diff --git a/.github/workflows/_test.yml b/.github/workflows/_test.yml
index f631d29e..7c745fe7 100644
--- a/.github/workflows/_test.yml
+++ b/.github/workflows/_test.yml
@@ -35,6 +35,9 @@ jobs:
           uses: Swatinem/rust-cache@v2
           with:
             key: rust-${{ matrix.platform.runner }}-${{ matrix.python-version }}
+        - name: Rust tests (no default features)
+          run: cargo test --no-default-features --verbose
+
         - name: Rust tests
           run: cargo test --verbose
 
@@ -81,4 +84,4 @@ jobs:
             if [ $status -ne 0 ]; then
               echo "::error::Third-party notices validation failed. Please update /about.toml and rerun."
               exit $status
-            fi
\ No newline at end of file
+            fi
diff --git a/Cargo.toml b/Cargo.toml
index c25a3bd1..c9f9c711 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -15,6 +15,10 @@ lto = true
 name = "cocoindex_engine"
 crate-type = ["cdylib"]
 
+[features]
+default = ["legacy-states-v0"]
+legacy-states-v0 = []
+
 [dependencies]
 pyo3 = { version = "0.25.1", features = [
     "abi3-py311",
diff --git a/src/builder/exec_ctx.rs b/src/builder/exec_ctx.rs
index 0410d43b..646149f6 100644
--- a/src/builder/exec_ctx.rs
+++ b/src/builder/exec_ctx.rs
@@ -55,9 +55,14 @@ fn build_import_op_exec_ctx(
             let existing_keys_schema: &[schema::ValueType] =
                 if let Some(keys_schema) = &state.keys_schema {
                     keys_schema
-                } else if let Some(key_schema) = &state.key_schema {
-                    std::slice::from_ref(key_schema)
                 } else {
+                    #[cfg(feature = "legacy-states-v0")]
+                    if let Some(key_schema) = &state.key_schema {
+                        std::slice::from_ref(key_schema)
+                    } else {
+                        &[]
+                    }
+                    #[cfg(not(feature = "legacy-states-v0"))]
                     &[]
                 };
             if existing_keys_schema == keys_schema_no_attrs.as_ref() {
@@ -83,6 +88,7 @@ fn build_import_op_exec_ctx(
 
             // Keep this field for backward compatibility,
             // so users can still swap back to older version if needed.
+            #[cfg(feature = "legacy-states-v0")]
             key_schema: Some(if keys_schema_no_attrs.len() == 1 {
                 keys_schema_no_attrs[0].clone()
             } else {
diff --git a/src/setup/states.rs b/src/setup/states.rs
index 33ecafcc..683e39dd 100644
--- a/src/setup/states.rs
+++ b/src/setup/states.rs
@@ -176,6 +176,7 @@ pub struct SourceSetupState {
     pub keys_schema: Option<Box<[schema::ValueType]>>,
 
     /// DEPRECATED. For backward compatibility.
+    #[cfg(feature = "legacy-states-v0")]
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub key_schema: Option<schema::ValueType>,