diff --git a/server/lorax_server/utils/sources/s3.py b/server/lorax_server/utils/sources/s3.py
index 241c165f7..d0d71af6b 100644
--- a/server/lorax_server/utils/sources/s3.py
+++ b/server/lorax_server/utils/sources/s3.py
@@ -1,7 +1,7 @@
 import os
 import time
 from datetime import timedelta
-from typing import Optional, List, Any
+from typing import TYPE_CHECKING, Optional, List, Any, Tuple
 
 from loguru import logger
 from pathlib import Path
@@ -9,7 +9,6 @@
 from botocore.config import Config
 from huggingface_hub.constants import HUGGINGFACE_HUB_CACHE
 
-
 from huggingface_hub.utils import (
     LocalEntryNotFoundError,
     EntryNotFoundError,
@@ -17,8 +16,41 @@
 
 from .source import BaseModelSource, try_to_load_from_cache
 
+if TYPE_CHECKING:
+    from boto3.resources.factory.s3 import Bucket
+
+
+S3_PREFIX = "s3://"
+
+
+def _get_bucket_and_model_id(model_id: str) -> Tuple[str, str]:
+    if model_id.startswith(S3_PREFIX):
+        model_id_no_protocol = model_id[len(S3_PREFIX) :]
+        if "/" not in model_id_no_protocol:
+            raise ValueError(
+                f"Invalid model_id {model_id}. "
+                f"model_id should be of the form `s3://bucket_name/model_id`"
+            )
+        bucket_name, model_id = model_id_no_protocol.split("/", 1)
+        return bucket_name, model_id
+    
+    bucket = os.getenv("PREDIBASE_MODEL_BUCKET")
+    if not bucket:
+        # assume that the id preceding the first slash is the bucket name
+        if "/" not in model_id:
+            raise ValueError(
+                f"Invalid model_id {model_id}. "
+                f"model_id should be of the form `bucket_name/model_id` "
+                f"if PREDIBASE_MODEL_BUCKET environment variable is not set"
+            )
+        
+        bucket_name, model_id = model_id.split("/", 1)
+        return bucket_name, model_id
+    
+    return bucket, model_id
+    
 
-def _get_bucket_resource():
+def _get_bucket_resource(bucket_name: str) -> "Bucket":
     """Get the s3 client"""
     config = Config(
         retries=dict(
@@ -27,10 +59,7 @@ def _get_bucket_resource():
         )
     )
     s3 = boto3.resource('s3', config=config)
-    bucket = os.getenv("PREDIBASE_MODEL_BUCKET")
-    if not bucket:
-        raise ValueError("PREDIBASE_MODEL_BUCKET environment variable is not set")
-    return s3.Bucket(bucket)
+    return s3.Bucket(bucket_name)
 
 
 def get_s3_model_local_dir(model_id: str):
@@ -172,10 +201,11 @@ def __init__(self, model_id: str, revision: Optional[str] = "", extension: str =
             raise ValueError(f"model_id '{model_id}' is too short for prefix filtering")
 
         # TODO: add support for revisions of the same model
+        bucket, model_id = _get_bucket_and_model_id(model_id)
         self.model_id = model_id
         self.revision = revision
         self.extension = extension
-        self.bucket = _get_bucket_resource()
+        self.bucket = _get_bucket_resource(bucket)
 
     def remote_weight_files(self, extension: str = None):
         extension = extension or self.extension
diff --git a/server/tests/utils/test_s3.py b/server/tests/utils/test_s3.py
new file mode 100644
index 000000000..17476a85e
--- /dev/null
+++ b/server/tests/utils/test_s3.py
@@ -0,0 +1,47 @@
+import contextlib
+import os
+from typing import Optional
+
+import pytest
+
+from lorax_server.utils.sources.s3 import _get_bucket_and_model_id
+
+
+@contextlib.contextmanager
+def with_env_var(key: str, value: Optional[str]):
+    if value is None:
+        yield
+        return
+    
+    prev = os.environ.get(key)
+    try:
+        os.environ[key] = value
+        yield
+    finally:
+        if prev is None:
+            del os.environ[key]
+        else:
+            os.environ[key] = prev
+
+
+@pytest.mark.parametrize(
+    "s3_path, env_var, expected_bucket, expected_model_id",
+    [
+        ("s3://loras/foobar", None, "loras", "foobar"),
+        ("s3://loras/foo/bar", None, "loras", "foo/bar"),
+        ("s3://loras/foo/bar", "bucket", "loras", "foo/bar"),
+        ("loras/foobar", None, "loras", "foobar"),
+        ("loras/foo/bar", None, "loras", "foo/bar"),
+        ("loras/foo/bar", "bucket", "bucket", "loras/foo/bar"),
+    ]
+)
+def test_get_bucket_and_model_id(
+    s3_path: str,
+    env_var: Optional[str],
+    expected_bucket: str,
+    expected_model_id: str,
+):
+    with with_env_var("PREDIBASE_MODEL_BUCKET", env_var):
+        bucket, model_id = _get_bucket_and_model_id(s3_path)
+    assert bucket == expected_bucket
+    assert model_id == expected_model_id