diff --git a/internal/thinking/provider/antigravity/apply.go b/internal/thinking/provider/antigravity/apply.go
index a55f808d..7d5a5075 100644
--- a/internal/thinking/provider/antigravity/apply.go
+++ b/internal/thinking/provider/antigravity/apply.go
@@ -116,7 +116,16 @@ func (a *Applier) applyLevelFormat(body []byte, config thinking.ThinkingConfig)
 
 	level := string(config.Level)
 	result, _ = sjson.SetBytes(result, "request.generationConfig.thinkingConfig.thinkingLevel", level)
-	result, _ = sjson.SetBytes(result, "request.generationConfig.thinkingConfig.includeThoughts", true)
+
+	// Respect user's explicit includeThoughts setting from original body; default to true if not set
+	// Support both camelCase and snake_case variants
+	includeThoughts := true
+	if inc := gjson.GetBytes(body, "request.generationConfig.thinkingConfig.includeThoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+	} else if inc := gjson.GetBytes(body, "request.generationConfig.thinkingConfig.include_thoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+	}
+	result, _ = sjson.SetBytes(result, "request.generationConfig.thinkingConfig.includeThoughts", includeThoughts)
 	return result, nil
 }
 
@@ -129,14 +138,29 @@ func (a *Applier) applyBudgetFormat(body []byte, config thinking.ThinkingConfig,
 	result, _ = sjson.DeleteBytes(result, "request.generationConfig.thinkingConfig.include_thoughts")
 
 	budget := config.Budget
-	includeThoughts := false
-	switch config.Mode {
-	case thinking.ModeNone:
-		includeThoughts = false
-	case thinking.ModeAuto:
-		includeThoughts = true
-	default:
-		includeThoughts = budget > 0
+
+	// Determine includeThoughts: respect user's explicit setting from original body if provided
+	// Support both camelCase and snake_case variants
+	var includeThoughts bool
+	var userSetIncludeThoughts bool
+	if inc := gjson.GetBytes(body, "request.generationConfig.thinkingConfig.includeThoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+		userSetIncludeThoughts = true
+	} else if inc := gjson.GetBytes(body, "request.generationConfig.thinkingConfig.include_thoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+		userSetIncludeThoughts = true
+	}
+
+	if !userSetIncludeThoughts {
+		// No explicit setting, use default logic based on mode
+		switch config.Mode {
+		case thinking.ModeNone:
+			includeThoughts = false
+		case thinking.ModeAuto:
+			includeThoughts = true
+		default:
+			includeThoughts = budget > 0
+		}
 	}
 
 	// Apply Claude-specific constraints
diff --git a/internal/thinking/provider/gemini/apply.go b/internal/thinking/provider/gemini/apply.go
index 2c06a75a..39399c09 100644
--- a/internal/thinking/provider/gemini/apply.go
+++ b/internal/thinking/provider/gemini/apply.go
@@ -140,7 +140,16 @@ func (a *Applier) applyLevelFormat(body []byte, config thinking.ThinkingConfig)
 
 	level := string(config.Level)
 	result, _ = sjson.SetBytes(result, "generationConfig.thinkingConfig.thinkingLevel", level)
-	result, _ = sjson.SetBytes(result, "generationConfig.thinkingConfig.includeThoughts", true)
+
+	// Respect user's explicit includeThoughts setting from original body; default to true if not set
+	// Support both camelCase and snake_case variants
+	includeThoughts := true
+	if inc := gjson.GetBytes(body, "generationConfig.thinkingConfig.includeThoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+	} else if inc := gjson.GetBytes(body, "generationConfig.thinkingConfig.include_thoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+	}
+	result, _ = sjson.SetBytes(result, "generationConfig.thinkingConfig.includeThoughts", includeThoughts)
 	return result, nil
 }
 
@@ -153,18 +162,33 @@ func (a *Applier) applyBudgetFormat(body []byte, config thinking.ThinkingConfig)
 	result, _ = sjson.DeleteBytes(result, "generationConfig.thinkingConfig.include_thoughts")
 
 	budget := config.Budget
-	// ModeNone semantics:
-	//   - ModeNone + Budget=0: completely disable thinking
-	//   - ModeNone + Budget>0: forced to think but hide output (includeThoughts=false)
-	// When ZeroAllowed=false, ValidateConfig clamps Budget to Min while preserving ModeNone.
-	includeThoughts := false
-	switch config.Mode {
-	case thinking.ModeNone:
-		includeThoughts = false
-	case thinking.ModeAuto:
-		includeThoughts = true
-	default:
-		includeThoughts = budget > 0
+
+	// Determine includeThoughts: respect user's explicit setting from original body if provided
+	// Support both camelCase and snake_case variants
+	var includeThoughts bool
+	var userSetIncludeThoughts bool
+	if inc := gjson.GetBytes(body, "generationConfig.thinkingConfig.includeThoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+		userSetIncludeThoughts = true
+	} else if inc := gjson.GetBytes(body, "generationConfig.thinkingConfig.include_thoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+		userSetIncludeThoughts = true
+	}
+
+	if !userSetIncludeThoughts {
+		// No explicit setting, use default logic based on mode
+		// ModeNone semantics:
+		//   - ModeNone + Budget=0: completely disable thinking
+		//   - ModeNone + Budget>0: forced to think but hide output (includeThoughts=false)
+		// When ZeroAllowed=false, ValidateConfig clamps Budget to Min while preserving ModeNone.
+		switch config.Mode {
+		case thinking.ModeNone:
+			includeThoughts = false
+		case thinking.ModeAuto:
+			includeThoughts = true
+		default:
+			includeThoughts = budget > 0
+		}
 	}
 
 	result, _ = sjson.SetBytes(result, "generationConfig.thinkingConfig.thinkingBudget", budget)
diff --git a/internal/thinking/provider/geminicli/apply.go b/internal/thinking/provider/geminicli/apply.go
index f60c94a9..476e5b6d 100644
--- a/internal/thinking/provider/geminicli/apply.go
+++ b/internal/thinking/provider/geminicli/apply.go
@@ -101,7 +101,16 @@ func (a *Applier) applyLevelFormat(body []byte, config thinking.ThinkingConfig)
 
 	level := string(config.Level)
 	result, _ = sjson.SetBytes(result, "request.generationConfig.thinkingConfig.thinkingLevel", level)
-	result, _ = sjson.SetBytes(result, "request.generationConfig.thinkingConfig.includeThoughts", true)
+
+	// Respect user's explicit includeThoughts setting from original body; default to true if not set
+	// Support both camelCase and snake_case variants
+	includeThoughts := true
+	if inc := gjson.GetBytes(body, "request.generationConfig.thinkingConfig.includeThoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+	} else if inc := gjson.GetBytes(body, "request.generationConfig.thinkingConfig.include_thoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+	}
+	result, _ = sjson.SetBytes(result, "request.generationConfig.thinkingConfig.includeThoughts", includeThoughts)
 	return result, nil
 }
 
@@ -114,14 +123,29 @@ func (a *Applier) applyBudgetFormat(body []byte, config thinking.ThinkingConfig)
 	result, _ = sjson.DeleteBytes(result, "request.generationConfig.thinkingConfig.include_thoughts")
 
 	budget := config.Budget
-	includeThoughts := false
-	switch config.Mode {
-	case thinking.ModeNone:
-		includeThoughts = false
-	case thinking.ModeAuto:
-		includeThoughts = true
-	default:
-		includeThoughts = budget > 0
+
+	// Determine includeThoughts: respect user's explicit setting from original body if provided
+	// Support both camelCase and snake_case variants
+	var includeThoughts bool
+	var userSetIncludeThoughts bool
+	if inc := gjson.GetBytes(body, "request.generationConfig.thinkingConfig.includeThoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+		userSetIncludeThoughts = true
+	} else if inc := gjson.GetBytes(body, "request.generationConfig.thinkingConfig.include_thoughts"); inc.Exists() {
+		includeThoughts = inc.Bool()
+		userSetIncludeThoughts = true
+	}
+
+	if !userSetIncludeThoughts {
+		// No explicit setting, use default logic based on mode
+		switch config.Mode {
+		case thinking.ModeNone:
+			includeThoughts = false
+		case thinking.ModeAuto:
+			includeThoughts = true
+		default:
+			includeThoughts = budget > 0
+		}
 	}
 
