diff --git a/litellm-rust/crates/callbacks-legacy-python/src/adapter.rs b/litellm-rust/crates/callbacks-legacy-python/src/adapter.rs
index 75a635e9c63..14a56a145d6 100644
--- a/litellm-rust/crates/callbacks-legacy-python/src/adapter.rs
+++ b/litellm-rust/crates/callbacks-legacy-python/src/adapter.rs
@@ -367,6 +367,15 @@ impl PythonLifecycle for LegacyLogging {
     fn emit(&mut self, py: Python<'_>, event: LifecycleEvent<'_>) -> PyResult<LifecycleStep> {
         match event {
             LifecycleEvent::Started { .. } => Ok(LifecycleStep::Done),
+            LifecycleEvent::Machine(MachineEvent::RequestResent { body }) => {
+                self.body = Some(
+                    to_py(py, body)?
+                        .into_bound(py)
+                        .cast_into::<PyDict>()?
+                        .unbind(),
+                );
+                Ok(LifecycleStep::Done)
+            }
             LifecycleEvent::Machine(MachineEvent::ResponseReceived { raw }) => {
                 let api_key = self
                     .context
@@ -492,9 +501,7 @@ mod deployment_hooks_tests {
 
     use litellm_host::event::{FailureOrigin, Timing};
     use litellm_host_python::{LifecycleEvent, LifecycleStep, PythonLifecycle};
-    use pyo3::exceptions::asyncio::CancelledError;
-    use pyo3::prelude::*;
-    use pyo3::types::PyDict;
+    use pyo3::{exceptions::asyncio::CancelledError, prelude::*, types::PyDict};
     use rstest::rstest;
 
     use super::LegacyLogging;
@@ -787,8 +794,10 @@ mod payload_tests {
     use serde_json::{Map, Value, json};
 
     use super::LegacyLogging;
-    use crate::PythonLogger;
-    use crate::test_support::{legacy_call, local, namespace, run};
+    use crate::{
+        PythonLogger,
+        test_support::{legacy_call, local, namespace, run},
+    };
 
     /// The payload phases of `Logging` on top of `StubLogger`, with `pre_call` handing the
     /// payload to the case's `on_pre_call`.
@@ -837,7 +846,7 @@ check = lambda: None
         body: Value,
         secret_fields: &[&str],
     ) -> WireRequest {
-        before_send_bound(&[], script, optional_params, body, secret_fields)
+        before_send_bound(&[], script, optional_params, body, secret_fields, None)
     }
 
     /// [`before_send_with_secrets`] with `bindings` placed in the namespace before `script` runs.
@@ -847,6 +856,7 @@ check = lambda: None
         optional_params: Value,
         body: Value,
         secret_fields: &[&str],
+        resent: Option<Value>,
     ) -> WireRequest {
         Python::initialize();
         Python::attach(|py| {
@@ -872,6 +882,13 @@ check = lambda: None
                 body,
             };
             let step = logging.before_send(py, Box::new(wire), &context).unwrap();
+            if let Some(body) = resent {
+                let resent = MachineEvent::RequestResent { body };
+                assert!(matches!(
+                    logging.emit(py, LifecycleEvent::Machine(&resent)).unwrap(),
+                    LifecycleStep::Done
+                ));
+            }
             let raw = MachineEvent::ResponseReceived {
                 raw: RawResponse {
                     body: "raw response".into(),
@@ -1127,6 +1144,23 @@ def check():
         );
     }
 
+    #[test]
+    fn post_call_logs_the_body_of_a_resent_request() {
+        before_send_bound(
+            &[],
+            c"
+def check():
+    _, _, additional_args = logger.post
+    assert additional_args['complete_input_dict'] == {'messages': []}, additional_args
+    assert logger.pre['complete_input_dict'] == {'messages': [{'role': 'user'}], 'thinking': {}}, logger.pre
+",
+            json!({}),
+            json!({"messages": [{"role": "user"}], "thinking": {}}),
+            &[],
+            Some(json!({"messages": []})),
+        );
+    }
+
     #[test]
     fn every_request_runs_the_full_pre_call_and_post_call() {
         let wire = before_send(
@@ -1293,6 +1327,7 @@ def check():
                 json!({}),
                 Value::Object(body.clone()),
                 &[],
+                None,
             );
 
