diff --git a/outlines/serve/vllm.py b/outlines/serve/vllm.py
index ee9c7000e..7bfd051ae 100644
--- a/outlines/serve/vllm.py
+++ b/outlines/serve/vllm.py
@@ -1,12 +1,11 @@
 """Make vLLM compatible with Outlines' guided generation."""
 import json
 import math
-from collections import defaultdict
-from typing import DefaultDict, List
+from typing import Dict, List, Tuple
 
 import torch
 
-from outlines.fsm.fsm import RegexFSM
+from outlines.fsm.fsm import FSMState, RegexFSM
 from outlines.fsm.json_schema import build_regex_from_object
 
 
@@ -29,7 +28,7 @@ def _patched_apply_logits_processors(
                 logits_row = logits[logits_row_idx]
                 token_ids = sampling_metadata.seq_data[seq_id].output_token_ids
                 for logits_processor in logits_processors:
-                    logits_row = logits_processor(seq_id, token_ids, logits_row)
+                    logits_row = logits_processor(token_ids, logits_row)
                 logits[logits_row_idx] = logits_row
                 logits_row_idx += 1
         else:
@@ -39,7 +38,58 @@ def _patched_apply_logits_processors(
     return logits
 
 
+def adapt_tokenizer(tokenizer):
+    """Adapt vLLM's tokenizer to use to compile the FSM.
+
+    The API of Outlines tokenizers is slightly different to that of
+    `transformers`. In addition, we need to handle the missing spaces to
+    Llama's tokenizer to be able to compile FSMs for this model.
+
+    """
+    tokenizer.vocabulary = tokenizer.get_vocab()
+    tokenizer.special_tokens = set(tokenizer.all_special_tokens)
+
+    def convert_token_to_string(token: str) -> str:
+        from transformers.file_utils import SPIECE_UNDERLINE
+
+        string = tokenizer.convert_tokens_to_string([token])
+
+        # A hack to handle missing spaces to HF's Llama tokenizers
+        if token.startswith(SPIECE_UNDERLINE) or token == "<0x20>":
+            return " " + string
+
+        return string
+
+    tokenizer.convert_token_to_string = convert_token_to_string
+
+    return tokenizer
+
+
+class CachedRegexFSM(RegexFSM):
+    def __init__(self, regex_string: str, adapted_tokenizer):
+        super().__init__(regex_string, adapted_tokenizer)
+        self.state_cache: Dict[int, FSMState] = {}
+
+    def get_state_by_token_ids(self, input_ids: Tuple[int]) -> FSMState:
+        state_key = hash(input_ids)
+
+        if not input_ids:
+            self.state_cache[state_key] = FSMState(0)
+
+        elif state_key not in self.state_cache:
+            prev_state_key = hash(input_ids[:-1])
+            prev_state = self.state_cache[prev_state_key]
+
+            last_token = input_ids[-1]
+            new_state = self.next_state(prev_state, last_token)
+            self.state_cache[state_key] = new_state
+
+        return self.state_cache[state_key]
+
+
 class RegexLogitsProcessor:
+    fsm_cache: Dict[str, CachedRegexFSM] = {}
+
     def __init__(self, regex_string, llm):
         """Compile the FSM that drives the regex-guided generation.
 
@@ -51,25 +101,19 @@ def __init__(self, regex_string, llm):
             An instance of `vllm.LLM`
 
         """
-        tokenizer = self.adapt_tokenizer(llm.tokenizer.tokenizer)
+        adapted_tokenizer = adapt_tokenizer(llm.tokenizer.tokenizer)
+
+        fsm = self.fsm_cache.get(regex_string)
+        if fsm is None:
+            fsm = CachedRegexFSM(regex_string, adapted_tokenizer)
+            self.fsm_cache[regex_string] = fsm
 
-        fsm = RegexFSM(regex_string, tokenizer)
         self.fsm = fsm
 
-    def __call__(
-        self, seq_id: int, input_ids: List[int], scores: torch.Tensor
-    ) -> torch.Tensor:
+    def __call__(self, input_ids: List[int], scores: torch.Tensor) -> torch.Tensor:
         """Use the FSM to bias the logits before sampling the next token."""
-
-        if len(input_ids) == 0:  # Initialize the fsm states
-            self.fsm_state: DefaultDict[int, int] = defaultdict(int)
-        else:
-            last_token = input_ids[-1]
-            self.fsm_state[seq_id] = self.fsm.next_state(
-                self.fsm_state[seq_id], last_token
-            )
-
-        allowed_tokens = self.fsm.allowed_token_ids(self.fsm_state[seq_id])
+        state = self.fsm.get_state_by_token_ids(tuple(input_ids))
+        allowed_tokens = self.fsm.allowed_token_ids(state)
 
         mask = torch.full((scores.shape[-1],), -math.inf, device=scores.device)
         mask[allowed_tokens] = 0
@@ -77,32 +121,6 @@ def __call__(
 
