diff --git a/api.md b/api.md
index 83650cb0..a702cec8 100644
--- a/api.md
+++ b/api.md
@@ -1,8 +1,8 @@
-# Top Level
+# Anthropic
 
-Custom Methods:
+Methods:
 
-- `count_tokens`
+- <code>client.<a href="./src/anthropic/_client.py">count_tokens</a>(\*args) -> int</code>
 
 # Completions
 
@@ -15,4 +15,3 @@ from anthropic.types import Completion
 Methods:
 
 - <code title="post /v1/complete">client.completions.<a href="./src/anthropic/resources/completions.py">create</a>(\*\*<a href="src/anthropic/types/completion_create_params.py">params</a>) -> <a href="./src/anthropic/types/completion.py">Completion</a></code>
-- <code title="post /v1/complete">client.completions.<a href="./src/anthropic/resources/completions.py">create</a>(\*\*<a href="src/anthropic/types/completion_create_params.py">params</a>) -> <a href="./src/anthropic/types/completion.py">Completion</a></code>
diff --git a/poetry.lock b/poetry.lock
index ebc71022..880e2961 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -95,13 +95,13 @@ uvloop = ["uvloop (>=0.15.2)"]
 
 [[package]]
 name = "certifi"
-version = "2022.9.24"
+version = "2023.5.7"
 description = "Python package for providing Mozilla's CA Bundle."
 optional = false
 python-versions = ">=3.6"
 files = [
-    {file = "certifi-2022.9.24-py3-none-any.whl", hash = "sha256:90c1a32f1d68f940488354e36370f6cca89f0f106db09518524c88d6ed83f382"},
-    {file = "certifi-2022.9.24.tar.gz", hash = "sha256:0d9c601124e5a6ba9712dbc60d9c53c21e34f5f641fe83002317394311bdce14"},
+    {file = "certifi-2023.5.7-py3-none-any.whl", hash = "sha256:c6c2e98f5c7869efca1f8916fed228dd91539f9f1b444c314c06eef02980c716"},
+    {file = "certifi-2023.5.7.tar.gz", hash = "sha256:0f0d56dc5a6ad56fd4ba36484d6cc34451e1c6548c61daad8c320169f91eddc7"},
 ]
 
 [[package]]
@@ -825,4 +825,4 @@ testing = ["flake8 (<5)", "func-timeout", "jaraco.functools", "jaraco.itertools"
 [metadata]
 lock-version = "2.0"
 python-versions = "^3.7"
-content-hash = "d91f45ecd0210a0a992caef1795f664e5f846ba00ffa4f2dc88c08ba3ebbedb4"
+content-hash = "b09fa7774c59e804a189a287dc33a71974b592eb5398dfa34e428d0aba3fc503"
diff --git a/pyproject.toml b/pyproject.toml
index a2e5a23a..fc3d7ee4 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -13,7 +13,7 @@ packages = [
 [tool.poetry.dependencies]
 python = "^3.7"
 httpx = ">= 0.23.0"
-pydantic = ">= 1.9.0, < 2.0"
+pydantic = "^1.9.0"
 typing-extensions = ">= 4.1.1"
 anyio = ">= 3.5.0"
 distro = ">= 1.7.0"
diff --git a/tests/test_tokenizer.py b/tests/test_tokenizer.py
new file mode 100644
index 00000000..87be4044
--- /dev/null
+++ b/tests/test_tokenizer.py
@@ -0,0 +1,76 @@
+import asyncio
+import threading
+import concurrent.futures
+from multiprocessing import Pool
+
+import pytest
+
+from anthropic import _tokenizers
+
+
+@pytest.fixture(autouse=True)
+def before_test() -> None:
+    # clear cache
+    _tokenizers._tokenizer = None
+
+
+def _sync_tokenizer_test() -> None:
+    tokenizer = _tokenizers.sync_get_tokenizer()
+    encoded_text = tokenizer.encode("hello world")  # type: ignore
+    assert len(encoded_text.ids) == 2  # type: ignore
+
+
+def test_threading() -> None:
+    failed = False
+
+    def target() -> None:
+        nonlocal failed
+
+        try:
+            _sync_tokenizer_test()
+        except Exception:
+            failed = True
+            raise
+
+    t1 = threading.Thread(target=target)
+    t2 = threading.Thread(target=target)
+
+    t1.start()
+    t2.start()
+    t1.join()
+    t2.join()
+
+    assert not failed
+
+
+def test_concurrent_futures() -> None:
+    with concurrent.futures.ThreadPoolExecutor() as executor:
+        future1 = executor.submit(_sync_tokenizer_test)
+        future2 = executor.submit(_sync_tokenizer_test)
+
+        future1.result()
+        future2.result()
+
+
+def test_multiprocessing() -> None:
+    with Pool(processes=10) as pool:
+        pool.apply(_sync_tokenizer_test)
+
+
+async def _async_tokenizer_test() -> None:
+    tokenizer = await _tokenizers.async_get_tokenizer()
+    encoded_text = tokenizer.encode("hello world")  # type: ignore
+    assert len(encoded_text.ids) == 2  # type: ignore
+
+
+async def test_asyncio_tasks() -> None:
+    loop = asyncio.get_event_loop()
+
+    task1 = loop.create_task(_async_tokenizer_test())
+    task2 = loop.create_task(_async_tokenizer_test())
+
+    await asyncio.gather(task1, task2)
+
+
+async def test_asyncio_gather() -> None:
+    await asyncio.gather(_async_tokenizer_test(), _async_tokenizer_test())