diff --git a/src/app/api/providers/[id]/test/route.ts b/src/app/api/providers/[id]/test/route.ts
index c4dccf9736..4d99aa0583 100644
--- a/src/app/api/providers/[id]/test/route.ts
+++ b/src/app/api/providers/[id]/test/route.ts
@@ -73,6 +73,21 @@ const OAUTH_TEST_CONFIG = {
     authPrefix: "Bearer ",
     refreshable: true,
   },
+  xai: {
+    url: "https://api.x.ai/v1/chat/completions",
+    method: "POST",
+    authHeader: "Authorization",
+    authPrefix: "Bearer ",
+    extraHeaders: { "Content-Type": "application/json" },
+    body: JSON.stringify({
+      model: "grok-4.3",
+      messages: [{ role: "user", content: "ping" }],
+      max_tokens: 1,
+      stream: false,
+      reasoning: { effort: "high" },
+    }),
+    refreshable: true,
+  },
   github: {
     url: "https://api.github.com/user",
     method: "GET",
@@ -561,7 +576,8 @@ export async function testOAuthConnection(
     // 400 because the probe body is invalid. A 400 from such a provider means auth
     // succeeded; only 401/403 means the token is bad.
     const accepted =
-      res.ok || (Array.isArray(config.acceptStatuses) && config.acceptStatuses.includes(res.status));
+      res.ok ||
+      (Array.isArray(config.acceptStatuses) && config.acceptStatuses.includes(res.status));
     if (accepted) {
       return {
         valid: true,
diff --git a/src/lib/providers/xai/thinking.ts b/src/lib/providers/xai/thinking.ts
index 8348d08864..0a984423ba 100644
--- a/src/lib/providers/xai/thinking.ts
+++ b/src/lib/providers/xai/thinking.ts
@@ -16,6 +16,13 @@ const VALID_EFFORTS = new Set(["minimal", "low", "medium", "high"]);
 
 export type ReasoningEffort = "minimal" | "low" | "medium" | "high";
 
+export function normalizeXaiReasoningEffort(effort: unknown): ReasoningEffort | undefined {
+  if (typeof effort !== "string") return undefined;
+  const normalized = effort.toLowerCase();
+  if (normalized === "max" || normalized === "xhigh") return "high";
+  return VALID_EFFORTS.has(normalized) ? (normalized as ReasoningEffort) : undefined;
+}
+
 /**
  * Map a numeric token budget to a discrete effort tier.
  *   <=0       → undefined (disabled)
@@ -69,7 +76,7 @@ interface ApplyThinkingOptions {
  */
 export function applyThinking(
   request: ThinkingRequest,
-  options: ApplyThinkingOptions = {},
+  options: ApplyThinkingOptions = {}
 ): ThinkingRequest {
   if (!request || typeof request !== "object") return request;
   const out: ThinkingRequest = { ...request };
@@ -77,14 +84,19 @@ export function applyThinking(
   // 1) Already xAI-native? Honor and stop.
   if (out.reasoning && typeof out.reasoning === "object") {
     const reasoning = out.reasoning as Record<string, unknown>;
-    if (typeof reasoning.effort === "string" && VALID_EFFORTS.has(reasoning.effort)) {
+    const normalizedEffort = normalizeXaiReasoningEffort(reasoning.effort);
+    if (normalizedEffort) {
+      if (reasoning.effort !== normalizedEffort) {
+        out.reasoning = { ...reasoning, effort: normalizedEffort };
+      }
       return out;
     }
   }
 
   // 2) OpenAI Chat reasoning_effort
-  if (typeof out.reasoning_effort === "string" && VALID_EFFORTS.has(out.reasoning_effort)) {
-    out.reasoning = { effort: out.reasoning_effort as ReasoningEffort };
+  const reasoningEffort = normalizeXaiReasoningEffort(out.reasoning_effort);
+  if (reasoningEffort) {
+    out.reasoning = { effort: reasoningEffort };
     delete out.reasoning_effort;
     return out;
   }
diff --git a/src/lib/providers/xai/translators/openai-chat.ts b/src/lib/providers/xai/translators/openai-chat.ts
index aa2bee6deb..e5c7274dd9 100644
--- a/src/lib/providers/xai/translators/openai-chat.ts
+++ b/src/lib/providers/xai/translators/openai-chat.ts
@@ -10,6 +10,7 @@
  *   - aggregated xAI response.completed → OpenAI ChatCompletion JSON
  *   - per-event xAI SSE → OpenAI ChatCompletion stream chunks
  */
+import { normalizeXaiReasoningEffort } from "../thinking.ts";
 