             prop_assert_eq!(wire.body, edit.sent(&body));
@@ -1307,15 +1342,18 @@ mod terminal_tests {
 
     use litellm_host::event::{FailureOrigin, Timing};
     use litellm_host_python::{LifecycleEvent, LifecycleStep, PythonLifecycle};
-    use pyo3::exceptions::PyRuntimeError;
-    use pyo3::exceptions::asyncio::CancelledError;
-    use pyo3::prelude::*;
-    use pyo3::types::PyDict;
+    use pyo3::{
+        exceptions::{PyRuntimeError, asyncio::CancelledError},
+        prelude::*,
+        types::PyDict,
+    };
     use rstest::rstest;
 
     use super::LegacyLogging;
-    use crate::PythonLogger;
-    use crate::test_support::{legacy_call, local, namespace, run};
+    use crate::{
+        PythonLogger,
+        test_support::{legacy_call, local, namespace, run},
+    };
 
     const TIMING: Timing = Timing {
         start_time: 0.0,
diff --git a/litellm-rust/crates/core/src/messages/handler.rs b/litellm-rust/crates/core/src/messages/handler.rs
index fe7e8bb4b80..46293eca08c 100644
--- a/litellm-rust/crates/core/src/messages/handler.rs
+++ b/litellm-rust/crates/core/src/messages/handler.rs
@@ -28,13 +28,17 @@ pub(super) async fn send(
     http_request(builder).await.map_err(network)
 }
 
+pub(super) fn http_error(status: u16, body: &str) -> Error {
+    Error::Transport(TransportError::Http {
+        status,
+        body: truncate_error_body(body),
+    })
+}
+
 pub(super) async fn provider_error(response: reqwest::Response) -> Error {
     let status = response.status().as_u16();
     match response.text().await {
-        Ok(text) => Error::Transport(TransportError::Http {
-            status,
-            body: truncate_error_body(&text),
-        }),
+        Ok(text) => http_error(status, &text),
         Err(error) => network(error),
     }
 }
diff --git a/litellm-rust/crates/core/src/messages/route.rs b/litellm-rust/crates/core/src/messages/route.rs
index 8cd3eaf3aa3..78d0db448a8 100644
--- a/litellm-rust/crates/core/src/messages/route.rs
+++ b/litellm-rust/crates/core/src/messages/route.rs
@@ -12,9 +12,12 @@ use litellm_host::{
     machine::{HostChannel, MachineFault, RouteMachine},
     route::Route,
 };
+use litellm_llms::base_llm::anthropic_messages::transformation::BaseAnthropicMessagesConfig;
 use litellm_secrets::source::SecretSource;
 use litellm_types::{
-    llms::anthropic_messages::anthropic_response::AnthropicMessagesResponse,
+    llms::anthropic_messages::{
+        anthropic_request::AnthropicMessagesRequest, anthropic_response::AnthropicMessagesResponse,
+    },
     utils::ProviderSpecificHeaders,
 };
 use serde_json::{Map, Value};
@@ -22,7 +25,7 @@ use serde_json::{Map, Value};
 use super::{
     Error,
     common_utils::messages_provider_config,
-    handler::{decode_response, network, provider_error, send},
+    handler::{decode_response, http_error, network, provider_error, send},
     prepare::{prepare_provider_request, resolve_provider},
     types::{MessagesRequest, MessagesShaping},
 };
@@ -183,9 +186,11 @@ async fn execute(
         )
         .await?;
     let response = send(&wire.url, &wire.headers, &wire.body, request.timeout).await?;
-    if !response.status().is_success() {
-        return Err(provider_error(response).await);
-    }
+    let response = if response.status().is_success() {
+        response
+    } else {
+        resend_after_error(&host, request.config, &wire, request.timeout, response).await?
+    };
     if stream {
         return relay(&host, response).await;
     }
@@ -198,6 +203,32 @@ async fn execute(
         .map(|message| MessagesOutput::Message(Box::new(message)))
 }
 
+async fn resend_after_error(
+    host: &MessagesHost,
+    config: &dyn BaseAnthropicMessagesConfig,
+    wire: &WireRequest,
+    timeout: Option<Duration>,
+    response: reqwest::Response,
+) -> Result<reqwest::Response, Error> {
+    let status = response.status().as_u16();
+    let text = response.text().await.map_err(network)?;
+    let Some(request) = serde_json::from_value::<AnthropicMessagesRequest>(wire.body.clone())
+        .ok()
+        .and_then(|request| config.request_after_http_error(status, &text, request))
+    else {
+        return Err(http_error(status, &text));
+    };
+    let body = serde_json::to_value(request)
+        .map_err(|error| Error::InvalidRequest(format!("invalid messages request: {error}")))?;
+    host.emit(MachineEvent::RequestResent { body: body.clone() })
+        .await?;
+    let response = send(&wire.url, &wire.headers, &body, timeout).await?;
+    if response.status().is_success() {
+        return Ok(response);
+    }
+    Err(provider_error(response).await)
+}
+
 /// Hands each upstream chunk to the caller as it arrives. A caller that stops reading
 /// ends the upstream read, and the call completes with what it delivered.
 async fn relay(
diff --git a/litellm-rust/crates/core/src/ocr/route.rs b/litellm-rust/crates/core/src/ocr/route.rs
index 7f83291bdab..1e25b35f3bc 100644
--- a/litellm-rust/crates/core/src/ocr/route.rs
+++ b/litellm-rust/crates/core/src/ocr/route.rs
@@ -410,9 +410,9 @@ mod azure_ai_tests {
     use litellm_llms::base_llm::ocr::error::Error;
     use serde_json::{Value, json};
 
-    use crate::ocr::route::LocalOcrHost;
-    use crate::ocr::test_support::{
-        MockResponse, mock_server, perform_ocr, perform_ocr_with, wire_request,
+    use crate::ocr::{
+        route::LocalOcrHost,
+        test_support::{MockResponse, mock_server, perform_ocr, perform_ocr_with, wire_request},
     };
 
     #[tokio::test]
@@ -712,8 +712,8 @@ mod azure_document_intelligence_tests {
     use rstest::rstest;
     use serde_json::{Value, json};
 
-    use crate::ocr::route::LocalOcrHost;
     use crate::ocr::{
+        route::LocalOcrHost,
         test_support::{
             MockResponse, mock_server, ocr_client, perform_ocr, perform_ocr_with, wire_request,
         },
@@ -1715,9 +1715,9 @@ mod reducto_tests {
     use rstest::rstest;
     use serde_json::{Value, json};
 
-    use crate::ocr::route::LocalOcrHost;
-    use crate::ocr::test_support::{
-        MockResponse, mock_server, perform_ocr, perform_ocr_with, wire_request,
+    use crate::ocr::{
+        route::LocalOcrHost,
+        test_support::{MockResponse, mock_server, perform_ocr, perform_ocr_with, wire_request},
     };
 
     fn request_body(request: &str) -> Value {
@@ -2776,8 +2776,8 @@ pub(crate) mod tests {
     use rstest::rstest;
     use serde_json::{Value, json};
 
-    use crate::ocr::route::{LocalOcrHost, OcrOp, OcrOpResult, ocr_machine};
     use crate::ocr::{
+        route::{LocalOcrHost, OcrOp, OcrOpResult, ocr_machine},
         test_support::{
             MockResponse, mock_server, ocr_client, perform_ocr, perform_ocr_with, wire_request,
         },
@@ -3059,6 +3059,7 @@ pub(crate) mod tests {
         match event {
             CallEvent::Started { .. } => "started",
             CallEvent::Machine(MachineEvent::ResponseReceived { .. }) => "response",
+            CallEvent::Machine(MachineEvent::RequestResent { .. }) => "resent",
             CallEvent::Succeeded { .. } => "success",
             CallEvent::Failed { .. } => "failure",
         }
diff --git a/litellm-rust/crates/host-python/src/driver.rs b/litellm-rust/crates/host-python/src/driver.rs
index 77a294d274b..4ec883d2cd9 100644
--- a/litellm-rust/crates/host-python/src/driver.rs
+++ b/litellm-rust/crates/host-python/src/driver.rs
@@ -1,22 +1,27 @@
-use std::sync::Arc;
-use std::task::Poll;
+use std::{sync::Arc, task::Poll};
 
 use futures_util::future::{AbortHandle, Abortable};
-use litellm_host::event::{FailureOrigin, Timing, epoch_seconds};
-use litellm_host::host::{Demand, HostOp, HostResult, HostStep};
-use litellm_host::machine::{HostFailure, Machine, MachineStep};
-use litellm_host::route::Route;
-use pyo3::exceptions::{PyBaseException, PyException, PyRuntimeError};
-use pyo3::gc::{PyTraverseError, PyVisit};
-use pyo3::prelude::*;
-use pyo3::types::PyDict;
+use litellm_host::{
+    event::{FailureOrigin, Timing, epoch_seconds},
+    host::{Demand, HostOp, HostResult, HostStep},
+    machine::{HostFailure, Machine, MachineStep},
+    route::Route,
+};
+use pyo3::{
+    exceptions::{PyBaseException, PyException, PyRuntimeError},
+    gc::{PyTraverseError, PyVisit},
+    prelude::*,
+    types::PyDict,
+};
 use tokio::sync::Mutex;
 
-use crate::adapter::{
-    InvokeError, LifecycleEvent, LifecycleStep, PythonLifecycle, RouteHost, missing_state,
+use crate::{
+    adapter::{
+        InvokeError, LifecycleEvent, LifecycleStep, PythonLifecycle, RouteHost, missing_state,
+    },
+    execution::{poll_async_value, run_async_value, run_sync_value},
+    handle::{Execution, ExecutionBody, ExecutionStep},
 };
-use crate::execution::{poll_async_value, run_async_value, run_sync_value};
-use crate::handle::{Execution, ExecutionBody, ExecutionStep};
 
 type RouteOf<H> = <H as RouteHost>::Route;
 type ErrorOf<H> = <RouteOf<H> as Route>::Error;
@@ -528,10 +533,14 @@ where
 mod tests {
     use std::sync::{Arc, Mutex};
 
-    use litellm_host::event::{MachineEvent, RequestContext, WireRequest};
-    use litellm_host::machine::{Interrupted, Step};
-    use pyo3::exceptions::{PyBaseException, PyValueError};
-    use pyo3::types::PyDict;
+    use litellm_host::{
+        event::{MachineEvent, RequestContext, WireRequest},
+        machine::{Interrupted, Step},
+    };
+    use pyo3::{
+        exceptions::{PyBaseException, PyValueError},
+        types::PyDict,
+    };
 
     use super::*;
 
@@ -793,6 +802,9 @@ sys.modules.setdefault('litellm.rust_bridge', types.ModuleType('litellm.rust_bri
                 LifecycleEvent::Machine(MachineEvent::ResponseReceived { raw }) => {
                     format!("response:{}", raw.body)
                 }
+                LifecycleEvent::Machine(MachineEvent::RequestResent { body }) => {
+                    format!("resent:{body}")
+                }
                 LifecycleEvent::Succeeded { response, .. } => {
                     format!("succeeded:{}", response.bind(py))
                 }
diff --git a/litellm-rust/crates/host/src/event.rs b/litellm-rust/crates/host/src/event.rs
index 182dab657d3..e22d91bb69e 100644
--- a/litellm-rust/crates/host/src/event.rs
+++ b/litellm-rust/crates/host/src/event.rs
@@ -55,6 +55,7 @@ pub enum FailureOrigin {
 /// What a machine reports while it runs.
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum MachineEvent {
+    RequestResent { body: Value },
     ResponseReceived { raw: RawResponse },
 }
 
diff --git a/litellm-rust/crates/llms/src/anthropic/common_utils.rs b/litellm-rust/crates/llms/src/anthropic/common_utils.rs
index 797ab16cd76..9b2a2438b99 100644
--- a/litellm-rust/crates/llms/src/anthropic/common_utils.rs
+++ b/litellm-rust/crates/llms/src/anthropic/common_utils.rs
@@ -232,6 +232,20 @@ fn retain_blocks(
         .collect()
 }
 
