diff --git a/app/services/studio_music_spec.py b/app/services/studio_music_spec.py
index 0865e534..cc908748 100644
--- a/app/services/studio_music_spec.py
+++ b/app/services/studio_music_spec.py
@@ -343,7 +343,8 @@ def _check_lora_names(cls, values):
     @model_validator(mode="after")
     def _check_semantics(self):
         _non_blank(self.prompt, "input.params.prompt")
-        _non_blank(self.alt_prompt, "input.params.alt_prompt")
+        # Caption/style is optional. ACE-Step accepts an empty alt_prompt;
+        # MiniMax-Music3 still rejects a blank caption in its handler.
         _non_blank(self.model_type, "input.params.model_type")
         if self.model_type not in STUDIO_MUSIC_MODEL_TYPES:
             raise ValueError("input.params.model_type is not a registered local music model")
diff --git a/tests/test_studio_music_spec.py b/tests/test_studio_music_spec.py
index bbf7ccc1..3c1d06c9 100644
--- a/tests/test_studio_music_spec.py
+++ b/tests/test_studio_music_spec.py
@@ -103,6 +103,19 @@ def test_instrumental_marker_remains_literal_and_is_not_rewritten():
     assert frozen["effective"]["input"]["params"]["alt_prompt"] == command["input"]["params"]["alt_prompt"]
 
 
+def test_empty_or_omitted_alt_prompt_is_admitted():
+    blank = music_command()
+    blank["input"]["params"]["alt_prompt"] = ""
+    frozen_blank = freeze_studio_music_spec(blank)
+    assert frozen_blank["effective"]["input"]["params"]["alt_prompt"] == ""
+
+    omitted = music_command()
+    omitted["input"]["params"].pop("alt_prompt")
+    frozen_omitted = freeze_studio_music_spec(omitted)
+    assert "alt_prompt" not in frozen_omitted["original"]["input"]["params"]
+    assert frozen_omitted["effective"]["input"]["params"].get("alt_prompt", "") == ""
+
+
 def test_fingerprint_excludes_intent_but_covers_workspace_collection_and_content():
     first = freeze_studio_music_spec(music_command("first"))
     second = freeze_studio_music_spec(music_command("second"))
diff --git a/ui/src/features/studio/musicGenerationSpec.ts b/ui/src/features/studio/musicGenerationSpec.ts
index a8f5dee2..0c70164c 100644
--- a/ui/src/features/studio/musicGenerationSpec.ts
+++ b/ui/src/features/studio/musicGenerationSpec.ts
@@ -341,7 +341,9 @@ function assertMusicParams(value: unknown): asserts value is StudioMusicParams {
   }
   assertCatalogValue(value, paramsSchema, 'input.params')
   requiredText(value.prompt, 'input.params.prompt', MAX_PROMPT_LENGTH)
-  requiredText(value.alt_prompt, 'input.params.alt_prompt', MAX_PROMPT_LENGTH)
+  // alt_prompt is optional in the generated catalog (default ""). Requiring a
+  // non-blank caption blocked Studio Generate and Wizard start_generation
+  // when the user wrote lyrics or [Instrumental] without filling Style.
   requiredText(value.model_type, 'input.params.model_type', MAX_WORKSPACE_LENGTH)
   assertMusicSelectors(value)
   assertAudioReferences(value)
diff --git a/ui/tests/musicGenerationCommands.test.ts b/ui/tests/musicGenerationCommands.test.ts
index 843c0eb5..475cc355 100644
--- a/ui/tests/musicGenerationCommands.test.ts
+++ b/ui/tests/musicGenerationCommands.test.ts
@@ -196,6 +196,20 @@ test('music builder retains inactive sentinels but rejects active modes, TTS and
   )
 })
 
+test('music builder admits empty or omitted style captions', { concurrency: false }, () => {
+  const blank = command('music-blank-caption', { alt_prompt: '' })
+  assert.equal(blank.input.params.alt_prompt, '')
+  assert.equal(blank.input.params.prompt, nativeParams().prompt)
+
+  const { alt_prompt: _omitted, ...withoutCaption } = nativeParams()
+  const omitted = createStudioMusicGenerationCommand({
+    ...withoutCaption,
+    workspace: 'music-workspace',
+  }, 'music-omitted-caption')
+  assert.equal('alt_prompt' in omitted.input.params, false)
+  assert.equal(omitted.input.params.prompt, withoutCaption.prompt)
+})
+
 test('form projection preserves music text, language, refs and sentinels while rejecting active stale controls', { concurrency: false }, () => {
   const source = {
     ...nativeParams(),