diff --git a/cli_demo.py b/cli_demo.py
index 51b1b13..4ff5b41 100644
--- a/cli_demo.py
+++ b/cli_demo.py
@@ -11,6 +11,7 @@ import platform
 import shutil
 from copy import deepcopy
 
+import torch
 from transformers import AutoModelForCausalLM, AutoTokenizer
 from transformers.generation import GenerationConfig
 from transformers.trainer_utils import set_seed
@@ -64,6 +65,13 @@ def _load_model_tokenizer(args):
     return model, tokenizer, config
 
 
+def _gc():
+    import gc
+    gc.collect()
+    if torch.cuda.is_available():
+        torch.cuda.empty_cache()
+
+
 def _clear_screen():
     if platform.system() == "Windows":
         os.system("cls")
@@ -129,10 +137,12 @@ def main():
             elif command in ['clear', 'cl']:
                 _clear_screen()
                 print(_WELCOME_MSG)
+                _gc()
                 continue
             elif command in ['clear-history', 'clh']:
                 print(f'[INFO] All {len(history)} history cleared')
                 history.clear()
+                _gc()
                 continue
             elif command in ['help', 'h']:
                 print(_HELP_MSG)
diff --git a/examples/add_merges.py b/examples/add_merges.py
new file mode 100644
index 0000000..5a7288d
--- /dev/null
+++ b/examples/add_merges.py
@@ -0,0 +1,226 @@
+import argparse
+import base64
+import collections
+import logging
+import unicodedata
+from pathlib import Path
+
+import regex as re
+from tqdm.contrib.logging import tqdm_logging_redirect
+
+PAT_STR = r"""(?i:'s|'t|'re|'ve|'m|'ll|'d)|[^\r\n\p{L}\p{N}]?\p{L}+|\p{N}| ?[^\s\p{L}\p{N}]+[\r\n]*|\s*[\r\n]+|\s+(?!\S)|\s+"""
+
+
+logger = logging.getLogger(__name__)
+
+logging.basicConfig(
+    level=logging.DEBUG, format="[%(asctime)s] %(levelname)s - %(message)s"
+)
+
+
+def load_tiktoken_bpe(tiktoken_bpe_file: str) -> "dict[bytes, int]":
+    contents = open(tiktoken_bpe_file, "rb").read()
+    return {
+        base64.b64decode(token): int(rank)
+        for token, rank in (line.split() for line in contents.splitlines() if line)
+    }
+
+
+def dump_tiktoken_bpe(bpe_ranks: "dict[bytes, int]", tiktoken_bpe_file: str) -> None:
+    with open(tiktoken_bpe_file, "wb") as f:
+        for token, rank in sorted(bpe_ranks.items(), key=lambda x: x[1]):
+            f.write(base64.b64encode(token) + b" " + str(rank).encode() + b"\n")
+
+
+def bytes_to_pieces(the_bytes: bytes) -> "tuple[bytes]":
+    return tuple(bytes([byte]) for byte in the_bytes)
+
+
+def get_pairs(pieces: "tuple[bytes]") -> "set[tuple[bytes, bytes]]":
+    return set(zip(pieces[:-1], pieces[1:]))
+
+
+def get_stats(
+    vocab: "dict[tuple[bytes, ...], int]",
+) -> "dict[tuple[bytes, bytes], int]":
+    pairs = collections.defaultdict(int)
+    for word, freq in vocab.items():
+        for i in range(len(word) - 1):
+            pairs[(word[i], word[i + 1])] += freq
+    return pairs
+
+
+def merge_vocab(
+    pair: "tuple[bytes, bytes]", vocab: "dict[tuple[bytes, ...], int]"
+) -> "dict[tuple[bytes, ...], int]":
+    return {apply_bp(pieces, pair): freq for pieces, freq in vocab.items()}
+
+
+def apply_bp(
+    pieces: "tuple[bytes, ...]", pair: "tuple[bytes, bytes]"
+) -> "tuple[bytes, ...]":
+    new_pieces = []
+    first, second = pair
+    i = 0
+    while i < len(pieces):
+        try:
+            j = pieces.index(first, i)
+            new_pieces.extend(pieces[i:j])
+            i = j
+        except:
+            new_pieces.extend(pieces[i:])
+            break
+
+        if pieces[i] == first and i < len(pieces) - 1 and pieces[i + 1] == second:
+            new_pieces.append(first + second)
+            i += 2
