diff --git a/python/langsmith/run_helpers.py b/python/langsmith/run_helpers.py
index 473082b58..c19d30491 100644
--- a/python/langsmith/run_helpers.py
+++ b/python/langsmith/run_helpers.py
@@ -74,20 +74,23 @@ def tracing_context(
     tags: Optional[List[str]] = None,
     metadata: Optional[Dict[str, Any]] = None,
     parent_run: Optional[run_trees.Span] = None,
-    headers: Optional[Dict[str, str]] = None,
+    headers: Optional[Union[Dict[str, str], Any]] = None,
 ) -> Generator[None, None, None]:
     """Set the tracing context for a block of code."""
     parent_run_ = get_current_span()
     _PROJECT_NAME.set(project_name)
-    _TAGS.set(tags)
-    _METADATA.set(metadata)
     if parent_run is not None:
         _PARENT_RUN_TREE.set(parent_run)
     elif headers is not None:
         parent_run = run_trees.Span.from_headers(headers)
+        if parent_run:
+            tags = sorted(set(tags or []) | set(parent_run.tags or []))
+            metadata = {**parent_run.metadata, **(metadata or {})}
         _PARENT_RUN_TREE.set(parent_run)
     else:
         _PARENT_RUN_TREE.set(None)
+    _TAGS.set(tags)
+    _METADATA.set(metadata)
     try:
         yield
     finally:
@@ -96,6 +99,7 @@ def tracing_context(
         _METADATA.set(None)
         _PARENT_RUN_TREE.set(parent_run_)
 
+
 # Alias for backwards compatibility
 get_current_run_tree = get_current_span
 get_run_tree_context = get_current_run_tree
diff --git a/python/langsmith/run_trees.py b/python/langsmith/run_trees.py
index 56c2a75fa..957bbe5a5 100644
--- a/python/langsmith/run_trees.py
+++ b/python/langsmith/run_trees.py
@@ -284,7 +284,7 @@ def from_headers(cls, headers: Dict[str, str], **kwargs: Any) -> Optional[Span]:
 
         langsmith_trace = headers.get(f"{LANGSMITH_PREFIX}trace")
         if not langsmith_trace:
-            return None
+            return  # type: ignore[return-value]
 
         parent_dotted_order = langsmith_trace.strip()
         parsed_dotted_order = _parse_dotted_order(parent_dotted_order)
@@ -350,11 +350,11 @@ def from_header(cls, header_value: Optional[str]) -> _Baggage:
         try:
             for item in header_value.split(","):
                 key, value = item.split("=", 1)
-                if key == f"{LANGSMITH_PREFIX}-metadata":
+                if key == f"{LANGSMITH_PREFIX}metadata":
                     metadata = json.loads(urllib.parse.unquote(value))
-                elif key == f"{LANGSMITH_PREFIX}-tags":
+                elif key == f"{LANGSMITH_PREFIX}tags":
                     tags = urllib.parse.unquote(value).split(",")
-                elif key == f"{LANGSMITH_PREFIX}-id":
+                elif key == f"{LANGSMITH_PREFIX}id":
                     id_ = UUID(value)
         except Exception as e:
             logger.warning(f"Error parsing baggage header: {e}")
@@ -383,7 +383,7 @@ def _parse_dotted_order(dotted_order: str) -> List[Tuple[datetime, UUID]]:
     """Parse the dotted order string."""
     parts = dotted_order.split(".")
     return [
-        (datetime.strptime(part[:23], "%Y%m%dT%H%M%S%fZ"), UUID(part[23:]))
+        (datetime.strptime(part[:-36], "%Y%m%dT%H%M%S%fZ"), UUID(part[-36:]))
         for part in parts
     ]
 
diff --git a/python/poetry.lock b/python/poetry.lock
index c9d9f3cbd..75a67b5ba 100644
--- a/python/poetry.lock
+++ b/python/poetry.lock
@@ -343,6 +343,25 @@ files = [
 [package.extras]
 testing = ["hatch", "pre-commit", "pytest", "tox"]
 
