diff --git a/skills/baoyu-imagine/scripts/providers/replicate.test.ts b/skills/baoyu-imagine/scripts/providers/replicate.test.ts
index c9a7972..0379745 100644
--- a/skills/baoyu-imagine/scripts/providers/replicate.test.ts
+++ b/skills/baoyu-imagine/scripts/providers/replicate.test.ts
@@ -6,6 +6,7 @@ import {
   buildInput,
   extractOutputUrl,
   generateImage,
+  getDefaultOutputExtension,
   parseModelId,
   validateArgs,
 } from "./replicate.ts";
@@ -241,6 +242,12 @@ test("Replicate output extraction supports string, array, and object URLs", () =
   );
 });
 
+test("Replicate default output extension matches model family behavior", () => {
+  assert.equal(getDefaultOutputExtension("bytedance/seedream-4.5"), ".jpg");
+  assert.equal(getDefaultOutputExtension("bytedance/seedream-5-lite"), ".png");
+  assert.equal(getDefaultOutputExtension("google/nano-banana-2"), ".png");
+});
+
 test("Replicate generateImage validates arguments before making API requests", async () => {
   const previousToken = process.env.REPLICATE_API_TOKEN;
   process.env.REPLICATE_API_TOKEN = "test-token";
diff --git a/skills/baoyu-imagine/scripts/providers/replicate.ts b/skills/baoyu-imagine/scripts/providers/replicate.ts
index 3481651..b6b0535 100644
--- a/skills/baoyu-imagine/scripts/providers/replicate.ts
+++ b/skills/baoyu-imagine/scripts/providers/replicate.ts
@@ -200,6 +200,12 @@ function buildWanInput(prompt: string, model: string, args: CliArgs, referenceIm
   return input;
 }
 
+export function getDefaultOutputExtension(model: string): ".png" | ".jpg" {
+  if (isSeedream45Model(model)) return ".jpg";
+  if (isSeedream5LiteModel(model)) return ".png";
+  return ".png";
+}
+
 export function validateArgs(model: string, args: CliArgs): void {
   if (isNanoBananaModel(model) && args.n > 1) {
     throw new Error("Nano Banana models on Replicate do not support --n yet because their current schema does not expose a multi-image count field.");