diff --git a/stac_fastapi/api/stac_fastapi/api/models.py b/stac_fastapi/api/stac_fastapi/api/models.py
index 704cf6ed0..1a23add72 100644
--- a/stac_fastapi/api/stac_fastapi/api/models.py
+++ b/stac_fastapi/api/stac_fastapi/api/models.py
@@ -86,12 +86,12 @@ def create_get_request_model(
 
 
 def create_post_request_model(
-    extensions, base_model: BaseSearchPostRequest = BaseSearchGetRequest
+    extensions, base_model: BaseSearchPostRequest = BaseSearchPostRequest
 ):
     """Wrap create_request_model to create the POST request model."""
     return create_request_model(
         "SearchPostRequest",
-        base_model=BaseSearchPostRequest,
+        base_model=base_model,
         extensions=extensions,
         request_type="POST",
     )
diff --git a/stac_fastapi/extensions/stac_fastapi/extensions/core/filter/request.py b/stac_fastapi/extensions/stac_fastapi/extensions/core/filter/request.py
index afd5b947c..26e8b5797 100644
--- a/stac_fastapi/extensions/stac_fastapi/extensions/core/filter/request.py
+++ b/stac_fastapi/extensions/stac_fastapi/extensions/core/filter/request.py
@@ -1,13 +1,28 @@
 """Filter extension request models."""
 
+from enum import Enum
 from typing import Any, Dict, Optional
 
 import attr
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 
 from stac_fastapi.types.search import APIRequest
 
 
+class FilterLang(str, Enum):
+    """Choices for filter-lang value in a POST request.
+
+    Based on https://github.com/radiantearth/stac-api-spec/tree/master/fragments/filter#queryables
+
+    Note the addition of cql2-json, which is used by the pgstac backend,
+    but is not included in the spec above.
+    """
+
+    cql_json = "cql-json"
+    cql2_json = "cql2-json"
+    cql_text = "cql-text"
+
+
 @attr.s
 class FilterExtensionGetRequest(APIRequest):
     """Filter extension GET request model."""
@@ -19,3 +34,5 @@ class FilterExtensionPostRequest(BaseModel):
     """Filter extension POST request model."""
 
     filter: Optional[Dict[str, Any]] = None
+    filter_crs: Optional[str] = Field(alias="filter-crs", default=None)
+    filter_lang: Optional[FilterLang] = Field(alias="filter-lang", default=None)
diff --git a/stac_fastapi/pgstac/stac_fastapi/pgstac/core.py b/stac_fastapi/pgstac/stac_fastapi/pgstac/core.py
index c0ba8e183..b05afce51 100644
--- a/stac_fastapi/pgstac/stac_fastapi/pgstac/core.py
+++ b/stac_fastapi/pgstac/stac_fastapi/pgstac/core.py
@@ -120,7 +120,7 @@ async def _search_base(
         pool = request.app.state.readpool
 
         # pool = kwargs["request"].app.state.readpool
-        req = search_request.json(exclude_none=True)
+        req = search_request.json(exclude_none=True, by_alias=True)
 
         try:
             async with pool.acquire() as conn:
diff --git a/stac_fastapi/pgstac/stac_fastapi/pgstac/types/search.py b/stac_fastapi/pgstac/stac_fastapi/pgstac/types/search.py
index a13126f1e..e64221830 100644
--- a/stac_fastapi/pgstac/stac_fastapi/pgstac/types/search.py
+++ b/stac_fastapi/pgstac/stac_fastapi/pgstac/types/search.py
@@ -1,6 +1,6 @@
 """stac_fastapi.types.search module."""
 
-from typing import Optional
+from typing import Dict, Optional
 
 from pydantic import validator
 
@@ -14,6 +14,7 @@ class PgstacSearch(BaseSearchPostRequest):
     """
 
     datetime: Optional[str] = None
+    conf: Optional[Dict] = None
 
     @validator("datetime")
     def validate_datetime(cls, v):