diff --git a/internal/registry/model_definitions.go b/internal/registry/model_definitions.go
index f0fb60cb..b8ca8757 100644
--- a/internal/registry/model_definitions.go
+++ b/internal/registry/model_definitions.go
@@ -788,6 +788,7 @@ func LookupStaticModelInfo(modelID string) *ModelInfo {
 	if modelID == "" {
 		return nil
 	}
+
 	allModels := [][]*ModelInfo{
 		GetClaudeModels(),
 		GetGeminiModels(),
@@ -805,5 +806,16 @@ func LookupStaticModelInfo(modelID string) *ModelInfo {
 			}
 		}
 	}
+
+	// Check Antigravity static config
+	if cfg := GetAntigravityModelConfig()[modelID]; cfg != nil && cfg.Thinking != nil {
+		return &ModelInfo{
+			ID:                  modelID,
+			Name:                cfg.Name,
+			Thinking:            cfg.Thinking,
+			MaxCompletionTokens: cfg.MaxCompletionTokens,
+		}
+	}
+
 	return nil
 }
diff --git a/internal/thinking/apply.go b/internal/thinking/apply.go
index 8ee60b8d..44566cab 100644
--- a/internal/thinking/apply.go
+++ b/internal/thinking/apply.go
@@ -40,7 +40,7 @@ func RegisterProvider(name string, applier ProviderApplier) {
 // letting the upstream service validate the configuration.
 func IsUserDefinedModel(modelInfo *registry.ModelInfo) bool {
 	if modelInfo == nil {
-		return false
+		return true
 	}
 	return modelInfo.UserDefined
 }
@@ -87,28 +87,28 @@ func ApplyThinking(body []byte, model string, provider string) ([]byte, error) {
 	}
 
 	// 2. Parse suffix and get modelInfo
+	// First try dynamic registry, then fall back to static lookup
 	suffixResult := ParseSuffix(model)
 	baseModel := suffixResult.ModelName
 	modelInfo := registry.GetGlobalRegistry().GetModelInfo(baseModel)
+	if modelInfo == nil {
+		modelInfo = registry.LookupStaticModelInfo(baseModel)
+	}
 
 	// 3. Model capability check
-	if modelInfo == nil {
-		log.WithField("model", model).Debug("thinking: nil modelInfo, passthrough")
-		return body, nil
+	if IsUserDefinedModel(modelInfo) {
+		return applyUserDefinedModel(body, modelInfo, provider, suffixResult)
 	}
 	if modelInfo.Thinking == nil {
-		if IsUserDefinedModel(modelInfo) {
-			return applyUserDefinedModel(body, modelInfo, provider, suffixResult)
-		}
 		config := extractThinkingConfig(body, provider)
 		if hasThinkingConfig(config) {
 			log.WithFields(log.Fields{
-				"model":    modelInfo.ID,
+				"model":    baseModel,
 				"provider": provider,
 			}).Debug("thinking: model does not support thinking, stripping config")
 			return StripThinkingConfig(body, provider), nil
 		}
-		log.WithField("model", modelInfo.ID).Debug("thinking: model does not support thinking, passthrough")
+		log.WithField("model", baseModel).Debug("thinking: model does not support thinking, passthrough")
 		return body, nil
 	}
 
@@ -212,6 +212,14 @@ func parseSuffixToConfig(rawSuffix string) ThinkingConfig {
 // applyUserDefinedModel applies thinking configuration for user-defined models
 // without ThinkingSupport validation.
 func applyUserDefinedModel(body []byte, modelInfo *registry.ModelInfo, provider string, suffixResult SuffixResult) ([]byte, error) {
+	// Get model ID for logging
+	modelID := ""
+	if modelInfo != nil {
+		modelID = modelInfo.ID
+	} else {
+		modelID = suffixResult.ModelName
+	}
+
 	// Get config: suffix priority over body
 	var config ThinkingConfig
 	if suffixResult.HasSuffix {
@@ -222,7 +230,7 @@ func applyUserDefinedModel(body []byte, modelInfo *registry.ModelInfo, provider
 
 	if !hasThinkingConfig(config) {
 		log.WithFields(log.Fields{
-			"model":        modelInfo.ID,
+			"model":        modelID,
 			"provider":     provider,
 			"user_defined": true,
 			"passthrough":  true,
@@ -233,7 +241,7 @@ func applyUserDefinedModel(body []byte, modelInfo *registry.ModelInfo, provider
 	applier := GetProviderApplier(provider)
 	if applier == nil {
 		log.WithFields(log.Fields{
-			"model":        modelInfo.ID,
+			"model":        modelID,
 			"provider":     provider,
 			"user_defined": true,
 			"passthrough":  true,
@@ -242,7 +250,7 @@ func applyUserDefinedModel(body []byte, modelInfo *registry.ModelInfo, provider
 	}
 
 	log.WithFields(log.Fields{
-		"model":        modelInfo.ID,
+		"model":        modelID,
 		"provider":     provider,
 		"user_defined": true,
 		"passthrough":  false,
diff --git a/internal/thinking/apply_test.go b/internal/thinking/apply_test.go
index d89fff32..b49079db 100644
--- a/internal/thinking/apply_test.go
+++ b/internal/thinking/apply_test.go
@@ -150,7 +150,7 @@ func TestIsUserDefinedModel(t *testing.T) {
 		modelInfo *registry.ModelInfo
 		want      bool
 	}{
-		{"nil modelInfo", nil, false},
+		{"nil modelInfo", nil, true},
 		{"not user-defined no flag", &registry.ModelInfo{ID: "test"}, false},
 		{"not user-defined with type", &registry.ModelInfo{ID: "test", Type: "openai"}, false},
 		{"user-defined with flag", &registry.ModelInfo{ID: "test", Type: "openai", UserDefined: true}, true},
diff --git a/internal/thinking/provider/claude/apply.go b/internal/thinking/provider/claude/apply.go
index e1409389..979ecd75 100644
--- a/internal/thinking/provider/claude/apply.go
+++ b/internal/thinking/provider/claude/apply.go
@@ -54,7 +54,7 @@ func init() {
 //	}
 func (a *Applier) Apply(body []byte, config thinking.ThinkingConfig, modelInfo *registry.ModelInfo) ([]byte, error) {
 	if modelInfo == nil {
-		return body, nil
+		return applyCompatibleClaude(body, config)
 	}
 	if modelInfo.Thinking == nil {
 		if modelInfo.Type == "" {
diff --git a/internal/thinking/provider/codex/apply.go b/internal/thinking/provider/codex/apply.go
index 386185a6..228bb6fe 100644
--- a/internal/thinking/provider/codex/apply.go
+++ b/internal/thinking/provider/codex/apply.go
@@ -45,7 +45,7 @@ func init() {
 //	}
 func (a *Applier) Apply(body []byte, config thinking.ThinkingConfig, modelInfo *registry.ModelInfo) ([]byte, error) {
 	if modelInfo == nil {
-		return body, nil
+		return applyCompatibleCodex(body, config)
 	}
 	if modelInfo.Thinking == nil {
 		if modelInfo.Type == "" {
diff --git a/internal/thinking/provider/gemini/apply.go b/internal/thinking/provider/gemini/apply.go
index eebc44d8..bb574c31 100644
--- a/internal/thinking/provider/gemini/apply.go
+++ b/internal/thinking/provider/gemini/apply.go
@@ -60,7 +60,7 @@ func init() {
 //	}
 func (a *Applier) Apply(body []byte, config thinking.ThinkingConfig, modelInfo *registry.ModelInfo) ([]byte, error) {
 	if modelInfo == nil {
-		return body, nil
+		return a.applyCompatible(body, config)
 	}
 	if modelInfo.Thinking == nil {
 		if modelInfo.Type == "" {
diff --git a/internal/thinking/provider/gemini/apply_test.go b/internal/thinking/provider/gemini/apply_test.go
index 5f762a2f..1af2fa83 100644
--- a/internal/thinking/provider/gemini/apply_test.go
+++ b/internal/thinking/provider/gemini/apply_test.go
@@ -450,8 +450,9 @@ func TestGeminiApplyNilModelInfo(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Apply() with nil modelInfo should not error, got: %v", err)
 	}
-	if string(result) != string(body) {
-		t.Fatalf("Apply() with nil modelInfo should return original body, got: %s", result)
+	// nil modelInfo now applies compatible config
+	if !gjson.GetBytes(result, "generationConfig.thinkingConfig.thinkingBudget").Exists() {
+		t.Fatalf("Apply() with nil modelInfo should apply thinking config, got: %s", result)
 	}
 }
 
diff --git a/internal/thinking/provider/geminicli/apply.go b/internal/thinking/provider/geminicli/apply.go
index a4607107..eb6d82a4 100644
--- a/internal/thinking/provider/geminicli/apply.go
+++ b/internal/thinking/provider/geminicli/apply.go
@@ -30,7 +30,7 @@ func init() {
 // Apply applies thinking configuration to Gemini CLI request body.
 func (a *Applier) Apply(body []byte, config thinking.ThinkingConfig, modelInfo *registry.ModelInfo) ([]byte, error) {
 	if modelInfo == nil {
-		return body, nil
+		return a.applyCompatible(body, config)
 	}
 	if modelInfo.Thinking == nil {
 		if modelInfo.Type == "" {
diff --git a/internal/thinking/provider/geminicli/apply_test.go b/internal/thinking/provider/geminicli/apply_test.go
index a606457c..6bf77dd2 100644
--- a/internal/thinking/provider/geminicli/apply_test.go
+++ b/internal/thinking/provider/geminicli/apply_test.go
@@ -241,8 +241,9 @@ func TestGeminiCLIApplyNilModelInfo(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Apply() with nil modelInfo should not error, got: %v", err)
 	}
-	if string(result) != string(body) {
-		t.Fatalf("Apply() with nil modelInfo should return original body, got: %s", result)
+	// nil modelInfo now applies compatible config
+	if !gjson.GetBytes(result, "request.generationConfig.thinkingConfig.thinkingBudget").Exists() {
+		t.Fatalf("Apply() with nil modelInfo should apply thinking config, got: %s", result)
 	}
 }
 
@@ -277,9 +278,9 @@ func TestGeminiCLIApplyModeBudgetWithLevels(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Apply() error = %v", err)
 	}
-	// ModeBudget with Levels model: Apply returns body unchanged (conversion is upper layer's job)
-	if string(result) != string(body) {
-		t.Fatalf("Apply() ModeBudget with Levels should return original body, got: %s", result)
+	// ModeBudget applies budget format directly without conversion to levels
+	if !gjson.GetBytes(result, "request.generationConfig.thinkingConfig.thinkingBudget").Exists() {
+		t.Fatalf("Apply() ModeBudget should apply budget format, got: %s", result)
 	}
 }
 
diff --git a/internal/thinking/provider/openai/apply.go b/internal/thinking/provider/openai/apply.go
index 810faf34..aea1c055 100644
--- a/internal/thinking/provider/openai/apply.go
+++ b/internal/thinking/provider/openai/apply.go
@@ -42,7 +42,7 @@ func init() {
 //	}
 func (a *Applier) Apply(body []byte, config thinking.ThinkingConfig, modelInfo *registry.ModelInfo) ([]byte, error) {
 	if modelInfo == nil {
-		return body, nil
+		return applyCompatibleOpenAI(body, config)
 	}
 	if modelInfo.Thinking == nil {
 		if modelInfo.Type == "" {
diff --git a/internal/thinking/provider/openai/apply_test.go b/internal/thinking/provider/openai/apply_test.go
index 88c1800a..5be01e4e 100644
--- a/internal/thinking/provider/openai/apply_test.go
+++ b/internal/thinking/provider/openai/apply_test.go
@@ -43,12 +43,14 @@ func TestApplierImplementsInterface(t *testing.T) {
 func TestApplyNilModelInfo(t *testing.T) {
 	applier := NewApplier()
 	body := []byte(`{"model":"gpt-5.2"}`)
-	got, err := applier.Apply(body, thinking.ThinkingConfig{}, nil)
+	config := thinking.ThinkingConfig{Mode: thinking.ModeLevel, Level: thinking.LevelHigh}
+	got, err := applier.Apply(body, config, nil)
 	if err != nil {
 		t.Fatalf("expected nil error, got %v", err)
 	}
-	if string(got) != string(body) {
-		t.Fatalf("expected body unchanged, got %s", string(got))
+	// nil modelInfo now applies compatible config
+	if !gjson.GetBytes(got, "reasoning_effort").Exists() {
+		t.Fatalf("expected reasoning_effort applied, got %s", string(got))
 	}
 }