diff --git a/scripts/flaky_tests.py b/scripts/flaky_tests.py
index 878840fcee..919a9278a9 100755
--- a/scripts/flaky_tests.py
+++ b/scripts/flaky_tests.py
@@ -5,10 +5,11 @@ import json
 import logging
 import os
 from collections import defaultdict
-from typing import DefaultDict, Dict
+from typing import Any, DefaultDict, Dict, Optional
 
 import psycopg2
 import psycopg2.extras
+import toml
 
 FLAKY_TESTS_QUERY = """
     SELECT
@@ -58,6 +59,24 @@ def main(args: argparse.Namespace):
     else:
         pageserver_virtual_file_io_engine_parameter = ""
 
+    # re-use existing records of flaky tests from before parametrization by compaction_algorithm
+    def get_pageserver_default_tenant_config_compaction_algorithm() -> Optional[Dict[str, Any]]:
+        """Duplicated from parametrize.py"""
+        toml_table = os.getenv("PAGESERVER_DEFAULT_TENANT_CONFIG_COMPACTION_ALGORITHM")
+        if toml_table is None:
+            return None
+        v = toml.loads(toml_table)
+        assert isinstance(v, dict)
+        return v
+
+    pageserver_default_tenant_config_compaction_algorithm_parameter = ""
+    if (
+        explicit_default := get_pageserver_default_tenant_config_compaction_algorithm()
+    ) is not None:
+        pageserver_default_tenant_config_compaction_algorithm_parameter = (
+            f"-{explicit_default['kind']}"
+        )
+
     for row in rows:
         # We don't want to automatically rerun tests in a performance suite
         if row["parent_suite"] != "test_runner.regress":
@@ -66,10 +85,10 @@ def main(args: argparse.Namespace):
         if row["name"].endswith("]"):
             parametrized_test = row["name"].replace(
                 "[",
-                f"[{build_type}-pg{pg_version}{pageserver_virtual_file_io_engine_parameter}-",
+                f"[{build_type}-pg{pg_version}{pageserver_virtual_file_io_engine_parameter}{pageserver_default_tenant_config_compaction_algorithm_parameter}-",
             )
         else:
-            parametrized_test = f"{row['name']}[{build_type}-pg{pg_version}{pageserver_virtual_file_io_engine_parameter}]"
+            parametrized_test = f"{row['name']}[{build_type}-pg{pg_version}{pageserver_virtual_file_io_engine_parameter}{pageserver_default_tenant_config_compaction_algorithm_parameter}]"
 
         res[row["parent_suite"]][row["suite"]][parametrized_test] = True
 
diff --git a/test_runner/fixtures/neon_fixtures.py b/test_runner/fixtures/neon_fixtures.py
index 8432655370..62a4b974a3 100644
--- a/test_runner/fixtures/neon_fixtures.py
+++ b/test_runner/fixtures/neon_fixtures.py
@@ -467,6 +467,7 @@ class NeonEnvBuilder:
         initial_timeline: Optional[TimelineId] = None,
         pageserver_virtual_file_io_engine: Optional[str] = None,
         pageserver_aux_file_policy: Optional[AuxFileStore] = None,
+        pageserver_default_tenant_config_compaction_algorithm: Optional[Dict[str, Any]] = None,
     ):
         self.repo_dir = repo_dir
         self.rust_log_override = rust_log_override
@@ -507,6 +508,14 @@ class NeonEnvBuilder:
 
         self.pageserver_virtual_file_io_engine: Optional[str] = pageserver_virtual_file_io_engine
 
+        self.pageserver_default_tenant_config_compaction_algorithm: Optional[
+            Dict[str, Any]
+        ] = pageserver_default_tenant_config_compaction_algorithm
+        if self.pageserver_default_tenant_config_compaction_algorithm is not None:
+            log.debug(
+                f"Overriding pageserver default compaction algorithm to {self.pageserver_default_tenant_config_compaction_algorithm}"
+            )
+
         self.pageserver_get_vectored_impl: Optional[str] = None
         if os.getenv("PAGESERVER_GET_VECTORED_IMPL", "") == "vectored":
             self.pageserver_get_vectored_impl = "vectored"
@@ -1103,6 +1112,11 @@ class NeonEnv:
                 ps_cfg["get_impl"] = config.pageserver_get_impl
             if config.pageserver_validate_vectored_get is not None:
                 ps_cfg["validate_vectored_get"] = config.pageserver_validate_vectored_get
+            if config.pageserver_default_tenant_config_compaction_algorithm is not None:
+                tenant_config = ps_cfg.setdefault("tenant_config", {})
+                tenant_config[
+                    "compaction_algorithm"
+                ] = config.pageserver_default_tenant_config_compaction_algorithm
 
