Use **CI_PIPELINE_IID**

app/models/ci/pipeline.rb

@@ -494,7 +494,7 @@ module Ci
     def predefined_variables
       Gitlab::Ci::Variables::Collection.new
         .append(key: 'CI_PIPELINE_ID', value: id.to_s)
-        .append(key: 'CI_PIPELINE_IID_PER_PROJECT', value: iid.to_s)
+        .append(key: 'CI_PIPELINE_IID', value: iid.to_s)
         .append(key: 'CI_CONFIG_PATH', value: ci_yaml_file_path)
         .append(key: 'CI_PIPELINE_SOURCE', value: source.to_s)
     end

doc/ci/variables/README.md

@@ -60,7 +60,7 @@ future GitLab releases.**
 | **CI_RUNNER_REVISION**          | all    | 10.6   | GitLab Runner revision that is executing the current job |
 | **CI_RUNNER_EXECUTABLE_ARCH**   | all    | 10.6   | The OS/architecture of the GitLab Runner executable (note that this is not necessarily the same as the environment of the executor) |
 | **CI_PIPELINE_ID**              | 8.10   | 0.5    | The unique id of the current pipeline that GitLab CI uses internally |
-| **CI_PIPELINE_IID_PER_PROJECT** | 10.8   | all    | The unique id of the current pipeline that GitLab CI uses internally (Incremented per project) |
+| **CI_PIPELINE_IID** | 10.8   | all    | The unique id of the current pipeline scoped to project |
 | **CI_PIPELINE_TRIGGERED**       | all    | all    | The flag to indicate that job was [triggered] |
 | **CI_PIPELINE_SOURCE**          | 10.0   | all    | Indicates how the pipeline was triggered. Possible options are: `push`, `web`, `trigger`, `schedule`, `api`, and `pipeline`. For pipelines created before GitLab 9.5, this will show as `unknown` |
 | **CI_PROJECT_DIR**              | all    | all    | The full path where the repository is cloned and where the job is run |