 	result, _ = sjson.SetBytes(result, "request.generationConfig.thinkingConfig.thinkingBudget", budget)
diff --git a/test/thinking_conversion_test.go b/test/thinking_conversion_test.go
index 83a0e139..fc20199e 100644
--- a/test/thinking_conversion_test.go
+++ b/test/thinking_conversion_test.go
@@ -1441,28 +1441,6 @@ func TestThinkingE2EMatrix_Body(t *testing.T) {
 			expectValue: "medium",
 			expectErr:   false,
 		},
-		// Case 9001: thinking_budget=64000 (snake_case) → high (Gemini -> Codex)
-		{
-			name:        "9001",
-			from:        "gemini",
-			to:          "codex",
-			model:       "level-model",
-			inputJSON:   `{"model":"level-model","contents":[{"role":"user","parts":[{"text":"hi"}]}],"generationConfig":{"thinkingConfig":{"thinking_budget":64000}}}`,
-			expectField: "reasoning.effort",
-			expectValue: "high",
-			expectErr:   false,
-		},
-		// Case 9002: thinking_level=high (snake_case) → reasoning_effort=high (Gemini -> OpenAI)
-		{
-			name:        "9002",
-			from:        "gemini",
-			to:          "openai",
-			model:       "level-model",
-			inputJSON:   `{"model":"level-model","contents":[{"role":"user","parts":[{"text":"hi"}]}],"generationConfig":{"thinkingConfig":{"thinking_level":"high"}}}`,
-			expectField: "reasoning_effort",
-			expectValue: "high",
-			expectErr:   false,
-		},
 		// Case 11: Claude no param → passthrough (no thinking)
 		{
 			name:        "11",
@@ -1473,17 +1451,6 @@ func TestThinkingE2EMatrix_Body(t *testing.T) {
 			expectField: "",
 			expectErr:   false,
 		},
-		// Case 9003: thinking_budget=8192 (snake_case) → thinking.budget_tokens=8192 (Gemini -> Claude)
-		{
-			name:        "9003",
-			from:        "gemini",
-			to:          "claude",
-			model:       "level-model",
-			inputJSON:   `{"model":"level-model","contents":[{"role":"user","parts":[{"text":"hi"}]}],"generationConfig":{"thinkingConfig":{"thinking_budget":8192}}}`,
-			expectField: "thinking.budget_tokens",
-			expectValue: "8192",
-			expectErr:   false,
-		},
 		// Case 12: thinking.budget_tokens=8192 → medium
 		{
 			name:        "12",
@@ -1557,19 +1524,6 @@ func TestThinkingE2EMatrix_Body(t *testing.T) {
 
 		// gemini-budget-model (Min=128, Max=20000, ZeroAllowed=false, DynamicAllowed=true)
 
-		// Case 9004: thinking_budget=8192 (snake_case) → passthrough+normalize to thinkingBudget (Gemini -> Gemini)
-		{
-			name:            "9004",
-			from:            "gemini",
-			to:              "gemini",
-			model:           "gemini-budget-model",
-			inputJSON:       `{"model":"gemini-budget-model","contents":[{"role":"user","parts":[{"text":"hi"}]}],"generationConfig":{"thinkingConfig":{"thinking_budget":8192}}}`,
-			expectField:     "generationConfig.thinkingConfig.thinkingBudget",
-			expectValue:     "8192",
-			includeThoughts: "true",
-			expectErr:       false,
-		},
-
 		// Case 18: No param → passthrough
 		{
 			name:        "18",