diff --git a/recipe_modules/pipeline/__init__.py b/recipe_modules/pipeline/__init__.py
new file mode 100644
index 0000000..e808c47
--- /dev/null
+++ b/recipe_modules/pipeline/__init__.py
@@ -0,0 +1,23 @@
+# Copyright 2022 The Pigweed 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
+#
+#     https://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.
+
+# pylint: disable=missing-docstring
+
+from PB.recipe_modules.pigweed.pipeline import properties
+
+DEPS = [
+    'recipe_engine/properties',
+]
+
+PROPERTIES = properties.InputProperties
diff --git a/recipe_modules/pipeline/api.py b/recipe_modules/pipeline/api.py
new file mode 100644
index 0000000..d23f3a7
--- /dev/null
+++ b/recipe_modules/pipeline/api.py
@@ -0,0 +1,38 @@
+# Copyright 2022 The Pigweed 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
+#
+#     https://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.
+"""Calls to build code."""
+
+from recipe_engine import recipe_api
+
+
+class PipelineApi(recipe_api.RecipeApi):
+    """Calls to build code."""
+
+    def __init__(self, props, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self._enabled = props.inside_a_pipeline
+        self._round = props.round
+        self._prev_iteration_builds = props.builds_from_previous_iteration
+
+    @property
+    def in_pipeline(self):
+        return self._enabled
+
+    @property
+    def round(self):
+        return self._round if self._enabled else None
+
+    @property
+    def builds_from_previous_iteration(self):
+        return tuple(self._prev_iteration_builds) if self._enabled else None
diff --git a/recipe_modules/pipeline/properties.proto b/recipe_modules/pipeline/properties.proto
new file mode 100644
index 0000000..a0cb0c6
--- /dev/null
+++ b/recipe_modules/pipeline/properties.proto
@@ -0,0 +1,27 @@
+// Copyright 2021 The Pigweed 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
+//
+//     https://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.
+syntax = "proto3";
+
+package recipe_modules.pigweed.pipeline;
+
+message InputProperties {
+  // Whether this build has been launched from a pipeline.
+  bool inside_a_pipeline = 1;
+
+  // Number of the round, zero-indexed.
+  int32 round = 2;
+
+  // List of all builds that were run in the previous iteration.
+  repeated int64 builds_from_previous_iteration = 3;
+}
diff --git a/recipe_modules/pipeline/test_api.py b/recipe_modules/pipeline/test_api.py
new file mode 100644
index 0000000..e26432f
--- /dev/null
+++ b/recipe_modules/pipeline/test_api.py
@@ -0,0 +1,31 @@
+# Copyright 2020 The Pigweed 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
+#
+#     https://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.
+"""Test API for pipeline."""
+
+from recipe_engine import recipe_test_api
+
+
+class EnvironmentTestApi(recipe_test_api.RecipeTestApi):
+    """Test API for pipeline."""
