diff --git a/litellm-rust/crates/inference-messages/src/types.rs b/litellm-rust/crates/inference-messages/src/types.rs
index ae346259559..638f709f265 100644
--- a/litellm-rust/crates/inference-messages/src/types.rs
+++ b/litellm-rust/crates/inference-messages/src/types.rs
@@ -122,6 +122,7 @@ mod tests {
                 "supports_reasoning": true,
                 "supports_adaptive_thinking": true,
                 "thinking_always_on": false,
+                "thinking_on_by_default": true,
                 "supports_legacy_thinking": false,
                 "supports_output_config": true,
                 "supports_sampling_params": false,
@@ -144,6 +145,7 @@ mod tests {
                 supports_reasoning: true,
                 supports_adaptive_thinking: true,
                 thinking_always_on: false,
+                thinking_on_by_default: true,
                 supports_legacy_thinking: false,
                 supports_output_config: true,
                 supports_sampling_params: false,
diff --git a/litellm-rust/crates/llms/src/anthropic/common_utils.rs b/litellm-rust/crates/llms/src/anthropic/common_utils.rs
index aec5d9ebc27..4292752f1c5 100644
--- a/litellm-rust/crates/llms/src/anthropic/common_utils.rs
+++ b/litellm-rust/crates/llms/src/anthropic/common_utils.rs
@@ -1882,6 +1882,7 @@ mod tests {
                 supports_reasoning: false,
                 supports_adaptive_thinking: false,
                 thinking_always_on: false,
+                thinking_on_by_default: false,
                 supports_legacy_thinking: false,
                 supports_output_config: false,
                 supports_sampling_params: true,
diff --git a/litellm-rust/crates/llms/src/anthropic/messages/thinking.rs b/litellm-rust/crates/llms/src/anthropic/messages/thinking.rs
index df1ae13fd28..fd0c07cd9a4 100644
--- a/litellm-rust/crates/llms/src/anthropic/messages/thinking.rs
+++ b/litellm-rust/crates/llms/src/anthropic/messages/thinking.rs
@@ -2,8 +2,8 @@ use litellm_llms_types::{
     formats::{
         chat_completions::ReasoningEffort,
         messages::{
-            EffortLevel, MessagesOptionalParams, MessagesRequest, OutputConfig, ThinkingConfig,
-            ThinkingDisplay,
+            ContextEdit, ContextManagement, EffortLevel, MessagesOptionalParams, MessagesRequest,
+            OutputConfig, ThinkingConfig, ThinkingDisplay,
         },
     },
     recognized::Recognized,
@@ -144,6 +144,60 @@ fn legacy_reasoning_effort(
     }
 }
 
+fn is_clear_thinking_edit(edit: &Recognized<ContextEdit>) -> bool {
+    match edit {
+        Recognized::Known(ContextEdit::ClearThinking { .. }) => true,
+        Recognized::Known(_) => false,
+        Recognized::Unrecognized(value) => value
+            .get("type")
+            .and_then(Value::as_str)
+            .is_some_and(|edit_type| edit_type.starts_with("clear_thinking_")),
+    }
+}
+
+/// Anthropic rejects `clear_thinking_*` edits without thinking. `context_management` goes
+/// only when such an edit was removed and nothing else is left in it.
+fn without_clear_thinking_edits(
+    context_management: Option<Recognized<ContextManagement>>,
+) -> Option<Recognized<ContextManagement>> {
+    match context_management {
+        Some(Recognized::Known(ContextManagement {
+            edits: Some(edits),
+            extra,
+        })) if edits.iter().any(is_clear_thinking_edit) => {
+            let kept: Vec<_> = edits
+                .into_iter()
+                .filter(|edit| !is_clear_thinking_edit(edit))
+                .collect();
+            (!kept.is_empty() || !extra.is_empty()).then(|| {
+                Recognized::Known(ContextManagement {
+                    edits: Some(kept),
+                    extra,
+                })
+            })
+        }
+        other => other,
+    }
+}
+
+fn without_thinking(
+    params: MessagesOptionalParams,
+    context: &ThinkingContext,
+) -> MessagesOptionalParams {
+    let thinks_without_thinking_param =
+        context.capabilities.thinking_always_on || context.capabilities.thinking_on_by_default;
+    let context_management = if thinks_without_thinking_param {
+        params.context_management
+    } else {
+        without_clear_thinking_edits(params.context_management)
+    };
+    MessagesOptionalParams {
+        thinking: None,
+        context_management,
+        ..params
+    }
+}
+
 fn translate_reasoning_effort(
     request: MessagesRequest,
     context: &ThinkingContext,
@@ -171,9 +225,8 @@ fn translate_reasoning_effort(
     ) else {
         return Ok(MessagesRequest {
             params: MessagesOptionalParams {
-                thinking: None,
                 output_config: None,
-                ..request.params
+                ..without_thinking(request.params, context)
             },
             ..request
         });
@@ -199,7 +252,13 @@ fn translate_reasoning_effort(
         });
     }
     let Some(budget) = fit_budget_to_max_tokens(budget, request.params.max_tokens) else {
-        return Ok(request);
+        if request.params.thinking.is_some() {
+            return Ok(request);
+        }
+        return Ok(MessagesRequest {
+            params: without_thinking(request.params, context),
+            ..request
+        });
     };
     let enabled = ThinkingConfig::enabled(budget);
     Ok(MessagesRequest {
@@ -277,15 +336,11 @@ fn translate_adaptive_effort_for_non_adaptive_model(
         _ => true,
     };
     if supports_effort_param(capabilities) && (!adaptive_thinking || level_accepted) {
+        if !adaptive_thinking {
+            return Ok(request);
+        }
         return Ok(MessagesRequest {
-            params: MessagesOptionalParams {
-                thinking: if adaptive_thinking {
-                    None
-                } else {
-                    request.params.thinking
-                },
-                ..request.params
-            },
+            params: without_thinking(request.params, context),
             ..request
         });
     }
@@ -294,13 +349,17 @@ fn translate_adaptive_effort_for_non_adaptive_model(
     } else {
         None
     };
+    let thinking = budget
+        .and_then(|budget| fit_budget_to_max_tokens(budget, request.params.max_tokens))
+        .map(|budget| Recognized::Known(ThinkingConfig::enabled(budget)));
+    let params = MessagesOptionalParams {
+        output_config: without_effort(request.params.output_config),
+        ..request.params
+    };
     Ok(MessagesRequest {
-        params: MessagesOptionalParams {
-            thinking: budget
-                .and_then(|budget| fit_budget_to_max_tokens(budget, request.params.max_tokens))
-                .map(|budget| Recognized::Known(ThinkingConfig::enabled(budget))),
-            output_config: without_effort(request.params.output_config),
-            ..request.params
+        params: match thinking {
+            Some(_) => MessagesOptionalParams { thinking, ..params },
+            None => without_thinking(params, context),
         },
         ..request
     })
@@ -458,6 +517,14 @@ mod tests {
         }
     }
 
+    #[fixture]
+    fn sonnet_5() -> MessagesModelCapabilities {
+        MessagesModelCapabilities {
+            thinking_on_by_default: true,
+            ..opus_4_7()
+        }
+    }
+
     #[fixture]
     fn newfamily_6() -> MessagesModelCapabilities {
         MessagesModelCapabilities {
@@ -625,6 +692,120 @@ mod tests {
         assert_eq!(translate(capabilities, input), Ok(request(expected)));
     }
 
