diff --git a/litellm/anthropic_beta_headers_config.json b/litellm/anthropic_beta_headers_config.json
index bdfddb48522..95d1db5c684 100644
--- a/litellm/anthropic_beta_headers_config.json
+++ b/litellm/anthropic_beta_headers_config.json
@@ -200,6 +200,7 @@
     "bash_20250124": null,
     "code-execution-2025-08-25": null,
     "compact-2026-01-12": "compact-2026-01-12",
+    "compact-2026-09-04": "compact-2026-09-04",
     "computer-use-2025-01-24": "computer-use-2025-01-24",
     "computer-use-2025-11-24": "computer-use-2025-11-24",
     "context-1m-2025-08-07": "context-1m-2025-08-07",
diff --git a/litellm/llms/bedrock/messages/invoke_transformations/anthropic_claude_transformation.py b/litellm/llms/bedrock/messages/invoke_transformations/anthropic_claude_transformation.py
index cf48fcf5c2f..c2437e67699 100644
--- a/litellm/llms/bedrock/messages/invoke_transformations/anthropic_claude_transformation.py
+++ b/litellm/llms/bedrock/messages/invoke_transformations/anthropic_claude_transformation.py
@@ -23,6 +23,7 @@ from litellm.llms.anthropic.common_utils import (
     OBJECT_MAPPING_ADAPTER,
     AnthropicModelInfo,
     carried_thinking_keys,
+    carries_signed_compaction_block,
     validated_object_mapping,
 )
 from litellm.llms.anthropic.messages.native.transformation import (
@@ -571,6 +572,22 @@ class AmazonAnthropicClaudeMessagesConfig(
             "edits": retained_edits,
         }
 
+    @staticmethod
+    def _add_compaction_beta_for_bedrock_invoke(anthropic_messages_request: dict, beta_set: set) -> None:
+        """
+        A top-level ``compaction`` request needs the ``compact-2026-09-04``
+        anthropic-beta; without it Bedrock answers 400 "compaction: Extra inputs
+        are not permitted". A later request that adopts the returned signed
+        block needs the same beta, so it is added for that block too, as the
+        Anthropic route does.
+
+        Ref: https://docs.aws.amazon.com/bedrock/latest/userguide/claude-messages-compaction.html
+        """
+        if isinstance(anthropic_messages_request.get("compaction"), dict) or carries_signed_compaction_block(
+            anthropic_messages_request.get("messages") or ()
+        ):
+            beta_set.add("compact-2026-09-04")
+
     def strips_beta_gated_fields_from_final_headers(self) -> bool:
         return False
 
@@ -639,6 +656,7 @@ class AmazonAnthropicClaudeMessagesConfig(
             anthropic_messages_request=anthropic_messages_request,
             beta_set=beta_set,
         )
+        self._add_compaction_beta_for_bedrock_invoke(anthropic_messages_request, beta_set)
 
         self._get_tool_search_beta_header_for_bedrock(
             model=model,
@@ -858,6 +876,16 @@ class AmazonAnthropicClaudeMessagesConfig(
         if filtered_betas:
             anthropic_messages_request["anthropic_beta"] = filtered_betas
 
+        # ``compaction`` travels only with its beta. A beta map without compact-2026-09-04
+        # (bedrock_mantle) or a non-object value keeps the earlier strip instead of a 400.
+        if "compaction" in anthropic_messages_request and not (
+            isinstance(anthropic_messages_request["compaction"], dict) and "compact-2026-09-04" in filtered_betas
+        ):
+            verbose_logger.debug(
+                "Bedrock Invoke: dropping `compaction`; compact-2026-09-04 is not served on this route"
+            )
+            anthropic_messages_request.pop("compaction")
+
         final_request: Final = OBJECT_MAPPING_ADAPTER.validate_python(anthropic_messages_request)  # pyright: ignore[reportUnknownArgumentType]  # built from the base signature's bare dict
         gated: Final = strip_beta_gated_native_request(
             {},
diff --git a/litellm/types/llms/bedrock.py b/litellm/types/llms/bedrock.py
index ff4f2c4fd1e..f71feeb364b 100644
--- a/litellm/types/llms/bedrock.py
+++ b/litellm/types/llms/bedrock.py
@@ -1257,6 +1257,13 @@ class BedrockInvokeAnthropicMessagesRequest(TypedDict, total=False):
     # other edit types (e.g. `clear_thinking_20251015`) never reach Bedrock.
     context_management: dict
 