             if self.pageserver_remote_storage is not None:
                 ps_cfg["remote_storage"] = remote_storage_to_toml_dict(
@@ -1304,6 +1318,7 @@ def _shared_simple_env(
     pg_version: PgVersion,
     pageserver_virtual_file_io_engine: str,
     pageserver_aux_file_policy: Optional[AuxFileStore],
+    pageserver_default_tenant_config_compaction_algorithm: Optional[Dict[str, Any]],
 ) -> Iterator[NeonEnv]:
     """
     # Internal fixture backing the `neon_simple_env` fixture. If TEST_SHARED_FIXTURES
@@ -1335,6 +1350,7 @@ def _shared_simple_env(
         test_output_dir=test_output_dir,
         pageserver_virtual_file_io_engine=pageserver_virtual_file_io_engine,
         pageserver_aux_file_policy=pageserver_aux_file_policy,
+        pageserver_default_tenant_config_compaction_algorithm=pageserver_default_tenant_config_compaction_algorithm,
     ) as builder:
         env = builder.init_start()
 
@@ -1375,6 +1391,7 @@ def neon_env_builder(
     top_output_dir: Path,
     pageserver_virtual_file_io_engine: str,
     pageserver_aux_file_policy: Optional[AuxFileStore] = None,
+    pageserver_default_tenant_config_compaction_algorithm: Optional[Dict[str, Any]] = None,
 ) -> Iterator[NeonEnvBuilder]:
     """
     Fixture to create a Neon environment for test.
@@ -1409,6 +1426,7 @@ def neon_env_builder(
         test_output_dir=test_output_dir,
         test_overlay_dir=test_overlay_dir,
         pageserver_aux_file_policy=pageserver_aux_file_policy,
+        pageserver_default_tenant_config_compaction_algorithm=pageserver_default_tenant_config_compaction_algorithm,
     ) as builder:
         yield builder
 
diff --git a/test_runner/fixtures/parametrize.py b/test_runner/fixtures/parametrize.py
index 77523a542b..0227285822 100644
--- a/test_runner/fixtures/parametrize.py
+++ b/test_runner/fixtures/parametrize.py
@@ -1,7 +1,8 @@
 import os
-from typing import Optional
+from typing import Any, Dict, Optional
 
 import pytest
+import toml
 from _pytest.python import Metafunc
 
 from fixtures.pg_version import PgVersion
@@ -37,6 +38,20 @@ def pageserver_aux_file_policy() -> Optional[AuxFileStore]:
     return None
 
 
+def get_pageserver_default_tenant_config_compaction_algorithm() -> Optional[Dict[str, Any]]:
+    toml_table = os.getenv("PAGESERVER_DEFAULT_TENANT_CONFIG_COMPACTION_ALGORITHM")
+    if toml_table is None:
+        return None
+    v = toml.loads(toml_table)
+    assert isinstance(v, dict)
+    return v
+
+
+@pytest.fixture(scope="function", autouse=True)
+def pageserver_default_tenant_config_compaction_algorithm() -> Optional[Dict[str, Any]]:
+    return get_pageserver_default_tenant_config_compaction_algorithm()
+
+
 def pytest_generate_tests(metafunc: Metafunc):
     if (bt := os.getenv("BUILD_TYPE")) is None:
         build_types = ["debug", "release"]
@@ -60,6 +75,16 @@ def pytest_generate_tests(metafunc: Metafunc):
     ):
         metafunc.parametrize("pageserver_virtual_file_io_engine", [io_engine])
 
+    # Same hack for pageserver_default_tenant_config_compaction_algorithm
+    if (
+        explicit_default := get_pageserver_default_tenant_config_compaction_algorithm()
+    ) is not None:
+        metafunc.parametrize(
+            "pageserver_default_tenant_config_compaction_algorithm",
+            [explicit_default],
+            ids=[explicit_default["kind"]],
+        )
+
     # For performance tests, parametrize also by platform
     if (
         "test_runner/performance" in metafunc.definition._nodeid