+pub fn is_anthropic_invalid_thinking_block_error(error_text: &str) -> bool {
+    let lower = error_text.to_lowercase();
+    lower.contains("thinking")
+        && ((lower.contains("signature")
+            && (lower.contains("invalid") || lower.contains("valid string")))
+            || lower.contains("must contain thinking"))
+}
+
+pub fn strip_thinking_blocks(messages: Vec<AnthropicMessage>) -> Vec<AnthropicMessage> {
+    retain_blocks(messages, |block| {
+        !block.is_type("thinking") && !block.is_type("redacted_thinking")
+    })
+}
+
 pub fn strip_empty_content_blocks(messages: Vec<AnthropicMessage>) -> Vec<AnthropicMessage> {
     retain_blocks(messages, |block| {
         !is_empty_text_block(block) && !is_empty_thinking_block(block)
@@ -1221,6 +1235,73 @@ mod tests {
         );
     }
 
+    #[rstest]
+    #[case::anthropic_invalid_signature(
+        r#"{"type":"error","error":{"type":"invalid_request_error","message":"messages.3.content.3: Invalid `signature` in `thinking` block"},"request_id":"req_1"}"#
+    )]
+    #[case::bedrock_signature_not_a_string(
+        r#"{"message":"messages.2.content.0.thinking.signature.str: Input should be a valid string"}"#
+    )]
+    #[case::vertex_signature_not_a_string(
+        "messages.4.content.1.thinking.signature.str: Input should be a valid string"
+    )]
+    #[case::empty_thinking_text(
+        r#"{"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0.thinking: each thinking block must contain thinking"}}"#
+    )]
+    #[case::shouting("MESSAGES.0.CONTENT.0: INVALID `SIGNATURE` IN `THINKING` BLOCK")]
+    fn invalid_thinking_block_errors_are_recognized(#[case] error_text: &str) {
+        assert!(is_anthropic_invalid_thinking_block_error(error_text));
+    }
+
+    #[rstest]
+    #[case::empty("")]
+    #[case::rate_limit("rate limit exceeded")]
+    #[case::unrelated_invalid_request("invalid_request_error: model not found")]
+    #[case::signature_without_invalid("thinking signature is malformed")]
+    #[case::invalid_signature_without_thinking(
+        "messages.0.content.0: Invalid `signature` in `tool_use` block"
+    )]
+    #[case::must_contain_without_thinking("each text block must contain text")]
+    fn other_errors_are_not_invalid_thinking_block_errors(#[case] error_text: &str) {
+        assert!(!is_anthropic_invalid_thinking_block_error(error_text));
+    }
+
+    #[rstest]
+    #[case::thinking_beside_text(
+        json!([
+            {"role": "user", "content": "hi"},
+            {"role": "assistant", "content": [
+                {"type": "thinking", "thinking": "plan", "signature": "sig"},
+                {"type": "text", "text": "hello"}
+            ]}
+        ]),
+        json!([
+            {"role": "user", "content": "hi"},
+            {"role": "assistant", "content": [{"type": "text", "text": "hello"}]}
+        ])
+    )]
+    #[case::redacted_thinking_beside_tool_use(
+        json!([{"role": "assistant", "content": [
+            {"type": "redacted_thinking", "data": "opaque"},
+            {"type": "tool_use", "id": "t1", "name": "Bash", "input": {}}
+        ]}]),
+        json!([{"role": "assistant", "content": [{"type": "tool_use", "id": "t1", "name": "Bash", "input": {}}]}])
+    )]
+    #[case::message_left_without_blocks_is_dropped(
+        json!([
+            {"role": "user", "content": "hi"},
+            {"role": "assistant", "content": [{"type": "thinking", "thinking": "plan", "signature": "sig"}]}
+        ]),
+        json!([{"role": "user", "content": "hi"}])
+    )]
+    #[case::history_without_thinking_is_kept(
+        json!([{"role": "assistant", "content": [{"type": "text", "text": "hello"}]}]),
+        json!([{"role": "assistant", "content": [{"type": "text", "text": "hello"}]}])
+    )]
+    fn strip_thinking_blocks_rewrites(#[case] input: Value, #[case] expected: Value) {
+        assert_eq!(apply(strip_thinking_blocks, input), expected);
+    }
+
     #[rstest]
     #[case::with_results(json!([{"type": "web_search_result", "url": "u", "title": "Rome", "snippet": "s", "page_age": null}]))]
     #[case::without_results(json!([]))]
diff --git a/litellm-rust/crates/llms/src/base_llm/anthropic_messages/transformation.rs b/litellm-rust/crates/llms/src/base_llm/anthropic_messages/transformation.rs
index 8db14687214..e2ef366df96 100644
--- a/litellm-rust/crates/llms/src/base_llm/anthropic_messages/transformation.rs
+++ b/litellm-rust/crates/llms/src/base_llm/anthropic_messages/transformation.rs
@@ -4,7 +4,10 @@ use litellm_types::llms::anthropic_messages::{
 };
 
 use crate::{
-    anthropic::experimental_pass_through::messages::thinking::ThinkingContext,
+    anthropic::{
+        common_utils::{is_anthropic_invalid_thinking_block_error, strip_thinking_blocks},
+        experimental_pass_through::messages::thinking::ThinkingContext,
+    },
     base_llm::chat::transformation::Error,
 };
 
@@ -103,6 +106,21 @@ pub trait BaseAnthropicMessagesConfig: Sync {
     fn request_headers(&self, headers: Headers, _request: &AnthropicMessagesRequest) -> Headers {
         headers
     }
+
+    fn request_after_http_error(
+        &self,
+        status: u16,
+        error_body: &str,
+        request: AnthropicMessagesRequest,
+    ) -> Option<AnthropicMessagesRequest> {
+        (status == 400 && is_anthropic_invalid_thinking_block_error(error_body)).then(|| {
+            AnthropicMessagesRequest {
+                thinking: None,
+                messages: strip_thinking_blocks(request.messages),
+                ..request
+            }
+        })
+    }
 }
 
 #[cfg(test)]
@@ -292,4 +310,58 @@ mod tests {
         };
         assert_eq!(config.authenticate(forwarded, api_key, &|_| None), expected);
     }
+
+    const INVALID_SIGNATURE: &str = r#"{"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0: Invalid `signature` in `thinking` block"}}"#;
+
+    fn replayed_thinking_request() -> AnthropicMessagesRequest {
+        serde_json::from_value(serde_json::json!({
+            "model": "claude",
+            "max_tokens": 2048,
+            "thinking": {"type": "enabled", "budget_tokens": 1024},
+            "output_config": {"effort": "high"},
+            "messages": [
+                {"role": "user", "content": "hi"},
+                {"role": "assistant", "content": [
+                    {"type": "thinking", "thinking": "plan", "signature": "stale"},
+                    {"type": "text", "text": "hello"}
+                ]},
+                {"role": "user", "content": "again"}
+            ]
+        }))
+        .unwrap()
+    }
+
+    #[test]
+    fn invalid_thinking_signature_is_retried_without_thinking() {
+        let retried = DefaultsConfig
+            .request_after_http_error(400, INVALID_SIGNATURE, replayed_thinking_request())
+            .map(|request| serde_json::to_value(request).unwrap());
+        assert_eq!(
+            retried,
+            Some(serde_json::json!({
+                "model": "claude",
+                "max_tokens": 2048,
+                "output_config": {"effort": "high"},
+                "messages": [
+                    {"role": "user", "content": "hi"},
+                    {"role": "assistant", "content": [{"type": "text", "text": "hello"}]},
+                    {"role": "user", "content": "again"}
+                ]
+            }))
+        );
+    }
+
+    #[rstest]
+    #[case::server_error_with_the_same_text(500, INVALID_SIGNATURE)]
+    #[case::unrelated_bad_request(400, "rate limit exceeded")]
+    fn other_http_errors_are_not_retried(#[case] status: u16, #[case] error_body: &str) {
+        assert_eq!(
+            DefaultsConfig.request_after_http_error(
+                status,
+                error_body,
+                replayed_thinking_request()
+            ),
+            None
+        );
+    }
 }
diff --git a/tests/test_litellm_rust/messages/test_callbacks.py b/tests/test_litellm_rust/messages/test_callbacks.py
index 2d172b94a0e..1309ead8b63 100644
--- a/tests/test_litellm_rust/messages/test_callbacks.py
+++ b/tests/test_litellm_rust/messages/test_callbacks.py
@@ -204,3 +204,109 @@ def test_native_sync_messages_returns_the_provider_message(messages_server: Reco
     assert_served_natively(messages_server)
     assert response["content"] == MESSAGES_RESPONSE["content"]
     assert len(recorder.wait_for("log_success_event")) == 1
+
+
+INVALID_SIGNATURE: Final = ResponseSpec(
+    body={
+        "type": "error",
+        "error": {
+            "type": "invalid_request_error",
+            "message": "messages.1.content.0: Invalid `signature` in `thinking` block",
+        },
+    },
+    status=400,
+)
+REPLAYED_THINKING: Final = (
+    {"role": "user", "content": "hi"},
+    {
+        "role": "assistant",
+        "content": [
+            {"type": "thinking", "thinking": "plan", "signature": "from-another-deployment"},
+            {"type": "text", "text": "hello"},
+        ],
+    },
+    {"role": "user", "content": "again"},
+)
+WITHOUT_THINKING: Final = [
+    {"role": "user", "content": "hi"},
+    {"role": "assistant", "content": [{"type": "text", "text": "hello"}]},
+    {"role": "user", "content": "again"},
+]
+
+
+def replayed_thinking(server: RecordingServer, **kwargs: object) -> dict[str, object]:
+    return arguments(
+        server,
+        model="anthropic/claude-haiku-4-5",
+        messages=[dict(message) for message in REPLAYED_THINKING],
+        max_tokens=2048,
+        thinking={"type": "enabled", "budget_tokens": 1024},
+        **kwargs,
+    )
+
+
+@pytest.mark.asyncio
+async def test_invalid_thinking_signature_is_resent_once_without_thinking_and_logged_as_resent(
+    messages_server: RecordingServer,
+) -> None:
+    messages_server.expected_requests = 2
+    messages_server.enqueue(INVALID_SIGNATURE)
+    recorder: Final = RecordingLogger()
+
+    response: Final = await litellm.anthropic.messages.acreate(
+        **replayed_thinking(messages_server, callbacks=[recorder])
+    )
+
+    assert response["content"] == MESSAGES_RESPONSE["content"]
+    first, second = (request.body for request in messages_server.requests)
+    assert first["thinking"] == {"type": "enabled", "budget_tokens": 1024}
+    assert first["messages"] == list(REPLAYED_THINKING)
+    assert second == {key: value for key, value in first.items() if key not in {"thinking", "messages"}} | {
+        "messages": WITHOUT_THINKING
+    }
+    success: Final = await recorder.wait_for_async("async_log_success_event")
+    assert len(success) == 1
+    assert success[0].kwargs["additional_args"]["complete_input_dict"] == second
+    assert "log_failure_event" not in recorder.names
+
+
+@pytest.mark.asyncio
+async def test_invalid_thinking_signature_twice_surfaces_the_second_error(messages_server: RecordingServer) -> None:
+    messages_server.expected_requests = 2
+    messages_server.enqueue(INVALID_SIGNATURE)
+    messages_server.enqueue(
+        ResponseSpec(
+            body={"type": "error", "error": {"type": "invalid_request_error", "message": "second"}}, status=400
+        )
+    )
+
+    with pytest.raises(litellm.BadRequestError, match="second"):
+        await litellm.anthropic.messages.acreate(**replayed_thinking(messages_server))
+
+
+@pytest.mark.asyncio
+async def test_other_bad_requests_are_not_resent(messages_server: RecordingServer) -> None:
+    messages_server.enqueue(
+        ResponseSpec(
+            body={"type": "error", "error": {"type": "invalid_request_error", "message": "prompt is too long"}},
+            status=400,
+        )
+    )
+
+    with pytest.raises(litellm.BadRequestError, match="prompt is too long"):
+        await litellm.anthropic.messages.acreate(**replayed_thinking(messages_server))
+
+
+@pytest.mark.asyncio
+async def test_invalid_thinking_signature_on_a_stream_is_resent_and_relayed(messages_server: RecordingServer) -> None:
+    messages_server.expected_requests = 2
+    messages_server.enqueue(INVALID_SIGNATURE)
+    messages_server.enqueue(STREAM)
+
+    stream: Final = await litellm.anthropic.messages.acreate(**replayed_thinking(messages_server, stream=True))
+    assert isinstance(stream, AsyncIterator)
+    chunks: Final = [chunk async for chunk in stream]
+
+    assert b"".join(chunks) == sse_payload()
+    assert messages_server.requests[1].body["messages"] == WITHOUT_THINKING
+    assert messages_server.requests[1].body["stream"] is True