+    #[rstest]
+    #[case::reasoning_effort_none(
+        haiku_4_5(),
+        serde_json::json!({"max_tokens": 8192, "reasoning_effort": "none"}),
+        false
+    )]
+    #[case::reasoning_effort_high(
+        haiku_4_5(),
+        serde_json::json!({"max_tokens": 8192, "reasoning_effort": "high"}),
+        true
+    )]
+    #[case::reasoning_effort_budget_cannot_fit(
+        haiku_4_5(),
+        serde_json::json!({"max_tokens": 1024, "reasoning_effort": "high"}),
+        false
+    )]
+    #[case::caller_thinking_kept_when_budget_cannot_fit(
+        haiku_4_5(),
+        serde_json::json!({
+            "max_tokens": 1024,
+            "reasoning_effort": "high",
+            "thinking": {"type": "enabled", "budget_tokens": 1000}
+        }),
+        true
+    )]
+    #[case::effort_model_drops_adaptive(opus_4_5(), claude_code_payload("high", 8192), false)]
+    #[case::adaptive_model_keeps_adaptive(sonnet_4_6(), claude_code_payload("high", 8192), true)]
+    #[case::non_reasoning_model(haiku_3_5(), claude_code_payload("high", 8192), false)]
+    #[case::legacy_thinking_model(haiku_4_5(), claude_code_payload("high", 8192), true)]
+    #[case::always_on_model_keeps_edit(
+        fable_5_1(),
+        serde_json::json!({"max_tokens": 8192, "reasoning_effort": "none"}),
+        true
+    )]
+    #[case::default_thinking_model_keeps_edit(
+        sonnet_5(),
+        serde_json::json!({"max_tokens": 8192, "reasoning_effort": "none"}),
+        true
+    )]
+    #[case::adaptive_model_without_default_thinking_drops_edit(
+        opus_4_7(),
+        serde_json::json!({"max_tokens": 8192, "reasoning_effort": "none"}),
+        false
+    )]
+    fn clear_thinking_edit_is_dropped_with_thinking_except_on_models_that_think_by_default(
+        #[case] capabilities: MessagesModelCapabilities,
+        #[case] fields: Value,
+        #[case] keeps_edit: bool,
+    ) {
+        let mut fields = fields;
+        fields.as_object_mut().unwrap().insert(
+            "context_management".into(),
+            serde_json::json!({"edits": [{"type": "clear_thinking_20251015", "keep": "all"}, {"type": "clear_tool_uses_20250919"}]}),
+        );
+        let thinks_without_thinking_param =
+            capabilities.thinking_always_on || capabilities.thinking_on_by_default;
+        let translated = serde_json::to_value(translate(capabilities, fields).unwrap()).unwrap();
+        let edit_types: Vec<&str> = translated["context_management"]["edits"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .filter_map(|edit| edit["type"].as_str())
+            .collect();
+        let expected: &[&str] = if keeps_edit {
+            &["clear_thinking_20251015", "clear_tool_uses_20250919"]
+        } else {
+            &["clear_tool_uses_20250919"]
+        };
+        assert_eq!(edit_types, expected);
+        assert_eq!(
+            translated.get("thinking").is_some(),
+            keeps_edit && !thinks_without_thinking_param
+        );
+    }
+
+    #[rstest]
+    #[case::only_clear_thinking_is_removed_whole(
+        serde_json::json!({"edits": [{"type": "clear_thinking_20251015"}]}),
+        None
+    )]
+    #[case::any_clear_thinking_version(
+        serde_json::json!({"edits": [{"type": "clear_thinking_20990101"}, {"type": "compact_20260112"}]}),
+        Some(serde_json::json!({"edits": [{"type": "compact_20260112"}]}))
+    )]
+    #[case::other_keys_kept(
+        serde_json::json!({"edits": [{"type": "clear_thinking_20251015"}], "extra": 1}),
+        Some(serde_json::json!({"edits": [], "extra": 1}))
+    )]
+    #[case::no_clear_thinking_untouched(
+        serde_json::json!({"edits": []}),
+        Some(serde_json::json!({"edits": []}))
+    )]
+    #[case::openai_list_untouched(
+        serde_json::json!([{"type": "compaction"}]),
+        Some(serde_json::json!([{"type": "compaction"}]))
+    )]
+    fn clear_thinking_edits_are_removed(
+        #[case] context_management: Value,
+        #[case] expected: Option<Value>,
+    ) {
+        let translated = translate(
+            haiku_4_5(),
+            serde_json::json!({"max_tokens": 8192, "reasoning_effort": "none", "context_management": context_management}),
+        )
+        .unwrap();
+        assert_eq!(
+            serde_json::to_value(translated)
+                .unwrap()
+                .get("context_management")
+                .cloned(),
+            expected
+        );
+    }
+
     #[rstest]
     #[case::minimal_floors_at_min_budget("minimal", 1024)]
     #[case::low("low", 1024)]
diff --git a/litellm-rust/crates/llms/src/base_llm/messages/context.rs b/litellm-rust/crates/llms/src/base_llm/messages/context.rs
index e59a63813b0..1af17f9b975 100644
--- a/litellm-rust/crates/llms/src/base_llm/messages/context.rs
+++ b/litellm-rust/crates/llms/src/base_llm/messages/context.rs
@@ -32,6 +32,8 @@ pub struct MessagesModelCapabilities {
     #[serde(default)]
     pub thinking_always_on: bool,
     #[serde(default)]
+    pub thinking_on_by_default: bool,
+    #[serde(default)]
     pub supports_legacy_thinking: bool,
     #[serde(default)]
     pub supports_output_config: bool,
@@ -55,6 +57,7 @@ impl Default for MessagesModelCapabilities {
             supports_reasoning: false,
             supports_adaptive_thinking: false,
             thinking_always_on: false,
+            thinking_on_by_default: false,
             supports_legacy_thinking: false,
             supports_output_config: false,
             supports_sampling_params: true,
diff --git a/litellm-rust/crates/model-catalog/src/model_info.rs b/litellm-rust/crates/model-catalog/src/model_info.rs
index 8f7549c1c6d..6e0ab177d1e 100644
--- a/litellm-rust/crates/model-catalog/src/model_info.rs
+++ b/litellm-rust/crates/model-catalog/src/model_info.rs
@@ -155,6 +155,7 @@ pub struct ModelInfoFields {
     pub supports_adaptive_thinking: Option<bool>,
     pub supports_legacy_thinking: Option<bool>,
     pub thinking_always_on: Option<bool>,
+    pub thinking_on_by_default: Option<bool>,
     pub supports_tool_search: Option<bool>,
     pub supports_mid_conversation_system: Option<bool>,
     pub supports_anthropic_thinking_payload: Option<bool>,
diff --git a/litellm-rust/crates/model-catalog/src/wire/attributes.rs b/litellm-rust/crates/model-catalog/src/wire/attributes.rs
index 93c10a81524..2d47c1fdb0d 100644
--- a/litellm-rust/crates/model-catalog/src/wire/attributes.rs
+++ b/litellm-rust/crates/model-catalog/src/wire/attributes.rs
@@ -104,6 +104,7 @@ attributes! {
     /// Cloud regions the model is available in ('global' or region ids).
     supported_regions: Vec<String>,
     thinking_always_on: bool,
+    thinking_on_by_default: bool,
     token_count_framing: u64 as Count,
     token_count_model: TokenCountModel,
     token_count_tokenizer: TokenCountTokenizer,
diff --git a/litellm/llms/anthropic/chat/transformation.py b/litellm/llms/anthropic/chat/transformation.py
index d773e31c733..0ef4dbf5f70 100644
--- a/litellm/llms/anthropic/chat/transformation.py
+++ b/litellm/llms/anthropic/chat/transformation.py
@@ -2,7 +2,7 @@ import copy
 import json
 import re
 import time
-from collections.abc import Callable, Mapping, Sequence
+from collections.abc import Callable, Mapping, MutableMapping, Sequence
 from types import MappingProxyType
 from typing import TYPE_CHECKING, Any, ClassVar, Final, NoReturn, cast
 
@@ -48,7 +48,7 @@ from litellm.litellm_core_utils.prompt_templates.mid_conversation_system import
     place_mid_conversation_system,
     split_leading_system_run,
 )
-from litellm.litellm_core_utils.reasoning_effort_utils import OPAQUE_VALUE, warn_non_string_reasoning_effort
+from litellm.litellm_core_utils.reasoning_effort_utils import warn_non_string_reasoning_effort
 from litellm.llms.base_llm.base_utils import (
     ResponseFormatSchema,
     as_json_object,
@@ -123,6 +123,7 @@ from ..common_utils import (
     REFUSAL_STOP_FIELDS,
     AnthropicError,
     AnthropicModelInfo,
+    drop_clear_thinking_edits_for_model,
     eager_input_streaming_flag,
     process_anthropic_headers,
     refusal_provider_specific_fields,
@@ -183,6 +184,16 @@ def _tool_type(tool: object) -> str | None:
             return None
 
 
+def _requested_effort(reasoning_effort: object) -> str | None:
+    match reasoning_effort:
+        case str():
+            return reasoning_effort
+        case {"effort": str(effort)}:
+            return effort
+        case _:
+            return None
+
+
 def _is_openai_tool_search_tool(tool: object) -> bool:
     return _tool_type(tool) == "tool_search"
 
@@ -1835,6 +1846,10 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
         #      via ``data = {**optional_params}`` and would 400 with
         #      ``Extra inputs are not permitted``).
 
