diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b671f00a3..1f5fae3d4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -238,7 +238,7 @@ jobs:
       - run: uv add --dev --python 3.10 "googleapis-common-protos==1.70.0"
       - run: uv add --python 3.10 "protobuf<4"
       - run: uv sync --all-extras
-      - run: cargo install --locked nexgen --version 0.2.2 --features advanced --force
+      - run: cargo install --locked nexgen --version 0.2.3 --features advanced --force
       - run: poe build-develop
       - run: poe gen-protos
       - name: Check generation unchanged
diff --git a/CHANGELOG.md b/CHANGELOG.md
index be3444177..a3ca40991 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,10 @@ to include examples, links to docs, or any other relevant information.
 
 ### Changed
 
+- System Nexus Signal-with-Start Workflow operations now use the typed
+  `WorkflowOutboundInterceptor.start_signal_with_start_workflow` interception point instead of
+  the generic `WorkflowOutboundInterceptor.start_nexus_operation` method.
+
 ### Deprecated
 
 ### :boom: Breaking Changes
diff --git a/pyproject.toml b/pyproject.toml
index d05d2f8c6..ec621ea69 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -187,8 +187,13 @@ exclude = [
   # Ignore generated code
   'temporalio/api',
   'temporalio/bridge/proto',
+  'temporalio/nexus/system/workflow_service',
 ]
 
+[[tool.mypy.overrides]]
+module = "temporalio.nexus.system.workflow_service.*"
+ignore_errors = true
+
 [tool.pydocstyle]
 convention = "google"
 # https://github.com/PyCQA/pydocstyle/issues/363#issuecomment-625563088
diff --git a/scripts/gen_nexus_system_api.py b/scripts/gen_nexus_system_api.py
index 82f40a8f0..b45616434 100644
--- a/scripts/gen_nexus_system_api.py
+++ b/scripts/gen_nexus_system_api.py
@@ -35,7 +35,7 @@
     / "v1"
     / "request_response.proto"
 )
-NEX_GEN_VERSION = "0.2.2"
+NEX_GEN_VERSION = "0.2.3"
 
 
 def nex_gen_command() -> list[str]:
@@ -131,6 +131,7 @@ def generate_nexus_system_api() -> None:
                 str(wit_path),
                 str(wit_deps_dir),
                 "--native-api",
+                "--system-nexus",
                 "--support-file",
                 str(python_support_path),
                 "--descriptors",
diff --git a/temporalio/bridge/Cargo.lock b/temporalio/bridge/Cargo.lock
index 745d3b358..72f89d746 100644
--- a/temporalio/bridge/Cargo.lock
+++ b/temporalio/bridge/Cargo.lock
@@ -156,6 +156,12 @@ version = "0.22.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
 
+[[package]]
+name = "base64"
+version = "0.23.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac07cdecf99051d9a5238b80f35af32cdeba5b336e55d957b318b50137e18da5"
+
 [[package]]
 name = "bindgen"
 version = "0.72.1"
@@ -539,7 +545,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
 dependencies = [
  "libc",
- "windows-sys 0.52.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -923,7 +929,7 @@ version = "0.1.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "96547c2556ec9d12fb1578c4eaf448b04993e7fb79cbaad930a656880a6bdfa0"
 dependencies = [
- "base64",
+ "base64 0.22.1",
  "bytes",
  "futures-channel",
  "futures-util",
@@ -1512,7 +1518,7 @@ version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e8edd1efdd8ab23ba9cb9ace3d9987a72663d5d7c9f74fa00b51d6213645cf6c"
 dependencies = [
- "base64",
+ "base64 0.22.1",
  "serde",
 ]
 
@@ -1934,7 +1940,7 @@ dependencies = [
  "once_cell",
  "socket2",
  "tracing",
- "windows-sys 0.52.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -2068,7 +2074,7 @@ version = "0.13.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "219c5811de6525e5416c7d5d53bb656d3afdbc6c5af816e0802bcfa42dbdc1c3"
 dependencies = [
- "base64",
+ "base64 0.22.1",
  "bytes",
  "futures-channel",
  "futures-core",
@@ -2154,7 +2160,7 @@ dependencies = [
  "errno",
  "libc",
  "linux-raw-sys",
- "windows-sys 0.52.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -2213,7 +2219,7 @@ dependencies = [
  "security-framework",
  "security-framework-sys",
  "webpki-root-certs",
- "windows-sys 0.52.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -2554,7 +2560,7 @@ dependencies = [
  "getrandom 0.4.3",
  "once_cell",
  "rustix",
- "windows-sys 0.52.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -2587,7 +2593,7 @@ dependencies = [
  "anyhow",
  "async-trait",
  "backon",
- "base64",
+ "base64 0.23.1",
  "bon",
  "bytes",
  "derive_more",
@@ -2692,7 +2698,7 @@ name = "temporalio-protos"
 version = "0.7.0"
 dependencies = [
  "anyhow",
- "base64",
+ "base64 0.23.1",
  "derive_more",
  "http",
  "pbjson",
@@ -2926,7 +2932,7 @@ checksum = "ac2a5518c70fa84342385732db33fb3f44bc4cc748936eb5833d2df34d6445ef"
 dependencies = [
  "async-trait",
  "axum",
- "base64",
+ "base64 0.22.1",
  "bytes",
  "flate2",
  "h2",
@@ -3381,7 +3387,7 @@ version = "0.1.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c2a7b1c03c876122aa43f3020e6c3c3ee5c05081c9a00739faf7503aeba10d22"
 dependencies = [
- "windows-sys 0.52.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
diff --git a/temporalio/bridge/proto/workflow_commands/workflow_commands_pb2.py b/temporalio/bridge/proto/workflow_commands/workflow_commands_pb2.py
index 64fa8a255..0cdc02c6b 100644
--- a/temporalio/bridge/proto/workflow_commands/workflow_commands_pb2.py
+++ b/temporalio/bridge/proto/workflow_commands/workflow_commands_pb2.py
@@ -45,7 +45,7 @@
 )
 
