diff --git a/factscore/atomic_facts.py b/factscore/atomic_facts.py
index d237ef6..e5f9a62 100644
--- a/factscore/atomic_facts.py
+++ b/factscore/atomic_facts.py
@@ -18,12 +18,12 @@
 
 
 class AtomicFactGenerator(object):
-    def __init__(self, key_path, demon_dir, gpt3_cache_file=None):
+    def __init__(self, key_path, demon_dir, cache_file=None):
         self.nlp = spacy.load("en_core_web_sm")
         self.is_bio = True
         self.demon_path = os.path.join(demon_dir, "demons.json" if self.is_bio else "demons_complex.json")
 
-        self.openai_lm = OpenAIModel("InstructGPT", cache_file=gpt3_cache_file, key_path=key_path)
+        self.openai_lm = OpenAIModel("ChatGPT", cache_file=cache_file, key_path=key_path)
 
         # get the demos
         with open(self.demon_path, 'r') as f:
@@ -103,40 +103,35 @@ def get_init_atomic_facts_from_sentence(self, sentences, cost_estimate=None):
         n = 7 if is_bio else 8
 
         prompts = []
-        prompt_to_sent = {}
         atoms = {}
         for sentence in sentences:
             if sentence in atoms:
                 continue
             top_machings = best_demos(sentence, self.bm25, list(demons.keys()), k)
-            prompt = ""
+            prompt = []
 
             for i in range(n):
-                prompt = prompt + "Please breakdown the following sentence into independent facts: {}\n".format(list(demons.keys())[i])
-                for fact in demons[list(demons.keys())[i]]:
-                    prompt = prompt + "- {}\n".format(fact)
-                prompt = prompt + "\n"
+                prompt.append({"role": "user", "content": f"Please breakdown the following sentence into independent facts: {list(demons.keys())[i]}"})
+                prompt.append({"role": "assistant", "content": "\n".join(f"- {fact}" for fact in demons[list(demons.keys())[i]])})
 
             for match in top_machings:
-                prompt = prompt + "Please breakdown the following sentence into independent facts: {}\n".format(match)
-                for fact in demons[match]:
-                    prompt = prompt + "- {}\n".format(fact)
-                prompt = prompt + "\n"
-            prompt = prompt + "Please breakdown the following sentence into independent facts: {}\n".format(sentence)
+                prompt.append({"role": "user", "content": f"Please breakdown the following sentence into independent facts: {match}"})
+                prompt.append({"role": "assistant", "content": "\n".join(f"- {fact}" for fact in demons[match])})
+
+            prompt.append({"role": "user", "content": f"Please breakdown the following sentence into independent facts: {sentence}"})
             prompts.append(prompt)
-            prompt_to_sent[prompt] = sentence
 
         if cost_estimate:
             total_words_estimate = 0
             for prompt in prompts:
-                if cost_estimate == "consider_cache" and (prompt.strip() + "_0") in self.openai_lm.cache_dict:
+                if cost_estimate == "consider_cache" and self.openai_lm.cache_key(prompt) in self.openai_lm.cache_dict:
                     continue
-                total_words_estimate += len(prompt.split())
+                total_words_estimate += sum(len(m["content"].split()) for m in prompt)
             return total_words_estimate
         else:
-            for prompt in prompts:
+            for prompt, sentence in zip(prompts, sentences):
                 output, _ = self.openai_lm.generate(prompt)
-                atoms[prompt_to_sent[prompt]] = text_to_sentences(output)
+                atoms[sentence] = text_to_sentences(output)
 
             for key, value in demons.items():
                 if key not in atoms:
@@ -342,4 +337,4 @@ def main():
     print(para_breaks)
 
 if __name__ == "__main__":
-    main()
\ No newline at end of file
+    main()
diff --git a/factscore/factscorer.py b/factscore/factscorer.py
index 6793fe5..573acdd 100644
--- a/factscore/factscorer.py
+++ b/factscore/factscorer.py
@@ -94,7 +94,7 @@ def print_cost_estimates(self, total_words, task, model):
         if model == "davinci-003":
             rate = 0.02
         elif model == "gpt-3.5-turbo":
-            rate = 0.002
+            rate = 0.0015
 
         total_cost = total_tokens * rate / 1000
 
@@ -128,14 +128,14 @@ def get_score(self,
             if self.af_generator is None:
                 self.af_generator = AtomicFactGenerator(key_path=self.openai_key,
                                                         demon_dir=os.path.join(self.data_dir, "demos"),
-                                                        gpt3_cache_file=os.path.join(self.cache_dir, "InstructGPT.pkl"))
+                                                        cache_file=os.path.join(self.cache_dir, "ChatGPT.pkl"))
 
             # estimate the total cost of atomic fact generation
             total_words = 0
             for gen in generations:
                 total_words += self.af_generator.run(gen, cost_estimate=self.cost_estimate)
 
-            self.print_cost_estimates(total_words, task="atomic fact generation", model="davinci-003")
+            self.print_cost_estimates(total_words, task="atomic fact generation", model="gpt-3.5-turbo")
 
             if verbose:
                 topics = tqdm(topics)
diff --git a/factscore/lm.py b/factscore/lm.py
index bcdfe1f..4ab58ad 100644
--- a/factscore/lm.py
+++ b/factscore/lm.py
@@ -14,9 +14,17 @@ def load_model(self):
         # load the model and put it as self.model
         raise NotImplementedError()
 
+    def cache_key(self, prompt, sample_idx=0):
+        if isinstance(prompt, str):
+            prompt = prompt.strip() # it's important not to end with a whitespace
+
+        return f"{prompt}_{sample_idx}"
+
     def generate(self, prompt, sample_idx=0, max_sequence_length=2048, max_output_length=128):
-        prompt = prompt.strip() # it's important not to end with a whitespace
-        cache_key = f"{prompt}_{sample_idx}"
+        if isinstance(prompt, str):
+            prompt = prompt.strip() # it's important not to end with a whitespace
+
+        cache_key = self.cache_key(prompt, sample_idx=sample_idx)
 
         if cache_key in self.cache_dict:
             return self.cache_dict[cache_key]
@@ -24,7 +32,7 @@ def generate(self, prompt, sample_idx=0, max_sequence_length=2048, max_output_le
         if self.model is None:
             self.load_model()
 
-        if prompt.endswith(" True or False?\nAnswer:"):
+        if isinstance(prompt, str) and prompt.endswith(" True or False?\nAnswer:"):
             generated = self._generate(prompt, max_sequence_length=max_sequence_length, max_output_length=1)
         else:
             generated = self._generate(prompt, max_sequence_length=max_sequence_length, max_output_length=max_output_length)
diff --git a/factscore/openai_lm.py b/factscore/openai_lm.py
index 12e8adb..cd68935 100644
--- a/factscore/openai_lm.py
+++ b/factscore/openai_lm.py
@@ -24,6 +24,33 @@ def load_model(self):
         openai.api_key = api_key.strip()
         self.model = self.model_name
 
+    def _construct_messages(self, prompt):
+        if isinstance(prompt, str):
+            return [{"role": "user", "content": prompt}]
+
+        if isinstance(prompt, dict):
+            role = prompt.get("role", None)
+            if not _valid_role(role):
+                raise ValueError("Invalid role {role}!")
+
+            content = prompt.get("content", None)
+            if not isinstance(content, str):
+                raise ValueError("Invalid content! Must be a string.")
+
+            return [prompt]
+
+        if isinstance(prompt, list):
+            for i, m in enumerate(prompt, 1):
+                _validate_message(m)
+
+                if i > 1 and m["role"] == "system":
+                    raise ValueError("Only the first message can be a system message")
+
+                if i == len(prompt) and m["role"] != "user":
+                    raise ValueError("The last message must be a user message")
+
+            return prompt
+
     def _generate(self, prompt, max_sequence_length=2048, max_output_length=128):
         if self.add_n % self.save_interval == 0:
             self.save_cache()
@@ -31,9 +58,9 @@ def _generate(self, prompt, max_sequence_length=2048, max_output_length=128):
         # This should be about generating a response from the prompt, no matter what the application is
         if self.model_name == "ChatGPT":
             # Construct the prompt send to ChatGPT
-            message = [{"role": "user", "content": prompt}]
+            messages = self._construct_messages(prompt)
             # Call API
-            response = call_ChatGPT(message, temp=self.temp, max_len=max_sequence_length)
+            response = call_ChatGPT(messages, temp=self.temp, max_len=max_sequence_length)
             # Get the output from the response
             output = response["choices"][0]["message"]["content"]
             return output, response
@@ -46,7 +73,28 @@ def _generate(self, prompt, max_sequence_length=2048, max_output_length=128):
         else:
             raise NotImplementedError()
 
-def call_ChatGPT(message, model_name="gpt-3.5-turbo", max_len=1024, temp=0.7, verbose=False):
+
+ROLES = ["system", "user", "assistant"]
+
+
+def _valid_role(role):
+    return role in ROLES
+
+
+def _validate_message(message):
+    if not isinstance(message, dict):
+        raise ValueError("message must be a dict")
+
+    role = message.get("role", None)
+    if not _valid_role(role):
+        raise ValueError("Invalid role {role}!")
+
+    content = message.get("content", None)
+    if not isinstance(content, str):
+        raise ValueError("Invalid content! Must be a string.")
+
+
+def call_ChatGPT(messages, model_name="gpt-3.5-turbo", max_len=1024, temp=0.7, verbose=False):
     # call GPT-3 API until result is provided and then return it
     response = None
     received = False
@@ -54,7 +102,7 @@ def call_ChatGPT(message, model_name="gpt-3.5-turbo", max_len=1024, temp=0.7, ve
     while not received:
         try:
             response = openai.ChatCompletion.create(model=model_name,
-                                                    messages=message,
+                                                    messages=messages,
                                                     max_tokens=max_len,
                                                     temperature=temp)
             received = True
@@ -64,7 +112,7 @@ def call_ChatGPT(message, model_name="gpt-3.5-turbo", max_len=1024, temp=0.7, ve
             error = sys.exc_info()[0]
             if error == openai.error.InvalidRequestError:
                 # something is wrong: e.g. prompt too long
-                logging.critical(f"InvalidRequestError\nPrompt passed in:\n\n{message}\n\n")
+                logging.critical(f"InvalidRequestError\nPrompt passed in:\n\n{messages}\n\n")
                 assert False
             
             logging.error("API error: %s (%d). Waiting %dsec" % (error, num_rate_errors, np.power(2, num_rate_errors)))