 // ─── Types ────────────────────────────────────────────────────────────────────
 
@@ -192,8 +193,7 @@ export function chatRequestToXaiResponses(req: OpenAiChatRequest): XaiResponsesR
       input.push({
         type: "function_call_output",
         call_id: m.tool_call_id,
-        output:
-          typeof m.content === "string" ? m.content : JSON.stringify(m.content ?? ""),
+        output: typeof m.content === "string" ? m.content : JSON.stringify(m.content ?? ""),
       });
       continue;
     }
@@ -229,8 +229,15 @@ export function chatRequestToXaiResponses(req: OpenAiChatRequest): XaiResponsesR
   if (req.response_format) out.text = { format: req.response_format };
   if (req.parallel_tool_calls != null) out.parallel_tool_calls = req.parallel_tool_calls;
   if (req.seed != null) out.seed = req.seed;
-  if (req.reasoning_effort) out.reasoning = { effort: req.reasoning_effort };
-  if (req.reasoning) out.reasoning = req.reasoning;
+  if (req.reasoning_effort) {
+    const effort = normalizeXaiReasoningEffort(req.reasoning_effort);
+    if (effort) out.reasoning = { effort };
+  }
+  if (req.reasoning && typeof req.reasoning === "object") {
+    const reasoning = req.reasoning as Record<string, unknown>;
+    const effort = normalizeXaiReasoningEffort(reasoning.effort);
+    out.reasoning = effort ? { ...reasoning, effort } : reasoning;
+  }
   if (req.tool_choice) out.tool_choice = req.tool_choice;
 
   const tools = req.tools ? toolsPassthrough(req.tools) : undefined;
@@ -272,7 +279,7 @@ function extractAssistantTextAndCalls(completed: XaiCompleted): {
  */
 export function xaiCompletedToChatJson(
   completed: XaiCompleted,
-  origReq: OpenAiChatRequest | null = null,
+  origReq: OpenAiChatRequest | null = null
 ): object {
   const { text, toolCalls, refusal } = extractAssistantTextAndCalls(completed);
   const finishReason = toolCalls.length ? "tool_calls" : "stop";
@@ -296,8 +303,7 @@ export function xaiCompletedToChatJson(
     out.usage = {
       prompt_tokens: u.input_tokens ?? u.prompt_tokens ?? 0,
       completion_tokens: u.output_tokens ?? u.completion_tokens ?? 0,
-      total_tokens:
-        u.total_tokens ?? ((u.input_tokens ?? 0) + (u.output_tokens ?? 0)),
+      total_tokens: u.total_tokens ?? (u.input_tokens ?? 0) + (u.output_tokens ?? 0),
     };
   }
   return out;
diff --git a/tests/unit/xai-translators.test.ts b/tests/unit/xai-translators.test.ts
index 56ed994cd0..545c626cd0 100644
--- a/tests/unit/xai-translators.test.ts
+++ b/tests/unit/xai-translators.test.ts
@@ -9,23 +9,16 @@
 import test from "node:test";
 import assert from "node:assert/strict";
 
-const { budgetToEffort, applyThinking } = await import(
-  "../../src/lib/providers/xai/thinking.ts"
-);
-const { chatRequestToXaiResponses, xaiCompletedToChatJson } = await import(
-  "../../src/lib/providers/xai/translators/openai-chat.ts"
-);
-const {
-  openaiResponsesRequestToXai,
-  xaiCompletedToOpenaiResponses,
-  xaiSseEventToOpenaiResponses,
-} = await import("../../src/lib/providers/xai/translators/openai-responses.ts");
-const { claudeRequestToXaiResponses, xaiCompletedToClaudeJson } = await import(
-  "../../src/lib/providers/xai/translators/claude.ts"
-);
-const { geminiRequestToXaiResponses, xaiCompletedToGeminiJson } = await import(
-  "../../src/lib/providers/xai/translators/gemini.ts"
-);
+const { budgetToEffort, applyThinking, normalizeXaiReasoningEffort } =
+  await import("../../src/lib/providers/xai/thinking.ts");
+const { chatRequestToXaiResponses, xaiCompletedToChatJson } =
+  await import("../../src/lib/providers/xai/translators/openai-chat.ts");
+const { openaiResponsesRequestToXai, xaiCompletedToOpenaiResponses, xaiSseEventToOpenaiResponses } =
+  await import("../../src/lib/providers/xai/translators/openai-responses.ts");
+const { claudeRequestToXaiResponses, xaiCompletedToClaudeJson } =
+  await import("../../src/lib/providers/xai/translators/claude.ts");
+const { geminiRequestToXaiResponses, xaiCompletedToGeminiJson } =
+  await import("../../src/lib/providers/xai/translators/gemini.ts");
 