+        else:
+            new_pieces.append(pieces[i])
+            i += 1
+
+    return tuple(new_pieces)
+
+
+def bpe(word: bytes, merges: "dict[bytes,int]") -> "tuple[bytes, ...]":
+    pieces = bytes_to_pieces(word)
+    while len(pieces) > 1:
+        pairs = get_pairs(pieces)
+        pair = min(pairs, key=lambda pair: merges.get(pair[0] + pair[1], float("inf")))
+
+        if pair[0] + pair[1] not in merges:
+            break
+        pieces = apply_bp(pieces, pair)
+        # logger.debug(f"{[(p, p.decode('utf8', errors='replace')) for p in pieces]} {pair} {pieces}")
+    return pieces
+
+
+def best_pair_sort_key(
+    item: "tuple[dict[bytes, bytes], int]",
+) -> "tuple[int, int, int, str, bytes]":
+    # prefer to use the highest frequency or shortest length or lexi sort, sligtly slower
+    pair, freq = item
+    pair_bytes = pair[0] + pair[1]
+    pair_byte_length = len(pair_bytes)
+    pair_str = pair_bytes.decode("utf-8", errors="replace")
+    pair_str_length = len(pair_str)
+    return -freq, pair_str_length, pair_byte_length, pair_str, pair_bytes
+
+
+def learn_bpe(
+    freqs: "dict[str,int]", existing: "dict[bytes, int]"
+) -> "tuple[bytes, bytes]":
+    vocab = {bpe(k.encode("utf-8"), existing): v for k, v in freqs.items()}
+    vocab = {key: value for key, value in vocab.items() if len(key) > 1}
+    new_merges = []
+    with tqdm_logging_redirect() as bar:
+        while vocab:
+            pairs = get_stats(vocab)
+
+            best, freq = min(pairs.items(), key=best_pair_sort_key)
+
+            logger.debug(
+                f'{best} ({(best[0]+best[1]).decode("utf-8", errors="replace")}) is selected as the next merge with freq {freq}'
+            )
+            new_merges.append(best)
+
+            vocab = merge_vocab(best, vocab)
+            vocab = {key: value for key, value in vocab.items() if len(key) > 1}
+            bar.update()
+
+    return new_merges
+
+
+def load_expand_vocab(path: Path) -> "dict[str, int]":
+    freqs = {}
+    with open(path, "r", encoding="utf8") as fin:
+        for line in fin:
+            if not line.strip():
+                continue
+            word, freq = line.strip().split("\t")
+            word = unicodedata.normalize("NFC", word)
+            parts = re.findall(PAT_STR, word)
+            if len(parts) > 1:
+                logger.warning(
+                    f"{word} would be pre-tokenized to {parts}, and thus cannot be added to vocabulary"
+                )
+                continue
+            try:
+                freq = int(freq)
+            except ValueError as _:
+                freq = 1
+            if word in freqs:
+                logger.warning(
+                    f"{word} is repeated, the frequency is increased by this much"
+                )
+                freqs[word] += freq
+            else:
+                freqs[word] = freq
+    return freqs
+
+
+def make_new_merges_by_bpe(
+    input_path: Path, output_path: Path, expand_path: Path, start_id: int
+) -> None:
+    mergeable_ranks = load_tiktoken_bpe(input_path)
+
+    if not start_id or start_id == -1:
+        start_id = len(mergeable_ranks)
+    elif start_id < len(mergeable_ranks):
+        logger.warning(
+            f"start_id {start_id} is too small, existing merges will be overridden, DONOT DO THIS. changed to {len(mergeable_ranks)}"
+        )
+        start_id = len(mergeable_ranks)
+    else:
+        start_id = start_id
+
+    expand_vocab_freqs = load_expand_vocab(expand_path)
+    for word in list(expand_vocab_freqs):
+        token = word.encode("utf-8")
+        if token in mergeable_ranks:
+            logger.warning(f"word {word} is already a token {token}, skipping")
+            del expand_vocab_freqs[word]
+
+    logger.info(f"number of existing merges: {len(mergeable_ranks)}")
+    logger.info(f"number of words for expanding: {len(expand_vocab_freqs)}")
+
+    new_merges = learn_bpe(expand_vocab_freqs, mergeable_ranks)
+    logger.info(f"number of newly learned merges: {len(new_merges)}")
+
+    extra_merges = {p[0] + p[1]: i for i, p in enumerate(new_merges, start=start_id)}
+
+    dump_tiktoken_bpe(extra_merges, output_path)
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter
+    )
+    parser.add_argument("input_path", type=str, help="Path for input tiktoken file")
+    parser.add_argument(
+        "output_path",
+        type=str,
+        help="Path for output tiktoken file, containing only the new merges",
+    )
+    parser.add_argument(
+        "vocab_path",
+        type=str,
+        help="Path for words needed adding, each line is a word and its frequency separated by \\t",
+    )
+    # if the extended vocabulary is for fine-tuning, you better set those correctly (the default is for qwen.tiktoken)
+    # if the extended vocabulary is for pretraining from the start, no need
+    parser.add_argument(
+        "--start_id",
+        type=int,
+        default=151851,
+        help="The start id for new merges. For Qwen tokenizer, this should be 151851 (skipping the existing special tokens)",
+    )
+
+    args = parser.parse_args()
+
+    make_new_merges_by_bpe(
+        args.input_path, args.output_path, args.vocab_path, args.start_id
+    )
+
+
+if __name__ == "__main__":
+    main()
diff --git a/examples/qwen_extra.tiktoken b/examples/qwen_extra.tiktoken
new file mode 100644
index 0000000..e43b9e7
--- /dev/null
+++ b/examples/qwen_extra.tiktoken
@@ -0,0 +1,6 @@
+5LiA5Y+q54yr 151851
+5Y+q54yr 151852
+5piv5LiA5Y+q54yr 151853
+5oiR5piv5LiA5Y+q54yr 151854
+5L2g5piv5LiA5Y+q54yr 151855
+5LuW5piv5LiA5Y+q54yr 151856
diff --git a/examples/qwen_extra_vocab.txt b/examples/qwen_extra_vocab.txt
new file mode 100644
index 0000000..dc75145
--- /dev/null
+++ b/examples/qwen_extra_vocab.txt
@@ -0,0 +1,6 @@
+我是一只猫	20
+你是一只猫	10
+他是一只猫	5
+一只	200
+一只猫	100
+夸张的 比喻手法	20
\ No newline at end of file
diff --git a/examples/tokenizer_showcase.ipynb b/examples/tokenizer_showcase.ipynb
index dca893b..a56557d 100644
--- a/examples/tokenizer_showcase.ipynb
+++ b/examples/tokenizer_showcase.ipynb
@@ -9,8 +9,6 @@
      "name": "stderr",
      "output_type": "stream",
      "text": [
-      "TqdmWarning: IProgress not found. Please update jupyter and ipywidgets. See https://ipywidgets.readthedocs.io/en/stable/user_install.html\n",
-      "  from .autonotebook import tqdm as notebook_tqdm\n",
       "None of PyTorch, TensorFlow >= 2.0, or Flax have been found. Models won't be available and only tokenizers, configuration and file/data utilities can be used.\n"
      ]
     }
@@ -414,6 +412,142 @@
    "source": [
     "tokenizer._convert_token_to_id('<|extra_204|>')"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Vocabulary Expansion"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 19,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "{'input_ids': [35946, 99639, 91680, 100472], 'token_type_ids': [0, 0, 0, 0], 'attention_mask': [1, 1, 1, 1]}"
+      ]
+     },
+     "execution_count": 19,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "tokenizer(\"我是一只猫\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 20,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "[99639, 91680, 100472]"
+      ]
+     },
+     "execution_count": 20,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "tokenizer.encode(\"是一只猫\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 21,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "tokenizer = AutoTokenizer.from_pretrained('Qwen/Qwen-7B', trust_remote_code=True, extra_vocab_file=\"qwen_extra.tiktoken\")\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 22,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "151857"
+      ]
+     },
+     "execution_count": 22,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "len(tokenizer)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 23,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "{'input_ids': [151854], 'token_type_ids': [0], 'attention_mask': [1]}"
+      ]
+     },
+     "execution_count": 23,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "tokenizer(\"我是一只猫\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 24,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'我是一只猫'"
+      ]
+     },
+     "execution_count": 24,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "tokenizer.decode(tokenizer.encode(\"我是一只猫\"))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 25,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "[151853]"
+      ]
+     },
+     "execution_count": 25,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "tokenizer.encode(\"是一只猫\")"
+   ]
   }
  ],
  "metadata": {
@@ -432,7 +566,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.10.9"
+   "version": "3.10.12"
   },
   "orig_nbformat": 4
  },
diff --git a/openai_api.py b/openai_api.py
index 193ada4..934814f 100644
--- a/openai_api.py
+++ b/openai_api.py
@@ -21,12 +21,21 @@ from transformers import AutoTokenizer, AutoModelForCausalLM
 from transformers.generation import GenerationConfig
 
 
+def _gc(forced: bool = False):
+    global args
+    if args.disable_gc and not forced:
+        return
+
+    import gc
+    gc.collect()
+    if torch.cuda.is_available():
+        torch.cuda.empty_cache()
+
+
 @asynccontextmanager
 async def lifespan(app: FastAPI):  # collects GPU memory
     yield
-    if torch.cuda.is_available():
-        torch.cuda.empty_cache()
-        torch.cuda.ipc_collect()
+    _gc(forced=True)
 
 
 app = FastAPI(lifespan=lifespan)
@@ -392,6 +401,8 @@ async def create_chat_completion(request: ChatCompletionRequest):
             **gen_kwargs
         )
         print(f"<chat>\n{history}\n{query}\n<!-- *** -->\n{response}\n</chat>")
+    _gc()
+
     response = trim_stop_words(response, stop_words)
     if request.functions:
         choice_data = parse_response(response)
@@ -453,6 +464,8 @@ async def predict(
     yield "{}".format(chunk.model_dump_json(exclude_unset=True))
     yield "[DONE]"
 
+    _gc()
+
 
 def _get_args():
     parser = ArgumentParser()
@@ -476,6 +489,8 @@ def _get_args():
         help="Demo server name. Default: 127.0.0.1, which is only visible from the local computer."
         " If you want other computers to access your server, use 0.0.0.0 instead.",
     )
+    parser.add_argument("--disable-gc", action="store_true",
+                        help="Disable GC after each response generated.")
 
     args = parser.parse_args()
     return args
diff --git a/tokenization_note.md b/tokenization_note.md
index 085e04f..fe402d9 100644
--- a/tokenization_note.md
+++ b/tokenization_note.md
@@ -125,3 +125,122 @@ The new default is the same as
 {'input_ids': [1350, 445, 151643, 899], 'token_type_ids': [0, 0, 0, 0], 'attention_mask': [1, 1, 1, 1]}
 ```
 
+## Vocabulary Expansion
+
+> WARNING: Read carefully, be aware of what you are doing, and use at your own risk. 
