diff --git a/src/postgrest/run-unasync.py b/src/postgrest/run-unasync.py
index a0b811dd..260ec3be 100644
--- a/src/postgrest/run-unasync.py
+++ b/src/postgrest/run-unasync.py
@@ -2,11 +2,37 @@
 
 import unasync
 
+rules = (
+    unasync.Rule(
+        fromdir="/_async/",
+        todir="/_sync/",
+        additional_replacements={
+            "AsyncClient": "Client",
+            "AsyncPostgrestClient": "SyncPostgrestClient",
+            "async_postgrest_client": "sync_postgrest_client",
+            "AsyncFilterRequestBuilder": "SyncFilterRequestBuilder",
+            "AsyncSelectRequestBuilder": "SyncSelectRequestBuilder",
+            "AsyncQueryRequestBuilder": "SyncQueryRequestBuilder",
+            "AsyncSingleRequestBuilder": "SyncSingleRequestBuilder",
+            "AsyncMaybeSingleRequestBuilder": "SyncMaybeSingleRequestBuilder",
+            "AsyncExplainRequestBuilder": "SyncExplainRequestBuilder",
+            "AsyncRPCFilterRequestBuilder": "SyncRPCFilterRequestBuilder",
+            "AsyncRequestBuilder": "SyncRequestBuilder",
+            "AsyncHTTPTransport": "HTTPTransport",
+            "aclose": "close",
+            "asyncio.sleep": "time.sleep",
+            "import asyncio": "import time",
+            "postgrest._async.request_builder.AsyncSelectRequestBuilder.execute": "postgrest._sync.request_builder.SyncSelectRequestBuilder.execute",
+            "httpx._client.AsyncClient.request": "httpx._client.Client.request",
+            "@pytest.mark.asyncio\n": "",
+            "    @pytest.mark.asyncio\n": "",
+        },
+    ),
+    unasync._DEFAULT_RULE,
+)
 paths = Path("src/postgrest").glob("**/*.py")
 tests = Path("tests").glob("**/*.py")
 
-rules = (unasync._DEFAULT_RULE,)
-
 files = [str(p) for p in list(paths) + list(tests)]
 
 if __name__ == "__main__":
diff --git a/src/postgrest/src/postgrest/_async/request_builder.py b/src/postgrest/src/postgrest/_async/request_builder.py
index f5c34e5f..b9569ba8 100644
--- a/src/postgrest/src/postgrest/_async/request_builder.py
+++ b/src/postgrest/src/postgrest/_async/request_builder.py
@@ -60,6 +60,10 @@ class AsyncQueryRequestBuilder:
     def __init__(self, request: ReqConfig):
         self.request = request
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this query request builder."""
+        return self.__class__(self.request.clone())
+
     def select(self: QueryBuilderT, *columns: str) -> QueryBuilderT:
         _, params, _, _ = pre_select(*columns, count=None)
         self.request.params = self.request.params.add("select", params["select"])
@@ -102,6 +106,10 @@ class AsyncSingleRequestBuilder:
     def __init__(self, request: ReqConfig):
         self.request = request
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this single request builder."""
+        return self.__class__(self.request.clone())
+
     def retry(self, enabled: bool) -> Self:
         self.request.retry_enabled = enabled
         return self
@@ -135,6 +143,10 @@ class AsyncExplainRequestBuilder:
     def __init__(self, request: ReqConfig):
         self.request = request
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this explain request builder."""
+        return self.__class__(self.request.clone())
+
     def retry(self, enabled: bool) -> Self:
         self.request.retry_enabled = enabled
         return self
@@ -155,6 +167,10 @@ class AsyncMaybeSingleRequestBuilder:
     def __init__(self, request: ReqConfig):
         self.request = request
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this maybe single request builder."""
+        return self.__class__(self.request.clone())
+
     def retry(self, enabled: bool) -> Self:
         self.request.retry_enabled = enabled
         return self
@@ -301,6 +317,15 @@ def __init__(
         self.headers = headers
         self.auth = auth
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this request builder."""
+        return self.__class__(
+            session=self.session,
+            path=self.path,
+            headers=Headers(self.headers),
+            auth=self.auth,
+        )
+
     def select(
         self,
         *columns: str,
diff --git a/src/postgrest/src/postgrest/_sync/client.py b/src/postgrest/src/postgrest/_sync/client.py
index 58b2e8b0..d732d56b 100644
--- a/src/postgrest/src/postgrest/_sync/client.py
+++ b/src/postgrest/src/postgrest/_sync/client.py
@@ -17,9 +17,9 @@
 from ..types import CountMethod
 from ..version import __version__
 from .request_builder import (
-    RequestConfig,
     SyncRequestBuilder,
     SyncRPCFilterRequestBuilder,
+    RequestConfig,
 )
 