 DESCRIPTOR = _descriptor_pool.Default().AddSerializedFile(
-    b'\n;temporal/sdk/core/workflow_commands/workflow_commands.proto\x12\x19\x63oresdk.workflow_commands\x1a\x1egoogle/protobuf/duration.proto\x1a\x1fgoogle/protobuf/timestamp.proto\x1a\x1bgoogle/protobuf/empty.proto\x1a$temporal/api/common/v1/message.proto\x1a$temporal/api/enums/v1/workflow.proto\x1a%temporal/api/failure/v1/message.proto\x1a\'temporal/api/sdk/v1/user_metadata.proto\x1a,temporal/api/sdk/v1/event_group_marker.proto\x1a\x35temporal/sdk/core/child_workflow/child_workflow.proto\x1a#temporal/sdk/core/nexus/nexus.proto\x1a%temporal/sdk/core/common/common.proto"\xa9\x10\n\x0fWorkflowCommand\x12\x38\n\ruser_metadata\x18\x64 \x01(\x0b\x32!.temporal.api.sdk.v1.UserMetadata\x12\x42\n\x13\x65vent_group_markers\x18\x65 \x03(\x0b\x32%.temporal.api.sdk.v1.EventGroupMarker\x12<\n\x0bstart_timer\x18\x01 \x01(\x0b\x32%.coresdk.workflow_commands.StartTimerH\x00\x12H\n\x11schedule_activity\x18\x02 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\x01(\x0b\x32\x16.google.protobuf.EmptyH\x00\x12\x34\n\x08rejected\x18\x03 \x01(\x0b\x32 .temporal.api.failure.v1.FailureH\x00\x12\x34\n\tcompleted\x18\x04 \x01(\x0b\x32\x1f.temporal.api.common.v1.PayloadH\x00\x42\n\n\x08response"\x9a\x04\n\x16ScheduleNexusOperation\x12\x0b\n\x03seq\x18\x01 \x01(\r\x12\x10\n\x08\x65ndpoint\x18\x02 \x01(\t\x12\x0f\n\x07service\x18\x03 \x01(\t\x12\x11\n\toperation\x18\x04 \x01(\t\x12.\n\x05input\x18\x05 \x01(\x0b\x32\x1f.temporal.api.common.v1.Payload\x12<\n\x19schedule_to_close_timeout\x18\x06 \x01(\x0b\x32\x19.google.protobuf.Duration\x12X\n\x0cnexus_header\x18\x07 \x03(\x0b\x32\x42.coresdk.workflow_commands.ScheduleNexusOperation.NexusHeaderEntry\x12H\n\x11\x63\x61ncellation_type\x18\x08 \x01(\x0e\x32-.coresdk.nexus.NexusOperationCancellationType\x12<\n\x19schedule_to_start_timeout\x18\t \x01(\x0b\x32\x19.google.protobuf.Duration\x12\x39\n\x16start_to_close_timeout\x18\n \x01(\x0b\x32\x19.google.protobuf.Duration\x1a\x32\n\x10NexusHeaderEntry\x12\x0b\n\x03key\x18\x01 \x01(\t\x12\r\n\x05value\x18\x02 \x01(\t:\x02\x38\x01"*\n\x1bRequestCancelNexusOperation\x12\x0b\n\x03seq\x18\x01 \x01(\r*X\n\x18\x41\x63tivityCancellationType\x12\x0e\n\nTRY_CANCEL\x10\x00\x12\x1f\n\x1bWAIT_CANCELLATION_COMPLETED\x10\x01\x12\x0b\n\x07\x41\x42\x41NDON\x10\x02\x42\x36\xea\x02\x33Temporalio::Internal::Bridge::Api::WorkflowCommandsb\x06proto3'
 )
 
