feat: use thinkingLevel for Gemini 3 models per Google documentation

Per Google's official documentation, Gemini 3 models should use
thinkingLevel (string) instead of thinkingBudget (number) for
optimal performance.

From Google's Gemini Thinking docs:
> Use the thinkingLevel parameter with Gemini 3 models. While
> thinkingBudget is accepted for backwards compatibility, using
> it with Gemini 3 Pro may result in suboptimal performance.

Changes:
- Add model family detection functions (IsGemini3Model, IsGemini25Model,
  IsGemini3ProModel, IsGemini3FlashModel)
- Add ApplyGeminiThinkingLevel and ApplyGeminiCLIThinkingLevel functions
  for applying thinkingLevel config
- Add ValidateGemini3ThinkingLevel for model-specific level validation
- Add ThinkingBudgetToGemini3Level for backward compatibility conversion
- Update NormalizeGeminiThinkingBudget to convert budget to level for
  Gemini 3 models
- Update ApplyDefaultThinkingIfNeeded to not set a default level for
  Gemini 3 (lets API use its dynamic default "high")
- Update ConvertThinkingLevelToBudget to preserve thinkingLevel for
  Gemini 3 models
- Add Levels field to all Gemini 3 model definitions:
  - Gemini 3 Pro: ["low", "high"]
  - Gemini 3 Flash: ["minimal", "low", "medium", "high"]

Backward compatibility:
- Gemini 2.5 models continue to use thinkingBudget as before
- If thinkingBudget is provided for Gemini 3, it's converted to the
  appropriate thinkingLevel
- Existing configurations continue to work