+
+    def props(self, round, build_ids=()):
+        return self.m.properties(
+            **{
+                '$pigweed/pipeline': {
+                    'inside_a_pipeline': True,
+                    'round': round,
+                    'builds_from_previous_iteration': list(build_ids),
+                },
+            }
+        )
diff --git a/recipe_modules/pipeline/tests/full.expected/empty.json b/recipe_modules/pipeline/tests/full.expected/empty.json
new file mode 100644
index 0000000..7d97243
--- /dev/null
+++ b/recipe_modules/pipeline/tests/full.expected/empty.json
@@ -0,0 +1,9 @@
+[
+  {
+    "cmd": [],
+    "name": "not in pipeline"
+  },
+  {
+    "name": "$result"
+  }
+]
\ No newline at end of file
diff --git a/recipe_modules/pipeline/tests/full.expected/nopipeline.json b/recipe_modules/pipeline/tests/full.expected/nopipeline.json
new file mode 100644
index 0000000..7d97243
--- /dev/null
+++ b/recipe_modules/pipeline/tests/full.expected/nopipeline.json
@@ -0,0 +1,9 @@
+[
+  {
+    "cmd": [],
+    "name": "not in pipeline"
+  },
+  {
+    "name": "$result"
+  }
+]
\ No newline at end of file
diff --git a/recipe_modules/pipeline/tests/full.expected/round_0.json b/recipe_modules/pipeline/tests/full.expected/round_0.json
new file mode 100644
index 0000000..cc68ad8
--- /dev/null
+++ b/recipe_modules/pipeline/tests/full.expected/round_0.json
@@ -0,0 +1,17 @@
+[
+  {
+    "cmd": [],
+    "name": "in pipeline"
+  },
+  {
+    "cmd": [],
+    "name": "round 0"
+  },
+  {
+    "cmd": [],
+    "name": "0 previous builds"
+  },
+  {
+    "name": "$result"
+  }
+]
\ No newline at end of file
diff --git a/recipe_modules/pipeline/tests/full.expected/round_1.json b/recipe_modules/pipeline/tests/full.expected/round_1.json
new file mode 100644
index 0000000..b0e3d4e
--- /dev/null
+++ b/recipe_modules/pipeline/tests/full.expected/round_1.json
@@ -0,0 +1,21 @@
+[
+  {
+    "cmd": [],
+    "name": "in pipeline"
+  },
+  {
+    "cmd": [],
+    "name": "round 1"
+  },
+  {
+    "cmd": [],
+    "name": "1 previous builds"
+  },
+  {
+    "cmd": [],
+    "name": "previous build 123"
+  },
+  {
+    "name": "$result"
+  }
+]
\ No newline at end of file
diff --git a/recipe_modules/pipeline/tests/full.expected/round_4.json b/recipe_modules/pipeline/tests/full.expected/round_4.json
new file mode 100644
index 0000000..90cad80
--- /dev/null
+++ b/recipe_modules/pipeline/tests/full.expected/round_4.json
@@ -0,0 +1,29 @@
+[
+  {
+    "cmd": [],
+    "name": "in pipeline"
+  },
+  {
+    "cmd": [],
+    "name": "round 4"
+  },
+  {
+    "cmd": [],
+    "name": "3 previous builds"
+  },
+  {
+    "cmd": [],
+    "name": "previous build 123"
+  },
+  {
+    "cmd": [],
+    "name": "previous build 456"
+  },
+  {
+    "cmd": [],
+    "name": "previous build 789"
+  },
+  {
+    "name": "$result"
+  }
+]
\ No newline at end of file
diff --git a/recipe_modules/pipeline/tests/full.py b/recipe_modules/pipeline/tests/full.py
new file mode 100644
index 0000000..1f8431c
--- /dev/null
+++ b/recipe_modules/pipeline/tests/full.py
@@ -0,0 +1,74 @@
+# Copyright 2022 The Pigweed 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
+#
+#     https://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.
+"""Full test of pipeline module."""
+
+from recipe_engine import post_process
+
+DEPS = [
+    'fuchsia/status_check',
+    'pigweed/pipeline',
+    'recipe_engine/step',
+]
+
+
+def RunSteps(api):
+    if not api.pipeline.in_pipeline:
+        api.step('not in pipeline', None)
+        return
+
+    api.step('in pipeline', None)
+
+    api.step(f'round {api.pipeline.round}', None)
+
+    prev_builds = api.pipeline.builds_from_previous_iteration
+    api.step(f'{len(prev_builds)} previous builds', None)
+    for build in prev_builds:
+        api.step(f'previous build {build}', None)
+
+
+def GenTests(api):  # pylint: disable=invalid-name
+    def ran(x):
+        return api.post_process(post_process.MustRun, x)
+
+    yield (api.status_check.test('nopipeline') + ran('not in pipeline'))
+
+    yield (
+        api.status_check.test('round_0')
+        + api.pipeline.props(0, [])
+        + ran('in pipeline')
+        + ran('round 0')
+        + ran('0 previous builds')
+    )
+
+    yield (