+[[package]]
+name = "fastapi"
+version = "0.110.1"
+description = "FastAPI framework, high performance, easy to learn, fast to code, ready for production"
+optional = false
+python-versions = ">=3.8"
+files = [
+    {file = "fastapi-0.110.1-py3-none-any.whl", hash = "sha256:5df913203c482f820d31f48e635e022f8cbfe7350e4830ef05a3163925b1addc"},
+    {file = "fastapi-0.110.1.tar.gz", hash = "sha256:6feac43ec359dfe4f45b2c18ec8c94edb8dc2dfc461d417d9e626590c071baad"},
+]
+
+[package.dependencies]
+pydantic = ">=1.7.4,<1.8 || >1.8,<1.8.1 || >1.8.1,<2.0.0 || >2.0.0,<2.0.1 || >2.0.1,<2.1.0 || >2.1.0,<3.0.0"
+starlette = ">=0.37.2,<0.38.0"
+typing-extensions = ">=4.8.0"
+
+[package.extras]
+all = ["email-validator (>=2.0.0)", "httpx (>=0.23.0)", "itsdangerous (>=1.1.0)", "jinja2 (>=2.11.2)", "orjson (>=3.2.1)", "pydantic-extra-types (>=2.0.0)", "pydantic-settings (>=2.0.0)", "python-multipart (>=0.0.7)", "pyyaml (>=5.3.1)", "ujson (>=4.0.1,!=4.0.2,!=4.1.0,!=4.2.0,!=4.3.0,!=5.0.0,!=5.1.0)", "uvicorn[standard] (>=0.12.0)"]
+
 [[package]]
 name = "freezegun"
 version = "1.4.0"
@@ -1126,6 +1145,24 @@ files = [
     {file = "sniffio-1.3.1.tar.gz", hash = "sha256:f4324edc670a0f49750a81b895f35c3adb843cca46f0530f79fc1babb23789dc"},
 ]
 
+[[package]]
+name = "starlette"
+version = "0.37.2"
+description = "The little ASGI library that shines."
+optional = false
+python-versions = ">=3.8"
+files = [
+    {file = "starlette-0.37.2-py3-none-any.whl", hash = "sha256:6fe59f29268538e5d0d182f2791a479a0c64638e6935d1c6989e63fb2699c6ee"},
+    {file = "starlette-0.37.2.tar.gz", hash = "sha256:9af890290133b79fc3db55474ade20f6220a364a0402e0b556e7cd5e1e093823"},
+]
+
+[package.dependencies]
+anyio = ">=3.4.0,<5"
+typing-extensions = {version = ">=3.10.0", markers = "python_version < \"3.10\""}
+
+[package.extras]
+full = ["httpx (>=0.22.0)", "itsdangerous", "jinja2", "python-multipart (>=0.0.7)", "pyyaml"]
+
 [[package]]
 name = "tomli"
 version = "2.0.1"
@@ -1299,6 +1336,25 @@ h2 = ["h2 (>=4,<5)"]
 socks = ["pysocks (>=1.5.6,!=1.5.7,<2.0)"]
 zstd = ["zstandard (>=0.18.0)"]
 
+[[package]]
+name = "uvicorn"
+version = "0.29.0"
+description = "The lightning-fast ASGI server."
+optional = false
+python-versions = ">=3.8"
+files = [
+    {file = "uvicorn-0.29.0-py3-none-any.whl", hash = "sha256:2c2aac7ff4f4365c206fd773a39bf4ebd1047c238f8b8268ad996829323473de"},
+    {file = "uvicorn-0.29.0.tar.gz", hash = "sha256:6a69214c0b6a087462412670b3ef21224fa48cae0e452b5883e8e8bdfdd11dd0"},
+]
+
+[package.dependencies]
+click = ">=7.0"
+h11 = ">=0.8"
+typing-extensions = {version = ">=4.0", markers = "python_version < \"3.11\""}
+
+[package.extras]
+standard = ["colorama (>=0.4)", "httptools (>=0.5.0)", "python-dotenv (>=0.13)", "pyyaml (>=5.1)", "uvloop (>=0.14.0,!=0.15.0,!=0.15.1)", "watchfiles (>=0.13)", "websockets (>=10.4)"]
+
 [[package]]
 name = "vcrpy"
 version = "6.0.1"
@@ -1547,4 +1603,4 @@ vcr = []
 [metadata]
 lock-version = "2.0"
 python-versions = ">=3.8.1,<4.0"
-content-hash = "3724956de2f14ef761403e17016a212a7de110b726184cf2e685425cb60261d1"
+content-hash = "a347c2aca058e8c1b9fbcdc7043a5ed53ba03485759adce207d249e4495e05c6"
diff --git a/python/pyproject.toml b/python/pyproject.toml
index 8c9fe1693..23a64e575 100644
--- a/python/pyproject.toml
+++ b/python/pyproject.toml
@@ -50,6 +50,8 @@ pytest-cov = "^4.1.0"
 dataclasses-json = "^0.6.4"
 types-tqdm = "^4.66.0.20240106"
 vcrpy = "^6.0.1"
+fastapi = "^0.110.1"
+uvicorn = "^0.29.0"
 
