diff --git a/aider/history.py b/aider/history.py
index 36d148344..2aeda9483 100644
--- a/aider/history.py
+++ b/aider/history.py
@@ -1,8 +1,6 @@
 import argparse
 import json
 
-import tiktoken
-
 from aider import models, prompts
 from aider.dump import dump  # noqa: F401
 from aider.sendchat import simple_send_with_retries
diff --git a/aider/models/__init__.py b/aider/models/__init__.py
index ed9d684f7..f299009c6 100644
--- a/aider/models/__init__.py
+++ b/aider/models/__init__.py
@@ -1,6 +1,4 @@
 from .model import Model
-from .openai import OpenAIModel
-from .openrouter import OpenRouterModel
 
 GPT4 = Model.create("gpt-4")
 GPT35 = Model.create("gpt-3.5-turbo")
diff --git a/aider/models/openrouter.py b/aider/models/openrouter.py
index 6c78b560a..4cb99c9d7 100644
--- a/aider/models/openrouter.py
+++ b/aider/models/openrouter.py
@@ -23,7 +23,7 @@ class OpenRouterModel(Model):
         self.tokenizer = tiktoken.get_encoding("cl100k_base")
 
         global cached_model_details
-        if cached_model_details == None:
+        if cached_model_details is None:
             cached_model_details = openai.Model.list().data
         found = next(
             (details for details in cached_model_details if details.get("id") == name), None