pt-BR/settings.json
@@ -506,6 +506,7 @@
 			"none": "Nenhum",
 			"minimal": "Mínimo (mais rápido)",
 			"high": "Alto",
+			"xhigh": "Muito alto",
 			"medium": "Médio",
 			"low": "Baixo"
 		},
diff --git a/webview-ui/src/i18n/locales/ru/settings.json b/webview-ui/src/i18n/locales/ru/settings.json
index e71ddfd936b..a6ab5805100 100644
--- a/webview-ui/src/i18n/locales/ru/settings.json
+++ b/webview-ui/src/i18n/locales/ru/settings.json
@@ -506,6 +506,7 @@
 			"none": "Нет",
 			"minimal": "Минимальный (самый быстрый)",
 			"high": "Высокие",
+			"xhigh": "Очень высокие",
 			"medium": "Средние",
 			"low": "Низкие"
 		},
diff --git a/webview-ui/src/i18n/locales/tr/settings.json b/webview-ui/src/i18n/locales/tr/settings.json
index 0e17e1a6cc9..0d07eec8885 100644
--- a/webview-ui/src/i18n/locales/tr/settings.json
+++ b/webview-ui/src/i18n/locales/tr/settings.json
@@ -506,6 +506,7 @@
 			"none": "Yok",
 			"minimal": "Minimal (en hızlı)",
 			"high": "Yüksek",
+			"xhigh": "Çok yüksek",
 			"medium": "Orta",
 			"low": "Düşük"
 		},
diff --git a/webview-ui/src/i18n/locales/vi/settings.json b/webview-ui/src/i18n/locales/vi/settings.json
index f164db9ac90..f0dc935fa06 100644
--- a/webview-ui/src/i18n/locales/vi/settings.json
+++ b/webview-ui/src/i18n/locales/vi/settings.json
@@ -506,6 +506,7 @@
 			"none": "Không",
 			"minimal": "Tối thiểu (nhanh nhất)",
 			"high": "Cao",
+			"xhigh": "Rất cao",
 			"medium": "Trung bình",
 			"low": "Thấp"
 		},
diff --git a/webview-ui/src/i18n/locales/zh-CN/settings.json b/webview-ui/src/i18n/locales/zh-CN/settings.json
index 2c9327c94db..873f9d2e87b 100644
--- a/webview-ui/src/i18n/locales/zh-CN/settings.json
+++ b/webview-ui/src/i18n/locales/zh-CN/settings.json
@@ -506,6 +506,7 @@
 			"none": "无",
 			"minimal": "最小 (最快)",
 			"high": "高",
+			"xhigh": "超高",
 			"medium": "中",
 			"low": "低"
 		},
diff --git a/webview-ui/src/i18n/locales/zh-TW/settings.json b/webview-ui/src/i18n/locales/zh-TW/settings.json
index 67957e87afb..ca584a606e4 100644
--- a/webview-ui/src/i18n/locales/zh-TW/settings.json
+++ b/webview-ui/src/i18n/locales/zh-TW/settings.json
@@ -506,6 +506,7 @@
 			"none": "無",
 			"minimal": "最小 (最快)",
 			"high": "高",
+			"xhigh": "超高",
 			"medium": "中",
 			"low": "低"
 		},