internal/registry/model_definitions.go

@@ -160,7 +160,7 @@ func GetGeminiModels() []*ModelInfo {
 			InputTokenLimit:            1048576,
 			OutputTokenLimit:           65536,
 			SupportedGenerationMethods: []string{"generateContent", "countTokens", "createCachedContent", "batchGenerateContent"},
-			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true},
+			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"low", "high"}},
 		},
 		{
 			ID:                         "gemini-3-pro-image-preview",
@@ -175,7 +175,7 @@ func GetGeminiModels() []*ModelInfo {
 			InputTokenLimit:            1048576,
 			OutputTokenLimit:           65536,
 			SupportedGenerationMethods: []string{"generateContent", "countTokens", "createCachedContent", "batchGenerateContent"},
-			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true},
+			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"low", "high"}},
 		},
 	}
 }
@@ -240,7 +240,7 @@ func GetGeminiVertexModels() []*ModelInfo {
 			InputTokenLimit:            1048576,
 			OutputTokenLimit:           65536,
 			SupportedGenerationMethods: []string{"generateContent", "countTokens", "createCachedContent", "batchGenerateContent"},
-			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true},
+			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"low", "high"}},
 		},
 		{
 			ID:                         "gemini-3-flash-preview",
@@ -255,7 +255,7 @@ func GetGeminiVertexModels() []*ModelInfo {
 			InputTokenLimit:            1048576,
 			OutputTokenLimit:           65536,
 			SupportedGenerationMethods: []string{"generateContent", "countTokens", "createCachedContent", "batchGenerateContent"},
-			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true},
+			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"minimal", "low", "medium", "high"}},
 		},
 		{
 			ID:                         "gemini-3-pro-image-preview",
@@ -270,7 +270,7 @@ func GetGeminiVertexModels() []*ModelInfo {
 			InputTokenLimit:            1048576,
 			OutputTokenLimit:           65536,
 			SupportedGenerationMethods: []string{"generateContent", "countTokens", "createCachedContent", "batchGenerateContent"},
-			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true},
+			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"low", "high"}},
 		},
 	}
 }
@@ -336,7 +336,7 @@ func GetGeminiCLIModels() []*ModelInfo {
 			InputTokenLimit:            1048576,
 			OutputTokenLimit:           65536,
 			SupportedGenerationMethods: []string{"generateContent", "countTokens", "createCachedContent", "batchGenerateContent"},
-			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true},
+			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"low", "high"}},
 		},
 		{
 			ID:                         "gemini-3-flash-preview",
@@ -351,7 +351,7 @@ func GetGeminiCLIModels() []*ModelInfo {
 			InputTokenLimit:            1048576,
 			OutputTokenLimit:           65536,
 			SupportedGenerationMethods: []string{"generateContent", "countTokens", "createCachedContent", "batchGenerateContent"},
-			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true},
+			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"minimal", "low", "medium", "high"}},
 		},
 	}
 }
@@ -417,7 +417,7 @@ func GetAIStudioModels() []*ModelInfo {
 			InputTokenLimit:            1048576,
 			OutputTokenLimit:           65536,
 			SupportedGenerationMethods: []string{"generateContent", "countTokens", "createCachedContent", "batchGenerateContent"},
-			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true},
+			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"low", "high"}},
 		},
 		{
 			ID:                         "gemini-3-flash-preview",
@@ -432,7 +432,7 @@ func GetAIStudioModels() []*ModelInfo {
 			InputTokenLimit:            1048576,
 			OutputTokenLimit:           65536,
 			SupportedGenerationMethods: []string{"generateContent", "countTokens", "createCachedContent", "batchGenerateContent"},
-			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true},
+			Thinking:                   &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"minimal", "low", "medium", "high"}},
 		},
 		{
 			ID:                         "gemini-pro-latest",
@@ -743,8 +743,9 @@ func GetAntigravityModelConfig() map[string]*AntigravityModelConfig {
 		"gemini-2.5-flash":                        {Thinking: &ThinkingSupport{Min: 0, Max: 24576, ZeroAllowed: true, DynamicAllowed: true}, Name: "models/gemini-2.5-flash"},
 		"gemini-2.5-flash-lite":                   {Thinking: &ThinkingSupport{Min: 0, Max: 24576, ZeroAllowed: true, DynamicAllowed: true}, Name: "models/gemini-2.5-flash-lite"},
 		"gemini-2.5-computer-use-preview-10-2025": {Name: "models/gemini-2.5-computer-use-preview-10-2025"},
-		"gemini-3-pro-preview":                    {Thinking: &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true}, Name: "models/gemini-3-pro-preview"},
+		"gemini-3-pro-preview":                    {Thinking: &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"low", "high"}}, Name: "models/gemini-3-pro-preview"},
-		"gemini-3-pro-image-preview":              {Thinking: &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true}, Name: "models/gemini-3-pro-image-preview"},
+		"gemini-3-pro-image-preview":              {Thinking: &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"low", "high"}}, Name: "models/gemini-3-pro-image-preview"},
+		"gemini-3-flash-preview":                  {Thinking: &ThinkingSupport{Min: 128, Max: 32768, ZeroAllowed: false, DynamicAllowed: true, Levels: []string{"minimal", "low", "medium", "high"}}, Name: "models/gemini-3-flash-preview"},
 		"gemini-claude-sonnet-4-5-thinking":       {Thinking: &ThinkingSupport{Min: 1024, Max: 200000, ZeroAllowed: false, DynamicAllowed: true}, MaxCompletionTokens: 64000},
 		"gemini-claude-opus-4-5-thinking":         {Thinking: &ThinkingSupport{Min: 1024, Max: 200000, ZeroAllowed: false, DynamicAllowed: true}, MaxCompletionTokens: 64000},
 	}

internal/runtime/executor/aistudio_executor.go

@@ -324,7 +324,7 @@ func (e *AIStudioExecutor) translateRequest(req cliproxyexecutor.Request, opts c
 	payload := sdktranslator.TranslateRequest(from, to, req.Model, bytes.Clone(req.Payload), stream)
 	payload = ApplyThinkingMetadata(payload, req.Metadata, req.Model)
 	payload = util.ApplyDefaultThinkingIfNeeded(req.Model, payload)
-	payload = util.ConvertThinkingLevelToBudget(payload)
+	payload = util.ConvertThinkingLevelToBudget(payload, req.Model)
 	payload = util.NormalizeGeminiThinkingBudget(req.Model, payload)
 	payload = util.StripThinkingConfigIfUnsupported(req.Model, payload)
 	payload = fixGeminiImageAspectRatio(req.Model, payload)

internal/util/gemini_thinking.go

@@ -1,6 +1,7 @@
 package util
 
 import (
+	"regexp"
 	"strings"
 
 	"github.com/tidwall/gjson"
@@ -13,6 +14,44 @@ const (
 	GeminiOriginalModelMetadataKey   = "gemini_original_model"
 )
 