 _ACTIVITYCANCELLATIONTYPE = DESCRIPTOR.enum_types_by_name["ActivityCancellationType"]
@@ -484,8 +484,8 @@
     _SIGNALEXTERNALWORKFLOWEXECUTION_HEADERSENTRY._serialized_options = b"8\001"
     _SCHEDULENEXUSOPERATION_NEXUSHEADERENTRY._options = None
     _SCHEDULENEXUSOPERATION_NEXUSHEADERENTRY._serialized_options = b"8\001"
-    _ACTIVITYCANCELLATIONTYPE._serialized_start = 8633
-    _ACTIVITYCANCELLATIONTYPE._serialized_end = 8721
+    _ACTIVITYCANCELLATIONTYPE._serialized_start = 8672
+    _ACTIVITYCANCELLATIONTYPE._serialized_end = 8760
     _WORKFLOWCOMMAND._serialized_start = 518
     _WORKFLOWCOMMAND._serialized_end = 2607
     _STARTTIMER._serialized_start = 2609
@@ -497,57 +497,57 @@
     _SCHEDULEACTIVITY_HEADERSENTRY._serialized_start = 3468
     _SCHEDULEACTIVITY_HEADERSENTRY._serialized_end = 3547
     _SCHEDULELOCALACTIVITY._serialized_start = 3550
-    _SCHEDULELOCALACTIVITY._serialized_end = 4300
+    _SCHEDULELOCALACTIVITY._serialized_end = 4339
     _SCHEDULELOCALACTIVITY_HEADERSENTRY._serialized_start = 3468
     _SCHEDULELOCALACTIVITY_HEADERSENTRY._serialized_end = 3547
-    _REQUESTCANCELACTIVITY._serialized_start = 4302
-    _REQUESTCANCELACTIVITY._serialized_end = 4338
-    _REQUESTCANCELLOCALACTIVITY._serialized_start = 4340
-    _REQUESTCANCELLOCALACTIVITY._serialized_end = 4381
-    _QUERYRESULT._serialized_start = 4384
-    _QUERYRESULT._serialized_end = 4540
-    _QUERYSUCCESS._serialized_start = 4542
-    _QUERYSUCCESS._serialized_end = 4607
-    _COMPLETEWORKFLOWEXECUTION._serialized_start = 4609
-    _COMPLETEWORKFLOWEXECUTION._serialized_end = 4685
-    _FAILWORKFLOWEXECUTION._serialized_start = 4687
-    _FAILWORKFLOWEXECUTION._serialized_end = 4761
-    _CONTINUEASNEWWORKFLOWEXECUTION._serialized_start = 4764
-    _CONTINUEASNEWWORKFLOWEXECUTION._serialized_end = 5678
-    _CONTINUEASNEWWORKFLOWEXECUTION_MEMOENTRY._serialized_start = 5521
-    _CONTINUEASNEWWORKFLOWEXECUTION_MEMOENTRY._serialized_end = 5597
+    _REQUESTCANCELACTIVITY._serialized_start = 4341
+    _REQUESTCANCELACTIVITY._serialized_end = 4377
+    _REQUESTCANCELLOCALACTIVITY._serialized_start = 4379
+    _REQUESTCANCELLOCALACTIVITY._serialized_end = 4420
+    _QUERYRESULT._serialized_start = 4423
+    _QUERYRESULT._serialized_end = 4579
+    _QUERYSUCCESS._serialized_start = 4581
+    _QUERYSUCCESS._serialized_end = 4646
+    _COMPLETEWORKFLOWEXECUTION._serialized_start = 4648
+    _COMPLETEWORKFLOWEXECUTION._serialized_end = 4724
+    _FAILWORKFLOWEXECUTION._serialized_start = 4726
+    _FAILWORKFLOWEXECUTION._serialized_end = 4800
+    _CONTINUEASNEWWORKFLOWEXECUTION._serialized_start = 4803
+    _CONTINUEASNEWWORKFLOWEXECUTION._serialized_end = 5717
+    _CONTINUEASNEWWORKFLOWEXECUTION_MEMOENTRY._serialized_start = 5560
+    _CONTINUEASNEWWORKFLOWEXECUTION_MEMOENTRY._serialized_end = 5636
     _CONTINUEASNEWWORKFLOWEXECUTION_HEADERSENTRY._serialized_start = 3468
     _CONTINUEASNEWWORKFLOWEXECUTION_HEADERSENTRY._serialized_end = 3547
-    _CANCELWORKFLOWEXECUTION._serialized_start = 5680
-    _CANCELWORKFLOWEXECUTION._serialized_end = 5756
-    _SETPATCHMARKER._serialized_start = 5758
-    _SETPATCHMARKER._serialized_end = 5812
-    _STARTCHILDWORKFLOWEXECUTION._serialized_start = 5815
-    _STARTCHILDWORKFLOWEXECUTION._serialized_end = 6989
+    _CANCELWORKFLOWEXECUTION._serialized_start = 5719
+    _CANCELWORKFLOWEXECUTION._serialized_end = 5795
+    _SETPATCHMARKER._serialized_start = 5797
+    _SETPATCHMARKER._serialized_end = 5851
+    _STARTCHILDWORKFLOWEXECUTION._serialized_start = 5854
+    _STARTCHILDWORKFLOWEXECUTION._serialized_end = 7028
     _STARTCHILDWORKFLOWEXECUTION_HEADERSENTRY._serialized_start = 3468
     _STARTCHILDWORKFLOWEXECUTION_HEADERSENTRY._serialized_end = 3547
-    _STARTCHILDWORKFLOWEXECUTION_MEMOENTRY._serialized_start = 5521
-    _STARTCHILDWORKFLOWEXECUTION_MEMOENTRY._serialized_end = 5597
-    _CANCELCHILDWORKFLOWEXECUTION._serialized_start = 6991
-    _CANCELCHILDWORKFLOWEXECUTION._serialized_end = 7065
-    _REQUESTCANCELEXTERNALWORKFLOWEXECUTION._serialized_start = 7068
-    _REQUESTCANCELEXTERNALWORKFLOWEXECUTION._serialized_end = 7210
-    _SIGNALEXTERNALWORKFLOWEXECUTION._serialized_start = 7213
-    _SIGNALEXTERNALWORKFLOWEXECUTION._serialized_end = 7612
+    _STARTCHILDWORKFLOWEXECUTION_MEMOENTRY._serialized_start = 5560
+    _STARTCHILDWORKFLOWEXECUTION_MEMOENTRY._serialized_end = 5636
+    _CANCELCHILDWORKFLOWEXECUTION._serialized_start = 7030
+    _CANCELCHILDWORKFLOWEXECUTION._serialized_end = 7104
+    _REQUESTCANCELEXTERNALWORKFLOWEXECUTION._serialized_start = 7107
+    _REQUESTCANCELEXTERNALWORKFLOWEXECUTION._serialized_end = 7249
+    _SIGNALEXTERNALWORKFLOWEXECUTION._serialized_start = 7252
+    _SIGNALEXTERNALWORKFLOWEXECUTION._serialized_end = 7651
     _SIGNALEXTERNALWORKFLOWEXECUTION_HEADERSENTRY._serialized_start = 3468
     _SIGNALEXTERNALWORKFLOWEXECUTION_HEADERSENTRY._serialized_end = 3547
-    _CANCELSIGNALWORKFLOW._serialized_start = 7614
-    _CANCELSIGNALWORKFLOW._serialized_end = 7649
-    _UPSERTWORKFLOWSEARCHATTRIBUTES._serialized_start = 7651
-    _UPSERTWORKFLOWSEARCHATTRIBUTES._serialized_end = 7752
-    _MODIFYWORKFLOWPROPERTIES._serialized_start = 7754
-    _MODIFYWORKFLOWPROPERTIES._serialized_end = 7833
-    _UPDATERESPONSE._serialized_start = 7836
-    _UPDATERESPONSE._serialized_end = 8046
-    _SCHEDULENEXUSOPERATION._serialized_start = 8049
-    _SCHEDULENEXUSOPERATION._serialized_end = 8587
-    _SCHEDULENEXUSOPERATION_NEXUSHEADERENTRY._serialized_start = 8537
-    _SCHEDULENEXUSOPERATION_NEXUSHEADERENTRY._serialized_end = 8587
-    _REQUESTCANCELNEXUSOPERATION._serialized_start = 8589
-    _REQUESTCANCELNEXUSOPERATION._serialized_end = 8631
+    _CANCELSIGNALWORKFLOW._serialized_start = 7653
+    _CANCELSIGNALWORKFLOW._serialized_end = 7688
+    _UPSERTWORKFLOWSEARCHATTRIBUTES._serialized_start = 7690
+    _UPSERTWORKFLOWSEARCHATTRIBUTES._serialized_end = 7791
+    _MODIFYWORKFLOWPROPERTIES._serialized_start = 7793
+    _MODIFYWORKFLOWPROPERTIES._serialized_end = 7872
+    _UPDATERESPONSE._serialized_start = 7875
+    _UPDATERESPONSE._serialized_end = 8085
+    _SCHEDULENEXUSOPERATION._serialized_start = 8088
+    _SCHEDULENEXUSOPERATION._serialized_end = 8626
+    _SCHEDULENEXUSOPERATION_NEXUSHEADERENTRY._serialized_start = 8576
+    _SCHEDULENEXUSOPERATION_NEXUSHEADERENTRY._serialized_end = 8626
+    _REQUESTCANCELNEXUSOPERATION._serialized_start = 8628
+    _REQUESTCANCELNEXUSOPERATION._serialized_end = 8670
 # @@protoc_insertion_point(module_scope)
diff --git a/temporalio/bridge/proto/workflow_commands/workflow_commands_pb2.pyi b/temporalio/bridge/proto/workflow_commands/workflow_commands_pb2.pyi
index 510643132..ad4a5f487 100644
--- a/temporalio/bridge/proto/workflow_commands/workflow_commands_pb2.pyi
+++ b/temporalio/bridge/proto/workflow_commands/workflow_commands_pb2.pyi
@@ -620,6 +620,7 @@ class ScheduleLocalActivity(google.protobuf.message.Message):
     RETRY_POLICY_FIELD_NUMBER: builtins.int
     LOCAL_RETRY_THRESHOLD_FIELD_NUMBER: builtins.int
     CANCELLATION_TYPE_FIELD_NUMBER: builtins.int
+    INCLUDE_ARGUMENTS_INTO_MARKER_FIELD_NUMBER: builtins.int
     seq: builtins.int
     """Lang's incremental sequence number, used as the operation identifier"""
     activity_id: builtins.str
@@ -684,6 +685,11 @@ class ScheduleLocalActivity(google.protobuf.message.Message):
     confirmed. Lang should default this to `WAIT_CANCELLATION_COMPLETED`, even though proto
     will default to `TRY_CANCEL` automatically.
     """
+    include_arguments_into_marker: builtins.bool
+    """If set, the local activity arguments will be included in the resulting marker under the
+    `input` key. This is disabled by default to avoid increasing history size unless the lang
+    SDK explicitly chooses to expose it.
+    """
     def __init__(
         self,
         *,
@@ -706,6 +712,7 @@ class ScheduleLocalActivity(google.protobuf.message.Message):
         retry_policy: temporalio.api.common.v1.message_pb2.RetryPolicy | None = ...,
         local_retry_threshold: google.protobuf.duration_pb2.Duration | None = ...,
         cancellation_type: global___ActivityCancellationType.ValueType = ...,
+        include_arguments_into_marker: builtins.bool = ...,
     ) -> None: ...
     def HasField(
         self,
@@ -739,6 +746,8 @@ class ScheduleLocalActivity(google.protobuf.message.Message):
             b"cancellation_type",
             "headers",
             b"headers",
+            "include_arguments_into_marker",
+            b"include_arguments_into_marker",
             "local_retry_threshold",
             b"local_retry_threshold",
             "original_schedule_time",
diff --git a/temporalio/bridge/sdk-core b/temporalio/bridge/sdk-core
index b860e3f14..85b71d7ec 160000
--- a/temporalio/bridge/sdk-core
+++ b/temporalio/bridge/sdk-core
@@ -1 +1 @@
-Subproject commit b860e3f14f68af64bd4d0e372b3c78b2ce9ecff1
+Subproject commit 85b71d7ecd4f2bf677fa1cee17f3fbc1ab10f1b9
diff --git a/temporalio/bridge/src/envconfig.rs b/temporalio/bridge/src/envconfig.rs
index 7ce2f4664..0b21d1987 100644
--- a/temporalio/bridge/src/envconfig.rs
+++ b/temporalio/bridge/src/envconfig.rs
@@ -19,6 +19,11 @@ fn data_source_to_dict(py: Python, ds: &DataSource) -> PyResult<Py<PyAny>> {
     match ds {
         DataSource::Path(p) => dict.set_item("path", p)?,
         DataSource::Data(d) => dict.set_item("data", PyBytes::new(py, d))?,
+        _ => {
+            return Err(PyRuntimeError::new_err(
+                "unsupported configuration data source",
+            ))
+        }
     };
     Ok(dict.into())
 }
diff --git a/temporalio/bridge/src/worker.rs b/temporalio/bridge/src/worker.rs
index 321dc6560..e74698e94 100644
--- a/temporalio/bridge/src/worker.rs
+++ b/temporalio/bridge/src/worker.rs
@@ -900,10 +900,10 @@ fn convert_versioning_strategy(
         WorkerVersioningStrategy::DeploymentBased(options) => {
             temporalio_sdk_core::WorkerVersioningStrategy::WorkerDeploymentBased(
                 temporalio_common::worker::WorkerDeploymentOptions::new(
-                    temporalio_common::worker::WorkerDeploymentVersion {
-                        deployment_name: options.version.deployment_name,
-                        build_id: options.version.build_id,
-                    },
+                    temporalio_common::worker::WorkerDeploymentVersion::builder()
+                        .deployment_name(options.version.deployment_name)
+                        .build_id(options.version.build_id)
+                        .build(),
                 )
                 .use_worker_versioning(options.use_worker_versioning)
                 .maybe_default_versioning_behavior(if options.use_worker_versioning {
diff --git a/temporalio/contrib/opentelemetry/_interceptor.py b/temporalio/contrib/opentelemetry/_interceptor.py
index eb22f8be6..6dca4596e 100644
--- a/temporalio/contrib/opentelemetry/_interceptor.py
+++ b/temporalio/contrib/opentelemetry/_interceptor.py
@@ -33,6 +33,7 @@
 import temporalio.client
 import temporalio.converter
 import temporalio.exceptions
+import temporalio.nexus.system.workflow_service.models
 import temporalio.worker
 import temporalio.workflow
 from temporalio.exceptions import ApplicationError, ApplicationErrorCategory
@@ -433,6 +434,10 @@ class _InputWithStringHeaders(Protocol):
     headers: Mapping[str, str] | None
 