 
@@ -119,9 +119,9 @@ def __enter__(self) -> SyncPostgrestClient:
         return self
 
     def __exit__(self, exc_type, exc, tb) -> None:
-        self.aclose()
+        self.close()
 
-    def aclose(self) -> None:
+    def close(self) -> None:
         """Close the underlying HTTP connections."""
         self.session.close()
 
diff --git a/src/postgrest/src/postgrest/_sync/request_builder.py b/src/postgrest/src/postgrest/_sync/request_builder.py
index df502b69..7bb7e784 100644
--- a/src/postgrest/src/postgrest/_sync/request_builder.py
+++ b/src/postgrest/src/postgrest/_sync/request_builder.py
@@ -1,9 +1,9 @@
 from __future__ import annotations
 
-import time
+import asyncio
 from typing import Any, Generic, Literal, Optional, TypeVar, Union, overload
 
-from httpx import BasicAuth, Client, Headers, QueryParams, Response
+from httpx import Client, BasicAuth, Headers, QueryParams, Response
 from pydantic import ValidationError
 from typing_extensions import Self, override
 from yarl import URL
@@ -51,7 +51,7 @@ def send_with_retry(req: ReqConfig) -> Response:
         resp = req.send(headers)
         if resp.is_success or not req.should_retry(resp, attempt_count=attempt_count):
             break
-        time.sleep(get_retry_delay(resp, attempt_count))
+        asyncio.sleep(get_retry_delay(resp, attempt_count))
         attempt_count += 1
     return resp
 
@@ -60,6 +60,10 @@ class SyncQueryRequestBuilder:
     def __init__(self, request: ReqConfig):
         self.request = request
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this query request builder."""
+        return self.__class__(self.request.clone())
+
     def select(self: QueryBuilderT, *columns: str) -> QueryBuilderT:
         _, params, _, _ = pre_select(*columns, count=None)
         self.request.params = self.request.params.add("select", params["select"])
@@ -102,6 +106,10 @@ class SyncSingleRequestBuilder:
     def __init__(self, request: ReqConfig):
         self.request = request
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this single request builder."""
+        return self.__class__(self.request.clone())
+
     def retry(self, enabled: bool) -> Self:
         self.request.retry_enabled = enabled
         return self
@@ -135,6 +143,10 @@ class SyncExplainRequestBuilder:
     def __init__(self, request: ReqConfig):
         self.request = request
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this explain request builder."""
+        return self.__class__(self.request.clone())
+
     def retry(self, enabled: bool) -> Self:
         self.request.retry_enabled = enabled
         return self
@@ -155,6 +167,10 @@ class SyncMaybeSingleRequestBuilder:
     def __init__(self, request: ReqConfig):
         self.request = request
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this maybe single request builder."""
+        return self.__class__(self.request.clone())
+
     def retry(self, enabled: bool) -> Self:
         self.request.retry_enabled = enabled
         return self
@@ -301,6 +317,15 @@ def __init__(
         self.headers = headers
         self.auth = auth
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this request builder."""
+        return self.__class__(
+            session=self.session,
+            path=self.path,
+            headers=Headers(self.headers),
+            auth=self.auth,
+        )
+
     def select(
         self,
         *columns: str,
@@ -313,7 +338,7 @@ def select(
             *columns: The names of the columns to fetch.
             count: The method to use to get the count of rows returned.
         Returns:
-            :class:`SyncSelectRequestBuilder`
+            :class:`AsyncSelectRequestBuilder`
         """
         method, params, headers, json = pre_select(*columns, count=count, head=head)
         headers.update(self.headers)
@@ -348,7 +373,7 @@ def insert(
                 Otherwise, use the default value for the column.
                 Only applies for bulk inserts.
         Returns:
-            :class:`SyncQueryRequestBuilder`
+            :class:`AsyncQueryRequestBuilder`
         """
         method, params, headers, json = pre_insert(
             json,
@@ -392,7 +417,7 @@ def upsert(
                 not when merging with existing rows under `ignoreDuplicates: false`.
                 This also only applies when doing bulk upserts.
         Returns:
-            :class:`SyncQueryRequestBuilder`
+            :class:`AsyncQueryRequestBuilder`
         """
         method, params, headers, json = pre_upsert(
             json,
@@ -428,7 +453,7 @@ def update(
             count: The method to use to get the count of rows returned.
             returning: Either 'minimal' or 'representation'
         Returns:
-            :class:`SyncFilterRequestBuilder`
+            :class:`AsyncFilterRequestBuilder`
         """
         method, params, headers, json = pre_update(
             json,
@@ -459,7 +484,7 @@ def delete(
             count: The method to use to get the count of rows returned.
             returning: Either 'minimal' or 'representation'
         Returns:
-            :class:`SyncFilterRequestBuilder`
+            :class:`AsyncFilterRequestBuilder`
         """
         method, params, headers, json = pre_delete(
             count=count,
diff --git a/src/postgrest/src/postgrest/base_request_builder.py b/src/postgrest/src/postgrest/base_request_builder.py
index fcbad9ad..45a07736 100644
--- a/src/postgrest/src/postgrest/base_request_builder.py
+++ b/src/postgrest/src/postgrest/base_request_builder.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import copy
 import json
 import sys
 from json import JSONDecodeError
@@ -76,6 +77,19 @@ def __init__(
         self.auth = auth
         self.retry_enabled = retry_enabled
 