+        api.status_check.test('round_1')
+        + api.pipeline.props(1, [123])
+        + ran('in pipeline')
+        + ran('round 1')
+        + ran('1 previous builds')
+        + ran('previous build 123')
+    )
+
+    yield (
+        api.status_check.test('round_4')
+        + api.pipeline.props(4, [123, 456, 789])
+        + ran('in pipeline')
+        + ran('round 4')
+        + ran('3 previous builds')
+        + ran('previous build 123')
+        + ran('previous build 456')
+        + ran('previous build 789')
+    )
+
+    yield api.status_check.test('empty')
diff --git a/recipes/pipeline.expected/first_round_failure.json b/recipes/pipeline.expected/first_round_failure.json
index e050645..6d3c550 100644
--- a/recipes/pipeline.expected/first_round_failure.json
+++ b/recipes/pipeline.expected/first_round_failure.json
@@ -17,7 +17,7 @@
     ],
     "infra_step": true,
     "name": "round 0.schedule",
-    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"a\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}, {\"scheduleBuild\": {\"builder\": {\"builder\": \"b\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
+    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"a\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"properties\": {\"$pigweed/pipeline\": {\"builds_from_previous_iteration\": [], \"inside_a_pipeline\": true, \"round\": 0.0}}, \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}, {\"scheduleBuild\": {\"builder\": {\"builder\": \"b\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"properties\": {\"$pigweed/pipeline\": {\"builds_from_previous_iteration\": [], \"inside_a_pipeline\": true, \"round\": 0.0}}, \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
@@ -57,6 +57,13 @@
       "@@@STEP_LOG_LINE@request@          \"luci.buildbucket.parent_tracking\": false@@@",
       "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", @@@",
+      "@@@STEP_LOG_LINE@request@        \"properties\": {@@@",
+      "@@@STEP_LOG_LINE@request@          \"$pigweed/pipeline\": {@@@",
+      "@@@STEP_LOG_LINE@request@            \"builds_from_previous_iteration\": [], @@@",
+      "@@@STEP_LOG_LINE@request@            \"inside_a_pipeline\": true, @@@",
+      "@@@STEP_LOG_LINE@request@            \"round\": 0.0@@@",
+      "@@@STEP_LOG_LINE@request@          }@@@",
+      "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", @@@",
       "@@@STEP_LOG_LINE@request@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@request@          \"parentRunId\": \"fake-task-id\"@@@",
@@ -91,6 +98,13 @@
       "@@@STEP_LOG_LINE@request@          \"luci.buildbucket.parent_tracking\": false@@@",
       "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", @@@",
+      "@@@STEP_LOG_LINE@request@        \"properties\": {@@@",
+      "@@@STEP_LOG_LINE@request@          \"$pigweed/pipeline\": {@@@",
+      "@@@STEP_LOG_LINE@request@            \"builds_from_previous_iteration\": [], @@@",
+      "@@@STEP_LOG_LINE@request@            \"inside_a_pipeline\": true, @@@",
+      "@@@STEP_LOG_LINE@request@            \"round\": 0.0@@@",
+      "@@@STEP_LOG_LINE@request@          }@@@",
+      "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", @@@",
       "@@@STEP_LOG_LINE@request@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@request@          \"parentRunId\": \"fake-task-id\"@@@",
diff --git a/recipes/pipeline.expected/one_builder.json b/recipes/pipeline.expected/one_builder.json
index 2fd146a..ecc3439 100644
--- a/recipes/pipeline.expected/one_builder.json
+++ b/recipes/pipeline.expected/one_builder.json
@@ -15,7 +15,7 @@
     ],
     "infra_step": true,
     "name": "round 0.schedule",
-    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"a\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
+    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"a\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"properties\": {\"$pigweed/pipeline\": {\"builds_from_previous_iteration\": [], \"inside_a_pipeline\": true, \"round\": 0.0}}, \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
@@ -45,6 +45,13 @@
       "@@@STEP_LOG_LINE@request@          \"luci.buildbucket.parent_tracking\": false@@@",