 
+class _InputWithModelHeaders(Protocol):
+    headers: Mapping[str, Any] | None
+
+
 class _InputWithOperationContext(Generic[_ContextT], Protocol):
     ctx: _ContextT
 
@@ -684,6 +689,18 @@ def _context_carrier_to_headers(
             }
         return headers
 
+    def _context_carrier_to_model_headers(
+        self,
+        carrier: _CarrierDict,
+        headers: Mapping[str, Any] | None,
+    ) -> Mapping[str, Any]:
+        if carrier:
+            return {
+                **(headers or {}),
+                self.header_key: carrier,
+            }
+        return headers or {}
+
     def _completed_span(
         self,
         span_name: str,
@@ -691,6 +708,7 @@ def _completed_span(
         link_context_carrier: _CarrierDict | None = None,
         add_to_outbound: _InputWithHeaders | None = None,
         add_to_outbound_str: _InputWithStringHeaders | None = None,
+        add_to_outbound_model: _InputWithModelHeaders | None = None,
         new_span_even_on_replay: bool = False,
         additional_attributes: opentelemetry.util.types.Attributes = None,
         exception: Exception | None = None,
@@ -742,6 +760,11 @@ def _completed_span(
                     updated_context_carrier, add_to_outbound_str.headers
                 )
 
+            if add_to_outbound_model:
+                add_to_outbound_model.headers = self._context_carrier_to_model_headers(
+                    updated_context_carrier, add_to_outbound_model.headers
+                )
+
     def _set_on_context(
         self, context: opentelemetry.context.Context
     ) -> opentelemetry.context.Context:
@@ -830,6 +853,19 @@ async def start_nexus_operation(
 
         return await super().start_nexus_operation(input)
 
+    async def start_signal_with_start_workflow(
+        self,
+        request: temporalio.nexus.system.workflow_service.models.SignalWithStartWorkflowRequest,
+    ) -> temporalio.workflow.NexusOperationHandle[
+        temporalio.nexus.system.workflow_service.models.SignalWithStartWorkflowResponse
+    ]:
+        self.root._completed_span(
+            "SignalWithStartWorkflow",
+            kind=opentelemetry.trace.SpanKind.CLIENT,
+            add_to_outbound_model=request,
+        )
+        return await super().start_signal_with_start_workflow(request)
+
 
 def _carrier_to_nexus_headers(
     carrier: _CarrierDict, initial: Mapping[str, str] | None = None
diff --git a/temporalio/contrib/opentelemetry/_otel_interceptor.py b/temporalio/contrib/opentelemetry/_otel_interceptor.py
index c120fcd03..ff07f0f1d 100644
--- a/temporalio/contrib/opentelemetry/_otel_interceptor.py
+++ b/temporalio/contrib/opentelemetry/_otel_interceptor.py
@@ -32,6 +32,7 @@
 import temporalio.api.common.v1
 import temporalio.client
 import temporalio.converter
+import temporalio.nexus.system.workflow_service.models
 import temporalio.worker
 import temporalio.workflow
 from temporalio.contrib.opentelemetry._tracer_provider import (
@@ -600,3 +601,15 @@ async def start_nexus_operation(
         ):
             input.headers = _context_to_nexus_headers(input.headers or {})
             return await super().start_nexus_operation(input)
+
+    async def start_signal_with_start_workflow(
+        self,
+        request: temporalio.nexus.system.workflow_service.models.SignalWithStartWorkflowRequest,
+    ) -> temporalio.workflow.NexusOperationHandle[
+        temporalio.nexus.system.workflow_service.models.SignalWithStartWorkflowResponse
+    ]:
+        with self._workflow_maybe_span(
+            "SignalWithStartWorkflow", kind=opentelemetry.trace.SpanKind.CLIENT
+        ):
+            request.headers = _context_to_headers(request.headers or {})
+            return await super().start_signal_with_start_workflow(request)
diff --git a/temporalio/nexus/system/workflow_service/__init__.py b/temporalio/nexus/system/workflow_service/__init__.py
index 49f7e4c12..3d7dac503 100644
--- a/temporalio/nexus/system/workflow_service/__init__.py
+++ b/temporalio/nexus/system/workflow_service/__init__.py
@@ -1,4 +1,4 @@
-# Generated by nexgen v0.2.2. DO NOT EDIT!
+# Generated by nexgen v0.2.3. DO NOT EDIT!
 
 from __future__ import annotations
 
diff --git a/temporalio/nexus/system/workflow_service/_support/__init__.py b/temporalio/nexus/system/workflow_service/_support/__init__.py
index a07fc7273..f56c1cca7 100644
--- a/temporalio/nexus/system/workflow_service/_support/__init__.py
+++ b/temporalio/nexus/system/workflow_service/_support/__init__.py
@@ -1,4 +1,4 @@
-# Generated by nexgen v0.2.2. DO NOT EDIT!
+# Generated by nexgen v0.2.3. DO NOT EDIT!
 