+        requested_params: Final = cast(  # cast-ok: non_default_params is the untyped dict of the shared signature
+            Mapping[str, object], non_default_params
+        )
+
         for param, value in non_default_params.items():
             if param == "max_tokens" or param == "max_completion_tokens":
                 optional_params["max_tokens"] = value if isinstance(value, int) else max(1, int(round(value)))
@@ -1948,11 +1963,9 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
                 # send. Coerce to the effort string before mapping — same
                 # shape-tolerance the GPT-5 path already implements in
                 # `_normalize_reasoning_effort_for_chat_completion`.
-                effort_value = value
-                if isinstance(effort_value, dict):
-                    effort_value = effort_value.get("effort")
-                if not isinstance(effort_value, str):
-                    warn_non_string_reasoning_effort(OPAQUE_VALUE.validate_python(value), model)
+                effort_value = _requested_effort(requested_params[param])
+                if effort_value is None:
+                    warn_non_string_reasoning_effort(requested_params[param], model)
                     continue
                 mapped_thinking = AnthropicConfig._map_reasoning_effort(
                     reasoning_effort=effort_value,
@@ -2004,6 +2017,14 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
             ):
                 optional_params["service_tier"] = anthropic_tier  # rebind-ok: in-place fill is this method's contract
 
+        mapped_params: Final = cast(  # cast-ok: optional_params is the untyped dict of the shared signature
+            MutableMapping[str, object], optional_params
+        )
+        if "thinking" not in mapped_params and (
+            "thinking" in requested_params or _requested_effort(requested_params.get("reasoning_effort")) is not None
+        ):
+            drop_clear_thinking_edits_for_model(mapped_params, model, self._resolved_provider)
+
         ## handle thinking tokens
         self.update_optional_params_with_thinking_tokens(
             non_default_params=non_default_params, optional_params=optional_params
@@ -2290,7 +2311,11 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
             and not any_assistant_message_has_thinking_blocks(messages)
         ):
             if litellm.modify_params:
-                optional_params.pop("thinking", None)
+                mapped_params: Final = cast(  # cast-ok: optional_params is the untyped dict of the shared signature
+                    MutableMapping[str, object], optional_params
+                )
+                mapped_params.pop("thinking", None)
+                drop_clear_thinking_edits_for_model(mapped_params, model, self._resolved_provider)
                 litellm.verbose_logger.warning(
                     "Dropping 'thinking' param because the last assistant message with tool_calls "
                     "has no thinking_blocks. The model won't use extended thinking for this turn."
diff --git a/litellm/llms/anthropic/common_utils.py b/litellm/llms/anthropic/common_utils.py
index e1f9a7d540f..7a55dece712 100644
--- a/litellm/llms/anthropic/common_utils.py
+++ b/litellm/llms/anthropic/common_utils.py
@@ -1975,17 +1975,67 @@ def strip_encrypted_reasoning_blocks_from_anthropic_messages(
     return [m for m in stripped if m is not None]
 
 
+def _is_clear_thinking_edit(edit: object) -> bool:
+    match edit:
+        case {"type": str(edit_type)}:
+            return edit_type.startswith("clear_thinking_")
+        case _:
+            return False
+
+
+def drop_clear_thinking_edits(params: MutableMapping[str, object]) -> None:  # mutable-ok: edits in place
+    """
+    Remove the ``clear_thinking_*`` context-management edits, which Anthropic
+    rejects without ``thinking``.  ``context_management`` itself goes only when
+    such an edit was removed and nothing else is left in it.
+    """
+    raw_context_management: Final = params.get("context_management")
+    if not isinstance(raw_context_management, dict):
+        return
+    context_management: Final = OBJECT_MAPPING_ADAPTER.validate_python(raw_context_management)
+    raw_edits: Final = context_management.get("edits")
+    if not isinstance(raw_edits, list):
+        return
+    edits: Final = OBJECT_LIST_ADAPTER.validate_python(raw_edits)
+    kept_edits: Final = [edit for edit in edits if not _is_clear_thinking_edit(edit)]
+    if len(kept_edits) == len(edits):
+        return
+    if not kept_edits and len(context_management) == 1:
+        params.pop("context_management")
+        return
+    params["context_management"] = {  # rebind-ok: callers mutate their request params in place
+        **context_management,
+        "edits": kept_edits,
+    }
+
+
+def drop_clear_thinking_edits_for_model(
+    params: MutableMapping[str, object],  # mutable-ok: edits in place
+    model: str,
+    custom_llm_provider: str,
+) -> None:
+    """Remove the clear_thinking edits unless the model still thinks without a ``thinking`` param."""
+    thinks_without_thinking_param: Final = any(
+        AnthropicModelInfo.supports_model_capability(model, capability, custom_llm_provider)
+        for capability in ("thinking_always_on", "thinking_on_by_default")
+    )
+    if not thinks_without_thinking_param:
+        drop_clear_thinking_edits(params)
+
+
 def strip_thinking_blocks_from_anthropic_messages_request_dict(
     data: dict[str, object],
 ) -> None:
     """
     Mutate an Anthropic Messages-style request dict: strip thinking blocks from
-    ``messages`` and remove the top-level ``thinking`` extended-thinking param.
+    ``messages`` and remove ``thinking`` with its dependent context-management
+    edits (see :func:`drop_clear_thinking_edits`).
     """
     msgs: Final = data.get("messages")
     if isinstance(msgs, list):
         data["messages"] = strip_thinking_blocks_from_anthropic_messages(msgs)
     data.pop("thinking", None)
+    drop_clear_thinking_edits(data)
 
 
 _DROP_ANTHROPIC_MESSAGE: Final = object()
diff --git a/litellm/llms/anthropic/messages/native/transformation.py b/litellm/llms/anthropic/messages/native/transformation.py
index 5281ad99620..1c3c66a64dd 100644
--- a/litellm/llms/anthropic/messages/native/transformation.py
+++ b/litellm/llms/anthropic/messages/native/transformation.py
@@ -1,4 +1,4 @@
-from collections.abc import AsyncIterator, Mapping, Sequence
+from collections.abc import AsyncIterator, Mapping, MutableMapping, Sequence
 from typing import ClassVar, Final
 
 import httpx
@@ -46,6 +46,7 @@ from ...common_utils import (
     AnthropicError,
     AnthropicModelInfo,
     context_management_betas,
+    drop_clear_thinking_edits_for_model,
     is_claude_model_target,
     merge_anthropic_beta_headers,
     optionally_handle_anthropic_oauth,
@@ -115,6 +116,16 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
     def _resolved_provider(self) -> str:
         return self.custom_llm_provider or "anthropic"
 
+    def _drop_thinking(
+        self,
+        optional_params: MutableMapping[str, object],  # mutable-ok: edits optional params in place
+        model: str,
+        custom_llm_provider: str,
+        max_tokens: int | None,
+    ) -> None:
+        optional_params.pop("thinking", None)
+        drop_clear_thinking_edits_for_model(optional_params, model, custom_llm_provider)
+
     def get_supported_anthropic_messages_params(self, model: str) -> list:
         return [
             "messages",
@@ -464,9 +475,8 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
             messages=messages,
         )
 
-    @staticmethod
     def _translate_reasoning_effort_to_anthropic(
-        model: str, optional_params: dict, max_tokens: int | None, custom_llm_provider: str
+        self, model: str, optional_params: dict[str, object], max_tokens: int | None, custom_llm_provider: str
     ) -> None:
         """Map OpenAI-style ``reasoning_effort`` to native Anthropic params.
 
@@ -495,13 +505,15 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
             raise AnthropicError(message=str(e.message), status_code=400)
 
         if mapped_thinking is None:
-            optional_params.pop("thinking", None)
+            self._drop_thinking(optional_params, model, custom_llm_provider, max_tokens)
             optional_params.pop("output_config", None)
             return
 
         fitted_thinking: Final = AnthropicConfig.cap_thinking_budget_to_max_tokens(mapped_thinking, max_tokens)
         if fitted_thinking is None:
             verbose_logger.warning(DROP_UNFITTING_REASONING_EFFORT_WARNING, reasoning_effort, model, max_tokens)
+            if "thinking" not in optional_params:
+                self._drop_thinking(optional_params, model, custom_llm_provider, max_tokens)
             return
 
         optional_params.setdefault("thinking", fitted_thinking)
@@ -525,9 +537,8 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
             existing_output_config.setdefault("effort", mapped_effort)
             optional_params["output_config"] = existing_output_config
 
-    @staticmethod
     def _translate_adaptive_effort_for_non_adaptive_model(
-        model: str, optional_params: dict, max_tokens: int | None, custom_llm_provider: str
+        self, model: str, optional_params: dict[str, object], max_tokens: int | None, custom_llm_provider: str
     ) -> None:
         """Translate the 4.6+ adaptive-thinking interface (``thinking.type=adaptive``
         and/or ``output_config.effort``) down to what an older Anthropic model
@@ -590,7 +601,7 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
             or AnthropicConfig.validate_effort_for_model(model, effort, custom_llm_provider) is None
         ):
             if adaptive_thinking:
-                optional_params.pop("thinking", None)
+                self._drop_thinking(optional_params, model, custom_llm_provider, max_tokens)
             return
 
         supports_thinking: Final = AnthropicModelInfo.supports_model_capability(
@@ -618,7 +629,7 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
             optional_params["thinking"] = capped_thinking
         else:
             verbose_logger.warning(DROP_UNSUPPORTED_ADAPTIVE_EFFORT_WARNING, model)
-            optional_params.pop("thinking", None)
+            self._drop_thinking(optional_params, model, custom_llm_provider, max_tokens)
 
         if isinstance(output_config, dict) and "effort" in output_config:
             residual: Final = {k: v for k, v in output_config.items() if k != "effort"}
@@ -703,7 +714,7 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
         )
         self._translate_reasoning_effort_to_anthropic(
             model=model,
-            optional_params=anthropic_messages_optional_request_params,
+            optional_params=anthropic_messages_optional_request_params,  # pyright: ignore[reportUnknownArgumentType]  # the request params arrive as a bare dict
             max_tokens=max_tokens,
             custom_llm_provider=self._resolved_provider,
         )
@@ -727,7 +738,7 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
 
         self._translate_adaptive_effort_for_non_adaptive_model(
             model=model,
-            optional_params=anthropic_messages_optional_request_params,
+            optional_params=anthropic_messages_optional_request_params,  # pyright: ignore[reportUnknownArgumentType]  # the request params arrive as a bare dict
             max_tokens=max_tokens,
             custom_llm_provider=self._resolved_provider,
         )
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 e5d6a168d57..a001a634066 100644
--- a/litellm/llms/bedrock/messages/invoke_transformations/anthropic_claude_transformation.py
+++ b/litellm/llms/bedrock/messages/invoke_transformations/anthropic_claude_transformation.py
@@ -1,4 +1,4 @@
-from collections.abc import AsyncIterator, Mapping, Sequence
+from collections.abc import AsyncIterator, Mapping, MutableMapping, Sequence
 from types import MappingProxyType
 from typing import TYPE_CHECKING, Any, Final, cast
 
@@ -100,6 +100,18 @@ class AmazonAnthropicClaudeMessagesConfig(
     def beta_headers_provider(self) -> str:
         return self.custom_llm_provider or "bedrock"
 
+    def _drop_thinking(
+        self,
+        optional_params: MutableMapping[str, object],  # mutable-ok: edits optional params in place
+        model: str,
+        custom_llm_provider: str,
+        max_tokens: int | None,
+    ) -> None:
+        """Keep the clear_thinking edit: it makes
+        ``_ensure_thinking_for_clear_thinking_context_management`` add thinking back,
+        and ``_filter_context_management_for_bedrock_invoke`` strips it before sending."""
+        optional_params.pop("thinking", None)
+
     def should_strip_billing_metadata(self) -> bool:
         return True
 
diff --git a/litellm/llms/bedrock_mantle/messages/transformation.py b/litellm/llms/bedrock_mantle/messages/transformation.py
index aa6510f0491..5b5bc7b230f 100644
--- a/litellm/llms/bedrock_mantle/messages/transformation.py
+++ b/litellm/llms/bedrock_mantle/messages/transformation.py
@@ -1,8 +1,9 @@
-from collections.abc import Mapping
+from collections.abc import Mapping, MutableMapping
 from types import MappingProxyType
 from typing import Final
 
 from litellm.litellm_core_utils.url_utils import join_api_base
+from litellm.llms.anthropic.common_utils import drop_clear_thinking_edits_for_model
 from litellm.llms.bedrock.base_aws_llm import BaseAWSLLM
 from litellm.llms.bedrock.common_utils import MANTLE_MESSAGES_PATH
 from litellm.llms.bedrock.messages.mantle_transformation import AmazonMantleMessagesConfig
@@ -45,6 +46,26 @@ class BedrockMantleAnthropicMessagesConfig(BedrockMantleAuthMixin, AmazonMantleM
         }
     )
 
+    def _drop_thinking(
+        self,
+        optional_params: MutableMapping[str, object],  # mutable-ok: edits optional params in place
+        model: str,
+        custom_llm_provider: str,
+        max_tokens: int | None,
+    ) -> None:
+        super()._drop_thinking(optional_params, model, custom_llm_provider, max_tokens)
+        if not self._adds_thinking_back_for_clear_thinking(optional_params, model, max_tokens):
+            drop_clear_thinking_edits_for_model(optional_params, model, custom_llm_provider)
+
+    def _adds_thinking_back_for_clear_thinking(
+        self, optional_params: Mapping[str, object], model: str, max_tokens: int | None
+    ) -> bool:
+        trial_request: Final = {
+            "context_management": optional_params.get("context_management"),
+            "max_tokens": max_tokens,
+        }
+        return self._ensure_thinking_for_clear_thinking_context_management(trial_request, model, drop_params=False)
+
     def __init__(self, aws_signer: BaseAWSLLM | None = None) -> None:
         AmazonMantleMessagesConfig.__init__(self)
         self._aws_signer = aws_signer or self
diff --git a/litellm/llms/bigmodel/messages/transformation.py b/litellm/llms/bigmodel/messages/transformation.py
index 82ce59631f1..5197e18e908 100644
--- a/litellm/llms/bigmodel/messages/transformation.py
+++ b/litellm/llms/bigmodel/messages/transformation.py
@@ -154,15 +154,13 @@ class BigModelMessagesConfig(OpenAILikeAnthropicMessagesConfig):
             model, normalized, request_body, litellm_logging_obj
         )
 
-    @staticmethod
     def _translate_reasoning_effort_to_anthropic(
-        model: str, optional_params: Mapping[str, object], max_tokens: int | None, custom_llm_provider: str
+        self, model: str, optional_params: Mapping[str, object], max_tokens: int | None, custom_llm_provider: str
     ) -> None:
         return None
 
-    @staticmethod
     def _translate_adaptive_effort_for_non_adaptive_model(
-        model: str, optional_params: Mapping[str, object], max_tokens: int | None, custom_llm_provider: str
+        self, model: str, optional_params: Mapping[str, object], max_tokens: int | None, custom_llm_provider: str
     ) -> None:
         return None
 
diff --git a/litellm/model_prices_and_context_window_backup.json b/litellm/model_prices_and_context_window_backup.json
index 1d18903bb07..3f7ca4194a6 100644
--- a/litellm/model_prices_and_context_window_backup.json
+++ b/litellm/model_prices_and_context_window_backup.json
@@ -1939,6 +1939,7 @@
     "anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.25e-06,
         "cache_creation_input_token_cost_above_1hr": 1e-05,
@@ -2025,6 +2026,7 @@
     "global.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.25e-06,
         "cache_creation_input_token_cost_above_1hr": 1e-05,
@@ -2111,6 +2113,7 @@
     "us.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.875e-06,
         "cache_creation_input_token_cost_above_1hr": 1.1e-05,
@@ -2197,6 +2200,7 @@
     "eu.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.875e-06,
         "cache_creation_input_token_cost_above_1hr": 1.1e-05,
@@ -2278,6 +2282,7 @@
     "au.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.875e-06,
         "cache_creation_input_token_cost_above_1hr": 1.1e-05,
@@ -2364,6 +2369,7 @@
     "jp.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.875e-06,
         "cache_creation_input_token_cost_above_1hr": 1.1e-05,
@@ -2760,6 +2766,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -2804,6 +2811,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -2848,6 +2856,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -2892,6 +2901,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -2936,6 +2946,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -2980,6 +2991,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -3827,6 +3839,7 @@
         "deprecation_date": "2027-07-08",
         "supports_mid_conversation_system": true,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "input_cost_per_token": 5e-06,
         "output_cost_per_token": 2.5e-05,
         "litellm_provider": "azure_ai",
@@ -3964,6 +3977,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -16169,6 +16183,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -16702,6 +16717,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -21562,6 +21578,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://www.databricks.com/product/pricing/proprietary-foundation-model-serving",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_function_calling": true,
         "supports_mid_conversation_system": true,
@@ -21719,6 +21736,7 @@
         "prompt_cache_min_tokens": 1024,
         "source": "https://www.databricks.com/product/pricing/proprietary-foundation-model-serving",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_function_calling": true,
         "supports_mid_conversation_system": true,
@@ -33155,6 +33173,7 @@
             "/v1/messages"
         ],
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_function_calling": true,
         "supports_parallel_function_calling": true,
         "supports_reasoning": true,
@@ -33222,6 +33241,7 @@
             "/v1/messages"
         ],
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_function_calling": true,
         "supports_parallel_function_calling": true,
         "supports_reasoning": true,
@@ -33265,6 +33285,7 @@
             "/v1/messages"
         ],
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_function_calling": true,
         "supports_parallel_function_calling": true,
         "supports_reasoning": true,
@@ -49386,6 +49407,7 @@
         "prompt_cache_min_tokens": 1024,
         "source": "https://aws.amazon.com/bedrock/pricing/",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -49463,6 +49485,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -51863,6 +51886,7 @@
         "regional_endpoint_uplift_multiplier": 1.1,
         "supports_mid_conversation_system": true,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "cache_creation_input_token_cost": 6.25e-06,
         "cache_creation_input_token_cost_above_1hr": 1e-05,
         "cache_creation_input_token_cost_batches": 3.125e-06,
@@ -51901,6 +51925,7 @@
         "regional_endpoint_uplift_multiplier": 1.1,
         "supports_mid_conversation_system": true,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "cache_creation_input_token_cost": 6.25e-06,
         "cache_creation_input_token_cost_above_1hr": 1e-05,
         "cache_creation_input_token_cost_batches": 3.125e-06,
@@ -52144,6 +52169,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -59497,6 +59523,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -63607,6 +63634,14 @@
                     "thinking_always_on": true
                 }
             },
+            {
+                "name": "claude-thinking-on-by-default",
+                "pattern": "claude-[a-z]+-[5-9](?!\\d)(?:[-._]\\d{1,2}(?!\\d))?",
+                "description": "Claude at major version 5 or higher, in any id shape that contains claude-<family>-<major>, so new minors such as claude-sonnet-5-1 and provider-namespaced ids match. Every Claude 5 model thinks when a request carries no thinking param, so a clear_thinking context-management edit stays valid when LiteLLM drops thinking. Two-digit majors are deliberately not matched so ids like claude-opus-41 (4.1) are not read as major 41.",
+                "model_info": {
+                    "thinking_on_by_default": true
+                }
+            },
             {
                 "name": "claude-mid-conversation-system",
                 "pattern": "claude-[a-z]+-(?:4[-._](?:[89]|[1-9]\\d)(?!\\d)|[5-9](?!\\d)(?:[-._]\\d{1,2}(?!\\d))?)",
@@ -65707,6 +65742,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://deepinfra.com/pricing",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_function_calling": true,
         "supports_reasoning": true,
         "supports_response_schema": true,
@@ -66022,6 +66058,7 @@
         "prompt_cache_min_tokens": 1024,
         "source": "https://deepinfra.com/pricing",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_function_calling": true,
         "supports_reasoning": true,
         "supports_response_schema": true,
@@ -68035,6 +68072,7 @@
         "output_cost_per_token": 1.2e-05,
         "prompt_cache_min_tokens": 1024,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -68110,6 +68148,7 @@
         "output_cost_per_token": 3e-05,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -68323,6 +68362,7 @@
         "output_cost_per_token": 1.2e-05,
         "prompt_cache_min_tokens": 1024,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -68388,6 +68428,7 @@
         "output_cost_per_token": 3e-05,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -69225,6 +69266,7 @@
         "litellm_provider": "perplexity",
         "mode": "responses",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "prompt_cache_min_tokens": 512,
         "supports_web_search": true,
         "supports_function_calling": true,
@@ -69248,6 +69290,7 @@
         "litellm_provider": "perplexity",
         "mode": "responses",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_web_search": true,
         "supports_function_calling": true,
         "input_cost_per_token": 2e-06,
@@ -71324,6 +71367,7 @@
         "supports_vision": true,
         "supports_web_search": true,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "prompt_cache_min_tokens": 512,
         "supports_sampling_params": false
     },
@@ -71344,6 +71388,7 @@
         "supports_vision": true,
         "prompt_cache_min_tokens": 1024,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_sampling_params": false
     },
     "aihubmix/coding-glm-5.3": {
@@ -74024,6 +74069,7 @@
     "apac.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "litellm_provider": "bedrock_converse",
         "supports_tool_search": true,
@@ -74138,6 +74184,7 @@
         "max_output_tokens": 128000,
         "mode": "chat",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75628,6 +75675,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75680,6 +75728,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75724,6 +75773,7 @@
         "thinking_always_on": false,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -75771,6 +75821,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75807,6 +75858,7 @@
         "max_output_tokens": 128000,
         "mode": "chat",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75863,6 +75915,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75909,6 +75962,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -75949,6 +76003,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://pricing.us-east-1.amazonaws.com/offers/v1.0/aws/AmazonBedrockFoundationModels/current/index.json",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -75990,6 +76045,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://pricing.us-east-1.amazonaws.com/offers/v1.0/aws/AmazonBedrockFoundationModels/current/index.json",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -76036,6 +76092,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -76087,6 +76144,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -76133,6 +76191,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -76160,6 +76219,7 @@
         "litellm_provider": "perplexity",
         "mode": "responses",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_web_search": true,
         "supports_function_calling": true,
         "input_cost_per_token": 1e-07,
@@ -76190,6 +76250,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://pricing.us-east-1.amazonaws.com/offers/v1.0/aws/AmazonBedrockFoundationModels/current/index.json",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -76241,6 +76302,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -76291,6 +76353,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -76335,6 +76398,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -78094,6 +78158,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -78308,6 +78373,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -78472,6 +78538,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -80454,6 +80521,7 @@
         "prompt_cache_min_tokens": 512.0,
         "source": "https://www.databricks.com/product/pricing/proprietary-foundation-model-serving",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_anthropic_thinking_payload": true,
         "supports_assistant_prefill": false,
         "supports_function_calling": true,
diff --git a/litellm/rust_bridge/host/model_capabilities.py b/litellm/rust_bridge/host/model_capabilities.py
index cbf59dfb97b..321a6de8581 100644
--- a/litellm/rust_bridge/host/model_capabilities.py
+++ b/litellm/rust_bridge/host/model_capabilities.py
@@ -27,6 +27,7 @@ def anthropic_model_capabilities(model: str, custom_llm_provider: str | None) ->
         "supports_reasoning": supports("supports_reasoning"),
         "supports_adaptive_thinking": supports("supports_adaptive_thinking"),
         "thinking_always_on": supports("thinking_always_on"),
+        "thinking_on_by_default": supports("thinking_on_by_default"),
         "supports_legacy_thinking": supports("supports_legacy_thinking"),
         "supports_output_config": supports("supports_output_config"),
         "supports_sampling_params": AnthropicModelInfo._supports_sampling_params(resolved_model),  # pyright: ignore[reportPrivateUsage]  # same gate the handler applies
diff --git a/litellm/types/utils.py b/litellm/types/utils.py
index db865c7488a..1b09e9441c5 100644
--- a/litellm/types/utils.py
+++ b/litellm/types/utils.py
@@ -223,6 +223,7 @@ class ProviderSpecificModelInfo(TypedDict, total=False):
     supports_adaptive_thinking: bool | None
     supports_legacy_thinking: ReadOnly[bool | None]
     thinking_always_on: ReadOnly[bool | None]
+    thinking_on_by_default: ReadOnly[bool | None]
     supports_tool_search: bool | None
     supports_mid_conversation_system: bool | None
     supports_url_context: bool | None
diff --git a/litellm/utils.py b/litellm/utils.py
index 560d0c31e4a..0d8433311de 100644
--- a/litellm/utils.py
+++ b/litellm/utils.py
@@ -7353,6 +7353,7 @@ def get_model_info_helper(
                 supports_adaptive_thinking=_model_info.get("supports_adaptive_thinking", None),
                 supports_legacy_thinking=_model_info.get("supports_legacy_thinking", None),
                 thinking_always_on=_model_info.get("thinking_always_on", None),
+                thinking_on_by_default=_model_info.get("thinking_on_by_default", None),
                 supports_tool_search=_model_info.get("supports_tool_search", None),
                 supports_mid_conversation_system=_model_info.get("supports_mid_conversation_system", None),
                 supports_anthropic_thinking_payload=_model_info.get("supports_anthropic_thinking_payload", None),
diff --git a/model_prices_and_context_window.json b/model_prices_and_context_window.json
index 1d18903bb07..3f7ca4194a6 100644
--- a/model_prices_and_context_window.json
+++ b/model_prices_and_context_window.json
@@ -1939,6 +1939,7 @@
     "anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.25e-06,
         "cache_creation_input_token_cost_above_1hr": 1e-05,
@@ -2025,6 +2026,7 @@
     "global.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.25e-06,
         "cache_creation_input_token_cost_above_1hr": 1e-05,
@@ -2111,6 +2113,7 @@
     "us.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.875e-06,
         "cache_creation_input_token_cost_above_1hr": 1.1e-05,
@@ -2197,6 +2200,7 @@
     "eu.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.875e-06,
         "cache_creation_input_token_cost_above_1hr": 1.1e-05,
@@ -2278,6 +2282,7 @@
     "au.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.875e-06,
         "cache_creation_input_token_cost_above_1hr": 1.1e-05,
@@ -2364,6 +2369,7 @@
     "jp.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "cache_creation_input_token_cost": 6.875e-06,
         "cache_creation_input_token_cost_above_1hr": 1.1e-05,
@@ -2760,6 +2766,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -2804,6 +2811,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -2848,6 +2856,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -2892,6 +2901,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -2936,6 +2946,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -2980,6 +2991,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -3827,6 +3839,7 @@
         "deprecation_date": "2027-07-08",
         "supports_mid_conversation_system": true,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "input_cost_per_token": 5e-06,
         "output_cost_per_token": 2.5e-05,
         "litellm_provider": "azure_ai",
@@ -3964,6 +3977,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -16169,6 +16183,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -16702,6 +16717,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -21562,6 +21578,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://www.databricks.com/product/pricing/proprietary-foundation-model-serving",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_function_calling": true,
         "supports_mid_conversation_system": true,
@@ -21719,6 +21736,7 @@
         "prompt_cache_min_tokens": 1024,
         "source": "https://www.databricks.com/product/pricing/proprietary-foundation-model-serving",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_function_calling": true,
         "supports_mid_conversation_system": true,
@@ -33155,6 +33173,7 @@
             "/v1/messages"
         ],
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_function_calling": true,
         "supports_parallel_function_calling": true,
         "supports_reasoning": true,
@@ -33222,6 +33241,7 @@
             "/v1/messages"
         ],
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_function_calling": true,
         "supports_parallel_function_calling": true,
         "supports_reasoning": true,
@@ -33265,6 +33285,7 @@
             "/v1/messages"
         ],
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_function_calling": true,
         "supports_parallel_function_calling": true,
         "supports_reasoning": true,
@@ -49386,6 +49407,7 @@
         "prompt_cache_min_tokens": 1024,
         "source": "https://aws.amazon.com/bedrock/pricing/",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -49463,6 +49485,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -51863,6 +51886,7 @@
         "regional_endpoint_uplift_multiplier": 1.1,
         "supports_mid_conversation_system": true,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "cache_creation_input_token_cost": 6.25e-06,
         "cache_creation_input_token_cost_above_1hr": 1e-05,
         "cache_creation_input_token_cost_batches": 3.125e-06,
@@ -51901,6 +51925,7 @@
         "regional_endpoint_uplift_multiplier": 1.1,
         "supports_mid_conversation_system": true,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "cache_creation_input_token_cost": 6.25e-06,
         "cache_creation_input_token_cost_above_1hr": 1e-05,
         "cache_creation_input_token_cost_batches": 3.125e-06,
@@ -52144,6 +52169,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -59497,6 +59523,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -63607,6 +63634,14 @@
                     "thinking_always_on": true
                 }
             },
+            {
+                "name": "claude-thinking-on-by-default",
+                "pattern": "claude-[a-z]+-[5-9](?!\\d)(?:[-._]\\d{1,2}(?!\\d))?",
+                "description": "Claude at major version 5 or higher, in any id shape that contains claude-<family>-<major>, so new minors such as claude-sonnet-5-1 and provider-namespaced ids match. Every Claude 5 model thinks when a request carries no thinking param, so a clear_thinking context-management edit stays valid when LiteLLM drops thinking. Two-digit majors are deliberately not matched so ids like claude-opus-41 (4.1) are not read as major 41.",
+                "model_info": {
+                    "thinking_on_by_default": true
+                }
+            },
             {
                 "name": "claude-mid-conversation-system",
                 "pattern": "claude-[a-z]+-(?:4[-._](?:[89]|[1-9]\\d)(?!\\d)|[5-9](?!\\d)(?:[-._]\\d{1,2}(?!\\d))?)",
@@ -65707,6 +65742,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://deepinfra.com/pricing",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_function_calling": true,
         "supports_reasoning": true,
         "supports_response_schema": true,
@@ -66022,6 +66058,7 @@
         "prompt_cache_min_tokens": 1024,
         "source": "https://deepinfra.com/pricing",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_function_calling": true,
         "supports_reasoning": true,
         "supports_response_schema": true,
@@ -68035,6 +68072,7 @@
         "output_cost_per_token": 1.2e-05,
         "prompt_cache_min_tokens": 1024,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -68110,6 +68148,7 @@
         "output_cost_per_token": 3e-05,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -68323,6 +68362,7 @@
         "output_cost_per_token": 1.2e-05,
         "prompt_cache_min_tokens": 1024,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -68388,6 +68428,7 @@
         "output_cost_per_token": 3e-05,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -69225,6 +69266,7 @@
         "litellm_provider": "perplexity",
         "mode": "responses",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "prompt_cache_min_tokens": 512,
         "supports_web_search": true,
         "supports_function_calling": true,
@@ -69248,6 +69290,7 @@
         "litellm_provider": "perplexity",
         "mode": "responses",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_web_search": true,
         "supports_function_calling": true,
         "input_cost_per_token": 2e-06,
@@ -71324,6 +71367,7 @@
         "supports_vision": true,
         "supports_web_search": true,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "prompt_cache_min_tokens": 512,
         "supports_sampling_params": false
     },
@@ -71344,6 +71388,7 @@
         "supports_vision": true,
         "prompt_cache_min_tokens": 1024,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_sampling_params": false
     },
     "aihubmix/coding-glm-5.3": {
@@ -74024,6 +74069,7 @@
     "apac.anthropic.claude-opus-5": {
         "bedrock_converse_supports_strict_tools": false,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "litellm_provider": "bedrock_converse",
         "supports_tool_search": true,
@@ -74138,6 +74184,7 @@
         "max_output_tokens": 128000,
         "mode": "chat",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75628,6 +75675,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75680,6 +75728,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75724,6 +75773,7 @@
         "thinking_always_on": false,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -75771,6 +75821,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75807,6 +75858,7 @@
         "max_output_tokens": 128000,
         "mode": "chat",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75863,6 +75915,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -75909,6 +75962,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -75949,6 +76003,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://pricing.us-east-1.amazonaws.com/offers/v1.0/aws/AmazonBedrockFoundationModels/current/index.json",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -75990,6 +76045,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://pricing.us-east-1.amazonaws.com/offers/v1.0/aws/AmazonBedrockFoundationModels/current/index.json",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -76036,6 +76092,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -76087,6 +76144,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -76133,6 +76191,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -76160,6 +76219,7 @@
         "litellm_provider": "perplexity",
         "mode": "responses",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_web_search": true,
         "supports_function_calling": true,
         "input_cost_per_token": 1e-07,
@@ -76190,6 +76250,7 @@
         "prompt_cache_min_tokens": 512,
         "source": "https://pricing.us-east-1.amazonaws.com/offers/v1.0/aws/AmazonBedrockFoundationModels/current/index.json",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -76241,6 +76302,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -76291,6 +76353,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -76335,6 +76398,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
@@ -78094,6 +78158,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -78308,6 +78373,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -78472,6 +78538,7 @@
             "search_context_size_medium": 0.01
         },
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_mid_conversation_system": true,
         "supports_assistant_prefill": false,
         "supports_computer_use": true,
@@ -80454,6 +80521,7 @@
         "prompt_cache_min_tokens": 512.0,
         "source": "https://www.databricks.com/product/pricing/proprietary-foundation-model-serving",
         "supports_adaptive_thinking": true,
+        "thinking_on_by_default": true,
         "supports_anthropic_thinking_payload": true,
         "supports_assistant_prefill": false,
         "supports_function_calling": true,
diff --git a/tests/unit/llms/anthropic/chat/test_anthropic_chat_transformation.py b/tests/unit/llms/anthropic/chat/test_anthropic_chat_transformation.py
index cbb60caa57b..ed67f5221d6 100644
--- a/tests/unit/llms/anthropic/chat/test_anthropic_chat_transformation.py
+++ b/tests/unit/llms/anthropic/chat/test_anthropic_chat_transformation.py
@@ -9849,3 +9849,108 @@ def test_transform_request_tool_config_point_without_tools_drops_the_key():
     assert "cache_control_injection_points" not in data
     assert "tools" not in data
     assert litellm_params["metadata"] == {}
+
+
+CLEAR_THINKING_EDIT: Final = {"type": "clear_thinking_20251015", "keep": "all"}
+CLEAR_TOOL_USES_EDIT: Final = {"type": "clear_tool_uses_20250919"}
+
+
+def _edits_for(keeps_thinking: bool) -> list[dict[str, str]]:
+    return [CLEAR_THINKING_EDIT, CLEAR_TOOL_USES_EDIT] if keeps_thinking else [CLEAR_TOOL_USES_EDIT]
+
+
+@pytest.mark.parametrize(
+    ("model", "params", "keeps_thinking"),
+    [
+        pytest.param(
+            "claude-haiku-4-5",
+            {"thinking": {"type": "adaptive"}, "max_tokens": 1000},
+            False,
+            id="adaptive-unfit-dropped",
+        ),
+        pytest.param(
+            "claude-haiku-4-5", {"thinking": {"type": "adaptive"}, "max_tokens": 8192}, True, id="adaptive-translated"
+        ),
+        pytest.param("claude-sonnet-4-5", {"reasoning_effort": "none"}, False, id="reasoning-effort-none"),
+        pytest.param(
+            "claude-sonnet-4-5", {"reasoning_effort": {"effort": "none"}}, False, id="reasoning-effort-dict-none"
+        ),
+        pytest.param("claude-sonnet-4-5", {"reasoning_effort": "high"}, True, id="reasoning-effort-high"),
+    ],
+)
+@pytest.mark.parametrize("context_management_first", [True, False])
+def test_map_openai_params_drops_clear_thinking_edit_exactly_when_thinking_is(
+    model: str, params: dict[str, object], keeps_thinking: bool, context_management_first: bool
+) -> None:
+    context_management: Final = {"context_management": {"edits": [CLEAR_THINKING_EDIT, CLEAR_TOOL_USES_EDIT]}}
+    rest: Final = {"max_tokens": 8192, **params}
+    result: Final = AnthropicConfig().map_openai_params(
+        non_default_params={**context_management, **rest}
+        if context_management_first
+        else {**rest, **context_management},
+        optional_params={},
+        model=model,
+        drop_params=False,
+    )
+
+    assert ("thinking" in result) is keeps_thinking
+    assert result["context_management"] == {"edits": _edits_for(keeps_thinking)}
+
+
+@pytest.mark.parametrize(
+    ("model", "reasoning_effort"),
+    [
+        pytest.param("claude-fable-5", "none", id="always-on-model"),
+        pytest.param("claude-sonnet-4-5", {"summary": "concise"}, id="effort-less-dict"),
+    ],
+)
+def test_map_openai_params_keeps_clear_thinking_edit_when_thinking_was_not_dropped(
+    model: str, reasoning_effort: str | dict[str, str]
+) -> None:
+    result: Final = AnthropicConfig().map_openai_params(
+        non_default_params={
+            "context_management": {"edits": [CLEAR_THINKING_EDIT]},
+            "max_tokens": 8192,
+            "reasoning_effort": reasoning_effort,
+        },
+        optional_params={},
+        model=model,
+        drop_params=False,
+    )
+
+    assert result["context_management"] == {"edits": [CLEAR_THINKING_EDIT]}
+
+
+@pytest.mark.parametrize(
+    ("model", "modify_params", "keeps_thinking", "keeps_edit"),
+    [
+        pytest.param("claude-sonnet-4-5", True, False, False, id="dropped"),
+        pytest.param("claude-sonnet-4-5", False, True, True, id="modify-params-off"),
+        pytest.param("claude-fable-5", True, False, True, id="always-on-keeps-edit"),
+    ],
+)
+def test_transform_request_drops_clear_thinking_edit_with_thinking_for_tool_turn_without_thinking_blocks(
+    monkeypatch: pytest.MonkeyPatch, model: str, modify_params: bool, keeps_thinking: bool, keeps_edit: bool
+) -> None:
+    monkeypatch.setattr(litellm, "modify_params", modify_params)
+    result: Final = AnthropicConfig().transform_request(
+        model=model,
+        messages=[
+            {"role": "user", "content": "Look it up"},
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [{"id": "call_1", "type": "function", "function": {"name": "lookup", "arguments": "{}"}}],
+            },
+            {"role": "tool", "tool_call_id": "call_1", "content": "found"},
+        ],
+        optional_params={
+            "thinking": {"type": "enabled", "budget_tokens": 1024},
+            "context_management": {"edits": [CLEAR_THINKING_EDIT, CLEAR_TOOL_USES_EDIT]},
+        },
+        litellm_params={},
+        headers={},
+    )
+
+    assert ("thinking" in result) is keeps_thinking
+    assert result["context_management"] == {"edits": _edits_for(keeps_edit)}
diff --git a/tests/unit/llms/anthropic/messages/native/test_anthropic_messages_effort.py b/tests/unit/llms/anthropic/messages/native/test_anthropic_messages_effort.py
index 94476139313..6220c31ba04 100644
--- a/tests/unit/llms/anthropic/messages/native/test_anthropic_messages_effort.py
+++ b/tests/unit/llms/anthropic/messages/native/test_anthropic_messages_effort.py
@@ -1,3 +1,5 @@
+from typing import Final
+
 import pytest
 
 from litellm.constants import (
@@ -334,3 +336,70 @@ def test_reasoning_effort_budget_capped_for_openai_like_messages_upstream():
 
     assert result["thinking"] == {"type": "enabled", "budget_tokens": 3999}
     assert result["max_tokens"] == 4000
+
+
+CLEAR_THINKING_EDIT: Final = {"type": "clear_thinking_20251015", "keep": "all"}
+CLEAR_TOOL_USES_EDIT: Final = {"type": "clear_tool_uses_20250919"}
+
+
+@pytest.mark.parametrize(
+    ("model", "params", "keeps_thinking"),
+    [
+        pytest.param("claude-sonnet-4-5", {"reasoning_effort": "none"}, False, id="reasoning-effort-none"),
+        pytest.param("claude-haiku-4-5", {"reasoning_effort": "high"}, True, id="reasoning-effort-high"),
+        pytest.param(
+            "claude-haiku-4-5",
+            {"max_tokens": 1024, "reasoning_effort": "high"},
+            False,
+            id="reasoning-effort-budget-cannot-fit",
+        ),
+        pytest.param(
+            "claude-haiku-4-5",
+            {"max_tokens": 1024, "reasoning_effort": "high", "thinking": {"type": "enabled", "budget_tokens": 1000}},
+            True,
+            id="caller-thinking-kept-when-budget-cannot-fit",
+        ),
+        pytest.param("claude-opus-4-5", _claude_code_payload(effort="high"), False, id="effort-model-drops-adaptive"),
+        pytest.param("claude-sonnet-4-6", _claude_code_payload(effort="high"), True, id="adaptive-model"),
+        pytest.param("claude-3-5-haiku-latest", _claude_code_payload(), False, id="non-reasoning-model"),
+        pytest.param("claude-haiku-4-5", _claude_code_payload(), True, id="legacy-thinking-model"),
+        pytest.param(
+            "claude-opus-4-8", {"reasoning_effort": "none"}, False, id="adaptive-model-without-default-thinking"
+        ),
+    ],
+)
+def test_clear_thinking_edit_dropped_exactly_when_thinking_is(
+    model: str, params: dict[str, object], keeps_thinking: bool
+) -> None:
+    result: Final = _transform(
+        model,
+        {
+            "max_tokens": 8192,
+            **params,
+            "context_management": {"edits": [CLEAR_THINKING_EDIT, CLEAR_TOOL_USES_EDIT]},
+        },
+    )
+
+    assert ("thinking" in result) is keeps_thinking
+    expected_edits: Final = [CLEAR_THINKING_EDIT, CLEAR_TOOL_USES_EDIT] if keeps_thinking else [CLEAR_TOOL_USES_EDIT]
+    assert result["context_management"] == {"edits": expected_edits}
+
+
+@pytest.mark.parametrize(
+    "model",
+    [
+        "claude-fable-5",
+        "claude-sonnet-5",
+        "claude-opus-5",
+        "claude-haiku-5-5",
+        pytest.param("claude-sonnet-5-1", id="unmapped-claude-5-minor"),
+        pytest.param("claude-opus-5-2-20270101", id="unmapped-dated-claude-5-minor"),
+    ],
+)
+def test_clear_thinking_edit_kept_when_model_thinks_without_thinking_param(model: str) -> None:
+    result: Final = _transform(
+        model,
+        {"max_tokens": 8192, "reasoning_effort": "none", "context_management": {"edits": [CLEAR_THINKING_EDIT]}},
+    )
+
+    assert result["context_management"] == {"edits": [CLEAR_THINKING_EDIT]}
diff --git a/tests/unit/llms/anthropic/test_anthropic_common_utils.py b/tests/unit/llms/anthropic/test_anthropic_common_utils.py
index 0808ce0ec3c..d321980f2b8 100644
--- a/tests/unit/llms/anthropic/test_anthropic_common_utils.py
+++ b/tests/unit/llms/anthropic/test_anthropic_common_utils.py
@@ -1612,6 +1612,52 @@ class TestAnthropicThinkingSignatureSelfHeal:
         assert "thinking" not in data
         assert data["messages"] == []
 
+    def test_strip_thinking_request_dict_drops_clear_thinking_edits(self) -> None:
+        from litellm.llms.anthropic.common_utils import (
+            strip_thinking_blocks_from_anthropic_messages_request_dict,
+        )
+
+        data: Final[dict[str, object]] = {
+            "messages": [{"role": "assistant", "content": [{"type": "thinking", "thinking": "unsigned"}]}],
+            "thinking": {"type": "adaptive"},
+            "context_management": {"edits": [{"type": "clear_thinking_20251015", "keep": "all"}]},
+        }
+        strip_thinking_blocks_from_anthropic_messages_request_dict(data)
+        assert "context_management" not in data
+
+    @pytest.mark.parametrize(
+        ("context_management", "expected"),
+        [
+            pytest.param(
+                {"edits": [{"type": "clear_thinking_20990101"}, {"type": "clear_tool_uses_20250919"}]},
+                {"edits": [{"type": "clear_tool_uses_20250919"}]},
+                id="any-clear-thinking-version-dropped-others-kept",
+            ),
+            pytest.param({"edits": [{"type": "clear_thinking_20251015"}]}, None, id="emptied-removed"),
+            pytest.param(
+                {"edits": [{"type": "clear_thinking_20251015"}], "extra": 1},
+                {"edits": [], "extra": 1},
+                id="other-keys-kept",
+            ),
+            pytest.param({"edits": []}, {"edits": []}, id="empty-edits-untouched"),
+            pytest.param("clear_thinking_20251015", "clear_thinking_20251015", id="non-dict-untouched"),
+            pytest.param({"edits": "clear_thinking"}, {"edits": "clear_thinking"}, id="non-list-edits-untouched"),
+            pytest.param(
+                {"edits": ["clear_thinking_20251015", {"type": "clear_thinking_20251015"}]},
+                {"edits": ["clear_thinking_20251015"]},
+                id="non-dict-edit-kept",
+            ),
+        ],
+    )
+    def test_drop_clear_thinking_edits(self, context_management: object, expected: object) -> None:
+        from litellm.llms.anthropic.common_utils import (
+            drop_clear_thinking_edits,
+        )
+
+        params: Final[dict[str, object]] = {"context_management": context_management}
+        drop_clear_thinking_edits(params)
+        assert params == ({} if expected is None else {"context_management": expected})
+
     def test_strip_empty_content_blocks_from_anthropic_messages(self):
         """Covers #22930.  The core regression scenario: an assistant message
         with an empty text block alongside ``tool_use`` loses the empty block
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 0bd480dcdbc..1491525f6ce 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
@@ -2195,6 +2195,36 @@ def test_bedrock_invoke_transform_emits_adaptive_thinking_for_opus_4_8():
     assert result["output_config"]["effort"] == "low"
 
 
+@pytest.mark.parametrize(
+    "thinking_params",
+    [
+        pytest.param({"thinking": {"type": "adaptive"}, "output_config": {"effort": "high"}}, id="adaptive-effort"),
+        pytest.param({"reasoning_effort": "none"}, id="reasoning-effort-none"),
+    ],
+)
+def test_bedrock_invoke_keeps_thinking_for_clear_thinking_edit_when_base_drops_thinking(
+    thinking_params: dict[str, object],
+) -> None:
+    from litellm.types.router import GenericLiteLLMParams
+
+    result: Final = AmazonAnthropicClaudeMessagesConfig().transform_anthropic_messages_request(
+        model="anthropic.claude-opus-4-5-20251101-v1:0",
+        messages=[{"role": "user", "content": "hi"}],
+        anthropic_messages_optional_request_params={
+            "max_tokens": 32000,
+            **thinking_params,
+            "context_management": {
+                "edits": [{"type": "clear_thinking_20251015", "keep": "all"}, {"type": "clear_tool_uses_20250919"}]
+            },
+        },
+        litellm_params=GenericLiteLLMParams(),
+        headers={},
+    )
+
+    assert result["thinking"] == {"type": "enabled", "budget_tokens": BEDROCK_MIN_THINKING_BUDGET_TOKENS}
+    assert result["context_management"] == {"edits": [{"type": "clear_tool_uses_20250919"}]}
+
+
 def test_bedrock_invoke_transform_normalizes_system_role_message_into_system():
     """Bedrock Invoke rejects ``role: "system"`` entries in ``messages`` on some
     Claude aliases; they must be moved into the top-level ``system`` field
@@ -4488,7 +4518,10 @@ async def test_bedrock_messages_fallback_to_anthropic_sends_the_tool_names_bedro
                     "aws_region_name": "us-east-1",
                 },
             },
-            {"model_name": "anthropic-claude", "litellm_params": {"model": "anthropic/claude-opus-4-8", "api_key": "test"}},
+            {
+                "model_name": "anthropic-claude",
+                "litellm_params": {"model": "anthropic/claude-opus-4-8", "api_key": "test"},
+            },
         ],
         fallbacks=[{"bedrock-claude": ["anthropic-claude"]}],
         num_retries=0,
diff --git a/tests/unit/llms/bedrock_mantle/test_bedrock_mantle_messages_transformation.py b/tests/unit/llms/bedrock_mantle/test_bedrock_mantle_messages_transformation.py
index 432d0912248..34f0f7d2e0c 100644
--- a/tests/unit/llms/bedrock_mantle/test_bedrock_mantle_messages_transformation.py
+++ b/tests/unit/llms/bedrock_mantle/test_bedrock_mantle_messages_transformation.py
@@ -19,6 +19,7 @@ import respx
 
 import litellm
 from litellm.caching.llm_caching_handler import LLMClientCache
+from litellm.constants import BEDROCK_MIN_THINKING_BUDGET_TOKENS
 from litellm.llms.bedrock.base_aws_llm import BaseAWSLLM
 from litellm.llms.bedrock_mantle.messages.transformation import (
     BedrockMantleAnthropicMessagesConfig,
@@ -224,6 +225,86 @@ class TestRequestBody:
         )
         assert "stream" not in body
 
+    @pytest.mark.parametrize(
+        ("model", "thinking_params", "expected_thinking", "expected_edit_types"),
+        [
+            pytest.param(
+                "anthropic.claude-3-5-haiku-20241022-v1:0",
+                {"thinking": {"type": "adaptive"}},
+                None,
+                ["clear_tool_uses_20250919"],
+                id="no-thinking-support-drops-edit",
+            ),
+            pytest.param(
+                "anthropic.claude-3-5-haiku-20241022-v1:0",
+                {},
+                None,
+                ["clear_thinking_20251015", "clear_tool_uses_20250919"],
+                id="caller-edit-without-thinking-forwarded",
+            ),
+            pytest.param(
+                "anthropic.claude-opus-4-5-20251101-v1:0",
+                {"thinking": {"type": "adaptive"}, "output_config": {"effort": "high"}},
+                {"type": "enabled", "budget_tokens": BEDROCK_MIN_THINKING_BUDGET_TOKENS},
+                ["clear_thinking_20251015", "clear_tool_uses_20250919"],
+                id="thinking-added-back-keeps-edit",
+            ),
+            pytest.param(
+                "anthropic.claude-opus-4-5-20251101-v1:0",
+                {"max_tokens": BEDROCK_MIN_THINKING_BUDGET_TOKENS, "reasoning_effort": "none"},
+                None,
+                ["clear_tool_uses_20250919"],
+                id="max-tokens-too-small-to-add-thinking-back-drops-edit",
+            ),
+            pytest.param(
+                "anthropic.claude-mythos-preview",
+                {},
+                None,
+                ["clear_thinking_20251015", "clear_tool_uses_20250919"],
+                id="always-on-model-keeps-edit",
+            ),
+            pytest.param(
+                "anthropic.claude-sonnet-4-6",
+                {"thinking": {"type": "adaptive"}},
+                {"type": "adaptive"},
+                ["clear_thinking_20251015", "clear_tool_uses_20250919"],
+                id="adaptive-thinking-keeps-edit",
+            ),
+        ],
+    )
+    def test_clear_thinking_edit_dropped_only_with_dropped_thinking(
+        self,
+        model: str,
+        thinking_params: dict[str, object],
+        expected_thinking: dict[str, object] | None,
+        expected_edit_types: list[str],
+    ) -> None:
+        body: Final = BedrockMantleAnthropicMessagesConfig().transform_anthropic_messages_request(
+            model=model,
+            messages=[{"role": "user", "content": "ping"}],
+            anthropic_messages_optional_request_params={
+                "max_tokens": 32000,
+                **thinking_params,
+                "context_management": {
+                    "edits": [{"type": "clear_thinking_20251015", "keep": "all"}, {"type": "clear_tool_uses_20250919"}]
+                },
+            },
+            litellm_params=GenericLiteLLMParams(),
+            headers={},
+        )
+        assert body.get("thinking") == expected_thinking
+        assert [edit["type"] for edit in body["context_management"]["edits"]] == expected_edit_types
+
+    def test_disabled_thinking_without_edits_is_untouched(self) -> None:
+        body: Final = BedrockMantleAnthropicMessagesConfig().transform_anthropic_messages_request(
+            model="anthropic.claude-3-5-haiku-20241022-v1:0",
+            messages=[{"role": "user", "content": "ping"}],
+            anthropic_messages_optional_request_params={"max_tokens": 8, "thinking": {"type": "disabled"}},
+            litellm_params=GenericLiteLLMParams(),
+            headers={},
+        )
+        assert body["thinking"] == {"type": "disabled"}
+
     def test_body_hoists_wrapped_defer_loading_and_drops_custom(self):
         schema: Final = {"type": "object", "properties": {}}
         body = BedrockMantleAnthropicMessagesConfig().transform_anthropic_messages_request(
diff --git a/tests/unit/test_model_prices_and_context_window.py b/tests/unit/test_model_prices_and_context_window.py
index 8ca678a94ad..26323295176 100644
--- a/tests/unit/test_model_prices_and_context_window.py
+++ b/tests/unit/test_model_prices_and_context_window.py
@@ -60,6 +60,7 @@ class _CopilotThinkingCapabilities(BaseModel):
     supports_adaptive_thinking: bool | None = None
     supports_legacy_thinking: bool | None = None
     thinking_always_on: bool | None = None
+    thinking_on_by_default: bool | None = None
 
 
 def _copilot_endpoint_rows(path: Path) -> Mapping[str, _CopilotEndpointRow]:
@@ -87,6 +88,7 @@ _THINKING_KEYS: Final[tuple[str, ...]] = (
     "supports_adaptive_thinking",
     "supports_legacy_thinking",
     "thinking_always_on",
+    "thinking_on_by_default",
 )
 
 
diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
index 5cf872f4ea7..d6346768748 100644
--- a/tests/unit/test_utils.py
+++ b/tests/unit/test_utils.py
@@ -1211,6 +1211,7 @@ _COST_MAP_ROW_SCHEMA: Final = {
             "supports_anthropic_thinking_payload": {"type": "boolean"},
             "supports_legacy_thinking": {"type": "boolean"},
             "thinking_always_on": {"type": "boolean"},
+            "thinking_on_by_default": {"type": "boolean"},
             "supports_mid_conversation_system": {"type": "boolean"},
             "supports_sampling_params": {"type": "boolean"},
             "supports_output_config": {"type": "boolean"},