 [tool.poetry.group.lint.dependencies]
 openai = "^1.10"
diff --git a/python/tests/integration_tests/fake_server.py b/python/tests/integration_tests/fake_server.py
new file mode 100644
index 000000000..a0a411e97
--- /dev/null
+++ b/python/tests/integration_tests/fake_server.py
@@ -0,0 +1,24 @@
+from fastapi import FastAPI, Request
+
+from langsmith import traceable
+from langsmith.run_helpers import get_current_span, tracing_context
+
+fake_app = FastAPI()
+
+
+@traceable
+def fake_function():
+    span = get_current_span()
+    assert span is not None
+    parent_run = span.parent_run
+    assert parent_run is not None
+    assert "did-propagate" in span.tags
+    assert span.metadata["some-cool-value"] == 42
+    return "Fake function response"
+
+
+@fake_app.post("/fake-route")
+async def fake_route(request: Request):
+    with tracing_context(headers=request.headers):
+        fake_function()
+    return {"message": "Fake route response"}
diff --git a/python/tests/integration_tests/test_context_propagation.py b/python/tests/integration_tests/test_context_propagation.py
new file mode 100644
index 000000000..5166a92ee
--- /dev/null
+++ b/python/tests/integration_tests/test_context_propagation.py
@@ -0,0 +1,47 @@
+import asyncio
+
+import pytest
+from httpx import AsyncClient
+
+from langsmith import traceable
+from langsmith.run_helpers import get_current_span
+from tests.integration_tests.fake_server import fake_app
+
+
+@pytest.fixture(scope="module")
+def event_loop():
+    loop = asyncio.get_event_loop()
+    yield loop
+    loop.close()
+
+
+@pytest.fixture(scope="module")
+async def fake_server():
+    from uvicorn import Config, Server
+
+    config = Config(app=fake_app, loop="asyncio", port=8000, log_level="info")
+    server = Server(config=config)
+
+    asyncio.create_task(server.serve())
+    await asyncio.sleep(0.1)
+
+    yield
+
+    await server.shutdown()
+
+
+@traceable
+async def the_parent_function():
+    async with AsyncClient(app=fake_app, base_url="http://localhost:8000") as client:
+        headers = {}
+        if span := get_current_span():
+            headers.update(span.to_headers())
+        return await client.post("/fake-route", headers=headers)
+
+
+@pytest.mark.asyncio
+async def test_tracing_fake_server(fake_server):
+    response = await the_parent_function(
+        langsmith_extra={"metadata": {"some-cool-value": 42}, "tags": ["did-propagate"]}
+    )
+    assert response.status_code == 200
diff --git a/python/tests/unit_tests/test_run_trees.py b/python/tests/unit_tests/test_run_trees.py
index fa88e623c..92c398b2d 100644
--- a/python/tests/unit_tests/test_run_trees.py
+++ b/python/tests/unit_tests/test_run_trees.py
@@ -1,5 +1,9 @@
 from concurrent.futures import ThreadPoolExecutor
+from datetime import datetime
 from unittest.mock import MagicMock
+from uuid import UUID
+
+import pytest
 
 from langsmith import run_trees
 from langsmith.client import Client
@@ -13,3 +17,45 @@ def test_run_tree_accepts_tpe() -> None:
         client=mock_client,
         executor=ThreadPoolExecutor(),
     )
+
+
+@pytest.mark.parametrize(
+    "inputs, expected",
+    [
+        (
+            "20240412T202937370454Z152ce25c-064e-4742-bf36-8bb0389f8805.20240412T202937627763Zfe8b541f-e75a-4ee6-b92d-732710897194.20240412T202937708023Z625b30ed-2fbb-4387-81b1-cb5d6221e5b4.20240412T202937775748Z448dc09f-ad54-4475-b3a4-fa43018ca621.20240412T202937981350Z4cd59ea4-491e-4ed9-923f-48cd93e03755.20240412T202938078862Zcd168cf7-ee72-48c2-8ec0-50ab09821973.20240412T202938152278Z32481c1a-b83c-4b53-a52e-1ea893ffba51",
+            [
+                (
+                    datetime(2024, 4, 12, 20, 29, 37, 370454),
+                    UUID("152ce25c-064e-4742-bf36-8bb0389f8805"),
+                ),
+                (
+                    datetime(2024, 4, 12, 20, 29, 37, 627763),
+                    UUID("fe8b541f-e75a-4ee6-b92d-732710897194"),
+                ),
+                (
+                    datetime(2024, 4, 12, 20, 29, 37, 708023),
+                    UUID("625b30ed-2fbb-4387-81b1-cb5d6221e5b4"),
+                ),
+                (
+                    datetime(2024, 4, 12, 20, 29, 37, 775748),
+                    UUID("448dc09f-ad54-4475-b3a4-fa43018ca621"),
+                ),
+                (
+                    datetime(2024, 4, 12, 20, 29, 37, 981350),
+                    UUID("4cd59ea4-491e-4ed9-923f-48cd93e03755"),
+                ),
+                (
+                    datetime(2024, 4, 12, 20, 29, 38, 78862),
+                    UUID("cd168cf7-ee72-48c2-8ec0-50ab09821973"),
+                ),
+                (
+                    datetime(2024, 4, 12, 20, 29, 38, 152278),
+                    UUID("32481c1a-b83c-4b53-a52e-1ea893ffba51"),
+                ),
+            ],
+        ),
+    ],
+)
+def test_parse_dotted_order(inputs, expected):
+    assert run_trees._parse_dotted_order(inputs) == expected