+> There are certain caveats regarding how your vocabulary is produced.
+
+The tokenizer of Qwen models are based on BPE and you cannot directly expand the vocabulary by adding words to the vocabulary. 
+The intermediate merges are needed for tokenization.
+Please follow the steps to obtain such information.
+
+1. Prepare a plain text file `qwen_extra_vocab.txt`, where each line contains a token and its frequency separated by `\t`. 
+
+   An example is given below:
+   ```
+   我是一只猫	20
+   你是一只猫	10
+   他是一只猫	5
+   一只	200
+   一只猫	100
+   夸张的 比喻手法	20
+   ```
+   The frequencies are needed to compute the BPE.
+
+   
+
+2. Prepare the base vocabulary file, e.g., `qwen.tiktoken`, and determine the start index for new tokens.
+   
+   There are 151,643 regular tokens and 208 control tokens in the vocabulary for Qwen models. 
+   For simplicity, the start index can be set as 151,851, which is the default value. 
+   You can, of course, override the many inactive control tokens, but you will need to modify the tokenizer code. 
+
+3. Run the following command:
+   ```
+   python add_merges.py qwen.tiktoken qwen_extra.tiktoken qwen_extra_vocab.txt
+   ```
+   `add_merges.py` can be found [here](examples/add_merges.py).
+   It will learn the new merges based on the provided `qwen_extra_vocab.txt`. 
+   The new tokens and their indices will be stored in `qwen_extra.tiktoken`. 
+   Modify the paths as you wish.
+
+   It is a pure Python implementation, so please expect it to be slow if you are adding a lot of words.
+
+   Please note that not all words can be added due to pre-tokenization. 
+   You will get warnings if you try to add such word:
+   ```
+   WARNING - 夸张的 比喻手法 would be pre-tokenized to ['夸张的', ' 比喻手法'], and thus cannot be added to vocabulary
+   WARNING - word 一只 is already a token b'\xe4\xb8\x80\xe5\x8f\xaa', skipping
+   INFO - number of existing merges: 151643
+   INFO - number of words for expanding: 4
+   DEBUG - (b'\xe4\xb8\x80\xe5\x8f\xaa', b'\xe7\x8c\xab') (一只猫) is selected as the next merge with freq 100
+   DEBUG - (b'\xe5\x8f\xaa', b'\xe7\x8c\xab') (只猫) is selected as the next merge with freq 35
+   DEBUG - (b'\xe6\x98\xaf\xe4\xb8\x80', b'\xe5\x8f\xaa\xe7\x8c\xab') (是一只猫) is selected as the next merge with freq 35
+   DEBUG - (b'\xe6\x88\x91', b'\xe6\x98\xaf\xe4\xb8\x80\xe5\x8f\xaa\xe7\x8c\xab') (我是一只猫) is selected as the next merge with freq 20
+   DEBUG - (b'\xe4\xbd\xa0', b'\xe6\x98\xaf\xe4\xb8\x80\xe5\x8f\xaa\xe7\x8c\xab') (你是一只猫) is selected as the next merge with freq 10
+   DEBUG - (b'\xe4\xbb\x96', b'\xe6\x98\xaf\xe4\xb8\x80\xe5\x8f\xaa\xe7\x8c\xab') (他是一只猫) is selected as the next merge with freq 5
+   INFO - number of newly learned merges: 6
+   ```
+
+The `qwen_extra.tiktoken` will contain the following lines:
+```
+5LiA5Y+q54yr 151851
+5Y+q54yr 151852
+5piv5LiA5Y+q54yr 151853
+5oiR5piv5LiA5Y+q54yr 151854
+5L2g5piv5LiA5Y+q54yr 151855
+5LuW5piv5LiA5Y+q54yr 151856
+```
+
+You may use the file as follows in your code:
+``` python
+from transformers import AutoTokenizer
+
+>>> tokenizer = AutoTokenizer.from_pretrained("Qwen/Qwen-7B", trust_remote_code=True, extra_vocab_file="qwen_extra.tiktoken")
+
+>>> len(tokenizer)
+151857
+
+>>> tokenizer("我是一只猫")
+{'input_ids': [151854], 'token_type_ids': [0], 'attention_mask': [1]}
+```
+Note: You need the latest tokenizer code, i.e., after 2013-10-08, to use the `extra_vocab_file` argument.
