diff --git a/Firestore/core/CMakeLists.txt b/Firestore/core/CMakeLists.txt
index 65238165549..cb405074816 100644
--- a/Firestore/core/CMakeLists.txt
+++ b/Firestore/core/CMakeLists.txt
@@ -137,7 +137,6 @@ target_compile_definitions(
 target_link_libraries(
   firestore_util PUBLIC
   absl::base
-  absl::flat_hash_map
   absl::memory
   absl::meta
   absl::optional
@@ -250,7 +249,6 @@ target_link_libraries(
   firestore_core PUBLIC
   LevelDB::LevelDB
   absl::base
-  absl::flat_hash_map
   absl::memory
   absl::meta
   absl::optional
diff --git a/Firestore/core/src/model/object_value.cc b/Firestore/core/src/model/object_value.cc
index 3b812fe535d..d1660aa40cd 100644
--- a/Firestore/core/src/model/object_value.cc
+++ b/Firestore/core/src/model/object_value.cc
@@ -19,6 +19,7 @@
 #include <algorithm>
 #include <map>
 #include <set>
+#include <unordered_map>
 
 #include "Firestore/Protos/nanopb/google/firestore/v1/document.nanopb.h"
 #include "Firestore/core/src/model/value_util.h"
@@ -227,10 +228,12 @@ ObjectValue ObjectValue::FromFieldsEntry(
   return ObjectValue{std::move(value)};
 }
 
+// TODO(b/443765747) Revert back to absl::flat_hash_map after the absl version
+// is upgraded to later than 20250127.0
 ObjectValue ObjectValue::FromAggregateFieldsEntry(
     google_firestore_v1_AggregationResult_AggregateFieldsEntry* fields_entry,
     pb_size_t count,
-    const absl::flat_hash_map<std::string, std::string>& aliasMap) {
+    const std::unordered_map<std::string, std::string>& aliasMap) {
   Message<google_firestore_v1_Value> value;
   value->which_value_type = google_firestore_v1_Value_map_value_tag;
 
@@ -246,7 +249,9 @@ ObjectValue ObjectValue::FromAggregateFieldsEntry(
         // using the client-side alias.
         ByteString serverAlias(entry.key);
         std::string serverAliasString = serverAlias.ToString();
-        HARD_ASSERT(aliasMap.contains(serverAliasString),
+        // TODO(b/443765747) Revert back to aliasMap.contains(serverAliasString)
+        // after the absl version is upgraded to later than 20250127.0
+        HARD_ASSERT(aliasMap.find(serverAliasString) != aliasMap.end(),
                     "%s not present in aliasMap", serverAlias.ToString());
 
         ByteString clientAlias(aliasMap.find(serverAliasString)->second);
diff --git a/Firestore/core/src/model/object_value.h b/Firestore/core/src/model/object_value.h
index a306a92705e..9dcf819831b 100644
--- a/Firestore/core/src/model/object_value.h
+++ b/Firestore/core/src/model/object_value.h
@@ -21,6 +21,7 @@
 #include <ostream>
 #include <set>
 #include <string>
+#include <unordered_map>
 #include <utility>
 
 #include "Firestore/Protos/nanopb/google/firestore/v1/document.nanopb.h"
@@ -78,10 +79,12 @@ class ObjectValue {
    * @param count Count of fields in `fields_entry`.
    * @return The created `ObjectValue`.
    */
+  // TODO(b/443765747) Revert back to absl::flat_hash_map after the absl version
+  // is upgraded to later than 20250127.0
   static ObjectValue FromAggregateFieldsEntry(
       google_firestore_v1_AggregationResult_AggregateFieldsEntry* fields_entry,
       pb_size_t count,
-      const absl::flat_hash_map<std::string, std::string>& aliasMap);
+      const std::unordered_map<std::string, std::string>& aliasMap);
 
   /** Recursively extracts the FieldPaths that are set in this ObjectValue. */
   FieldMask ToFieldMask() const;
diff --git a/Firestore/core/src/remote/datastore.cc b/Firestore/core/src/remote/datastore.cc
index 47a8fb716b5..83eef482622 100644
--- a/Firestore/core/src/remote/datastore.cc
+++ b/Firestore/core/src/remote/datastore.cc
@@ -16,6 +16,7 @@
 
 #include "Firestore/core/src/remote/datastore.h"
 
+#include <unordered_map>
 #include <unordered_set>
 #include <utility>
 
@@ -281,7 +282,9 @@ void Datastore::RunAggregateQueryWithCredentials(
     const core::Query& query,
     const std::vector<AggregateField>& aggregates,
     api::AggregateQueryCallback&& callback) {
-  absl::flat_hash_map<std::string, std::string> aliasMap;
+  // TODO(b/443765747) Revert back to absl::flat_hash_map after the absl version
+  // is upgraded to later than 20250127.0
+  std::unordered_map<std::string, std::string> aliasMap;
   grpc::ByteBuffer message =
       MakeByteBuffer(datastore_serializer_.EncodeAggregateQueryRequest(
           query, aggregates, aliasMap));
diff --git a/Firestore/core/src/remote/remote_objc_bridge.cc b/Firestore/core/src/remote/remote_objc_bridge.cc
index ae7fcb246ea..1eb27fbeed0 100644
--- a/Firestore/core/src/remote/remote_objc_bridge.cc
+++ b/Firestore/core/src/remote/remote_objc_bridge.cc
@@ -17,6 +17,7 @@
 #include "Firestore/core/src/remote/remote_objc_bridge.h"
 
