diff --git a/CHANGELOG.md b/CHANGELOG.md
index c562710..a485161 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Documentation
+- Documented (and pinned with tests) the OR syntax `list_entities(socioeconomic=...)` has always supported: pipe-separated values match entities holding any of the listed designations, e.g. `socioeconomic="OY|A2"`; values are SAM business-type codes (e.g. `OY` Black American Owned, `A6` SBA-certified 8(a), `A2` Woman Owned), not set-aside codes.
+
 ## [1.5.0] - 2026-08-04
 
 ### Added
diff --git a/docs/API_REFERENCE.md b/docs/API_REFERENCE.md
index e7c7560..a93f1d8 100644
--- a/docs/API_REFERENCE.md
+++ b/docs/API_REFERENCE.md
@@ -713,7 +713,7 @@ entities = client.list_entities(
 - `name` - Filter by entity name
 - `psc` - Filter by PSC code
 - `purpose_of_registration_code` - Filter by registration purpose
-- `socioeconomic` - Filter by socioeconomic status
+- `socioeconomic` - Filter by socioeconomic status; takes SAM business-type codes (e.g. `OY` Black American Owned, `A6` SBA-certified 8(a), `A2` Woman Owned — see `GET /api/business_types/`), not set-aside codes; accepts pipe-separated values for OR semantics, e.g. `socioeconomic="OY|A2"`
 - `state` - Filter by state
 - `total_awards_obligated_gte` / `total_awards_obligated_lte` - Obligation amount range
 - `uei` - Filter by UEI
diff --git a/tango/client.py b/tango/client.py
index 29d9f1b..dbfbe9f 100644
--- a/tango/client.py
+++ b/tango/client.py
@@ -2081,7 +2081,7 @@ def list_entities(
             name: Entity name filter
             psc: PSC code filter
             purpose_of_registration_code: Purpose of registration code
-            socioeconomic: Socioeconomic status filter
+            socioeconomic: Socioeconomic status filter; takes SAM business-type codes (e.g. "OY" Black American Owned, "A6" SBA-certified 8(a), "A2" Woman Owned — see `GET /api/business_types/`), not set-aside codes, and accepts pipe-separated values for OR semantics, e.g. ``socioeconomic="OY|A2"``
             state: State filter
             total_awards_obligated_gte: Total awards obligated >=
             total_awards_obligated_lte: Total awards obligated <=
diff --git a/tests/test_client.py b/tests/test_client.py
index 737c1b1..3ce0f1b 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -1992,6 +1992,22 @@ def test_list_psc_omits_unset_has_awards(self, mock_request):
         assert "has_awards" not in mock_request.call_args[1]["params"]
 
 
+class TestEntityFilters:
+    """The server ORs pipe-separated `socioeconomic` values; the SDK's job is to forward the string verbatim."""
+
+    @patch("tango.client.httpx.Client.request")
+    def test_list_entities_forwards_pipe_separated_socioeconomic(self, mock_request):
+        _stub_empty_page(mock_request)
+        TangoClient(api_key="test-key").list_entities(socioeconomic="OY|A2")
+        assert mock_request.call_args[1]["params"]["socioeconomic"] == "OY|A2"
+
+    @patch("tango.client.httpx.Client.request")
+    def test_list_entities_omits_unset_socioeconomic(self, mock_request):
+        _stub_empty_page(mock_request)
+        TangoClient(api_key="test-key").list_entities()
+        assert "socioeconomic" not in mock_request.call_args[1]["params"]
+
+
 class TestAgencyFilterDiagnostics:
     """`meta` from the API's agency-filter diagnostics.