 from __future__ import annotations
 
diff --git a/temporalio/nexus/system/workflow_service/_system_nexus_interceptor.py b/temporalio/nexus/system/workflow_service/_system_nexus_interceptor.py
new file mode 100644
index 000000000..2f5e54ee2
--- /dev/null
+++ b/temporalio/nexus/system/workflow_service/_system_nexus_interceptor.py
@@ -0,0 +1,96 @@
+# Generated by nexgen v0.2.3. DO NOT EDIT!
+
+from __future__ import annotations
+
+import abc
+import typing
+
+from temporalio.nexus.system import TEMPORAL_SYSTEM_ENDPOINT
+
+from . import models
+
+if typing.TYPE_CHECKING:
+    import temporalio.workflow
+    from temporalio.worker._interceptor import StartNexusOperationInput
+
+
+__all__ = [
+    "_start_system_nexus_operation",
+    "_SystemNexusWorkflowOutboundInterceptorBase",
+    "_SystemNexusWorkflowOutboundInterceptorTerminal",
+]
+
+
+_InputT = typing.TypeVar("_InputT")
+_OutputT = typing.TypeVar("_OutputT")
+
+
+async def _start_system_nexus_operation(
+    interceptor: _SystemNexusWorkflowOutboundInterceptorBase,
+    input: StartNexusOperationInput[_InputT, _OutputT],
+) -> temporalio.workflow.NexusOperationHandle[_OutputT]:
+    if (
+        input.service == "temporal.api.workflowservice.v1.WorkflowService"
+        and input.operation_name == "SignalWithStartWorkflowExecution"
+    ):
+        typed_input = typing.cast(
+            "StartNexusOperationInput[models.SignalWithStartWorkflowRequest, models.SignalWithStartWorkflowResponse]",
+            input,
+        )
+        # The dispatch check above establishes that this operation's response type is _OutputT.
+        return typing.cast(
+            "temporalio.workflow.NexusOperationHandle[_OutputT]",
+            await interceptor.start_signal_with_start_workflow(typed_input.input),
+        )
+    raise ValueError(
+        f"unsupported System Nexus operation: {input.service}/{input.operation_name}"
+    )
+
+
+class _SystemNexusWorkflowOutboundInterceptorBase(abc.ABC):
+    @abc.abstractmethod
+    def _next_system_nexus_interceptor(
+        self,
+    ) -> _SystemNexusWorkflowOutboundInterceptorBase: ...
+
+    async def start_signal_with_start_workflow(
+        self, request: models.SignalWithStartWorkflowRequest
+    ) -> temporalio.workflow.NexusOperationHandle[
+        models.SignalWithStartWorkflowResponse
+    ]:
+        """Intercept the SignalWithStartWorkflow operation."""
+        return await self._next_system_nexus_interceptor().start_signal_with_start_workflow(
+            request
+        )
+
+
+class _SystemNexusWorkflowOutboundInterceptorTerminal(abc.ABC):
+    @abc.abstractmethod
+    async def _outbound_start_nexus_operation(
+        self,
+        input: StartNexusOperationInput[_InputT, _OutputT],
+    ) -> temporalio.workflow.NexusOperationHandle[_OutputT]: ...
+
+    async def start_signal_with_start_workflow(
+        self, request: models.SignalWithStartWorkflowRequest
+    ) -> temporalio.workflow.NexusOperationHandle[
+        models.SignalWithStartWorkflowResponse
+    ]:
+        from temporalio.worker._interceptor import StartNexusOperationInput
+        from temporalio.workflow import NexusOperationCancellationType
+
+        return await self._outbound_start_nexus_operation(
+            StartNexusOperationInput(
+                endpoint=TEMPORAL_SYSTEM_ENDPOINT,
+                service="temporal.api.workflowservice.v1.WorkflowService",
+                operation="SignalWithStartWorkflowExecution",
+                input=request,
+                output_type=models.SignalWithStartWorkflowResponse,
+                schedule_to_close_timeout=None,
+                schedule_to_start_timeout=None,
+                start_to_close_timeout=None,
+                cancellation_type=NexusOperationCancellationType.WAIT_COMPLETED,
+                headers=None,
+                summary=None,
+            )
+        )
diff --git a/temporalio/nexus/system/workflow_service/models.py b/temporalio/nexus/system/workflow_service/models.py
index 5361e77b6..7e0c9f2eb 100644
--- a/temporalio/nexus/system/workflow_service/models.py
+++ b/temporalio/nexus/system/workflow_service/models.py
@@ -1,4 +1,4 @@
-# Generated by nexgen v0.2.2. DO NOT EDIT!
+# Generated by nexgen v0.2.3. DO NOT EDIT!
 
 from __future__ import annotations
 
@@ -46,9 +46,41 @@
 )
 
 
+@dataclasses.dataclass(slots=True, kw_only=True)
+class SignalWithStartWorkflowRequest:
+    """
+    .. warning::
+        This API is experimental and subject to change.
+    """
+
+    workflow: str | collections.abc.Callable[..., collections.abc.Awaitable[object]]
+    args: list[typing.Any] | None = None
+    id: str
+    task_queue: str
+    signal: str | collections.abc.Callable[..., None | collections.abc.Awaitable[None]]
+    signal_args: list[typing.Any] | None = None
+    execution_timeout: datetime.timedelta | None = None
+    run_timeout: datetime.timedelta | None = None
+    task_timeout: datetime.timedelta | None = None
+    id_reuse_policy: temporalio.common.WorkflowIDReusePolicy = (
+        temporalio.common.WorkflowIDReusePolicy.ALLOW_DUPLICATE
+    )
+    id_conflict_policy: temporalio.common.WorkflowIDConflictPolicy | None = None
+    retry_policy: temporalio.common.RetryPolicy | None = None
+    cron_schedule: str | None = None
+    memo: collections.abc.Mapping[str, typing.Any] | None = None
+    search_attributes: temporalio.common.TypedSearchAttributes | None = None
+    priority: temporalio.common.Priority | None = None
+    versioning_override: temporalio.common.VersioningOverride | None = None
+    start_delay: datetime.timedelta | None = None
+    user_metadata: UserMetadata | None = None
+    namespace: str = dataclasses.field(default_factory=workflow_namespace)
+    headers: collections.abc.Mapping[str, typing.Any] | None = None
+
+
 class _SignalWithStartWorkflowRequestTransferTypeConverter(
     temporalio.converter.TransferTypeConverter[
-        "SignalWithStartWorkflowRequest",
+        SignalWithStartWorkflowRequest,
         temporalio.api.workflowservice.v1.request_response_pb2.SignalWithStartWorkflowExecutionRequest,
     ]
 ):
@@ -63,8 +95,8 @@ class _SignalWithStartWorkflowRequestTransferTypeConverter(
     def from_transfer_type(
         self,
         value: temporalio.api.workflowservice.v1.request_response_pb2.SignalWithStartWorkflowExecutionRequest,
-        type_hint: type["SignalWithStartWorkflowRequest"],
-    ) -> "SignalWithStartWorkflowRequest":
+        type_hint: type[SignalWithStartWorkflowRequest],
+    ) -> SignalWithStartWorkflowRequest:
         if not value.HasField("workflow_type"):
             raise ValueError(
                 "missing required field SignalWithStartWorkflowRequest.workflow"
@@ -142,7 +174,7 @@ def from_transfer_type(
     @typing_extensions.override
     def to_transfer_type(
         self,
-        value: "SignalWithStartWorkflowRequest",
+        value: SignalWithStartWorkflowRequest,
     ) -> temporalio.api.workflowservice.v1.request_response_pb2.SignalWithStartWorkflowExecutionRequest:
         message = temporalio.api.workflowservice.v1.request_response_pb2.SignalWithStartWorkflowExecutionRequest()
         message.workflow_type.CopyFrom(workflow_type_to_proto(value.workflow))
@@ -200,44 +232,20 @@ def to_transfer_type(
         return message
 
 
-@temporalio.converter.transfer_type_convertible(
+_ = temporalio.converter.transfer_type_convertible(
     _SignalWithStartWorkflowRequestTransferTypeConverter
-)
-@dataclasses.dataclass(slots=True, kw_only=True)
-class SignalWithStartWorkflowRequest:
-    """
-    .. warning::
-        This API is experimental and subject to change.
-    """
+)(SignalWithStartWorkflowRequest)
 
-    workflow: str | collections.abc.Callable[..., collections.abc.Awaitable[object]]
-    args: list[typing.Any] | None = None
-    id: str
-    task_queue: str
-    signal: str | collections.abc.Callable[..., None | collections.abc.Awaitable[None]]
-    signal_args: list[typing.Any] | None = None
-    execution_timeout: datetime.timedelta | None = None
-    run_timeout: datetime.timedelta | None = None
-    task_timeout: datetime.timedelta | None = None
-    id_reuse_policy: temporalio.common.WorkflowIDReusePolicy = (
-        temporalio.common.WorkflowIDReusePolicy.ALLOW_DUPLICATE
-    )
-    id_conflict_policy: temporalio.common.WorkflowIDConflictPolicy | None = None
-    retry_policy: temporalio.common.RetryPolicy | None = None
-    cron_schedule: str | None = None
-    memo: collections.abc.Mapping[str, typing.Any] | None = None
-    search_attributes: temporalio.common.TypedSearchAttributes | None = None
-    priority: temporalio.common.Priority | None = None
-    versioning_override: temporalio.common.VersioningOverride | None = None
-    start_delay: datetime.timedelta | None = None
-    user_metadata: UserMetadata | None = None
-    namespace: str = dataclasses.field(default_factory=workflow_namespace)
-    headers: collections.abc.Mapping[str, typing.Any] | None = None
+
+@dataclasses.dataclass(slots=True)
+class UserMetadata:
+    static_summary: typing.Any | None = None
+    static_details: typing.Any | None = None
 
 
 class _UserMetadataTransferTypeConverter(
     temporalio.converter.TransferTypeConverter[
-        "UserMetadata", temporalio.api.sdk.v1.user_metadata_pb2.UserMetadata
+        UserMetadata, temporalio.api.sdk.v1.user_metadata_pb2.UserMetadata
     ]
 ):
     transfer_type: type[temporalio.api.sdk.v1.user_metadata_pb2.UserMetadata] | None = (
@@ -248,8 +256,8 @@ class _UserMetadataTransferTypeConverter(
     def from_transfer_type(
         self,
         value: temporalio.api.sdk.v1.user_metadata_pb2.UserMetadata,
-        type_hint: type["UserMetadata"],
-    ) -> "UserMetadata":
+        type_hint: type[UserMetadata],
+    ) -> UserMetadata:
         return UserMetadata(
             static_summary=payload_from_proto(value.summary)
             if value.HasField("summary")
@@ -262,7 +270,7 @@ def from_transfer_type(
     @typing_extensions.override
     def to_transfer_type(
         self,
-        value: "UserMetadata",
+        value: UserMetadata,
     ) -> temporalio.api.sdk.v1.user_metadata_pb2.UserMetadata:
         message = temporalio.api.sdk.v1.user_metadata_pb2.UserMetadata()
         if value.static_summary is not None:
@@ -272,16 +280,25 @@ def to_transfer_type(
         return message
 
 
-@temporalio.converter.transfer_type_convertible(_UserMetadataTransferTypeConverter)
+_ = temporalio.converter.transfer_type_convertible(_UserMetadataTransferTypeConverter)(
+    UserMetadata
+)
+
+
 @dataclasses.dataclass(slots=True)
-class UserMetadata:
-    static_summary: typing.Any | None = None
-    static_details: typing.Any | None = None
+class SignalWithStartWorkflowResponse:
+    """
+    .. warning::
+        This API is experimental and subject to change.
+    """
+
+    run_id: str | None = None
+    started: bool | None = None
 
 
 class _SignalWithStartWorkflowResponseTransferTypeConverter(
     temporalio.converter.TransferTypeConverter[
-        "SignalWithStartWorkflowResponse",
+        SignalWithStartWorkflowResponse,
         temporalio.api.workflowservice.v1.request_response_pb2.SignalWithStartWorkflowExecutionResponse,
     ]
 ):
@@ -296,8 +313,8 @@ class _SignalWithStartWorkflowResponseTransferTypeConverter(
     def from_transfer_type(
         self,
         value: temporalio.api.workflowservice.v1.request_response_pb2.SignalWithStartWorkflowExecutionResponse,
-        type_hint: type["SignalWithStartWorkflowResponse"],
-    ) -> "SignalWithStartWorkflowResponse":
+        type_hint: type[SignalWithStartWorkflowResponse],
+    ) -> SignalWithStartWorkflowResponse:
         return SignalWithStartWorkflowResponse(
             run_id=value.run_id if bool(value.run_id) else None,
             started=value.started if bool(value.started) else None,
@@ -306,7 +323,7 @@ def from_transfer_type(
     @typing_extensions.override
     def to_transfer_type(
         self,
-        value: "SignalWithStartWorkflowResponse",
+        value: SignalWithStartWorkflowResponse,
     ) -> temporalio.api.workflowservice.v1.request_response_pb2.SignalWithStartWorkflowExecutionResponse:
         message = temporalio.api.workflowservice.v1.request_response_pb2.SignalWithStartWorkflowExecutionResponse()
         if value.run_id is not None:
@@ -316,15 +333,6 @@ def to_transfer_type(
         return message
 
 
-@temporalio.converter.transfer_type_convertible(
+_ = temporalio.converter.transfer_type_convertible(
     _SignalWithStartWorkflowResponseTransferTypeConverter
-)
-@dataclasses.dataclass(slots=True)
-class SignalWithStartWorkflowResponse:
-    """
-    .. warning::
-        This API is experimental and subject to change.
-    """
-
-    run_id: str | None = None
-    started: bool | None = None
+)(SignalWithStartWorkflowResponse)
diff --git a/temporalio/nexus/system/workflow_service/operations/__init__.py b/temporalio/nexus/system/workflow_service/operations/__init__.py
index 3c550f69c..e5abdafea 100644
--- a/temporalio/nexus/system/workflow_service/operations/__init__.py
+++ b/temporalio/nexus/system/workflow_service/operations/__init__.py
@@ -1,3 +1,3 @@
-# Generated by nexgen v0.2.2. DO NOT EDIT!
+# Generated by nexgen v0.2.3. DO NOT EDIT!
 