+    def clone(self: Self) -> Self:
+        """Create an independent clone of this request configuration."""
+        return self.__class__(
+            session=self.session,
+            path=self.path,
+            http_method=self.http_method,
+            headers=Headers(self.headers),
+            params=QueryParams(self.params),
+            auth=self.auth,
+            json=copy.deepcopy(self.json) if self.json is not None else None,
+            retry_enabled=self.retry_enabled,
+        )
+
     @overload
     def send(
         self: RequestConfig[Client], additional_headers: Headers
@@ -282,6 +296,12 @@ def __init__(self, request: RequestConfig[C]) -> None:
         self.request: RequestConfig[C] = request
         self.negate_next = False
 
+    def clone(self: Self) -> Self:
+        """Create a clone of this filter request builder with independent query parameters and headers."""
+        cloned = self.__class__(self.request.clone())
+        cloned.negate_next = self.negate_next
+        return cloned
+
     @property
     def not_(self: Self) -> Self:
         """Whether the filter applied next should be negated."""
diff --git a/src/postgrest/tests/_async/test_filter_request_builder.py b/src/postgrest/tests/_async/test_filter_request_builder.py
index f6e6fecd..f113d61c 100644
--- a/src/postgrest/tests/_async/test_filter_request_builder.py
+++ b/src/postgrest/tests/_async/test_filter_request_builder.py
@@ -335,3 +335,36 @@ def test_max_affected_returns_self(filter_request_builder):
     builder = filter_request_builder.max_affected(1)
 
     assert builder is filter_request_builder
+
+
+def test_filter_builder_clone_isolation(filter_request_builder: AsyncFilterRequestBuilder):
+    builder = filter_request_builder.eq("org_id", 42)
+    cloned = builder.clone()
+
+    cloned.eq("status", "active")
+    builder.eq("status", "archived")
+
+    assert str(builder.request.params) == "org_id=eq.42&status=eq.archived"
+    assert str(cloned.request.params) == "org_id=eq.42&status=eq.active"
+
+
+def test_filter_builder_clone_negate_next(filter_request_builder: AsyncFilterRequestBuilder):
+    builder = filter_request_builder.not_
+    cloned = builder.clone()
+
+    assert cloned.negate_next is True
+
+    cloned.eq("name", "Alice")
+    assert str(cloned.request.params) == "name=not.eq.Alice"
+    assert cloned.negate_next is False
+    assert builder.negate_next is True
+
+
+def test_filter_builder_clone_headers_isolation(filter_request_builder: AsyncFilterRequestBuilder):
+    builder = filter_request_builder.eq("id", 1)
+    cloned = builder.clone()
+
+    cloned.max_affected(5)
+
+    assert "prefer" in cloned.request.headers
+    assert "prefer" not in builder.request.headers
diff --git a/src/postgrest/tests/_async/test_request_builder.py b/src/postgrest/tests/_async/test_request_builder.py
index c755e70d..d02f436a 100644
--- a/src/postgrest/tests/_async/test_request_builder.py
+++ b/src/postgrest/tests/_async/test_request_builder.py
@@ -569,3 +569,41 @@ def test_single_with_csv_data(
         )
         assert isinstance(result.data, str)
         assert result.data == csv_api_response
+
+
+class TestClone:
+    def test_request_builder_clone(self, request_builder: AsyncRequestBuilder):
+        cloned = request_builder.clone()
+        cloned.headers["X-Custom"] = "test-value"
+
+        assert "X-Custom" in cloned.headers
+        assert "X-Custom" not in request_builder.headers
+
+    def test_select_builder_clone_branching(
+        self, request_builder: AsyncRequestBuilder
+    ):
+        base = request_builder.select("*").eq("tenant_id", "t1")
+        branch_a = base.clone().order("created_at", desc=True).limit(10)
+        branch_b = base.clone().order("name").range(20, 30)
+
+        assert str(base.request.params) == "select=%2A&tenant_id=eq.t1"
+        assert (
+            str(branch_a.request.params)
+            == "select=%2A&tenant_id=eq.t1&order=created_at.desc&limit=10"
+        )
+        assert (
+            str(branch_b.request.params)
+            == "select=%2A&tenant_id=eq.t1&order=name.asc&offset=20&limit=11"
+        )
+
+    def test_single_builder_clone(self, request_builder: AsyncRequestBuilder):
+        single = request_builder.select("*").single()
+        cloned = single.clone()
+
+        cloned.request.headers["X-Single-Test"] = "val"
+
+        assert (
+            cloned.request.headers["Accept"] == "application/vnd.pgrst.object+json"
+        )
+        assert "X-Single-Test" in cloned.request.headers
+        assert "X-Single-Test" not in single.request.headers
diff --git a/src/postgrest/tests/_sync/test_client.py b/src/postgrest/tests/_sync/test_client.py
index 08955089..95b13e67 100644
--- a/src/postgrest/tests/_sync/test_client.py
+++ b/src/postgrest/tests/_sync/test_client.py
@@ -3,10 +3,10 @@
 
