diff --git a/tools/internal_ci/linux/grpc_interop_matrix.cfg b/tools/internal_ci/linux/grpc_interop_matrix.cfg
index ae59e930f77..7178d83e2c5 100644
--- a/tools/internal_ci/linux/grpc_interop_matrix.cfg
+++ b/tools/internal_ci/linux/grpc_interop_matrix.cfg
@@ -16,7 +16,6 @@
 
 # Location of the continuous shell script in repository.
 build_file: "grpc/tools/internal_ci/linux/grpc_interop_matrix.sh"
-# grpc_interop tests can take 1 hours to complete.
 timeout_mins: 300
 action {
   define_artifacts {
@@ -24,3 +23,8 @@ action {
     regex: "github/grpc/reports/**"
   }
 }
+
+env_vars {
+  key: "RUN_TESTS_FLAGS"
+  value: "--language=all --release=all --allow_flakes --report_file=sponge_log.xml --bq_result_table interop_results"
+}
diff --git a/tools/internal_ci/linux/grpc_interop_matrix.sh b/tools/internal_ci/linux/grpc_interop_matrix.sh
index 4c24c434883..fea365eeff5 100755
--- a/tools/internal_ci/linux/grpc_interop_matrix.sh
+++ b/tools/internal_ci/linux/grpc_interop_matrix.sh
@@ -22,4 +22,4 @@ cd $(dirname $0)/../../..
 
 source tools/internal_ci/helper_scripts/prepare_build_linux_rc
 
-tools/interop_matrix/run_interop_matrix_tests.py --language=all --release=all --allow_flakes --report_file=sponge_log.xml --bq_result_table interop_results $@
+tools/interop_matrix/run_interop_matrix_tests.py $RUN_TESTS_FLAGS
\ No newline at end of file
diff --git a/tools/internal_ci/linux/pull_request/grpc_interop_matrix_adhoc.cfg b/tools/internal_ci/linux/pull_request/grpc_interop_matrix_adhoc.cfg
new file mode 100644
index 00000000000..6726384f188
--- /dev/null
+++ b/tools/internal_ci/linux/pull_request/grpc_interop_matrix_adhoc.cfg
@@ -0,0 +1,30 @@
+# Copyright 2017 gRPC authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Config file for the internal CI (in protobuf text format)
+
+# Location of the continuous shell script in repository.
+build_file: "grpc/tools/internal_ci/linux/grpc_interop_matrix.sh"
+timeout_mins: 300
+action {
+  define_artifacts {
+    regex: "**/sponge_log.xml"
+    regex: "github/grpc/reports/**"
+  }
+}
+
+env_vars {
+  key: "RUN_TESTS_FLAGS"
+  value: "--language=all --release=all --allow_flakes --report_file=sponge_log.xml"
+}