diff --git a/crates/lingua/src/providers/anthropic/adapter.rs b/crates/lingua/src/providers/anthropic/adapter.rs
index ea431eb6..5ad1bb38 100644
--- a/crates/lingua/src/providers/anthropic/adapter.rs
+++ b/crates/lingua/src/providers/anthropic/adapter.rs
@@ -565,10 +565,25 @@ impl ProviderAdapter for AnthropicAdapter {
             });
 
         let thinking_val = if use_adaptive_thinking {
+            // Same-provider Anthropic round-trips carry the original `thinking` in extras.
+            // Preserve its `display` so an explicit "summarized" opt-in survives; models
+            // that default `display` to "omitted" would otherwise return empty thinking.
+            let display = anthropic_extras_view
+                .thinking
+                .as_ref()
+                .map(|raw| serde_json::from_value::<Thinking>(raw.clone()))
+                .transpose()
+                .map_err(|e| {
+                    TransformError::FromUniversalFailed(format!(
+                        "invalid Anthropic thinking extras: {}",
+                        e
+                    ))
+                })?
+                .and_then(|thinking| thinking.display);
             Some(
                 serde_json::to_value(&Thinking {
                     budget_tokens: None,
-                    display: None,
+                    display,
                     thinking_type: ThinkingType::Adaptive,
                 })
                 .map_err(|e| TransformError::SerializationFailed(e.to_string()))?,
@@ -1736,7 +1751,7 @@ fn parse_content_block_start_event(payload: &Value) -> ContentBlockStartEventVie
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::providers::anthropic::generated::System;
+    use crate::providers::anthropic::generated::{System, ThinkingDisplayMode};
     use crate::serde_json::json;
     use crate::universal::UniversalReasoningSignature;
     use serde::Deserialize;
@@ -2595,6 +2610,44 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_anthropic_preserves_adaptive_thinking_display_round_trip() {
+        // Same-provider Anthropic round-trip: an explicit `thinking.display` must survive
+        // the adaptive-thinking rebuild.
+        for (model, display) in [
+            ("claude-sonnet-5", Some("summarized")),
+            ("claude-opus-5", Some("summarized")),
+            ("claude-opus-4-7", Some("omitted")),
+            ("claude-sonnet-5", None),
+        ] {
+            let adapter = AnthropicAdapter;
+            let mut thinking = json!({"type": "adaptive"});
+            if let Some(display) = display {
+                thinking["display"] = json!(display);
+            }
+            let payload = json!({
+                "model": model,
+                "max_tokens": 4096,
+                "messages": [{"role": "user", "content": "What is 2+2?"}],
+                "thinking": thinking
+            });
+
+            let universal = adapter.request_to_universal(payload).unwrap();
+            let result: CreateMessageParams =
+                serde_json::from_value(adapter.request_from_universal(&universal).unwrap())
+                    .unwrap();
+
+            let thinking = result.thinking.expect("thinking should be present");
+            assert_eq!(thinking.thinking_type, ThinkingType::Adaptive);
+            let expected_display: Option<ThinkingDisplayMode> =
+                display.map(|d| serde_json::from_value(json!(d)).unwrap());
+            assert_eq!(
+                thinking.display, expected_display,
+                "{model}: thinking.display should round-trip {display:?}"
+            );
+        }
+    }
+
     #[test]
     fn test_anthropic_opus_5_preserves_disabled_thinking_with_effort_round_trip() {
         let adapter = AnthropicAdapter;
diff --git a/crates/lingua/src/providers/bedrock_anthropic/adapter.rs b/crates/lingua/src/providers/bedrock_anthropic/adapter.rs
index cf4348a8..565de1ce 100644
--- a/crates/lingua/src/providers/bedrock_anthropic/adapter.rs
+++ b/crates/lingua/src/providers/bedrock_anthropic/adapter.rs
@@ -368,4 +368,37 @@ mod tests {
 
         assert_flat_invoke_body(transformed);
     }
+
+    #[test]
+    fn anthropic_messages_to_bedrock_preserves_adaptive_thinking_display() {
+        use crate::providers::anthropic::generated::{Thinking, ThinkingDisplayMode, ThinkingType};
+
+        #[derive(Deserialize)]
+        struct ThinkingBodyView {
+            thinking: Option<Thinking>,
+        }
+
+        for model in ["eu.anthropic.claude-sonnet-5", "eu.anthropic.claude-opus-5"] {
+            let input = json!({
+                "model": model,
+                "max_tokens": 1024,
+                "messages": [{"role": "user", "content": "hi"}],
+                "thinking": {"type": "adaptive", "display": "summarized"}
+            });
+
+            let universal = AnthropicAdapter.request_to_universal(input).unwrap();
+            let transformed = BedrockAnthropicAdapter::new()
+                .request_from_universal(&universal)
+                .unwrap();
+
+            let body: ThinkingBodyView = crate::serde_json::from_value(transformed).unwrap();
+            let thinking = body.thinking.expect("thinking should be present");
+            assert_eq!(thinking.thinking_type, ThinkingType::Adaptive, "{model}");
+            assert_eq!(
+                thinking.display,
+                Some(ThinkingDisplayMode::Summarized),
+                "{model}: thinking.display should be preserved"
+            );
+        }
+    }
 }