       "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", @@@",
+      "@@@STEP_LOG_LINE@request@        \"properties\": {@@@",
+      "@@@STEP_LOG_LINE@request@          \"$pigweed/pipeline\": {@@@",
+      "@@@STEP_LOG_LINE@request@            \"builds_from_previous_iteration\": [], @@@",
+      "@@@STEP_LOG_LINE@request@            \"inside_a_pipeline\": true, @@@",
+      "@@@STEP_LOG_LINE@request@            \"round\": 0.0@@@",
+      "@@@STEP_LOG_LINE@request@          }@@@",
+      "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", @@@",
       "@@@STEP_LOG_LINE@request@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@request@          \"parentRunId\": \"fake-task-id\"@@@",
diff --git a/recipes/pipeline.expected/second_round_failure.json b/recipes/pipeline.expected/second_round_failure.json
index 9a41969..9fad49e 100644
--- a/recipes/pipeline.expected/second_round_failure.json
+++ b/recipes/pipeline.expected/second_round_failure.json
@@ -16,7 +16,7 @@
     ],
     "infra_step": true,
     "name": "round 0.schedule",
-    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"a\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}, {\"scheduleBuild\": {\"builder\": {\"builder\": \"b\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
+    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"a\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"properties\": {\"$pigweed/pipeline\": {\"builds_from_previous_iteration\": [], \"inside_a_pipeline\": true, \"round\": 0.0}}, \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}, {\"scheduleBuild\": {\"builder\": {\"builder\": \"b\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"properties\": {\"$pigweed/pipeline\": {\"builds_from_previous_iteration\": [], \"inside_a_pipeline\": true, \"round\": 0.0}}, \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
@@ -56,6 +56,13 @@
       "@@@STEP_LOG_LINE@request@          \"luci.buildbucket.parent_tracking\": false@@@",
       "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", @@@",
+      "@@@STEP_LOG_LINE@request@        \"properties\": {@@@",
+      "@@@STEP_LOG_LINE@request@          \"$pigweed/pipeline\": {@@@",
+      "@@@STEP_LOG_LINE@request@            \"builds_from_previous_iteration\": [], @@@",
+      "@@@STEP_LOG_LINE@request@            \"inside_a_pipeline\": true, @@@",
+      "@@@STEP_LOG_LINE@request@            \"round\": 0.0@@@",
+      "@@@STEP_LOG_LINE@request@          }@@@",
+      "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", @@@",
       "@@@STEP_LOG_LINE@request@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@request@          \"parentRunId\": \"fake-task-id\"@@@",
@@ -90,6 +97,13 @@
       "@@@STEP_LOG_LINE@request@          \"luci.buildbucket.parent_tracking\": false@@@",
       "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", @@@",
+      "@@@STEP_LOG_LINE@request@        \"properties\": {@@@",
+      "@@@STEP_LOG_LINE@request@          \"$pigweed/pipeline\": {@@@",
+      "@@@STEP_LOG_LINE@request@            \"builds_from_previous_iteration\": [], @@@",
+      "@@@STEP_LOG_LINE@request@            \"inside_a_pipeline\": true, @@@",
+      "@@@STEP_LOG_LINE@request@            \"round\": 0.0@@@",
+      "@@@STEP_LOG_LINE@request@          }@@@",
+      "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", @@@",
       "@@@STEP_LOG_LINE@request@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@request@          \"parentRunId\": \"fake-task-id\"@@@",
@@ -275,7 +289,7 @@
     ],
     "infra_step": true,
     "name": "round 1.schedule",
-    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"c\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"requestId\": \"0-00000000-0000-0000-0000-00000000133d\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
+    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"c\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"properties\": {\"$pigweed/pipeline\": {\"builds_from_previous_iteration\": [1000.0, 1001.0], \"inside_a_pipeline\": true, \"round\": 1.0}}, \"requestId\": \"0-00000000-0000-0000-0000-00000000133d\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
@@ -305,6 +319,16 @@
       "@@@STEP_LOG_LINE@request@          \"luci.buildbucket.parent_tracking\": false@@@",
       "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", @@@",
+      "@@@STEP_LOG_LINE@request@        \"properties\": {@@@",
+      "@@@STEP_LOG_LINE@request@          \"$pigweed/pipeline\": {@@@",
+      "@@@STEP_LOG_LINE@request@            \"builds_from_previous_iteration\": [@@@",
+      "@@@STEP_LOG_LINE@request@              1000.0, @@@",
+      "@@@STEP_LOG_LINE@request@              1001.0@@@",
+      "@@@STEP_LOG_LINE@request@            ], @@@",
+      "@@@STEP_LOG_LINE@request@            \"inside_a_pipeline\": true, @@@",
+      "@@@STEP_LOG_LINE@request@            \"round\": 1.0@@@",
+      "@@@STEP_LOG_LINE@request@          }@@@",
+      "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"requestId\": \"0-00000000-0000-0000-0000-00000000133d\", @@@",
       "@@@STEP_LOG_LINE@request@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@request@          \"parentRunId\": \"fake-task-id\"@@@",
diff --git a/recipes/pipeline.expected/two_builders.json b/recipes/pipeline.expected/two_builders.json
index 754c9bf..d0b3a47 100644
--- a/recipes/pipeline.expected/two_builders.json
+++ b/recipes/pipeline.expected/two_builders.json
@@ -16,7 +16,7 @@
     ],
     "infra_step": true,
     "name": "round 0.schedule",
-    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"a\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}, {\"scheduleBuild\": {\"builder\": {\"builder\": \"b\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
+    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"a\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"properties\": {\"$pigweed/pipeline\": {\"builds_from_previous_iteration\": [], \"inside_a_pipeline\": true, \"round\": 0.0}}, \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}, {\"scheduleBuild\": {\"builder\": {\"builder\": \"b\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"properties\": {\"$pigweed/pipeline\": {\"builds_from_previous_iteration\": [], \"inside_a_pipeline\": true, \"round\": 0.0}}, \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
@@ -56,6 +56,13 @@
       "@@@STEP_LOG_LINE@request@          \"luci.buildbucket.parent_tracking\": false@@@",
       "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", @@@",
+      "@@@STEP_LOG_LINE@request@        \"properties\": {@@@",
+      "@@@STEP_LOG_LINE@request@          \"$pigweed/pipeline\": {@@@",
+      "@@@STEP_LOG_LINE@request@            \"builds_from_previous_iteration\": [], @@@",
+      "@@@STEP_LOG_LINE@request@            \"inside_a_pipeline\": true, @@@",
+      "@@@STEP_LOG_LINE@request@            \"round\": 0.0@@@",
+      "@@@STEP_LOG_LINE@request@          }@@@",
+      "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", @@@",
       "@@@STEP_LOG_LINE@request@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@request@          \"parentRunId\": \"fake-task-id\"@@@",
@@ -90,6 +97,13 @@
       "@@@STEP_LOG_LINE@request@          \"luci.buildbucket.parent_tracking\": false@@@",
       "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", @@@",
+      "@@@STEP_LOG_LINE@request@        \"properties\": {@@@",
+      "@@@STEP_LOG_LINE@request@          \"$pigweed/pipeline\": {@@@",
+      "@@@STEP_LOG_LINE@request@            \"builds_from_previous_iteration\": [], @@@",
+      "@@@STEP_LOG_LINE@request@            \"inside_a_pipeline\": true, @@@",
+      "@@@STEP_LOG_LINE@request@            \"round\": 0.0@@@",
+      "@@@STEP_LOG_LINE@request@          }@@@",
+      "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", @@@",
       "@@@STEP_LOG_LINE@request@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@request@          \"parentRunId\": \"fake-task-id\"@@@",
diff --git a/recipes/pipeline.expected/two_rounds.json b/recipes/pipeline.expected/two_rounds.json
index f9b3a26..becce31 100644
--- a/recipes/pipeline.expected/two_rounds.json
+++ b/recipes/pipeline.expected/two_rounds.json
@@ -15,7 +15,7 @@
     ],
     "infra_step": true,
     "name": "round 0.schedule",
-    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"a\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