         return biased_scores
 
-    def adapt_tokenizer(self, tokenizer):
-        """Adapt vLLM's tokenizer to use to compile the FSM.
-
-        The API of Outlines tokenizers is slightly different to that of
-        `transformers`. In addition we need to handle the missing spaces to
-        Llama's tokenizer to be able to compile FSMs for this model.
-
-        """
-        tokenizer.vocabulary = tokenizer.get_vocab()
-        tokenizer.special_tokens = set(tokenizer.all_special_tokens)
-
-        def convert_token_to_string(token: str) -> str:
-            from transformers.file_utils import SPIECE_UNDERLINE
-
-            string = tokenizer.convert_tokens_to_string([token])
-
-            # A hack to handle missing spaces to HF's Llama tokenizers
-            if token.startswith(SPIECE_UNDERLINE) or token == "<0x20>":
-                return " " + string
-
-            return string
-
-        tokenizer.convert_token_to_string = convert_token_to_string
-
-        return tokenizer
-
 
 class JSONLogitsProcessor(RegexLogitsProcessor):
     def __init__(self, schema, llm):
@@ -118,5 +136,7 @@ def __init__(self, schema, llm):
         """
         if isinstance(schema, dict):
             schema = json.dumps(schema)
+
         regex_string = build_regex_from_object(schema)
+
         super().__init__(regex_string, llm)
diff --git a/tests/serve/test_vllm.py b/tests/serve/test_vllm.py
new file mode 100644
index 000000000..77280f4e5
--- /dev/null
+++ b/tests/serve/test_vllm.py
@@ -0,0 +1,118 @@
+import re
+
+import torch
+
+from outlines.serve.vllm import RegexLogitsProcessor, _patched_apply_logits_processors
+
+
+class MockTokenizer:
+    vocabulary = {
+        **{chr(i): i for i in range(256)},
+        **{"eos": 256},
+    }
+    special_tokens = {"eos"}
+    eos_token_id = 256
+
+    @property
+    def inverse_vocabulary(self):
+        return {v: k for k, v in self.vocabulary.items()}
+
+    def decode(self, token_ids):
+        return "".join([self.inverse_vocabulary[t] for t in token_ids])
+
+    ####
+    # vLLM tokenizer features
+    ####
+    all_special_tokens = list(special_tokens)
+
+    def convert_tokens_to_string(self, token):
+        return token[0]
+
+    def get_vocab(self):
+        return MockTokenizer.vocabulary
+
+
+class MockTokenizerGroup:
+    tokenizer = MockTokenizer()
+
+
+class MockModel:
+    tokenizer = MockTokenizerGroup()
+
+
+def sample_from_logits(logits):
+    probs = torch.exp(logits) / torch.sum(torch.exp(logits))
+    return torch.multinomial(probs, 1).item()
+
+
+def test_time_regexp():
+    pattern = r"(0?[1-9]|1[0-2]):[0-5]\d\s?(am|pm)?"
+    llm = MockModel()
+    logits_processor = RegexLogitsProcessor(pattern, llm)
+
+    token_ids = []
+    while True:
+        random_scores = -10 + 20 * torch.rand(len(llm.tokenizer.vocabulary))
+        logits = logits_processor(
+            input_ids=token_ids,
+            scores=random_scores,
+        )
+        new_token_id = sample_from_logits(logits)
+        if new_token_id == llm.tokenizer.eos_token_id:
+            break
+        token_ids.append(new_token_id)
+
+    assert re.fullmatch(pattern, llm.tokenizer.decode(token_ids)) is not None
+
+
+def test_time_regexp_multiple_samples():
+    num_seq = 64
+
+    pattern = r"(0?[1-9]|1[0-2]):[0-5]\d\ ?(am|pm)?"
+    llm = MockModel()
+
+    class MockSeqData:
+        def __init__(self):
+            self.output_token_ids = []
+
+    class MockSamplingParams:
+        logits_processors = [RegexLogitsProcessor(pattern, llm)]
+
+    class MockSamplingMeta:
+        seq_groups = [[range(num_seq), MockSamplingParams()]]  # seq_ids
+        seq_data = {seq_id: MockSeqData() for seq_id in range(num_seq)}
+
+    sampling_meta = MockSamplingMeta()
+
+    results = []
+    while True:
+        complete_seq_ids = set()
+
+        logits = torch.randn(len(sampling_meta.seq_data), len(llm.tokenizer.vocabulary))
+        new_logits = _patched_apply_logits_processors(logits, sampling_meta)
+        seq_ids = sorted(sampling_meta.seq_groups[0][0])
+        for logits_row, seq_id in zip(new_logits, seq_ids):
+            new_token_id = sample_from_logits(logits_row)
+            if new_token_id == llm.tokenizer.eos_token_id:
+                complete_seq_ids.add(seq_id)
+                results.append(sampling_meta.seq_data[seq_id].output_token_ids)
+            else:
+                sampling_meta.seq_data[seq_id].output_token_ids.append(new_token_id)
+
+        if complete_seq_ids:
+            seq_datas = [
+                sd
+                for seq_id, sd in sampling_meta.seq_data.items()
+                if seq_id not in complete_seq_ids
+            ]
+            sampling_meta.seq_data = {
+                i: seq_data for i, seq_data in enumerate(seq_datas)
+            }
+            sampling_meta.seq_groups[0][0] = range(len(sampling_meta.seq_data))
+
+        if not sampling_meta.seq_data:
+            break
+
+    assert len(results) == num_seq
+    for result in results:
+        assert re.fullmatch(pattern, llm.tokenizer.decode(result)) is not None