diff --git a/packages/leann-core/src/leann/api.py b/packages/leann-core/src/leann/api.py
index e22633ad..6ac629a3 100644
--- a/packages/leann-core/src/leann/api.py
+++ b/packages/leann-core/src/leann/api.py
@@ -30,6 +30,15 @@
 
 logger = logging.getLogger(__name__)
 
+# Passage ID schemes recorded in <index>.meta.json["passage_id_scheme"].
+# - "sequential": today's default; IDs are str(insertion_index) (api.py:add_text).
+# - "content-hash": planned in #329; IDs are sha256(text)[:16], stable across
+#   file moves and reorderings.
+# Older indexes have no passage_id_scheme field — readers must default to
+# "sequential" when the key is absent. See #329 for the rollout plan.
+PASSAGE_ID_SCHEME_SEQUENTIAL = "sequential"
+PASSAGE_ID_SCHEME_CONTENT_HASH = "content-hash"
+
 
 def get_registered_backends() -> list[str]:
     """Get list of registered backend names."""
@@ -570,12 +579,13 @@ def build_index(self, index_path: str):
         builder_instance.build(embeddings, string_ids, index_path, **current_backend_kwargs)
         leann_meta_path = index_dir / f"{index_name}.meta.json"
         meta_data = {
-            "version": "1.0",
+            "version": "1.1",
             "backend_name": self.backend_name,
             "embedding_model": self.embedding_model,
             "dimensions": self.dimensions,
             "backend_kwargs": self.backend_kwargs,
             "embedding_mode": self.embedding_mode,
+            "passage_id_scheme": PASSAGE_ID_SCHEME_SEQUENTIAL,
             "passage_sources": [
                 {
                     "type": "jsonl",
@@ -714,12 +724,13 @@ def build_index_from_arrays(self, index_path: str, ids: list, embeddings: np.nda
         # Create metadata file
         leann_meta_path = index_dir / f"{index_name}.meta.json"
         meta_data = {
-            "version": "1.0",
+            "version": "1.1",
             "backend_name": self.backend_name,
             "embedding_model": self.embedding_model,
             "dimensions": self.dimensions,
             "backend_kwargs": self.backend_kwargs,
             "embedding_mode": self.embedding_mode,
+            "passage_id_scheme": PASSAGE_ID_SCHEME_SEQUENTIAL,
             "passage_sources": [
                 {
                     "type": "jsonl",
diff --git a/tests/test_passage_id_scheme.py b/tests/test_passage_id_scheme.py
new file mode 100644
index 00000000..33bc9710
--- /dev/null
+++ b/tests/test_passage_id_scheme.py
@@ -0,0 +1,45 @@
+import json
+
+import numpy as np
+from leann.api import PASSAGE_ID_SCHEME_SEQUENTIAL, LeannBuilder
+
+
+class _FakeBackendFactory:
+    class _Builder:
+        def build(self, embeddings, ids, index_path, **kwargs):
+            return None
+
+    def builder(self, **kwargs):
+        return self._Builder()
+
+
+def test_build_index_records_default_passage_id_scheme(tmp_path, monkeypatch):
+    monkeypatch.setattr(
+        "leann.api.compute_embeddings",
+        lambda chunks, *args, **kwargs: np.ones((len(chunks), 2), dtype=np.float32),
+    )
+    builder = LeannBuilder(backend_name="hnsw", dimensions=2)
+    builder.backend_factory = _FakeBackendFactory()
+    builder.add_text("alpha")
+
+    index_path = tmp_path / "documents.leann"
+    builder.build_index(str(index_path))
+
+    meta = json.loads((tmp_path / "documents.leann.meta.json").read_text(encoding="utf-8"))
+    assert meta["passage_id_scheme"] == PASSAGE_ID_SCHEME_SEQUENTIAL
+
+
+def test_build_index_from_arrays_records_default_passage_id_scheme(tmp_path):
+    builder = LeannBuilder(backend_name="hnsw", dimensions=2)
+    builder.backend_factory = _FakeBackendFactory()
+    builder.add_text("alpha")
+
+    index_path = tmp_path / "documents.leann"
+    builder.build_index_from_arrays(
+        str(index_path),
+        ids=["0"],
+        embeddings=np.ones((1, 2), dtype=np.float32),
+    )
+
+    meta = json.loads((tmp_path / "documents.leann.meta.json").read_text(encoding="utf-8"))
+    assert meta["passage_id_scheme"] == PASSAGE_ID_SCHEME_SEQUENTIAL