feat: support clear-thinking-20250115 beta feature

Author: fatelei

src/claude_agent_sdk/types.py

@@ -18,7 +18,10 @@
 PermissionMode = Literal["default", "acceptEdits", "plan", "bypassPermissions"]
 
 # SDK Beta features - see https://docs.anthropic.com/en/api/beta-headers
-SdkBeta = Literal["context-1m-2025-08-07"]
+SdkBeta = Literal[
+    "context-1m-2025-08-07",  # Extended 1M context window
+    "clear-thinking-20250115",  # Clear thinking blocks from previous turns to reduce token usage
+]
 
 # Agent definitions
 SettingSource = Literal["user", "project", "local"]

tests/test_transport.py

@@ -158,6 +158,21 @@ def test_build_command_with_max_thinking_tokens(self):
         assert "--max-thinking-tokens" in cmd
         assert "5000" in cmd
 
+    def test_build_command_with_betas(self):
+        """Test building CLI command with betas option."""
+
+        transport = SubprocessCLITransport(
+            prompt="test",
+            options=make_options(
+                betas=["context-1m-2025-08-07", "clear-thinking-20250115"]
+            ),
+        )
+
+        cmd = transport._build_command()
+        assert "--betas" in cmd
+        betas_index = cmd.index("--betas")
+        assert cmd[betas_index + 1] == "context-1m-2025-08-07,clear-thinking-20250115"
+
     def test_build_command_with_add_dirs(self):
         """Test building CLI command with add_dirs option."""
         from pathlib import Path