diff --git a/aider/litellm.py b/aider/litellm.py
index 2c0389b54..4c97c0a94 100644
--- a/aider/litellm.py
+++ b/aider/litellm.py
@@ -6,9 +6,23 @@ warnings.filterwarnings("ignore", category=UserWarning, module="pydantic")
 os.environ["OR_SITE_URL"] = "http://aider.chat"
 os.environ["OR_APP_NAME"] = "Aider"
 
-import litellm  # noqa: E402
+# `import litellm` takes 1.5 seconds, defer it!
 
-litellm.suppress_debug_info = True
-litellm.set_verbose = False
+
+class LazyLiteLLM:
+    def __init__(self):
+        self._lazy_module = None
+
+    def __getattr__(self, name):
+        if self._lazy_module is None:
+            self._lazy_module = __import__("litellm")
+
+            self._lazy_module.suppress_debug_info = True
+            self._lazy_module.set_verbose = False
+
+        return getattr(self._lazy_module, name)
+
+
+litellm = LazyLiteLLM()
 
 __all__ = [litellm]
diff --git a/aider/models.py b/aider/models.py
index 565890501..41dd3e6b7 100644
--- a/aider/models.py
+++ b/aider/models.py
@@ -15,6 +15,44 @@ from aider.litellm import litellm
 
 DEFAULT_MODEL_NAME = "gpt-4o"
 
+OPENAI_MODELS = """
+gpt-4
+gpt-4o
+gpt-4o-2024-05-13
+gpt-4-turbo-preview
+gpt-4-0314
+gpt-4-0613
+gpt-4-32k
+gpt-4-32k-0314
+gpt-4-32k-0613
+gpt-4-turbo
+gpt-4-turbo-2024-04-09
+gpt-4-1106-preview
+gpt-4-0125-preview
+gpt-4-vision-preview
+gpt-4-1106-vision-preview
+gpt-3.5-turbo
+gpt-3.5-turbo-0301
+gpt-3.5-turbo-0613
+gpt-3.5-turbo-1106
+gpt-3.5-turbo-0125
+gpt-3.5-turbo-16k
+gpt-3.5-turbo-16k-0613
+"""
+
+OPENAI_MODELS = [ln.strip for ln in OPENAI_MODELS.splitlines() if ln.strip()]
+
+ANTHROPIC_MODELS = """
+claude-2
+claude-2.1
+claude-3-haiku-20240307
+claude-3-opus-20240229
+claude-3-sonnet-20240229
+claude-3-5-sonnet-20240620
+"""
+
+ANTHROPIC_MODELS = [ln.strip for ln in ANTHROPIC_MODELS.splitlines() if ln.strip()]
+
 
 @dataclass
 class ModelSettings:
@@ -491,7 +529,25 @@ class Model:
         with Image.open(fname) as img:
             return img.size
 
+    def fast_validate_environment(self):
+        """Fast path for common models. Avoids forcing litellm import."""
+
+        model = self.name
+        if model in OPENAI_MODELS:
+            var = "OPENAI_API_KEY"
+        elif model in ANTHROPIC_MODELS:
+            var = "ANTHROPIC_API_KEY"
+        else:
+            return
+
+        if os.environ.get(var):
+            return dict(keys_in_environment=[var], missing_keys=[])
+
     def validate_environment(self):
+        res = self.fast_validate_environment()
+        if res:
+            return res
+
         # https://github.com/BerriAI/litellm/issues/3190
 
         model = self.name
diff --git a/aider/sendchat.py b/aider/sendchat.py
index 78e16ae64..43153d2ec 100644
--- a/aider/sendchat.py
+++ b/aider/sendchat.py
@@ -15,40 +15,49 @@ CACHE = None
 # CACHE = Cache(CACHE_PATH)
 
 
-def should_giveup(e):
-    if not hasattr(e, "status_code"):
-        return False
+def lazy_litellm_retry_decorator(func):
+    def wrapper(*args, **kwargs):
+        def should_giveup(e):
+            if not hasattr(e, "status_code"):
+                return False
 
-    if type(e) in (
-        httpx.ConnectError,
-        httpx.RemoteProtocolError,
-        httpx.ReadTimeout,
-    ):
-        return False
+            if type(e) in (
+                httpx.ConnectError,
+                httpx.RemoteProtocolError,
+                httpx.ReadTimeout,
+            ):
+                return False
 
-    return not litellm._should_retry(e.status_code)
+            return not litellm._should_retry(e.status_code)
+
+        decorated_func = backoff.on_exception(
+            backoff.expo,
+            (
+                httpx.ConnectError,
+                httpx.RemoteProtocolError,
+                httpx.ReadTimeout,
+                litellm.exceptions.APIConnectionError,
+                litellm.exceptions.APIError,
+                litellm.exceptions.RateLimitError,
+                litellm.exceptions.ServiceUnavailableError,
+                litellm.exceptions.Timeout,
+                litellm.llms.anthropic.AnthropicError,
+            ),
+            giveup=should_giveup,
+            max_time=60,
+            on_backoff=lambda details: print(
+                f"{details.get('exception','Exception')}\nRetry in {details['wait']:.1f} seconds."
+            ),
+        )(func)
+        return decorated_func(*args, **kwargs)
+
+    return wrapper
 
 
-@backoff.on_exception(
-    backoff.expo,
-    (
-        httpx.ConnectError,
-        httpx.RemoteProtocolError,
-        httpx.ReadTimeout,
-        litellm.exceptions.APIConnectionError,
-        litellm.exceptions.APIError,
-        litellm.exceptions.RateLimitError,
-        litellm.exceptions.ServiceUnavailableError,
-        litellm.exceptions.Timeout,
-        litellm.llms.anthropic.AnthropicError,
-    ),
-    giveup=should_giveup,
-    max_time=60,
-    on_backoff=lambda details: print(
-        f"{details.get('exception','Exception')}\nRetry in {details['wait']:.1f} seconds."
-    ),
-)
+@lazy_litellm_retry_decorator
 def send_with_retries(model_name, messages, functions, stream, temperature=0):
+    from aider.litellm import litellm
+
     kwargs = dict(
         model=model_name,
         messages=messages,