 from __future__ import annotations
diff --git a/temporalio/nexus/system/workflow_service/operations/signal_with_start_workflow.py b/temporalio/nexus/system/workflow_service/operations/signal_with_start_workflow.py
index 97eb8159a..c04b115b3 100644
--- a/temporalio/nexus/system/workflow_service/operations/signal_with_start_workflow.py
+++ b/temporalio/nexus/system/workflow_service/operations/signal_with_start_workflow.py
@@ -1,4 +1,4 @@
-# Generated by nexgen v0.2.2. DO NOT EDIT!
+# Generated by nexgen v0.2.3. DO NOT EDIT!
 
 from __future__ import annotations
 
diff --git a/temporalio/nexus/system/workflow_service/services.py b/temporalio/nexus/system/workflow_service/services.py
index 237565fff..9d46fe40a 100644
--- a/temporalio/nexus/system/workflow_service/services.py
+++ b/temporalio/nexus/system/workflow_service/services.py
@@ -1,4 +1,4 @@
-# Generated by nexgen v0.2.2. DO NOT EDIT!
+# Generated by nexgen v0.2.3. DO NOT EDIT!
 
 from __future__ import annotations
 
diff --git a/temporalio/worker/_interceptor.py b/temporalio/worker/_interceptor.py
index 4acf3c5d1..1bac84673 100644
--- a/temporalio/worker/_interceptor.py
+++ b/temporalio/worker/_interceptor.py
@@ -21,6 +21,9 @@
 import temporalio.nexus
 import temporalio.nexus._util
 import temporalio.workflow
+from temporalio.nexus.system.workflow_service._system_nexus_interceptor import (
+    _SystemNexusWorkflowOutboundInterceptorBase,
+)
 from temporalio.workflow import ContinueAsNewVersioningBehavior, VersioningIntent
 
 
@@ -414,12 +417,14 @@ async def handle_update_handler(self, input: HandleUpdateInput) -> Any:
         return await self.next.handle_update_handler(input)
 
 
-class WorkflowOutboundInterceptor:
+class WorkflowOutboundInterceptor(_SystemNexusWorkflowOutboundInterceptorBase):
     """Outbound interceptor to wrap calls made from within workflows.
 
     This should be extended by any workflow outbound interceptors.
     """
 
+    next: WorkflowOutboundInterceptor
+
     def __init__(self, next: WorkflowOutboundInterceptor) -> None:
         """Create the outbound interceptor.
 
@@ -429,6 +434,11 @@ def __init__(self, next: WorkflowOutboundInterceptor) -> None:
         """
         self.next = next
 
+    def _next_system_nexus_interceptor(
+        self,
+    ) -> _SystemNexusWorkflowOutboundInterceptorBase:
+        return self.next
+
     def continue_as_new(self, input: ContinueAsNewInput) -> NoReturn:
         """Called for every :py:func:`temporalio.workflow.continue_as_new` call."""
         self.next.continue_as_new(input)
diff --git a/temporalio/worker/_workflow_instance.py b/temporalio/worker/_workflow_instance.py
index 69b416f26..fca73c266 100644
--- a/temporalio/worker/_workflow_instance.py
+++ b/temporalio/worker/_workflow_instance.py
@@ -60,6 +60,10 @@
 import temporalio.nexus.system
 import temporalio.workflow
 from temporalio.converter import StorageDriverStoreContext, StorageDriverWorkflowInfo
+from temporalio.nexus.system.workflow_service._system_nexus_interceptor import (
+    _start_system_nexus_operation,
+    _SystemNexusWorkflowOutboundInterceptorTerminal,
+)
 from temporalio.service import __version__
 
 from ..api.failure.v1.message_pb2 import Failure
@@ -1732,7 +1736,23 @@ async def workflow_start_nexus_operation(
         headers: Mapping[str, str] | None,
         summary: str | None,
     ) -> temporalio.workflow.NexusOperationHandle[OutputT]:
-        # start_nexus_operation
+        if temporalio.nexus.system.is_system_endpoint(endpoint):
+            return await _start_system_nexus_operation(
+                self._outbound,
+                StartNexusOperationInput(
+                    endpoint=temporalio.nexus.system.TEMPORAL_SYSTEM_ENDPOINT,
+                    service=service,
+                    operation=operation,
+                    input=input,
+                    output_type=output_type,
+                    schedule_to_close_timeout=schedule_to_close_timeout,
+                    schedule_to_start_timeout=schedule_to_start_timeout,
+                    start_to_close_timeout=start_to_close_timeout,
+                    cancellation_type=cancellation_type,
+                    headers=None,
+                    summary=summary,
+                ),
+            )
         return await self._outbound.start_nexus_operation(
             StartNexusOperationInput(
                 endpoint=endpoint,
@@ -3131,11 +3151,18 @@ async def handle_update_handler(self, input: HandleUpdateInput) -> Any:
             return handler(*input.args)
 
 
-class _WorkflowOutboundImpl(WorkflowOutboundInterceptor):
+class _WorkflowOutboundImpl(
+    _SystemNexusWorkflowOutboundInterceptorTerminal, WorkflowOutboundInterceptor
+):
     def __init__(self, instance: _WorkflowInstanceImpl) -> None:  # type: ignore
         # We are intentionally not calling the base class's __init__ here
         self._instance = instance
 
+    async def _outbound_start_nexus_operation(
+        self, input: StartNexusOperationInput[InputT, OutputT]
+    ) -> temporalio.workflow.NexusOperationHandle[OutputT]:
+        return await self._instance._outbound_start_nexus_operation(input)
+
     def continue_as_new(self, input: ContinueAsNewInput) -> NoReturn:
         self._instance._outbound_continue_as_new(input)
 
diff --git a/tests/contrib/opentelemetry/test_opentelemetry.py b/tests/contrib/opentelemetry/test_opentelemetry.py
index 1bab931ac..0ea9530e6 100644
--- a/tests/contrib/opentelemetry/test_opentelemetry.py
+++ b/tests/contrib/opentelemetry/test_opentelemetry.py
@@ -88,6 +88,34 @@ class TracingWorkflowActionActivity:
     fail_on_non_replay_before_complete: bool = False
 
 
+@workflow.defn
+class SignalWithStartHeaderWorkflow:
+    def __init__(self) -> None:
+        self._signaled = False
+
+    @workflow.run
+    async def run(self) -> bool:
+        await workflow.wait_condition(lambda: self._signaled)
+        return "_tracer-data" in workflow.info().headers
+
+    @workflow.signal
+    def notify(self) -> None:
+        self._signaled = True
+
+
+@workflow.defn
+class SignalWithStartCallerWorkflow:
+    @workflow.run
+    async def run(self, target_id: str, task_queue: str) -> str:
+        handle = await workflow.signal_with_start_workflow(
+            SignalWithStartHeaderWorkflow.run,
+            id=target_id,
+            task_queue=task_queue,
+            signal=SignalWithStartHeaderWorkflow.notify,
+        )
+        return handle.id
+
+
 @dataclass
 class TracingWorkflowActionContinueAsNew:
     param: TracingWorkflowParam
@@ -229,6 +257,41 @@ def update_validator(self) -> None:
         pass
 