+    # `compaction` ({"type": "summarize", "instructions"?: str}) is the
+    # `compact-2026-09-04` beta: one summarization call that returns a single
+    # signed compaction block. Bedrock rejects it together with
+    # `context_management`. Ref:
+    # https://docs.aws.amazon.com/bedrock/latest/userguide/claude-messages-compaction.html
+    compaction: dict
+
 
 class BedrockBatchRecordKind(Enum):
     """
diff --git a/tests/unit/llms/bedrock/messages/invoke_transformations/test_anthropic_claude_transformation.py b/tests/unit/llms/bedrock/messages/invoke_transformations/test_anthropic_claude_transformation.py
index c4614dd636f..9c22fd7976f 100644
--- a/tests/unit/llms/bedrock/messages/invoke_transformations/test_anthropic_claude_transformation.py
+++ b/tests/unit/llms/bedrock/messages/invoke_transformations/test_anthropic_claude_transformation.py
@@ -1547,6 +1547,112 @@ def test_bedrock_messages_preserves_compact_context_management_and_adds_beta():
     assert result["max_tokens"] == 4096
 
 
+@pytest.mark.usefixtures("local_beta_headers_config")
+def test_bedrock_messages_keeps_compaction_param_and_adds_beta():
+    """
+    The ``compact-2026-09-04`` beta uses a top-level ``compaction`` parameter, not a
+    ``context_management`` edit. Bedrock InvokeModel accepts it with that beta and
+    returns one signed compaction block. Before this fix the top-level allowlist
+    dropped ``compaction``, so the request reached Bedrock as an ordinary turn.
+
+    Ref: https://docs.aws.amazon.com/bedrock/latest/userguide/claude-messages-compaction.html
+    """
+    from litellm.types.router import GenericLiteLLMParams
+
+    cfg = AmazonAnthropicClaudeMessagesConfig()
+    messages = [
+        {"role": "user", "content": [{"type": "text", "text": "Is CHG-TR-0042 Type IB in TR-TITCK?"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Type IB."}]},
+        {"role": "user", "content": [{"type": "text", "text": "Now KR-MFDS."}]},
+    ]
+    optional_params = {"max_tokens": 1024, "compaction": {"type": "summarize", "instructions": "Keep rule ids."}}
+
+    result = cfg.transform_anthropic_messages_request(
+        model="anthropic.claude-opus-5",
+        messages=messages,
+        anthropic_messages_optional_request_params=optional_params,
+        litellm_params=GenericLiteLLMParams(),
+        headers={},
+    )
+
+    assert result["compaction"] == {"type": "summarize", "instructions": "Keep rule ids."}
+    assert "compact-2026-09-04" in result["anthropic_beta"]
+    assert "context_management" not in result
+    assert set(result).issubset(cfg.BEDROCK_INVOKE_ALLOWED_TOP_LEVEL_FIELDS)
+
+
+@pytest.mark.usefixtures("local_beta_headers_config")
+def test_bedrock_messages_keeps_compact_2026_09_04_beta_for_adopting_request():
+    """
+    A request that adopts the signed block sends it first in ``messages`` and must
+    carry the ``compact-2026-09-04`` beta again. The bedrock beta map has to keep it.
+    """
+    from litellm.types.router import GenericLiteLLMParams
+
+    cfg = AmazonAnthropicClaudeMessagesConfig()
+    block = {"type": "compaction", "content": "<summary>TR-TITCK: Type IB.</summary>", "signature": "sig"}
+    messages = [{"role": "user", "content": [block, {"type": "text", "text": "Now KR-MFDS."}]}]
+
+    result = cfg.transform_anthropic_messages_request(
+        model="anthropic.claude-opus-5",
+        messages=messages,
+        anthropic_messages_optional_request_params={"max_tokens": 512},
+        litellm_params=GenericLiteLLMParams(),
+        headers={"anthropic-beta": "compact-2026-09-04"},
+    )
+
+    assert "compact-2026-09-04" in result["anthropic_beta"]
+    assert result["messages"][0]["content"][0] == block
+
+
+@pytest.mark.usefixtures("local_beta_headers_config")
+def test_bedrock_messages_adds_compact_2026_09_04_beta_for_signed_block_without_client_header():
+    """
+    A client that adopts the signed block but sends no anthropic-beta header still
+    needs ``compact-2026-09-04``; the Anthropic route adds it for the block, and so
+    does Bedrock Invoke.
+    """
+    from litellm.types.router import GenericLiteLLMParams
+
+    cfg = AmazonAnthropicClaudeMessagesConfig()
