fix: apply Opus 4.7 API contract to Claude Opus 4.8

crates/forge_app/src/transformers/model_specific_reasoning.rs

@@ -27,7 +27,14 @@ impl ModelSpecificReasoning {
 
     fn family(&self) -> AnthropicModelFamily {
         let id = self.model_id.to_lowercase();
-        if id.contains("opus-4-7") || id.contains("47-opus") {
+        if id.contains("opus-4-8")
+            || id.contains("48-opus")
+            || id.contains("opus-4-7")
+            || id.contains("47-opus")
+        {
+            // Opus 4.8 shares Opus 4.7's API contract: adaptive thinking only
+            // (legacy `budget_tokens` returns 400) and non-default sampling
+            // params (`temperature`/`top_p`/`top_k`) return 400.
             AnthropicModelFamily::AdaptiveOnly
         } else if id.contains("opus-4-6")
             || id.contains("46-opus")
@@ -82,7 +89,7 @@ impl Transformer for ModelSpecificReasoning {
                     warn!(
                         model = %self.model_id,
                         dropped_max_tokens = max_tokens,
-                        "Dropping `reasoning.max_tokens` for Opus 4.7: extended thinking budgets are unsupported. Use `reasoning.effort` to control thinking depth instead."
+                        "Dropping `reasoning.max_tokens` for Opus 4.7/4.8: extended thinking budgets are unsupported. Use `reasoning.effort` to control thinking depth instead."
                     );
                 }
                 context.temperature = None;
@@ -108,7 +115,7 @@ impl Transformer for ModelSpecificReasoning {
                     {
                         warn!(
                             model = %self.model_id,
-                            "Dropping `reasoning.effort`: the effort parameter is only supported on Opus 4.5, Opus 4.6, Sonnet 4.6, and Opus 4.7."
+                            "Dropping `reasoning.effort`: the effort parameter is only supported on Opus 4.5, Opus 4.6, Sonnet 4.6, Opus 4.7, and Opus 4.8."
                         );
                         reasoning.effort = None;
                     }
@@ -155,6 +162,64 @@ mod tests {
         assert_eq!(actual, expected);
     }
 
+    #[test]
+    fn test_opus_4_8_drops_max_tokens_and_sampling_params() {
+        // Opus 4.8 shares Opus 4.7's API contract: legacy `budget_tokens` and
+        // non-default sampling params both return 400, so they must be dropped.
+        let fixture = fixture_context_with_sampling().reasoning(ReasoningConfig {
+            enabled: Some(true),
+            max_tokens: Some(8000),
+            effort: Some(Effort::XHigh),
+            exclude: Some(true),
+        });
+
+        let actual = ModelSpecificReasoning::new("claude-opus-4-8").transform(fixture);
+
+        let expected = Context::default().reasoning(ReasoningConfig {
+            enabled: Some(true),
+            max_tokens: None,
+            effort: Some(Effort::XHigh),
+            exclude: Some(true),
+        });
+
+        assert_eq!(actual, expected);
+    }
+
+    #[test]
+    fn test_opus_4_8_strips_sampling_even_without_reasoning() {
+        let fixture = fixture_context_with_sampling();
+
+        let actual = ModelSpecificReasoning::new("claude-opus-4-8").transform(fixture);
+
+        let expected = Context::default();
+
+        assert_eq!(actual, expected);
+    }
+
+    #[test]
+    fn test_opus_4_8_bedrock_prefix_still_matches() {
+        // Bedrock region prefixes (`us.anthropic.claude-...`) must still be
+        // classified as AdaptiveOnly so sampling params are stripped and
+        // `max_tokens` is dropped.
+        let fixture = fixture_context_with_sampling().reasoning(ReasoningConfig {
+            enabled: Some(true),
+            max_tokens: Some(8000),
+            effort: Some(Effort::XHigh),
+            exclude: None,
+        });
+
+        let actual = ModelSpecificReasoning::new("us.anthropic.claude-opus-4-8").transform(fixture);
+
+        let expected = Context::default().reasoning(ReasoningConfig {
+            enabled: Some(true),
+            max_tokens: None,
+            effort: Some(Effort::XHigh),
+            exclude: None,
+        });
+
+        assert_eq!(actual, expected);
+    }
+
     #[test]
     fn test_opus_4_7_strips_sampling_even_without_reasoning() {
         let fixture = fixture_context_with_sampling();

crates/forge_repo/src/provider/anthropic.rs

@@ -92,13 +92,16 @@ impl<H: HttpInfra> Anthropic<H> {
 }
 
 /// Returns false when the model auto-enables interleaved thinking through
-/// adaptive thinking (Opus 4.7, Opus 4.6, Sonnet 4.6). When the model is
-/// unknown (e.g., listing endpoints), the flag is included because it is
+/// adaptive thinking (Opus 4.8, Opus 4.7, Opus 4.6, Sonnet 4.6). When the model
+/// is unknown (e.g., listing endpoints), the flag is included because it is
 /// harmless on non-chat endpoints and necessary on older chat models.
 fn interleaved_thinking_required(model: Option<&ModelId>) -> bool {
     let Some(model) = model else { return true };
     let id = model.as_str().to_lowercase();
-    !(id.contains("opus-4-7") || id.contains("opus-4-6") || id.contains("sonnet-4-6"))
+    !(id.contains("opus-4-8")
+        || id.contains("opus-4-7")
+        || id.contains("opus-4-6")
+        || id.contains("sonnet-4-6"))
 }
 
 impl<T: HttpInfra> Anthropic<T> {
@@ -801,8 +804,8 @@ mod tests {
 
     #[test]
     fn test_get_headers_drops_interleaved_thinking_for_4_6_plus_models() {
-        // Adaptive thinking auto-enables interleaved thinking on Opus 4.7,
-        // Opus 4.6, and Sonnet 4.6; the beta header is redundant there.
+        // Adaptive thinking auto-enables interleaved thinking on Opus 4.8,
+        // Opus 4.7, Opus 4.6, and Sonnet 4.6; the beta header is redundant there.
         let chat_url = Url::parse("https://api.anthropic.com/v1/messages").unwrap();
         let model_url = Url::parse("https://api.anthropic.com/v1/models").unwrap();
 
@@ -832,9 +835,11 @@ mod tests {
         );
 
         for model_id in [
+            "claude-opus-4-8",
             "claude-opus-4-7",
             "claude-opus-4-6",
             "claude-sonnet-4-6",
+            "us.anthropic.claude-opus-4-8",
             "us.anthropic.claude-opus-4-7",
             "global.anthropic.claude-sonnet-4-6",
         ] {