diff --git a/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go b/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
index fd8e0071..927d8ea3 100644
--- a/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
+++ b/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
@@ -48,16 +48,30 @@ func ConvertOpenAIRequestToAntigravity(modelName string, inputRawJSON []byte, _
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 		case "low":
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 1024))
+			if util.IsGemini3Model(modelName) {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingLevel", "low")
+			} else {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 1024))
+			}
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 		case "medium":
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 8192))
+			if !util.IsGemini3Model(modelName) {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 8192))
+			}
+			// Gemini 3: no thinkingLevel for medium, uses dynamic thinking (auto)
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 		case "high":
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 32768))
+			if util.IsGemini3Model(modelName) {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingLevel", "high")
+			} else {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 32768))
+			}
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 		default:
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
+			if !util.IsGemini3Model(modelName) {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
+			}
+			// Gemini 3: no thinkingLevel for auto/default, uses dynamic thinking
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 		}
 	}
@@ -88,12 +102,10 @@ func ConvertOpenAIRequestToAntigravity(modelName string, inputRawJSON []byte, _
 		}
 	}
 
-	// For gemini-3-pro-preview, always send default thinkingConfig when none specified.
-	// This matches the official Gemini CLI behavior which always sends:
-	// { thinkingBudget: -1, includeThoughts: true }
-	// See: ai-gemini-cli/packages/core/src/config/defaultModelConfigs.ts
-	if !gjson.GetBytes(out, "request.generationConfig.thinkingConfig").Exists() && modelName == "gemini-3-pro-preview" {
-		out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
+	// For Gemini 3 models, enable thought summaries when no thinkingConfig is specified.
+	// Don't set thinkingLevel - let API use dynamic thinking by default.
+	// See: https://ai.google.dev/gemini-api/docs/thinking#thinking-levels
+	if !gjson.GetBytes(out, "request.generationConfig.thinkingConfig").Exists() && util.IsGemini3Model(modelName) {
 		out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 	}
 
diff --git a/internal/translator/gemini-cli/openai/chat-completions/gemini-cli_openai_request.go b/internal/translator/gemini-cli/openai/chat-completions/gemini-cli_openai_request.go
index d14f1119..9feff2d1 100644
--- a/internal/translator/gemini-cli/openai/chat-completions/gemini-cli_openai_request.go
+++ b/internal/translator/gemini-cli/openai/chat-completions/gemini-cli_openai_request.go
@@ -48,16 +48,30 @@ func ConvertOpenAIRequestToGeminiCLI(modelName string, inputRawJSON []byte, _ bo
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 		case "low":
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 1024))
+			if util.IsGemini3Model(modelName) {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingLevel", "low")
+			} else {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 1024))
+			}
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 		case "medium":
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 8192))
+			if !util.IsGemini3Model(modelName) {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 8192))
+			}
+			// Gemini 3: no thinkingLevel for medium, uses dynamic thinking (auto)
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 		case "high":
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 32768))
+			if util.IsGemini3Model(modelName) {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingLevel", "high")
+			} else {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 32768))
+			}
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 		default:
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
+			if !util.IsGemini3Model(modelName) {
+				out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
+			}
+			// Gemini 3: no thinkingLevel for auto/default, uses dynamic thinking
 			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 		}
 	}
@@ -88,12 +102,10 @@ func ConvertOpenAIRequestToGeminiCLI(modelName string, inputRawJSON []byte, _ bo
 		}
 	}
 
-	// For gemini-3-pro-preview, always send default thinkingConfig when none specified.
-	// This matches the official Gemini CLI behavior which always sends:
-	// { thinkingBudget: -1, includeThoughts: true }
-	// See: ai-gemini-cli/packages/core/src/config/defaultModelConfigs.ts
-	if !gjson.GetBytes(out, "request.generationConfig.thinkingConfig").Exists() && modelName == "gemini-3-pro-preview" {
-		out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
+	// For Gemini 3 models, enable thought summaries when no thinkingConfig is specified.
+	// Don't set thinkingLevel - let API use dynamic thinking by default.
+	// See: https://ai.google.dev/gemini-api/docs/thinking#thinking-levels
+	if !gjson.GetBytes(out, "request.generationConfig.thinkingConfig").Exists() && util.IsGemini3Model(modelName) {
 		out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.include_thoughts", true)
 	}
 
diff --git a/internal/translator/gemini/openai/responses/gemini_openai-responses_request.go b/internal/translator/gemini/openai/responses/gemini_openai-responses_request.go
index 22ce913e..ba2c3b32 100644
--- a/internal/translator/gemini/openai/responses/gemini_openai-responses_request.go
+++ b/internal/translator/gemini/openai/responses/gemini_openai-responses_request.go
@@ -398,19 +398,37 @@ func ConvertOpenAIResponsesRequestToGemini(modelName string, inputRawJSON []byte
 			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", -1)
 			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.include_thoughts", true)
 		case "minimal":
-			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 1024))
+			if util.IsGemini3Model(modelName) {
+				out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingLevel", "low")
+			} else {
+				out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 1024))
+			}
 			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.include_thoughts", true)
 		case "low":
-			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 4096))
+			if util.IsGemini3Model(modelName) {
+				out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingLevel", "low")
+			} else {
+				out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 4096))
+			}
 			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.include_thoughts", true)
 		case "medium":
-			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 8192))
+			if !util.IsGemini3Model(modelName) {
+				out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 8192))
+			}
+			// Gemini 3: no thinkingLevel for medium, uses dynamic thinking (auto)
 			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.include_thoughts", true)
 		case "high":
-			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 32768))
+			if util.IsGemini3Model(modelName) {
+				out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingLevel", "high")
+			} else {
+				out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", util.NormalizeThinkingBudget(modelName, 32768))
+			}
 			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.include_thoughts", true)
 		default:
-			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", -1)
+			if !util.IsGemini3Model(modelName) {
+				out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", -1)
+			}
+			// Gemini 3: no thinkingLevel for auto/default, uses dynamic thinking
 			out, _ = sjson.Set(out, "generationConfig.thinkingConfig.include_thoughts", true)
 		}
 	}
@@ -435,14 +453,11 @@ func ConvertOpenAIResponsesRequestToGemini(modelName string, inputRawJSON []byte
 		}
 	}
 
-	// For gemini-3-pro-preview, always send default thinkingConfig when none specified.
-	// This matches the official Gemini CLI behavior which always sends:
-	// { thinkingBudget: -1, includeThoughts: true }
-	// See: ai-gemini-cli/packages/core/src/config/defaultModelConfigs.ts
-	if !gjson.Get(out, "generationConfig.thinkingConfig").Exists() && modelName == "gemini-3-pro-preview" {
-		out, _ = sjson.Set(out, "generationConfig.thinkingConfig.thinkingBudget", -1)
+	// For Gemini 3 models, enable thought summaries when no thinkingConfig is specified.
+	// Don't set thinkingLevel - let API use dynamic thinking by default.
+	// See: https://ai.google.dev/gemini-api/docs/thinking#thinking-levels
+	if !gjson.Get(out, "generationConfig.thinkingConfig").Exists() && util.IsGemini3Model(modelName) {
 		out, _ = sjson.Set(out, "generationConfig.thinkingConfig.include_thoughts", true)
-		// log.Debugf("Applied default thinkingConfig for gemini-3-pro-preview (matches Gemini CLI): thinkingBudget=-1, include_thoughts=true")
 	}
 
 	result := []byte(out)
diff --git a/internal/util/gemini_thinking.go b/internal/util/gemini_thinking.go
index d7481621..e4e05962 100644
--- a/internal/util/gemini_thinking.go
+++ b/internal/util/gemini_thinking.go
@@ -259,3 +259,9 @@ func ConvertThinkingLevelToBudget(body []byte) []byte {
 	}
 	return updated
 }
+
+// IsGemini3Model returns true if the model is a Gemini 3 model (uses thinkingLevel instead of thinkingBudget).
+func IsGemini3Model(model string) bool {
+	lower := strings.ToLower(model)
+	return strings.HasPrefix(lower, "gemini-3-")
+}