diff --git a/src/replicate/_client.py b/src/replicate/_client.py
index 390a552..a127590 100644
--- a/src/replicate/_client.py
+++ b/src/replicate/_client.py
@@ -102,6 +102,7 @@ def __init__(
         self,
         *,
         bearer_token: str | None = None,
+        api_token: str | None = None,  # Legacy compatibility parameter
         base_url: str | httpx.URL | None = None,
         timeout: Union[float, Timeout, None, NotGiven] = NOT_GIVEN,
         max_retries: int = DEFAULT_MAX_RETRIES,
@@ -125,6 +126,14 @@ def __init__(
 
         This automatically infers the `bearer_token` argument from the `REPLICATE_API_TOKEN` environment variable if it is not provided.
         """
+        # Handle legacy api_token parameter
+        if api_token is not None and bearer_token is not None:
+            raise ReplicateError(
+                "Cannot specify both 'bearer_token' and 'api_token'. Please use 'bearer_token' (recommended) or 'api_token' for legacy compatibility."
+            )
+        if api_token is not None:
+            bearer_token = api_token
+
         if bearer_token is None:
             bearer_token = _get_api_token_from_environment()
         if bearer_token is None:
@@ -477,6 +486,7 @@ def __init__(
         self,
         *,
         bearer_token: str | None = None,
+        api_token: str | None = None,  # Legacy compatibility parameter
         base_url: str | httpx.URL | None = None,
         timeout: Union[float, Timeout, None, NotGiven] = NOT_GIVEN,
         max_retries: int = DEFAULT_MAX_RETRIES,
@@ -500,6 +510,14 @@ def __init__(
 
         This automatically infers the `bearer_token` argument from the `REPLICATE_API_TOKEN` environment variable if it is not provided.
         """
+        # Handle legacy api_token parameter
+        if api_token is not None and bearer_token is not None:
+            raise ReplicateError(
+                "Cannot specify both 'bearer_token' and 'api_token'. Please use 'bearer_token' (recommended) or 'api_token' for legacy compatibility."
+            )
+        if api_token is not None:
+            bearer_token = api_token
+
         if bearer_token is None:
             bearer_token = _get_api_token_from_environment()
         if bearer_token is None:
diff --git a/tests/test_api_token_compatibility.py b/tests/test_api_token_compatibility.py
new file mode 100644
index 0000000..f45a541
--- /dev/null
+++ b/tests/test_api_token_compatibility.py
@@ -0,0 +1,88 @@
+"""Tests for api_token legacy compatibility during client instantiation."""
+
+from __future__ import annotations
+
+import pytest
+
+from replicate import Replicate, AsyncReplicate, ReplicateError
+from replicate._client import Client
+
+
+class TestApiTokenCompatibility:
+    """Test that api_token parameter works as a legacy compatibility option."""
+
+    def test_sync_client_with_api_token(self) -> None:
+        """Test that Replicate accepts api_token parameter."""
+        client = Replicate(api_token="test_token_123")
+        assert client.bearer_token == "test_token_123"
+
+    def test_async_client_with_api_token(self) -> None:
+        """Test that AsyncReplicate accepts api_token parameter."""
+        client = AsyncReplicate(api_token="test_token_123")
+        assert client.bearer_token == "test_token_123"
+
+    def test_sync_client_with_bearer_token(self) -> None:
+        """Test that Replicate still accepts bearer_token parameter."""
+        client = Replicate(bearer_token="test_token_123")
+        assert client.bearer_token == "test_token_123"
+
+    def test_async_client_with_bearer_token(self) -> None:
+        """Test that AsyncReplicate still accepts bearer_token parameter."""
+        client = AsyncReplicate(bearer_token="test_token_123")
+        assert client.bearer_token == "test_token_123"
+
+    def test_sync_client_both_tokens_error(self) -> None:
+        """Test that providing both api_token and bearer_token raises an error."""
+        with pytest.raises(ReplicateError, match="Cannot specify both 'bearer_token' and 'api_token'"):
+            Replicate(api_token="test_api", bearer_token="test_bearer")
+
+    def test_async_client_both_tokens_error(self) -> None:
+        """Test that providing both api_token and bearer_token raises an error."""
+        with pytest.raises(ReplicateError, match="Cannot specify both 'bearer_token' and 'api_token'"):
+            AsyncReplicate(api_token="test_api", bearer_token="test_bearer")
+
+    def test_sync_client_no_token_with_env(self, monkeypatch: pytest.MonkeyPatch) -> None:
+        """Test that client reads from environment when no token is provided."""
+        monkeypatch.setenv("REPLICATE_API_TOKEN", "env_token_123")
+        client = Replicate()
+        assert client.bearer_token == "env_token_123"
+
+    def test_async_client_no_token_with_env(self, monkeypatch: pytest.MonkeyPatch) -> None:
+        """Test that async client reads from environment when no token is provided."""
+        monkeypatch.setenv("REPLICATE_API_TOKEN", "env_token_123")
+        client = AsyncReplicate()
+        assert client.bearer_token == "env_token_123"
+
+    def test_sync_client_no_token_no_env(self, monkeypatch: pytest.MonkeyPatch) -> None:
+        """Test that client raises error when no token is provided and env is not set."""
+        monkeypatch.delenv("REPLICATE_API_TOKEN", raising=False)
+        with pytest.raises(ReplicateError, match="The bearer_token client option must be set"):
+            Replicate()
+
+    def test_async_client_no_token_no_env(self, monkeypatch: pytest.MonkeyPatch) -> None:
+        """Test that async client raises error when no token is provided and env is not set."""
+        monkeypatch.delenv("REPLICATE_API_TOKEN", raising=False)
+        with pytest.raises(ReplicateError, match="The bearer_token client option must be set"):
+            AsyncReplicate()
+
+    def test_legacy_client_alias(self) -> None:
+        """Test that legacy Client import still works as an alias."""
+        assert Client is Replicate
+
+    def test_legacy_client_with_api_token(self) -> None:
+        """Test that legacy Client alias works with api_token parameter."""
+        client = Client(api_token="test_token_123")
+        assert client.bearer_token == "test_token_123"
+        assert isinstance(client, Replicate)
+
+    def test_api_token_overrides_env(self, monkeypatch: pytest.MonkeyPatch) -> None:
+        """Test that explicit api_token overrides environment variable."""
+        monkeypatch.setenv("REPLICATE_API_TOKEN", "env_token")
+        client = Replicate(api_token="explicit_token")
+        assert client.bearer_token == "explicit_token"
+
+    def test_bearer_token_overrides_env(self, monkeypatch: pytest.MonkeyPatch) -> None:
+        """Test that explicit bearer_token overrides environment variable."""
+        monkeypatch.setenv("REPLICATE_API_TOKEN", "env_token")
+        client = Replicate(bearer_token="explicit_token")
+        assert client.bearer_token == "explicit_token"