 // ─── budgetToEffort ──────────────────────────────────────────────────────────
 
@@ -67,6 +60,21 @@ test("applyThinking: honors xAI-native reasoning.effort verbatim", () => {
   assert.equal((out as Record<string, unknown>).foo, 1);
 });
 
+test("normalizeXaiReasoningEffort: downgrades max/xhigh to xAI-supported high", () => {
+  assert.equal(normalizeXaiReasoningEffort("max"), "high");
+  assert.equal(normalizeXaiReasoningEffort("xhigh"), "high");
+  assert.equal(normalizeXaiReasoningEffort("HIGH"), "high");
+  assert.equal(normalizeXaiReasoningEffort("ultra"), undefined);
+});
+
+test("applyThinking: normalizes xAI-native max/xhigh to high", () => {
+  const maxOut = applyThinking({ reasoning: { effort: "max", summary: "auto" } });
+  assert.deepStrictEqual(maxOut.reasoning, { effort: "high", summary: "auto" });
+
+  const xhighOut = applyThinking({ reasoning: { effort: "xhigh" } });
+  assert.deepStrictEqual(xhighOut.reasoning, { effort: "high" });
+});
+
 test("applyThinking: rewrites OpenAI Chat reasoning_effort into reasoning.effort", () => {
   const req = { reasoning_effort: "medium" };
   const out = applyThinking(req);
@@ -74,6 +82,13 @@ test("applyThinking: rewrites OpenAI Chat reasoning_effort into reasoning.effort
   assert.equal(out.reasoning_effort, undefined);
 });
 
+test("applyThinking: rewrites OpenAI Chat max reasoning_effort into high", () => {
+  const req = { reasoning_effort: "max" };
+  const out = applyThinking(req);
+  assert.deepStrictEqual(out.reasoning, { effort: "high" });
+  assert.equal(out.reasoning_effort, undefined);
+});
+
 test("applyThinking: ignores invalid reasoning_effort values", () => {
   const req = { reasoning_effort: "ultra" };
   const out = applyThinking(req);
@@ -138,9 +153,7 @@ test("chatRequestToXaiResponses: converts system message to instructions", () =>
 test("chatRequestToXaiResponses: converts tool message to function_call_output", () => {
   const req = {
     model: "grok-4",
-    messages: [
-      { role: "tool", content: "result text", tool_call_id: "call_abc" },
-    ],
+    messages: [{ role: "tool", content: "result text", tool_call_id: "call_abc" }],
   };
   const out = chatRequestToXaiResponses(req);
   assert.equal(out.input[0].type, "function_call_output");
@@ -154,6 +167,18 @@ test("chatRequestToXaiResponses: promotes reasoning_effort to reasoning field",
   assert.deepStrictEqual(out.reasoning, { effort: "high" });
 });
 
+test("chatRequestToXaiResponses: normalizes max reasoning_effort for xAI", () => {
+  const req = { model: "grok-4.3", messages: [], reasoning_effort: "max" };
+  const out = chatRequestToXaiResponses(req);
+  assert.deepStrictEqual(out.reasoning, { effort: "high" });
+});
+
+test("chatRequestToXaiResponses: normalizes reasoning.effort for xAI", () => {
+  const req = { model: "grok-4.3", messages: [], reasoning: { effort: "max", summary: "auto" } };
+  const out = chatRequestToXaiResponses(req);
+  assert.deepStrictEqual(out.reasoning, { effort: "high", summary: "auto" });
+});
+
 test("chatRequestToXaiResponses: maps max_tokens to max_output_tokens", () => {
   const req = { model: "grok-4", messages: [], max_tokens: 512 };
   const out = chatRequestToXaiResponses(req);