+    block = {"type": "compaction", "content": "<summary>TR-TITCK: Type IB.</summary>", "signature": "sig"}
+    messages = [{"role": "user", "content": [block, {"type": "text", "text": "Now KR-MFDS."}]}]
+
+    result = cfg.transform_anthropic_messages_request(
+        model="anthropic.claude-opus-5",
+        messages=messages,
+        anthropic_messages_optional_request_params={"max_tokens": 512},
+        litellm_params=GenericLiteLLMParams(),
+        headers={},
+    )
+
+    assert result["anthropic_beta"] == ["compact-2026-09-04"]
+    assert result["messages"][0]["content"][0] == block
+
+
+@pytest.mark.usefixtures("local_beta_headers_config")
+@pytest.mark.parametrize("compaction", [None, "summarize", []])
+def test_bedrock_messages_drops_compaction_that_is_not_an_object(compaction):
+    """
+    Only an object ``compaction`` gets the beta. Any other value is dropped, as it
+    was before the field was allowed, instead of reaching Bedrock without its beta.
+    """
+    from litellm.types.router import GenericLiteLLMParams
+
+    cfg = AmazonAnthropicClaudeMessagesConfig()
+
+    result = cfg.transform_anthropic_messages_request(
+        model="anthropic.claude-opus-5",
+        messages=[{"role": "user", "content": [{"type": "text", "text": "Hi"}]}],
+        anthropic_messages_optional_request_params={"max_tokens": 512, "compaction": compaction},
+        litellm_params=GenericLiteLLMParams(),
+        headers={},
+    )
+
+    assert "compaction" not in result
+    assert "compact-2026-09-04" not in result.get("anthropic_beta", [])
+
+
 def test_bedrock_messages_filters_unsupported_context_management_edits():
     """
     Mixed edit lists must drop the LiteLLM-internal ``clear_thinking_20251015``
diff --git a/tests/unit/llms/bedrock/test_mantle.py b/tests/unit/llms/bedrock/test_mantle.py
index 63af0105f5b..d6a802366c7 100644
--- a/tests/unit/llms/bedrock/test_mantle.py
+++ b/tests/unit/llms/bedrock/test_mantle.py
@@ -796,3 +796,26 @@ async def test_mantle_anthropic_messages_streaming_sends_stream_and_passes_throu
     assert "event: message_start" in text
     assert '"text": "pong"' in text
     assert "event: message_stop" in text
+
+
+@pytest.mark.usefixtures("local_beta_headers_config")
+def test_mantle_messages_drops_compaction_without_its_beta():
+    """
+    The bedrock_mantle beta map has no compact-2026-09-04, so the beta is filtered
+    out on this route. ``compaction`` must go with it, or the body carries a field
+    that Bedrock refuses without the beta.
+    """
+    from litellm.types.router import GenericLiteLLMParams
+
+    config = AmazonMantleMessagesConfig()
+    headers: dict = {}
+    request = config.transform_anthropic_messages_request(
+        model="mantle/anthropic.claude-mythos-preview",
+        messages=[{"role": "user", "content": "Hello"}],
+        anthropic_messages_optional_request_params={"max_tokens": 100, "compaction": {"type": "summarize"}},
+        litellm_params=GenericLiteLLMParams(),
+        headers=headers,
+    )
+
+    assert "compaction" not in request
+    assert "compact-2026-09-04" not in headers.get("anthropic-beta", "")
diff --git a/tests/unit/test_anthropic_beta_headers_filtering.py b/tests/unit/test_anthropic_beta_headers_filtering.py
index a9bc741f800..d0fb6fe0f6e 100644
--- a/tests/unit/test_anthropic_beta_headers_filtering.py
+++ b/tests/unit/test_anthropic_beta_headers_filtering.py
@@ -99,7 +99,9 @@ class TestAnthropicBetaHeadersFiltering:
         filtered = filter_and_transform_beta_headers(
             beta_headers=all_headers, provider=provider
         )
-        assert ("compact-2026-09-04" in filtered) is (provider in ("anthropic", "azure_ai", "vertex_ai"))
+        # Bedrock InvokeModel serves the compact-2026-09-04 `compaction` parameter; Converse does not.
+        # https://docs.aws.amazon.com/bedrock/latest/userguide/claude-messages-compaction.html
+        assert ("compact-2026-09-04" in filtered) is (provider in ("anthropic", "azure_ai", "vertex_ai", "bedrock"))
         assert ("mid-conversation-tool-changes-2026-07-01" in filtered) is (provider != "bedrock_converse")
 
         for header in unsupported_headers: