diff --git a/design/src/auth.ts b/design/src/auth.ts
index a6bdc0cb43..614418ce97 100644
--- a/design/src/auth.ts
+++ b/design/src/auth.ts
@@ -4,19 +4,21 @@
  * Resolution order:
  * 1. ~/.gstack/openai.json → { "api_key": "sk-..." }
  * 2. OPENAI_API_KEY environment variable
- * 3. null (caller handles guided setup or fallback)
+ * 3. ~/.gstack/minimax.json → { "api_key": "sk-cp-..." }
+ * 4. null (caller handles guided setup or fallback)
  */
 
 import fs from "fs";
 import path from "path";
 
-const CONFIG_PATH = path.join(process.env.HOME || "~", ".gstack", "openai.json");
+const OPENAI_CONFIG_PATH = path.join(process.env.HOME || "~", ".gstack", "openai.json");
+const MINIMAX_CONFIG_PATH = path.join(process.env.HOME || "~", ".gstack", "minimax.json");
 
 export function resolveApiKey(): string | null {
   // 1. Check ~/.gstack/openai.json
   try {
-    if (fs.existsSync(CONFIG_PATH)) {
-      const content = fs.readFileSync(CONFIG_PATH, "utf-8");
+    if (fs.existsSync(OPENAI_CONFIG_PATH)) {
+      const content = fs.readFileSync(OPENAI_CONFIG_PATH, "utf-8");
       const config = JSON.parse(content);
       if (config.api_key && typeof config.api_key === "string") {
         return config.api_key;
@@ -34,14 +36,35 @@ export function resolveApiKey(): string | null {
   return null;
 }
 
+/**
+ * Check if MINIMAX_API_KEY is available (for MiniMax image generation).
+ */
+export function resolveMiniMaxApiKey(): string | null {
+  if (process.env.MINIMAX_API_KEY) {
+    return process.env.MINIMAX_API_KEY;
+  }
+  try {
+    if (fs.existsSync(MINIMAX_CONFIG_PATH)) {
+      const content = fs.readFileSync(MINIMAX_CONFIG_PATH, "utf-8");
+      const config = JSON.parse(content);
+      if (config.api_key && typeof config.api_key === "string") {
+        return config.api_key;
+      }
+    }
+  } catch {
+    // ignore
+  }
+  return null;
+}
+
 /**
  * Save an API key to ~/.gstack/openai.json with 0600 permissions.
  */
 export function saveApiKey(key: string): void {
-  const dir = path.dirname(CONFIG_PATH);
+  const dir = path.dirname(OPENAI_CONFIG_PATH);
   fs.mkdirSync(dir, { recursive: true });
-  fs.writeFileSync(CONFIG_PATH, JSON.stringify({ api_key: key }, null, 2));
-  fs.chmodSync(CONFIG_PATH, 0o600);
+  fs.writeFileSync(OPENAI_CONFIG_PATH, JSON.stringify({ api_key: key }, null, 2));
+  fs.chmodSync(OPENAI_CONFIG_PATH, 0o600);
 }
 
 /**
@@ -55,6 +78,7 @@ export function requireApiKey(): string {
     console.error("Run: $D setup");
     console.error("  or save to ~/.gstack/openai.json: { \"api_key\": \"sk-...\" }");
     console.error("  or set OPENAI_API_KEY environment variable");
+    console.error("  or save to ~/.gstack/minimax.json: { \"api_key\": \"sk-cp-...\" }");
     console.error("");
     console.error("Get a key at: https://platform.openai.com/api-keys");
     process.exit(1);
diff --git a/design/src/generate.ts b/design/src/generate.ts
index a34b715187..85dd8dc5b1 100644
--- a/design/src/generate.ts
+++ b/design/src/generate.ts
@@ -1,14 +1,18 @@
 /**
- * Generate UI mockups via OpenAI Responses API with image_generation tool.
+ * Generate UI mockups via OpenAI (gpt-4o) or MiniMax (image-01).
+ * OpenAI is tried first; falls back to MiniMax if OpenAI is unavailable or fails.
+ * Both can be configured via ~/.gstack/
  */
 
 import fs from "fs";
 import path from "path";
-import { requireApiKey } from "./auth";
+import { resolveApiKey, resolveMiniMaxApiKey } from "./auth";
 import { parseBrief } from "./brief";
 import { createSession, sessionPath } from "./session";
 import { checkMockup } from "./check";
 
