diff --git a/src/anthropic/lib/bedrock/_beta_messages.py b/src/anthropic/lib/bedrock/_beta_messages.py
index 332f6fba..62eaebc5 100644
--- a/src/anthropic/lib/bedrock/_beta_messages.py
+++ b/src/anthropic/lib/bedrock/_beta_messages.py
@@ -2,6 +2,8 @@
 
 from __future__ import annotations
 
+from typing import Any, Iterable
+
 from ... import _legacy_response
 from ..._compat import cached_property
 from ..._resource import SyncAPIResource, AsyncAPIResource
@@ -11,8 +13,93 @@
 __all__ = ["Messages", "AsyncMessages"]
 
 
+# Fields that Bedrock's stricter API validation rejects
+# - parsed_output: Added by tool_runner SDK to text blocks for structured output tracking
+# - caller: Added to tool_use blocks for code execution features
+BEDROCK_UNSUPPORTED_FIELDS = {"parsed_output", "caller"}
+
+
+def _sanitize_for_bedrock(messages: Iterable[Any] | None) -> list[Any] | None:
+    """Strip Bedrock-unsupported fields from message content blocks.
+
+    The tool_runner SDK adds internal tracking fields that Bedrock's stricter
+    API validation rejects with 400 errors. This function sanitizes messages
+    before sending to Bedrock.
+
+    Args:
+        messages: Iterable of message objects (dicts or Pydantic models)
+
+    Returns:
+        Sanitized list of messages with unsupported fields removed, or None if input is None
+    """
+    if messages is None:
+        return None
+
+    sanitized = []
+    for msg in messages:
+        if isinstance(msg, dict):
+            # Handle dict messages
+            sanitized_msg = dict(msg)
+            if "content" in sanitized_msg and isinstance(sanitized_msg["content"], list):
+                sanitized_content = []
+                for block in sanitized_msg["content"]:
+                    if isinstance(block, dict):
+                        # Remove unsupported fields from dict blocks
+                        sanitized_block = {k: v for k, v in block.items() if k not in BEDROCK_UNSUPPORTED_FIELDS}
+                        sanitized_content.append(sanitized_block)
+                    elif hasattr(block, "model_dump"):
+                        # Handle Pydantic models - convert to dict and remove unsupported fields
+                        block_dict = block.model_dump()
+                        for field in BEDROCK_UNSUPPORTED_FIELDS:
+                            block_dict.pop(field, None)
+                        sanitized_content.append(block_dict)
+                    else:
+                        # Keep other types as-is
+                        sanitized_content.append(block)
+                sanitized_msg["content"] = sanitized_content
+            sanitized.append(sanitized_msg)
+        elif hasattr(msg, "model_dump"):
+            # Handle Pydantic message models
+            msg_dict = msg.model_dump()
+            if "content" in msg_dict and isinstance(msg_dict["content"], list):
+                sanitized_content = []
+                for block in msg_dict["content"]:
+                    if isinstance(block, dict):
+                        sanitized_block = {k: v for k, v in block.items() if k not in BEDROCK_UNSUPPORTED_FIELDS}
+                        sanitized_content.append(sanitized_block)
+                    else:
+                        sanitized_content.append(block)
+                msg_dict["content"] = sanitized_content
+            sanitized.append(msg_dict)
+        else:
+            # Keep other message types as-is
+            sanitized.append(msg)
+
+    return sanitized
+
+
 class Messages(SyncAPIResource):
-    create = FirstPartyMessagesAPI.create
+    def create(self, *args, **kwargs):
+        """Create a message with sanitization for Bedrock compatibility."""
+        if "messages" in kwargs:
+            kwargs["messages"] = _sanitize_for_bedrock(kwargs["messages"])
+        return FirstPartyMessagesAPI.create(self, *args, **kwargs)
+
+    def parse(self, *args, **kwargs):
+        """Parse a message with sanitization for Bedrock compatibility."""
+        if "messages" in kwargs:
+            kwargs["messages"] = _sanitize_for_bedrock(kwargs["messages"])
+        return FirstPartyMessagesAPI.parse(self, *args, **kwargs)
+
+    def stream(self, *args, **kwargs):
+        """Stream a message with sanitization for Bedrock compatibility."""
+        if "messages" in kwargs:
+            kwargs["messages"] = _sanitize_for_bedrock(kwargs["messages"])
+        return FirstPartyMessagesAPI.stream(self, *args, **kwargs)
+
+    # tool_runner delegates to create/parse/stream internally, so it benefits
+    # from the sanitization automatically through method resolution
+    tool_runner = FirstPartyMessagesAPI.tool_runner
 
     @cached_property
     def with_raw_response(self) -> MessagesWithRawResponse:
@@ -35,7 +122,27 @@ def with_streaming_response(self) -> MessagesWithStreamingResponse:
 
 
 class AsyncMessages(AsyncAPIResource):
-    create = FirstPartyAsyncMessagesAPI.create
+    async def create(self, *args, **kwargs):
+        """Create a message with sanitization for Bedrock compatibility."""
+        if "messages" in kwargs:
+            kwargs["messages"] = _sanitize_for_bedrock(kwargs["messages"])
+        return await FirstPartyAsyncMessagesAPI.create(self, *args, **kwargs)
+
+    async def parse(self, *args, **kwargs):
+        """Parse a message with sanitization for Bedrock compatibility."""
+        if "messages" in kwargs:
+            kwargs["messages"] = _sanitize_for_bedrock(kwargs["messages"])
+        return await FirstPartyAsyncMessagesAPI.parse(self, *args, **kwargs)
+
+    async def stream(self, *args, **kwargs):
+        """Stream a message with sanitization for Bedrock compatibility."""
+        if "messages" in kwargs:
+            kwargs["messages"] = _sanitize_for_bedrock(kwargs["messages"])
+        return await FirstPartyAsyncMessagesAPI.stream(self, *args, **kwargs)
+
+    # tool_runner delegates to create/parse/stream internally, so it benefits
+    # from the sanitization automatically through method resolution
+    tool_runner = FirstPartyAsyncMessagesAPI.tool_runner
 
     @cached_property
     def with_raw_response(self) -> AsyncMessagesWithRawResponse: