diff --git a/CHANGELOG.md b/CHANGELOG.md
index c074bcce..8f8e88ae 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,15 @@
 
 This is the changelog for the open source version of tiktoken.
 
+## [v0.6.0]
+- Optimise regular expressions for a 20% performance improvement
+- Add `text-embedding-3-*` models to `encoding_for_model`
+- Check content hash for downloaded files
+- Allow pickling `Encoding` objects. Registered `Encoding` will be pickled by reference
+- Workaround PyO3 bug for frozenset conversion
+
+Thank you to @paplorinc, @mdwelsh, @Praneet460!
+
 ## [v0.5.2]
 - Build wheels for Python 3.12
 - Update version of PyO3 to allow multiple imports
diff --git a/Cargo.toml b/Cargo.toml
index fb69db74..14588580 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "tiktoken"
-version = "0.5.2"
+version = "0.6.0"
 edition = "2021"
 rust-version = "1.57.0"
 
@@ -16,6 +16,3 @@ fancy-regex = "0.11.0"
 regex = "1.8.3"
 rustc-hash = "1.1.0"
 bstr = "1.5.0"
-
-[profile.release]
-incremental = true
diff --git a/pyproject.toml b/pyproject.toml
index b48941d6..47aada31 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "tiktoken"
-version = "0.5.2"
+version = "0.6.0"
 description = "tiktoken is a fast BPE tokeniser for use with OpenAI's models"
 readme = "README.md"
 license = {file = "LICENSE"}
diff --git a/tiktoken/core.py b/tiktoken/core.py
index aa72c9d7..3e32d4ce 100644
--- a/tiktoken/core.py
+++ b/tiktoken/core.py
@@ -116,6 +116,10 @@ def encode(
             if match := _special_token_regex(disallowed_special).search(text):
                 raise_disallowed_special_token(match.group())
 
+        # https://github.com/PyO3/pyo3/pull/3632
+        if isinstance(allowed_special, frozenset):
+            allowed_special = set(allowed_special)
+
         try:
             return self._core_bpe.encode(text, allowed_special)
         except UnicodeEncodeError:
@@ -364,6 +368,26 @@ def _encode_only_native_bpe(self, text: str) -> list[int]:
     def _encode_bytes(self, text: bytes) -> list[int]:
         return self._core_bpe._encode_bytes(text)
 
+    def __getstate__(self) -> object:
+        import tiktoken.registry
+
+        # As an optimisation, pickle registered encodings by reference
+        if self is tiktoken.registry.ENCODINGS.get(self.name):
+            return self.name
+        return {
+            "name": self.name,
+            "pat_str": self._pat_str,
+            "mergeable_ranks": self._mergeable_ranks,
+            "special_tokens": self._special_tokens,
+        }
+
+    def __setstate__(self, value: object) -> None:
+        import tiktoken.registry
+
+        if isinstance(value, str):
+            self.__dict__ = tiktoken.registry.get_encoding(value).__dict__
+            return
+        self.__init__(**value)
 
 
 @functools.lru_cache(maxsize=128)
diff --git a/tiktoken/load.py b/tiktoken/load.py
index 45729b11..cc0a6a6d 100644
--- a/tiktoken/load.py
+++ b/tiktoken/load.py
@@ -27,12 +27,12 @@ def read_file(blobpath: str) -> bytes:
     return resp.content
 
 
-def check_hash(data: bytes, hash: str) -> bool:
-    data_hash = hashlib.sha256(data).hexdigest()
-    return data_hash == hash
+def check_hash(data: bytes, expected_hash: str) -> bool:
+    actual_hash = hashlib.sha256(data).hexdigest()
+    return actual_hash == expected_hash
 
 
-def read_file_cached(blobpath: str, expected_hash: Optional[str]=None) -> bytes:
+def read_file_cached(blobpath: str, expected_hash: Optional[str] = None) -> bytes:
     user_specified_cache = True
     if "TIKTOKEN_CACHE_DIR" in os.environ:
         cache_dir = os.environ["TIKTOKEN_CACHE_DIR"]
@@ -52,13 +52,15 @@ def read_file_cached(blobpath: str, expected_hash: Optional[str]=None) -> bytes:
     if os.path.exists(cache_path):
         with open(cache_path, "rb") as f:
             data = f.read()
-            if expected_hash and not check_hash(data, expected_hash):
-                raise ValueError(
-                    f"Hash mismatch for cached data from {blobpath} (expected {expected_hash}). "
-                    f"Please delete the cache file at {cache_path} and try again."
-                )
+        if expected_hash is None or check_hash(data, expected_hash):
             return data
 
+        # the cached file does not match the hash, remove it and re-fetch
+        try:
+            os.remove(cache_path)
+        except OSError:
+            pass
+
     contents = read_file(blobpath)
     if expected_hash and not check_hash(contents, expected_hash):
         raise ValueError(
@@ -81,7 +83,10 @@ def read_file_cached(blobpath: str, expected_hash: Optional[str]=None) -> bytes:
 
 
 def data_gym_to_mergeable_bpe_ranks(
-    vocab_bpe_file: str, encoder_json_file: str, vocab_bpe_hash: Optional[str]=None, encoder_json_hash: Optional[str]=None
+    vocab_bpe_file: str,
+    encoder_json_file: str,
+    vocab_bpe_hash: Optional[str] = None,
+    encoder_json_hash: Optional[str] = None,
 ) -> dict[bytes, int]:
     # NB: do not add caching to this function
     rank_to_intbyte = [b for b in range(2**8) if chr(b).isprintable() and chr(b) != " "]
@@ -135,7 +140,9 @@ def dump_tiktoken_bpe(bpe_ranks: dict[bytes, int], tiktoken_bpe_file: str) -> No
             f.write(base64.b64encode(token) + b" " + str(rank).encode() + b"\n")
 
 
-def load_tiktoken_bpe(tiktoken_bpe_file: str, expected_hash: Optional[str]=None) -> dict[bytes, int]:
+def load_tiktoken_bpe(
+    tiktoken_bpe_file: str, expected_hash: Optional[str] = None
+) -> dict[bytes, int]:
     # NB: do not add caching to this function
     contents = read_file_cached(tiktoken_bpe_file, expected_hash)
     return {