+// Gemini model family detection patterns
+var (
+	gemini3Pattern      = regexp.MustCompile(`(?i)^gemini[_-]?3[_-]`)
+	gemini3ProPattern   = regexp.MustCompile(`(?i)^gemini[_-]?3[_-]pro`)
+	gemini3FlashPattern = regexp.MustCompile(`(?i)^gemini[_-]?3[_-]flash`)
+	gemini25Pattern     = regexp.MustCompile(`(?i)^gemini[_-]?2\.?5[_-]`)
+)
+
+// IsGemini3Model returns true if the model is a Gemini 3 family model.
+// Gemini 3 models should use thinkingLevel (string) instead of thinkingBudget (number).
+func IsGemini3Model(model string) bool {
+	return gemini3Pattern.MatchString(model)
+}
+
+// IsGemini3ProModel returns true if the model is a Gemini 3 Pro variant.
+// Gemini 3 Pro supports thinkingLevel: "low", "high" (default: "high")
+func IsGemini3ProModel(model string) bool {
+	return gemini3ProPattern.MatchString(model)
+}
+
+// IsGemini3FlashModel returns true if the model is a Gemini 3 Flash variant.
+// Gemini 3 Flash supports thinkingLevel: "minimal", "low", "medium", "high" (default: "high")
+func IsGemini3FlashModel(model string) bool {
+	return gemini3FlashPattern.MatchString(model)
+}
+
+// IsGemini25Model returns true if the model is a Gemini 2.5 family model.
+// Gemini 2.5 models should use thinkingBudget (number).
+func IsGemini25Model(model string) bool {
+	return gemini25Pattern.MatchString(model)
+}
+
+// Gemini3ProThinkingLevels are the valid thinkingLevel values for Gemini 3 Pro models.
+var Gemini3ProThinkingLevels = []string{"low", "high"}
+
+// Gemini3FlashThinkingLevels are the valid thinkingLevel values for Gemini 3 Flash models.
+var Gemini3FlashThinkingLevels = []string{"minimal", "low", "medium", "high"}
+
 func ApplyGeminiThinkingConfig(body []byte, budget *int, includeThoughts *bool) []byte {
 	if budget == nil && includeThoughts == nil {
 		return body
@@ -69,10 +108,141 @@ func ApplyGeminiCLIThinkingConfig(body []byte, budget *int, includeThoughts *boo
 	return updated
 }
 