+const MINIMAX_API_HOST = process.env.MINIMAX_API_HOST || "https://api.minimaxi.com";
+
 export interface GenerateOptions {
   brief?: string;
   briefFile?: string;
@@ -26,11 +30,132 @@ export interface GenerateResult {
   checkResult?: { pass: boolean; issues: string };
 }
 
+function gcd(a: number, b: number): number {
+  return b === 0 ? a : gcd(b, a % b);
+}
+
+export function normalizeSizeForProvider(
+  size: string | undefined,
+  provider: "openai" | "minimax",
+): string {
+  if (!size) {
+    return provider === "minimax" ? "9:16" : "1536x1024";
+  }
+
+  const normalized = size.trim().toLowerCase();
+
+  if (provider === "minimax") {
+    const dimensions = normalized.match(/^(\d+)x(\d+)$/);
+    if (!dimensions) {
+      return normalized;
+    }
+
+    const width = Number(dimensions[1]);
+    const height = Number(dimensions[2]);
+    const divisor = gcd(width, height);
+    return `${width / divisor}:${height / divisor}`;
+  }
+
+  const ratio = normalized.match(/^(\d+):(\d+)$/);
+  if (!ratio) {
+    return normalized;
+  }
+
+  const width = Number(ratio[1]);
+  const height = Number(ratio[2]);
+
+  if (width === height) {
+    return "1024x1024";
+  }
+
+  return width > height ? "1536x1024" : "1024x1536";
+}
+
+/**
+ * Probe a provider by making a lightweight actual API call to verify the key works.
+ * Returns true if the call succeeds, false otherwise.
+ */
+async function probeProvider(
+  apiKey: string,
+  provider: "openai" | "minimax",
+  size: string,
+): Promise<boolean> {
+  const probePrompt = "A simple red circle on white background";
+  try {
+    if (provider === "openai") {
+      await callOpenAIImageGeneration(apiKey, probePrompt, size, "medium");
+    } else {
+      await callMiniMaxImageGeneration(apiKey, probePrompt, size, "medium");
+    }
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Call MiniMax Image API (image-01).
+ * Returns base64 image data.
+ */
+async function callMiniMaxImageGeneration(
+  apiKey: string,
+  prompt: string,
+  size: string, // e.g. "9:16", "1:1", "16:9"
+  quality: string,
+): Promise<{ responseId: string; imageData: string }> {
+  const controller = new AbortController();
+  const timeout = setTimeout(() => controller.abort(), 120_000);
+
+  try {
+    const response = await fetch(`${MINIMAX_API_HOST}/v1/image_generation`, {
+      method: "POST",
+      headers: {
+        "Authorization": `Bearer ${apiKey}`,
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({
+        model: "image-01",
+        prompt: prompt,
+        aspect_ratio: size,
+        response_format: "base64",
+        n: 1,
+        quality: quality === "high" ? "high" : "medium",
+      }),
+      signal: controller.signal,
+    });
+
+    if (!response.ok) {
+      const error = await response.text();
+      throw new Error(`MiniMax API error (${response.status}): ${error}`);
+    }
+
+    const data = await response.json() as any;
+
+    const statusCode = data.base_resp?.status_code;
+    if (statusCode !== 0 && statusCode !== undefined) {
+      const msg = data.base_resp?.status_msg || "Unknown error";
+      throw new Error(`MiniMax API error (code ${statusCode}): ${msg}`);
+    }
+
+    const imageBase64 = data.data?.image_base64?.[0];
+    if (!imageBase64) {
+      throw new Error("No image data in MiniMax response");
+    }
+
+    return {
+      responseId: data.id || `minimax-${Date.now()}`,
+      imageData: imageBase64,
+    };
+  } finally {
+    clearTimeout(timeout);
+  }
+}
+
 /**
  * Call OpenAI Responses API with image_generation tool.
  * Returns the response ID and base64 image data.
  */
-async function callImageGeneration(
+async function callOpenAIImageGeneration(
   apiKey: string,
   prompt: string,
   size: string,
@@ -88,17 +213,47 @@ async function callImageGeneration(
  * Generate a single mockup from a brief.
  */
 export async function generate(options: GenerateOptions): Promise<GenerateResult> {
-  const apiKey = requireApiKey();
-
   // Parse the brief
   const prompt = options.briefFile
     ? parseBrief(options.briefFile, true)
     : parseBrief(options.brief!, false);
 
-  const size = options.size || "1536x1024";
   const quality = options.quality || "high";
   const maxRetries = options.retry ?? 0;
 