 import pytest
 from httpx import (
-    BasicAuth,
     Client,
-    Headers,
     HTTPTransport,
+    BasicAuth,
+    Headers,
     Limits,
     Request,
     Response,
@@ -48,6 +48,7 @@ def test_simple(self, postgrest_client: SyncPostgrestClient):
         )
         assert session.headers.items() >= headers.items()
 
+    @pytest.mark.asyncio
     def test_custom_headers(self):
         with SyncPostgrestClient(
             "https://example.com", schema="pub", headers={"Custom-Header": "value"}
@@ -66,6 +67,7 @@ def test_custom_headers(self):
 
 
 class TestHttpxClientConstructor:
+    @pytest.mark.asyncio
     def test_custom_httpx_client(self) -> None:
         transport = HTTPTransport(
             retries=10,
@@ -113,14 +115,15 @@ def test_schema(postgrest_client: SyncPostgrestClient):
     assert subheaders.items() < client.headers.items()
 
 
-#
-# async def test_params_purged_after_execute(postgrest_client: SyncPostgrestClient):
+# @pytest.mark.asyncio
+# async def test_params_purged_after_execute(postgrest_client: AsyncPostgrestClient):
 #     assert len(postgrest_client.session.params) == 0
 #     with pytest.raises(APIError):
 #         await postgrest_client.from_("test").select("a", "b").eq("c", "d").execute()
 #     assert len(postgrest_client.session.params) == 0
 
 
+@pytest.mark.asyncio
 def test_response_status_code_outside_ok(postgrest_client: SyncPostgrestClient):
     with patch(
         "postgrest._sync.request_builder.SyncSelectRequestBuilder.execute",
@@ -149,8 +152,7 @@ def test_response_status_code_outside_ok(postgrest_client: SyncPostgrestClient):
 
 
 # https://github.com/supabase/postgrest-py/issues/595
-
-
+@pytest.mark.asyncio
 def test_response_client_invalid_response_but_valid_json(
     postgrest_client: SyncPostgrestClient,
 ):
diff --git a/src/postgrest/tests/_sync/test_filter_request_builder.py b/src/postgrest/tests/_sync/test_filter_request_builder.py
index 11cc9959..7d60a227 100644
--- a/src/postgrest/tests/_sync/test_filter_request_builder.py
+++ b/src/postgrest/tests/_sync/test_filter_request_builder.py
@@ -5,7 +5,7 @@
 from yarl import URL
 
 from postgrest import SyncFilterRequestBuilder
-from postgrest._sync.request_builder import RequestConfig
+from postgrest._async.request_builder import RequestConfig
 