 #include <map>
+#include <unordered_map>
 
 #include "Firestore/core/src/core/database_info.h"
 #include "Firestore/core/src/core/query.h"
@@ -272,11 +273,13 @@ DatastoreSerializer::MergeLookupResponses(
   return result;
 }
 
+// TODO(b/443765747) Revert back to absl::flat_hash_map after the absl version
+// is upgraded to later than 20250127.0
 Message<google_firestore_v1_RunAggregationQueryRequest>
 DatastoreSerializer::EncodeAggregateQueryRequest(
     const core::Query& query,
     const std::vector<AggregateField>& aggregates,
-    absl::flat_hash_map<std::string, std::string>& aliasMap) const {
+    std::unordered_map<std::string, std::string>& aliasMap) const {
   Message<google_firestore_v1_RunAggregationQueryRequest> result;
   auto encodedTarget = serializer_.EncodeQueryTarget(query.ToAggregateTarget());
   result->parent = encodedTarget.parent;
@@ -291,7 +294,9 @@ DatastoreSerializer::EncodeAggregateQueryRequest(
   // De-duplicate aggregates based on the alias.
   // Since aliases are auto-computed from the operation and path,
   // equal aggregate will have the same alias.
-  absl::flat_hash_map<std::string, AggregateField> uniqueAggregates;
+  // TODO(b/443765747) Revert back to absl::flat_hash_map after the absl version
+  // is upgraded to later than 20250127.0
+  std::unordered_map<std::string, AggregateField> uniqueAggregates;
   for (const AggregateField& aggregate : aggregates) {
     auto pair = std::pair<std::string, AggregateField>(
         aggregate.alias.StringValue(), aggregate);
@@ -365,9 +370,11 @@ DatastoreSerializer::EncodeAggregateQueryRequest(
   return result;
 }
 
+// TODO(b/443765747) Revert back to absl::flat_hash_map after the absl version
+// is upgraded to later than 20250127.0
 util::StatusOr<ObjectValue> DatastoreSerializer::DecodeAggregateQueryResponse(
     const grpc::ByteBuffer& response,
-    const absl::flat_hash_map<std::string, std::string>& aliasMap) const {
+    const std::unordered_map<std::string, std::string>& aliasMap) const {
   ByteBufferReader reader{response};
   auto message =
       Message<google_firestore_v1_RunAggregationQueryResponse>::TryParse(
diff --git a/Firestore/core/src/remote/remote_objc_bridge.h b/Firestore/core/src/remote/remote_objc_bridge.h
index 0aa2b93f988..66d02e48429 100644
--- a/Firestore/core/src/remote/remote_objc_bridge.h
+++ b/Firestore/core/src/remote/remote_objc_bridge.h
@@ -19,6 +19,7 @@
 
 #include <memory>
 #include <string>
+#include <unordered_map>
 #include <utility>
 #include <vector>
 
@@ -136,15 +137,19 @@ class DatastoreSerializer {
   util::StatusOr<std::vector<model::Document>> MergeLookupResponses(
       const std::vector<grpc::ByteBuffer>& responses) const;
 
+  // TODO(b/443765747) Revert back to absl::flat_hash_map after the absl version
+  // is upgraded to later than 20250127.0
   nanopb::Message<google_firestore_v1_RunAggregationQueryRequest>
   EncodeAggregateQueryRequest(
       const core::Query& query,
       const std::vector<model::AggregateField>& aggregates,
-      absl::flat_hash_map<std::string, std::string>& aliasMap) const;
+      std::unordered_map<std::string, std::string>& aliasMap) const;
 
+  // TODO(b/443765747) Revert back to absl::flat_hash_map after the absl version
+  // is upgraded to later than 20250127.0
   util::StatusOr<model::ObjectValue> DecodeAggregateQueryResponse(
       const grpc::ByteBuffer& response,
-      const absl::flat_hash_map<std::string, std::string>& aliasMap) const;
+      const std::unordered_map<std::string, std::string>& aliasMap) const;
 
   const Serializer& serializer() const {
     return serializer_;
diff --git a/Firestore/core/test/unit/api/aggregate_query_test.cc b/Firestore/core/test/unit/api/aggregate_query_test.cc
index 2a2ca9c7d6c..71a6f361a78 100644
--- a/Firestore/core/test/unit/api/aggregate_query_test.cc
+++ b/Firestore/core/test/unit/api/aggregate_query_test.cc
@@ -110,7 +110,9 @@ TEST(AggregateQuery, GetCallsGetAggregateOk) {
   aggregate_fields_entry[0].value.integer_value = 10;
 
   // Test alias map
-  absl::flat_hash_map<std::string, std::string> alias_map;
+  // TODO(b/443765747) Revert back to absl::flat_hash_map after the absl version
+  // is upgraded to later than 20250127.0
+  std::unordered_map<std::string, std::string> alias_map;
   alias_map["aggregate_0"] = "count";
 
   // Test ObjectValue result