+  // Probe for available provider: OpenAI first, then MiniMax
+  const openAIKey = resolveApiKey();
+  const miniMaxKey = resolveMiniMaxApiKey();
+
+  let provider: "openai" | "minimax" | null = null;
+  let apiKey: string | null = null;
+
+  if (openAIKey) {
+    const openAISize = normalizeSizeForProvider(options.size, "openai");
+    console.error(`Probing OpenAI...`);
+    if (await probeProvider(openAIKey, "openai", openAISize)) {
+      provider = "openai";
+      apiKey = openAIKey;
+    }
+  }
+
+  if (!provider && miniMaxKey) {
+    const miniMaxSize = normalizeSizeForProvider(options.size, "minimax");
+    console.error(`Probing MiniMax...`);
+    if (await probeProvider(miniMaxKey, "minimax", miniMaxSize)) {
+      provider = "minimax";
+      apiKey = miniMaxKey;
+    }
+  }
+
+  if (!provider) {
+    console.error(`Image generation requires one of the following API keys:`);
+    console.error(`- OpenAI: ~/.gstack/openai.json → { "api_key": "sk-..." }`);
+    console.error(`- MiniMax: ~/.gstack/minimax.json → { "api_key": "sk-cp-..." }`);
+    console.error(`Run $D setup to configure.`);
+    process.exit(1);
+  }
+
   let lastResult: GenerateResult | null = null;
 
   for (let attempt = 0; attempt <= maxRetries; attempt++) {
@@ -108,7 +263,20 @@ export async function generate(options: GenerateOptions): Promise<GenerateResult
 
     // Generate the image
     const startTime = Date.now();
-    const { responseId, imageData } = await callImageGeneration(apiKey, prompt, size, quality);
+    let responseId: string;
+    let imageData: string;
+    const size = normalizeSizeForProvider(options.size, provider);
+
+    if (provider === "minimax") {
+      const result = await callMiniMaxImageGeneration(apiKey!, prompt, size, quality);
+      responseId = result.responseId;
+      imageData = result.imageData;
+    } else {
+      const result = await callOpenAIImageGeneration(apiKey!, prompt, size, quality);
+      responseId = result.responseId;
+      imageData = result.imageData;
+    }
+
     const elapsed = ((Date.now() - startTime) / 1000).toFixed(1);
 
     // Write to disk
@@ -120,7 +288,8 @@ export async function generate(options: GenerateOptions): Promise<GenerateResult
     // Create session
     const session = createSession(responseId, prompt, options.output);
 
-    console.error(`Generated (${elapsed}s, ${(imageBuffer.length / 1024).toFixed(0)}KB) → ${options.output}`);
+    const model = provider === "minimax" ? "MiniMax-image-01" : "OpenAI-gpt-4o";
+    console.error(`Generated via ${model} (${elapsed}s, ${(imageBuffer.length / 1024).toFixed(0)}KB) → ${options.output}`);
 
     lastResult = {
       outputPath: options.output,
diff --git a/test/design-generate.test.ts b/test/design-generate.test.ts
new file mode 100644
index 0000000000..cc7271a917
--- /dev/null
+++ b/test/design-generate.test.ts
@@ -0,0 +1,22 @@
+import { describe, expect, test } from "bun:test";
+
+import { normalizeSizeForProvider } from "../design/src/generate";
+
+describe("normalizeSizeForProvider", () => {
+  test("uses provider defaults when size is omitted", () => {
+    expect(normalizeSizeForProvider(undefined, "openai")).toBe("1536x1024");
+    expect(normalizeSizeForProvider(undefined, "minimax")).toBe("9:16");
+  });
+
+  test("converts OpenAI WxH sizes into MiniMax aspect ratios", () => {
+    expect(normalizeSizeForProvider("1536x1024", "minimax")).toBe("3:2");
+    expect(normalizeSizeForProvider("1024x1536", "minimax")).toBe("2:3");
+    expect(normalizeSizeForProvider("1024x1024", "minimax")).toBe("1:1");
+  });
+
+  test("converts aspect ratios into OpenAI-supported orientations", () => {
+    expect(normalizeSizeForProvider("16:9", "openai")).toBe("1536x1024");
+    expect(normalizeSizeForProvider("9:16", "openai")).toBe("1024x1536");
+    expect(normalizeSizeForProvider("1:1", "openai")).toBe("1024x1024");
+  });
+});