+    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"a\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"properties\": {\"$pigweed/pipeline\": {\"builds_from_previous_iteration\": [], \"inside_a_pipeline\": true, \"round\": 0.0}}, \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
@@ -45,6 +45,13 @@
       "@@@STEP_LOG_LINE@request@          \"luci.buildbucket.parent_tracking\": false@@@",
       "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", @@@",
+      "@@@STEP_LOG_LINE@request@        \"properties\": {@@@",
+      "@@@STEP_LOG_LINE@request@          \"$pigweed/pipeline\": {@@@",
+      "@@@STEP_LOG_LINE@request@            \"builds_from_previous_iteration\": [], @@@",
+      "@@@STEP_LOG_LINE@request@            \"inside_a_pipeline\": true, @@@",
+      "@@@STEP_LOG_LINE@request@            \"round\": 0.0@@@",
+      "@@@STEP_LOG_LINE@request@          }@@@",
+      "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"requestId\": \"0-00000000-0000-0000-0000-000000001337\", @@@",
       "@@@STEP_LOG_LINE@request@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@request@          \"parentRunId\": \"fake-task-id\"@@@",
@@ -183,7 +190,7 @@
     ],
     "infra_step": true,
     "name": "round 1.schedule",
-    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"b\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
+    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"builder\": \"b\"}, \"experimental\": \"NO\", \"experiments\": {\"luci.buildbucket.parent_tracking\": false}, \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", \"properties\": {\"$pigweed/pipeline\": {\"builds_from_previous_iteration\": [1000.0], \"inside_a_pipeline\": true, \"round\": 1.0}}, \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"hide-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"parent_buildbucket_id\", \"value\": \"0\"}, {\"key\": \"skip-retry-in-gerrit\", \"value\": \"subbuild\"}, {\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
@@ -213,6 +220,15 @@
       "@@@STEP_LOG_LINE@request@          \"luci.buildbucket.parent_tracking\": false@@@",
       "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"fields\": \"builder,createTime,createdBy,critical,endTime,id,infra,input,number,output,startTime,status,updateTime\", @@@",
+      "@@@STEP_LOG_LINE@request@        \"properties\": {@@@",
+      "@@@STEP_LOG_LINE@request@          \"$pigweed/pipeline\": {@@@",
+      "@@@STEP_LOG_LINE@request@            \"builds_from_previous_iteration\": [@@@",
+      "@@@STEP_LOG_LINE@request@              1000.0@@@",
+      "@@@STEP_LOG_LINE@request@            ], @@@",
+      "@@@STEP_LOG_LINE@request@            \"inside_a_pipeline\": true, @@@",
+      "@@@STEP_LOG_LINE@request@            \"round\": 1.0@@@",
+      "@@@STEP_LOG_LINE@request@          }@@@",
+      "@@@STEP_LOG_LINE@request@        }, @@@",
       "@@@STEP_LOG_LINE@request@        \"requestId\": \"0-00000000-0000-0000-0000-00000000133a\", @@@",
       "@@@STEP_LOG_LINE@request@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@request@          \"parentRunId\": \"fake-task-id\"@@@",
diff --git a/recipes/pipeline.py b/recipes/pipeline.py
index 9bfc86e..c378dfb 100644
--- a/recipes/pipeline.py
+++ b/recipes/pipeline.py
@@ -33,6 +33,8 @@
 def RunSteps(api, props):
     """Launch sequences of builders."""
 
+    build_ids = []
+
     for i, round_property in enumerate(props.rounds):
         with api.step.nest(f'round {i}') as pres:
             builders = []
@@ -43,7 +45,19 @@
                 assert not builder_property.bucket
                 builders.append(builder_property.builder)
 
-            launched_builds = api.subbuild.launch(builders, pres)
+            extra_props = {
+                '$pigweed/pipeline': {
+                    'inside_a_pipeline': True,
+                    'round': i,
+                    'builds_from_previous_iteration': build_ids,
+                },
+            }
+
+            launched_builds = api.subbuild.launch(
+                builders, pres, extra_properties=extra_props
+            )
+            for builder, build in launched_builds.items():
+                pres.links[builder] = build.url
             build_ids = [x.build_id for x in launched_builds.values()]
             collected_builds = api.subbuild.collect(build_ids)