+Otherwise, you need to manually append `qwen.tiktoken` (of which path varies with your configuration) with the content from `qwen_extra.tiktoken`.
+
+Certainly, you will need to finetune the model for the new tokens to work.
+
+
+### Caveats
+
+
+The tokenizer of Qwen operates directly on UTF-8 byte sequences, unlike others, e.g., SentencePiece that operates on UTF-8 codepoints/characters and falls back to UTF-8 byte sequences for the unknown (IIRC). 
+The thing is if the frequencies are computed on limited data, the UTF-8 codepoint boundary may not be correctly recognized.
+In theory, it could be a problem for fine-tuned models using the expanded vocabulary with limited data.
+
+For example, it could happen that `b'\x80\xe5'` might be merged first for the UTF-8 byte sequence `b'\xe4\xb8\x80\xe5\x8f\xaa'` of the string `一只`, across the UTF-8 codepoint of `一`(`b'\xe4\xb8\x80'`) and `只` (`b'\xe5\x8f\xaa'`).
+Normally, this would work just fine for known words, but for actually unknown words, unusual merges may happen, which may not be well understood for the pre-trained model.
+
+Our advice is that to be safe, you should gather the UTF-8 codepoints from all the words you need to add, and also add them to the file with frequencies higher than the sum of the frequencies of the corresponding words.
+But since Qwen has most of the Chinese words, it could be okay to just add the Chinese words alone.
+
+For curious minds, you will also notice that in the given example, `一只` is a token and `只猫` is also learned as a new token. 
+The reason is that `是一` is also a token in Qwen and has higher merging priority than `一只`, such that the merging path for `是|一|只|猫` is `是一|只|猫 -> 是一|只猫 -> 是一只猫` (omitting the UTF-8 byte merges).
+
+This is the characteristic for plain BPE: it is based solely on distribution, meaning it does not have knowledge of which bytes can form a valid UTF-8 codepoint, character, or meaningful word.
+
+The byproduct is that text may be sub-tokenized differently in different contexts, even for words containing only ASCII characters.
+```python
+>>> tokenizer.tokenize("Panda")
+[b'P', b'anda']
+
+>>> tokenizer.tokenize(" Panda")
+[b' Panda']
+
+>>> tokenizer.tokenize("Pandas")
+[b'P', b'andas']
+
+>>> tokenizer.tokenize(" Pandas")
+[b' Pand', b'as']
+```
+This simply suggests that those combinations occur more frequently in the data.
+If you have vast amount of training data, it should not be a problem.
\ No newline at end of file
diff --git a/web_demo.py b/web_demo.py
index 8332433..a0147f9 100755
--- a/web_demo.py
+++ b/web_demo.py
@@ -107,6 +107,13 @@ def _parse_text(text):
     return text
 
 
+def _gc():
+    import gc
+    gc.collect()
+    if torch.cuda.is_available():
+        torch.cuda.empty_cache()
+
+
 def _launch_demo(args, model, tokenizer, config):
 
     def predict(_query, _chatbot, _task_history):
@@ -138,9 +145,7 @@ def _launch_demo(args, model, tokenizer, config):
     def reset_state(_chatbot, _task_history):
         _task_history.clear()
         _chatbot.clear()
-        import gc
-        gc.collect()
-        torch.cuda.empty_cache()
+        _gc()
         return _chatbot
 
     with gr.Blocks() as demo: