diff --git a/internal/reasoning/eino.go b/internal/reasoning/eino.go
index 7dbc1306..b27c9f8a 100644
--- a/internal/reasoning/eino.go
+++ b/internal/reasoning/eino.go
@@ -84,8 +84,9 @@ func ApplyToEinoChatModelConfig(cfg *einoopenai.ChatModelConfig, oa *config.Open
 	}
 }
 
-// applyClaudeExtendedThinking sets Anthropic Messages API `thinking` when absent from ExtraRequestFields.
-// Uses adaptive + summarized display by default (per Anthropic guidance for Claude 4.x); Sonnet 3.7 uses enabled+budget.
+// applyClaudeExtendedThinking sets Anthropic Messages API fields per official guidance:
+//   - Adaptive models (4.6+): thinking.type=adaptive; output_config.effort only when user sets effort (API default is high).
+//   - Sonnet 3.7: thinking.type=enabled + budget_tokens=10000 (doc example); effort is not mapped — use extra_request_fields for custom budget.
 func applyClaudeExtendedThinking(cfg *einoopenai.ChatModelConfig, mode, effort, model string) {
 	if cfg == nil || mode == "off" {
 		return
@@ -93,31 +94,60 @@ func applyClaudeExtendedThinking(cfg *einoopenai.ChatModelConfig, mode, effort,
 	if cfg.ExtraFields == nil {
 		cfg.ExtraFields = make(map[string]any)
 	}
-	if _, exists := cfg.ExtraFields["thinking"]; exists {
-		return
-	}
 	m := strings.ToLower(strings.TrimSpace(model))
-	thinking := map[string]any{
-		"type":    "adaptive",
-		"display": "summarized",
+	sonnet37 := isClaudeSonnet37(m)
+
+	if _, exists := cfg.ExtraFields["thinking"]; !exists {
+		cfg.ExtraFields["thinking"] = claudeThinkingForModel(m, sonnet37)
 	}
-	// Sonnet 3.7: manual extended thinking is the documented path.
-	if strings.Contains(m, "claude-3-7-sonnet") || strings.Contains(m, "3-7-sonnet") || strings.Contains(m, "sonnet-3.7") {
-		thinking = map[string]any{
+
+	applyClaudeOutputConfigEffort(cfg, effort, sonnet37)
+}
+
+// claudeSonnet37DefaultBudgetTokens matches Anthropic extended-thinking documentation examples (budget_tokens with max_tokens 16000).
+const claudeSonnet37DefaultBudgetTokens = 10000
+
+func isClaudeSonnet37(m string) bool {
+	return strings.Contains(m, "claude-3-7-sonnet") ||
+		strings.Contains(m, "3-7-sonnet") ||
+		strings.Contains(m, "sonnet-3.7")
+}
+
+func claudeThinkingForModel(m string, sonnet37 bool) map[string]any {
+	if sonnet37 {
+		return map[string]any{
 			"type":          "enabled",
-			"budget_tokens": 10000,
+			"budget_tokens": claudeSonnet37DefaultBudgetTokens,
 			"display":       "summarized",
 		}
 	}
-	// Opus 4.7+: manual enabled+budget rejected — keep adaptive only.
+	// Opus 4.7+: manual enabled+budget rejected — adaptive only.
 	if strings.Contains(m, "opus-4-7") || strings.Contains(m, "opus-4.7") {
-		thinking = map[string]any{
+		return map[string]any{
 			"type":    "adaptive",
 			"display": "summarized",
 		}
 	}
-	_ = effort // reserved: map to Anthropic effort / output_config when API stabilizes in one place
-	cfg.ExtraFields["thinking"] = thinking
+	return map[string]any{
+		"type":    "adaptive",
+		"display": "summarized",
+	}
+}
+
+// applyClaudeOutputConfigEffort sets top-level output_config.effort only when effort is explicitly configured.
+// Omitted effort uses the API default (high); do not inject effort on mode:on alone.
+func applyClaudeOutputConfigEffort(cfg *einoopenai.ChatModelConfig, effort string, sonnet37 bool) {
+	if cfg == nil || sonnet37 {
+		return
+	}
+	if _, exists := cfg.ExtraFields["output_config"]; exists {
+		return
+	}
+	e := effortStringForAPI(effort)
+	if e == "" {
+		return
+	}
+	cfg.ExtraFields["output_config"] = map[string]any{"effort": e}
 }
 
 func effectiveMode(sr *config.OpenAIReasoningConfig, client *ClientIntent, allowClient bool) string {
diff --git a/internal/reasoning/eino_test.go b/internal/reasoning/eino_test.go
index 5f23646f..1a9666e3 100644
--- a/internal/reasoning/eino_test.go
+++ b/internal/reasoning/eino_test.go
@@ -80,3 +80,80 @@ func TestApplyOpenAICompat_maxPassthrough(t *testing.T) {
 		t.Fatalf("max effort wire=%q, want max", got)
 	}
 }
+
+func TestApplyClaude_adaptiveOutputConfigEffort(t *testing.T) {
+	cfg := &einoopenai.ChatModelConfig{}
+	oa := &config.OpenAIConfig{
+		Provider: "claude",
+		Model:    "claude-opus-4-8",
+		Reasoning: config.OpenAIReasoningConfig{
+			Mode:   "on",
+			Effort: "xhigh",
+		},
+	}
+	ApplyToEinoChatModelConfig(cfg, oa, nil)
+	th, ok := cfg.ExtraFields["thinking"].(map[string]any)
+	if !ok || th["type"] != "adaptive" {
+		t.Fatalf("thinking=%#v", cfg.ExtraFields["thinking"])
+	}
+	oc, ok := cfg.ExtraFields["output_config"].(map[string]any)
+	if !ok {
+		t.Fatal("expected output_config")
+	}
+	if oc["effort"] != "xhigh" {
+		t.Fatalf("effort=%v", oc["effort"])
+	}
+}
+
+func TestApplyClaude_sonnet37OfficialBudget(t *testing.T) {
+	cfg := &einoopenai.ChatModelConfig{}
+	oa := &config.OpenAIConfig{
+		Provider: "claude",
+		Model:    "claude-3-7-sonnet-latest",
+		Reasoning: config.OpenAIReasoningConfig{
+			Mode:   "on",
+			Effort: "low", // 3.7 has no output_config.effort; effort is not mapped to budget_tokens
+		},
+	}
+	ApplyToEinoChatModelConfig(cfg, oa, nil)
+	th, ok := cfg.ExtraFields["thinking"].(map[string]any)
+	if !ok || th["type"] != "enabled" {
+		t.Fatalf("thinking=%#v", cfg.ExtraFields["thinking"])
+	}
+	if th["budget_tokens"] != claudeSonnet37DefaultBudgetTokens {
+		t.Fatalf("budget_tokens=%v, want official example %d", th["budget_tokens"], claudeSonnet37DefaultBudgetTokens)
+	}
+	if _, hasOC := cfg.ExtraFields["output_config"]; hasOC {
+		t.Fatal("sonnet 3.7 should not set output_config")
+	}
+}
+
+func TestApplyClaude_onWithoutEffortOmitsOutputConfig(t *testing.T) {
+	cfg := &einoopenai.ChatModelConfig{}
+	oa := &config.OpenAIConfig{
+		Provider: "claude",
+		Model:    "claude-sonnet-4-6",
+		Reasoning: config.OpenAIReasoningConfig{
+			Mode: "on",
+		},
+	}
+	ApplyToEinoChatModelConfig(cfg, oa, nil)
+	if _, hasOC := cfg.ExtraFields["output_config"]; hasOC {
+		t.Fatal("on without explicit effort should omit output_config (API default high)")
+	}
+}
+
+func TestApplyClaude_autoWithoutEffortSkipsOutputConfig(t *testing.T) {
+	cfg := &einoopenai.ChatModelConfig{}
+	oa := &config.OpenAIConfig{
+		Provider: "claude",
+		Model:    "claude-sonnet-4-6",
+		Reasoning: config.OpenAIReasoningConfig{
+			Mode: "auto",
+		},
+	}
+	ApplyToEinoChatModelConfig(cfg, oa, nil)
+	if _, hasOC := cfg.ExtraFields["output_config"]; hasOC {
+		t.Fatal("auto without effort should omit output_config")
+	}
+}