 
+@pytest.mark.requires_local_server
+async def test_workflow_signal_with_start_propagates_trace_headers(
+    client: Client, env: WorkflowEnvironment
+):
+    if env.supports_time_skipping:
+        pytest.skip("Nexus tests don't work with the Java test server")
+    provider = TracerProvider()
+    exporter = InMemorySpanExporter()
+    provider.add_span_processor(SimpleSpanProcessor(exporter))
+    tracer = get_tracer(__name__, tracer_provider=provider)
+    config = client.config()
+    config["interceptors"] = [TracingInterceptor(tracer)]
+    client = Client(**config)
+
+    async with Worker(
+        client,
+        task_queue=f"signal-with-start-{uuid.uuid4()}",
+        workflows=[SignalWithStartCallerWorkflow, SignalWithStartHeaderWorkflow],
+        workflow_runner=UnsandboxedWorkflowRunner(),
+    ) as worker:
+        target_id = f"signal-with-start-target-{uuid.uuid4()}"
+        with tracer.start_as_current_span("signal-with-start"):
+            caller = await client.start_workflow(
+                SignalWithStartCallerWorkflow.run,
+                args=[target_id, worker.task_queue],
+                id=f"signal-with-start-caller-{uuid.uuid4()}",
+                task_queue=worker.task_queue,
+            )
+            assert await caller.result() == target_id
+        assert await client.get_workflow_handle(target_id).result() is True
+    assert any(
+        span.name == "SignalWithStartWorkflow" for span in exporter.get_finished_spans()
+    )
+
+
 async def test_opentelemetry_tracing(client: Client, env: WorkflowEnvironment):
     # TODO(cretz): Fix
     if env.supports_time_skipping:
diff --git a/tests/contrib/opentelemetry/test_opentelemetry_plugin.py b/tests/contrib/opentelemetry/test_opentelemetry_plugin.py
index 12d0c5972..022645fee 100644
--- a/tests/contrib/opentelemetry/test_opentelemetry_plugin.py
+++ b/tests/contrib/opentelemetry/test_opentelemetry_plugin.py
@@ -122,6 +122,34 @@ async def run(self):
         return
 
 
+@workflow.defn
+class SignalWithStartHeaderWorkflow:
+    def __init__(self) -> None:
+        self._signaled = False
+
+    @workflow.run
+    async def run(self) -> bool:
+        await workflow.wait_condition(lambda: self._signaled)
+        return "_tracer-data" in workflow.info().headers
+
+    @workflow.signal
+    def notify(self) -> None:
+        self._signaled = True
+
+
+@workflow.defn
+class SignalWithStartCallerWorkflow:
+    @workflow.run
+    async def run(self, target_id: str, task_queue: str) -> str:
+        handle = await workflow.signal_with_start_workflow(
+            SignalWithStartHeaderWorkflow.run,
+            id=target_id,
+            task_queue=task_queue,
+            signal=SignalWithStartHeaderWorkflow.notify,
+        )
+        return handle.id
+
+
 async def test_otel_tracing_basic(client: Client, reset_otel_tracer_provider: Any):  # type: ignore[reportUnusedParameter]
     exporter = InMemorySpanExporter()
     provider = create_tracer_provider()
@@ -169,6 +197,41 @@ async def test_otel_tracing_basic(client: Client, reset_otel_tracer_provider: An
     )
 
 
+@pytest.mark.requires_local_server
+async def test_workflow_signal_with_start_propagates_trace_headers(
+    client: Client,
+    env: WorkflowEnvironment,
+    reset_otel_tracer_provider: Any,  # type: ignore[reportUnusedParameter]
+):
+    if env.supports_time_skipping:
+        pytest.skip("Nexus tests don't work with the Java test server")
+    exporter = InMemorySpanExporter()
+    provider = create_tracer_provider()
+    provider.add_span_processor(SimpleSpanProcessor(exporter))
+    opentelemetry.trace.set_tracer_provider(provider)
+    config = client.config()
+    config["plugins"] = [OpenTelemetryPlugin(add_temporal_spans=True)]
+    client = Client(**config)
+
+    async with new_worker(
+        client, SignalWithStartCallerWorkflow, SignalWithStartHeaderWorkflow
+    ) as worker:
+        target_id = f"signal-with-start-target-{uuid.uuid4()}"
+        with get_tracer(__name__).start_as_current_span("signal-with-start"):
+            caller = await client.start_workflow(
+                SignalWithStartCallerWorkflow.run,
+                args=[target_id, worker.task_queue],
+                id=f"signal-with-start-caller-{uuid.uuid4()}",
+                task_queue=worker.task_queue,
+                execution_timeout=timedelta(seconds=3),
+            )
+            assert await caller.result() == target_id
+        assert await client.get_workflow_handle(target_id).result() is True
+    assert any(
+        span.name == "SignalWithStartWorkflow" for span in exporter.get_finished_spans()
+    )
+
+
 @workflow.defn
 class ComprehensiveWorkflow:
     def __init__(self) -> None:
diff --git a/tests/nexus/test_temporal_system_nexus.py b/tests/nexus/test_temporal_system_nexus.py
index dc49f0302..d2abefa23 100644
--- a/tests/nexus/test_temporal_system_nexus.py
+++ b/tests/nexus/test_temporal_system_nexus.py
@@ -36,7 +36,6 @@
 from temporalio.testing import WorkflowEnvironment
 from temporalio.worker import (
     Interceptor,
-    StartNexusOperationInput,
     Worker,
     WorkflowInboundInterceptor,
     WorkflowInterceptorClassInput,
@@ -251,11 +250,16 @@ def init(self, outbound: WorkflowOutboundInterceptor) -> None:
 
 
 class _TracingWorkflowOutboundInterceptor(WorkflowOutboundInterceptor):
-    async def start_nexus_operation(
-        self, input: StartNexusOperationInput[Any, Any]
-    ) -> workflow.NexusOperationHandle[Any]:
-        interceptor_traces.append(("workflow.start_nexus_operation", input))
-        return await super().start_nexus_operation(input)
+    async def start_signal_with_start_workflow(
+        self, request: workflow_service_models.SignalWithStartWorkflowRequest
+    ) -> workflow.NexusOperationHandle[
+        workflow_service_models.SignalWithStartWorkflowResponse
+    ]:
+        request.headers = {**(request.headers or {}), "interceptor-header": "value"}
+        interceptor_traces.append(
+            ("workflow.start_signal_with_start_workflow", request)
+        )
+        return await super().start_signal_with_start_workflow(request)
 
 
 def _assert_stored_payloads_include(
@@ -270,15 +274,15 @@ def _assert_stored_payloads_include(
     assert expected_payload_data.issubset(stored_payload_data)
 
 
-def _assert_start_nexus_operation_interceptor_trace() -> None:
+def _assert_signal_with_start_workflow_interceptor_trace() -> None:
     assert len(interceptor_traces) == 1
     trace_name, trace_value = interceptor_traces.pop()
-    assert trace_name == "workflow.start_nexus_operation"
-    trace_input = cast(StartNexusOperationInput[Any, Any], trace_value)
-    request = trace_input.input
+    assert trace_name == "workflow.start_signal_with_start_workflow"
+    request = cast(workflow_service_models.SignalWithStartWorkflowRequest, trace_value)
     assert request.id == "system-nexus-workflow-id"
     assert request.signal == "test-signal"
     assert request.workflow == "test-workflow"
+    assert request.headers == {"interceptor-header": "value"}
 
 
 class _MarkingPayloadVisitor(VisitorFunctions):
@@ -708,7 +712,7 @@ async def test_external_workflow_handle_signal_with_start_workflow_uses_system_n
             b'"details-value"',
         },
     )
-    _assert_start_nexus_operation_interceptor_trace()
+    _assert_signal_with_start_workflow_interceptor_trace()
 
 
 # Cloud namespaces created by CI do not have the System Nexus dynamic config.