 
 @pytest.fixture
@@ -335,3 +335,36 @@ def test_max_affected_returns_self(filter_request_builder):
     builder = filter_request_builder.max_affected(1)
 
     assert builder is filter_request_builder
+
+
+def test_filter_builder_clone_isolation(filter_request_builder: SyncFilterRequestBuilder):
+    builder = filter_request_builder.eq("org_id", 42)
+    cloned = builder.clone()
+
+    cloned.eq("status", "active")
+    builder.eq("status", "archived")
+
+    assert str(builder.request.params) == "org_id=eq.42&status=eq.archived"
+    assert str(cloned.request.params) == "org_id=eq.42&status=eq.active"
+
+
+def test_filter_builder_clone_negate_next(filter_request_builder: SyncFilterRequestBuilder):
+    builder = filter_request_builder.not_
+    cloned = builder.clone()
+
+    assert cloned.negate_next is True
+
+    cloned.eq("name", "Alice")
+    assert str(cloned.request.params) == "name=not.eq.Alice"
+    assert cloned.negate_next is False
+    assert builder.negate_next is True
+
+
+def test_filter_builder_clone_headers_isolation(filter_request_builder: SyncFilterRequestBuilder):
+    builder = filter_request_builder.eq("id", 1)
+    cloned = builder.clone()
+
+    cloned.max_affected(5)
+
+    assert "prefer" in cloned.request.headers
+    assert "prefer" not in builder.request.headers
diff --git a/src/postgrest/tests/_sync/test_filter_request_builder_integration.py b/src/postgrest/tests/_sync/test_filter_request_builder_integration.py
index bc2e9af6..f136dcfa 100644
--- a/src/postgrest/tests/_sync/test_filter_request_builder_integration.py
+++ b/src/postgrest/tests/_sync/test_filter_request_builder_integration.py
@@ -123,7 +123,14 @@ def test_not_equal():
 
 
 def test_greater_than():
-    res = rest_client().from_("users").select("id, name").gt("id", 1).single().execute()
+    res = (
+        rest_client()
+        .from_("users")
+        .select("id, name")
+        .gt("id", 1)
+        .single()
+        .execute()
+    )
 
     assert res.data == {"id": 2, "name": "Jane"}
 
diff --git a/src/postgrest/tests/_sync/test_query_request_builder.py b/src/postgrest/tests/_sync/test_query_request_builder.py
index 58fbf2fc..e14e3719 100644
--- a/src/postgrest/tests/_sync/test_query_request_builder.py
+++ b/src/postgrest/tests/_sync/test_query_request_builder.py
@@ -5,7 +5,7 @@
 from yarl import URL
 
 from postgrest import SyncQueryRequestBuilder
-from postgrest._sync.request_builder import RequestConfig
+from postgrest._async.request_builder import RequestConfig
 
 
 @pytest.fixture
diff --git a/src/postgrest/tests/_sync/test_request_builder.py b/src/postgrest/tests/_sync/test_request_builder.py
index 443e05a6..689063be 100644
--- a/src/postgrest/tests/_sync/test_request_builder.py
+++ b/src/postgrest/tests/_sync/test_request_builder.py
@@ -1,4 +1,4 @@
-from typing import Any, Dict, Iterable, List
+from typing import Any, Iterable, Dict, List
 
 import pytest
 from httpx import Client, Headers, QueryParams, Request, Response
@@ -569,3 +569,41 @@ def test_single_with_csv_data(
         )
         assert isinstance(result.data, str)
         assert result.data == csv_api_response
+
+
+class TestClone:
+    def test_request_builder_clone(self, request_builder: SyncRequestBuilder):
+        cloned = request_builder.clone()
+        cloned.headers["X-Custom"] = "test-value"
+
+        assert "X-Custom" in cloned.headers
+        assert "X-Custom" not in request_builder.headers
+
+    def test_select_builder_clone_branching(
+        self, request_builder: SyncRequestBuilder
+    ):
+        base = request_builder.select("*").eq("tenant_id", "t1")
+        branch_a = base.clone().order("created_at", desc=True).limit(10)
+        branch_b = base.clone().order("name").range(20, 30)
+
+        assert str(base.request.params) == "select=%2A&tenant_id=eq.t1"
+        assert (
+            str(branch_a.request.params)
+            == "select=%2A&tenant_id=eq.t1&order=created_at.desc&limit=10"
+        )
+        assert (
+            str(branch_b.request.params)
+            == "select=%2A&tenant_id=eq.t1&order=name.asc&offset=20&limit=11"
+        )
+
+    def test_single_builder_clone(self, request_builder: SyncRequestBuilder):
+        single = request_builder.select("*").single()
+        cloned = single.clone()
+
+        cloned.request.headers["X-Single-Test"] = "val"
+
+        assert (
+            cloned.request.headers["Accept"] == "application/vnd.pgrst.object+json"
+        )
+        assert "X-Single-Test" in cloned.request.headers
+        assert "X-Single-Test" not in single.request.headers