+// ApplyGeminiThinkingLevel applies thinkingLevel config for Gemini 3 models.
+// For standard Gemini API format (generationConfig.thinkingConfig path).
+// Per Google's documentation, Gemini 3 models should use thinkingLevel instead of thinkingBudget.
+func ApplyGeminiThinkingLevel(body []byte, level string, includeThoughts *bool) []byte {
+	if level == "" && includeThoughts == nil {
+		return body
+	}
+	updated := body
+	if level != "" {
+		valuePath := "generationConfig.thinkingConfig.thinkingLevel"
+		rewritten, err := sjson.SetBytes(updated, valuePath, level)
+		if err == nil {
+			updated = rewritten
+		}
+	}
+	// Default to including thoughts when a level is set but no explicit include flag is provided.
+	incl := includeThoughts
+	if incl == nil && level != "" {
+		defaultInclude := true
+		incl = &defaultInclude
+	}
+	if incl != nil {
+		valuePath := "generationConfig.thinkingConfig.includeThoughts"
+		rewritten, err := sjson.SetBytes(updated, valuePath, *incl)
+		if err == nil {
+			updated = rewritten
+		}
+	}
+	return updated
+}
+
+// ApplyGeminiCLIThinkingLevel applies thinkingLevel config for Gemini 3 models.
+// For Gemini CLI API format (request.generationConfig.thinkingConfig path).
+// Per Google's documentation, Gemini 3 models should use thinkingLevel instead of thinkingBudget.
+func ApplyGeminiCLIThinkingLevel(body []byte, level string, includeThoughts *bool) []byte {
+	if level == "" && includeThoughts == nil {
+		return body
+	}
+	updated := body
+	if level != "" {
+		valuePath := "request.generationConfig.thinkingConfig.thinkingLevel"
+		rewritten, err := sjson.SetBytes(updated, valuePath, level)
+		if err == nil {
+			updated = rewritten
+		}
+	}
+	// Default to including thoughts when a level is set but no explicit include flag is provided.
+	incl := includeThoughts
+	if incl == nil && level != "" {
+		defaultInclude := true
+		incl = &defaultInclude
+	}
+	if incl != nil {
+		valuePath := "request.generationConfig.thinkingConfig.includeThoughts"
+		rewritten, err := sjson.SetBytes(updated, valuePath, *incl)
+		if err == nil {
+			updated = rewritten
+		}
+	}
+	return updated
+}
+
+// ValidateGemini3ThinkingLevel validates that the thinkingLevel is valid for the Gemini 3 model variant.
+// Returns the validated level (normalized to lowercase) and true if valid, or empty string and false if invalid.
+func ValidateGemini3ThinkingLevel(model, level string) (string, bool) {
+	if level == "" {
+		return "", false
+	}
+	normalized := strings.ToLower(strings.TrimSpace(level))
+
+	var validLevels []string
+	if IsGemini3ProModel(model) {
+		validLevels = Gemini3ProThinkingLevels
+	} else if IsGemini3FlashModel(model) {
+		validLevels = Gemini3FlashThinkingLevels
+	} else if IsGemini3Model(model) {
+		// Unknown Gemini 3 variant - allow all levels as fallback
+		validLevels = Gemini3FlashThinkingLevels
+	} else {
+		return "", false
+	}
+
+	for _, valid := range validLevels {
+		if normalized == valid {
+			return normalized, true
+		}
+	}
+	return "", false
+}
+
+// ThinkingBudgetToGemini3Level converts a thinkingBudget to a thinkingLevel for Gemini 3 models.
+// This provides backward compatibility when thinkingBudget is provided for Gemini 3 models.
+// Returns the appropriate thinkingLevel and true if conversion is possible.
+func ThinkingBudgetToGemini3Level(model string, budget int) (string, bool) {
+	if !IsGemini3Model(model) {
+		return "", false
+	}
+
+	// Map budget to level based on Google's documentation
+	// Gemini 3 Pro: "low", "high" (default: "high")
+	// Gemini 3 Flash: "minimal", "low", "medium", "high" (default: "high")
+	switch {
+	case budget == -1:
+		// Dynamic budget maps to "high" (API default)
+		return "high", true
+	case budget == 0:
+		// Zero budget - Gemini 3 doesn't support disabling thinking
+		// Map to lowest available level
+		if IsGemini3FlashModel(model) {
+			return "minimal", true
+		}
+		return "low", true
+	case budget > 0 && budget <= 512:
+		if IsGemini3FlashModel(model) {
+			return "minimal", true
+		}
+		return "low", true
+	case budget <= 1024:
+		return "low", true
+	case budget <= 8192:
+		if IsGemini3FlashModel(model) {
+			return "medium", true
+		}
+		return "low", true // Pro doesn't have medium, use low
+	default:
+		return "high", true
+	}
+}
+
 // modelsWithDefaultThinking lists models that should have thinking enabled by default
 // when no explicit thinkingConfig is provided.
 var modelsWithDefaultThinking = map[string]bool{
 	"gemini-3-pro-preview":       true,
+	"gemini-3-pro-image-preview": true,
+	"gemini-3-flash-preview":     true,
 }
 
 // ModelHasDefaultThinking returns true if the model should have thinking enabled by default.
@@ -83,6 +253,7 @@ func ModelHasDefaultThinking(model string) bool {
 // ApplyDefaultThinkingIfNeeded injects default thinkingConfig for models that require it.
 // For standard Gemini API format (generationConfig.thinkingConfig path).
 // Returns the modified body if thinkingConfig was added, otherwise returns the original.
+// For Gemini 3 models, uses thinkingLevel instead of thinkingBudget per Google's documentation.
 func ApplyDefaultThinkingIfNeeded(model string, body []byte) []byte {
 	if !ModelHasDefaultThinking(model) {
 		return body
@@ -90,6 +261,14 @@ func ApplyDefaultThinkingIfNeeded(model string, body []byte) []byte {
 	if gjson.GetBytes(body, "generationConfig.thinkingConfig").Exists() {
 		return body
 	}
+	// Gemini 3 models use thinkingLevel instead of thinkingBudget
+	if IsGemini3Model(model) {
+		// Don't set a default - let the API use its dynamic default ("high")
+		// Only set includeThoughts
+		updated, _ := sjson.SetBytes(body, "generationConfig.thinkingConfig.includeThoughts", true)
+		return updated
+	}
+	// Gemini 2.5 and other models use thinkingBudget
 	updated, _ := sjson.SetBytes(body, "generationConfig.thinkingConfig.thinkingBudget", -1)
 	updated, _ = sjson.SetBytes(updated, "generationConfig.thinkingConfig.include_thoughts", true)
 	return updated
@@ -98,6 +277,7 @@ func ApplyDefaultThinkingIfNeeded(model string, body []byte) []byte {
 // ApplyDefaultThinkingIfNeededCLI injects default thinkingConfig for models that require it.
 // For Gemini CLI API format (request.generationConfig.thinkingConfig path).
 // Returns the modified body if thinkingConfig was added, otherwise returns the original.
+// For Gemini 3 models, uses thinkingLevel instead of thinkingBudget per Google's documentation.
 func ApplyDefaultThinkingIfNeededCLI(model string, body []byte) []byte {
 	if !ModelHasDefaultThinking(model) {
 		return body
@@ -105,6 +285,14 @@ func ApplyDefaultThinkingIfNeededCLI(model string, body []byte) []byte {
 	if gjson.GetBytes(body, "request.generationConfig.thinkingConfig").Exists() {
 		return body
 	}
+	// Gemini 3 models use thinkingLevel instead of thinkingBudget
+	if IsGemini3Model(model) {
+		// Don't set a default - let the API use its dynamic default ("high")
+		// Only set includeThoughts
+		updated, _ := sjson.SetBytes(body, "request.generationConfig.thinkingConfig.includeThoughts", true)
+		return updated
+	}
+	// Gemini 2.5 and other models use thinkingBudget
 	updated, _ := sjson.SetBytes(body, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
 	updated, _ = sjson.SetBytes(updated, "request.generationConfig.thinkingConfig.include_thoughts", true)
 	return updated
@@ -128,12 +316,29 @@ func StripThinkingConfigIfUnsupported(model string, body []byte) []byte {
 
 // NormalizeGeminiThinkingBudget normalizes the thinkingBudget value in a standard Gemini
 // request body (generationConfig.thinkingConfig.thinkingBudget path).
+// For Gemini 3 models, converts thinkingBudget to thinkingLevel per Google's documentation.
 func NormalizeGeminiThinkingBudget(model string, body []byte) []byte {
 	const budgetPath = "generationConfig.thinkingConfig.thinkingBudget"
+	const levelPath = "generationConfig.thinkingConfig.thinkingLevel"
+
 	budget := gjson.GetBytes(body, budgetPath)
 	if !budget.Exists() {
 		return body
 	}
+
+	// For Gemini 3 models, convert thinkingBudget to thinkingLevel
+	if IsGemini3Model(model) {
+		if level, ok := ThinkingBudgetToGemini3Level(model, int(budget.Int())); ok {
+			updated, _ := sjson.SetBytes(body, levelPath, level)
+			updated, _ = sjson.DeleteBytes(updated, budgetPath)
+			return updated
+		}
+		// If conversion fails, just remove the budget (let API use default)
+		updated, _ := sjson.DeleteBytes(body, budgetPath)
+		return updated
+	}
+
+	// For Gemini 2.5 and other models, normalize the budget value
 	normalized := NormalizeThinkingBudget(model, int(budget.Int()))
 	updated, _ := sjson.SetBytes(body, budgetPath, normalized)
 	return updated
@@ -141,12 +346,29 @@ func NormalizeGeminiThinkingBudget(model string, body []byte) []byte {
 
 // NormalizeGeminiCLIThinkingBudget normalizes the thinkingBudget value in a Gemini CLI
 // request body (request.generationConfig.thinkingConfig.thinkingBudget path).
+// For Gemini 3 models, converts thinkingBudget to thinkingLevel per Google's documentation.
 func NormalizeGeminiCLIThinkingBudget(model string, body []byte) []byte {
 	const budgetPath = "request.generationConfig.thinkingConfig.thinkingBudget"
+	const levelPath = "request.generationConfig.thinkingConfig.thinkingLevel"
+
 	budget := gjson.GetBytes(body, budgetPath)
 	if !budget.Exists() {
 		return body
 	}
+
+	// For Gemini 3 models, convert thinkingBudget to thinkingLevel
+	if IsGemini3Model(model) {
+		if level, ok := ThinkingBudgetToGemini3Level(model, int(budget.Int())); ok {
+			updated, _ := sjson.SetBytes(body, levelPath, level)
+			updated, _ = sjson.DeleteBytes(updated, budgetPath)
+			return updated
+		}
+		// If conversion fails, just remove the budget (let API use default)
+		updated, _ := sjson.DeleteBytes(body, budgetPath)
+		return updated
+	}
+
+	// For Gemini 2.5 and other models, normalize the budget value
 	normalized := NormalizeThinkingBudget(model, int(budget.Int()))
 	updated, _ := sjson.SetBytes(body, budgetPath, normalized)
 	return updated
@@ -218,34 +440,42 @@ func ApplyReasoningEffortToGeminiCLI(body []byte, effort string) []byte {
 }
 
 // ConvertThinkingLevelToBudget checks for "generationConfig.thinkingConfig.thinkingLevel"
-// and converts it to "thinkingBudget".
+// and converts it to "thinkingBudget" for Gemini 2.5 models.
-// "high" -> 32768
+// For Gemini 3 models, preserves thinkingLevel as-is (does not convert).
-// "low" -> 128
+// Mappings for Gemini 2.5:
-// It removes "thinkingLevel" after conversion.
+//   - "high" -> 32768
-func ConvertThinkingLevelToBudget(body []byte) []byte {
+//   - "medium" -> 8192
+//   - "low" -> 1024
+//   - "minimal" -> 512
+//
+// It removes "thinkingLevel" after conversion (for Gemini 2.5 only).
+func ConvertThinkingLevelToBudget(body []byte, model string) []byte {
 	levelPath := "generationConfig.thinkingConfig.thinkingLevel"
 	res := gjson.GetBytes(body, levelPath)
 	if !res.Exists() {
 		return body
 	}
 
+	// For Gemini 3 models, preserve thinkingLevel - don't convert to budget
+	if IsGemini3Model(model) {
+		return body
+	}
+
 	level := strings.ToLower(res.String())
 	var budget int
 	switch level {
 	case "high":
 		budget = 32768
+	case "medium":
+		budget = 8192
 	case "low":
-		budget = 128
+		budget = 1024
+	case "minimal":
+		budget = 512
 	default:
-		// If unknown level, we might just leave it or default.
+		// Unknown level - remove it and let the API use defaults
-		// User only specified high and low. We'll assume we shouldn't touch it if it's something else,
+		updated, _ := sjson.DeleteBytes(body, levelPath)
-		// or maybe we should just remove the invalid level?
+		return updated
-		// For safety adhering to strict instructions: "If high... if low...".
-		// If it's something else, the upstream might fail anyway if we leave it,
-		// but let's just delete the level if we processed it.
-		// Actually, let's check if we need to do anything for other values.
-		// For now, only handle high/low.
-		return body
 	}
 
 	// Set budget
@@ -262,3 +492,50 @@ func ConvertThinkingLevelToBudget(body []byte) []byte {
 	}
 	return updated
 }
+
+// ConvertThinkingLevelToBudgetCLI checks for "request.generationConfig.thinkingConfig.thinkingLevel"
+// and converts it to "thinkingBudget" for Gemini 2.5 models.
+// For Gemini 3 models, preserves thinkingLevel as-is (does not convert).
+func ConvertThinkingLevelToBudgetCLI(body []byte, model string) []byte {
+	levelPath := "request.generationConfig.thinkingConfig.thinkingLevel"
+	res := gjson.GetBytes(body, levelPath)
+	if !res.Exists() {
+		return body
+	}
+
+	// For Gemini 3 models, preserve thinkingLevel - don't convert to budget
+	if IsGemini3Model(model) {
+		return body
+	}
+
+	level := strings.ToLower(res.String())
+	var budget int
+	switch level {
+	case "high":
+		budget = 32768
+	case "medium":
+		budget = 8192
+	case "low":
+		budget = 1024
+	case "minimal":
+		budget = 512
+	default:
+		// Unknown level - remove it and let the API use defaults
+		updated, _ := sjson.DeleteBytes(body, levelPath)
+		return updated
+	}
+
+	// Set budget
+	budgetPath := "request.generationConfig.thinkingConfig.thinkingBudget"
+	updated, err := sjson.SetBytes(body, budgetPath, budget)
+	if err != nil {
+		return body
+	}
+
+	// Remove level
+	updated, err = sjson.DeleteBytes(updated, levelPath)
+	if err != nil {
+		return body
+	}
+	return updated
+}