diff --git a/internal/translator/antigravity/claude/antigravity_claude_request.go b/internal/translator/antigravity/claude/antigravity_claude_request.go
index e6c74bdd..8c1a38c5 100644
--- a/internal/translator/antigravity/claude/antigravity_claude_request.go
+++ b/internal/translator/antigravity/claude/antigravity_claude_request.go
@@ -431,6 +431,33 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 		out, _ = sjson.SetRaw(out, "request.tools", toolsJSON)
 	}
 
+	// tool_choice
+	toolChoiceResult := gjson.GetBytes(rawJSON, "tool_choice")
+	if toolChoiceResult.Exists() {
+		toolChoiceType := ""
+		toolChoiceName := ""
+		if toolChoiceResult.IsObject() {
+			toolChoiceType = toolChoiceResult.Get("type").String()
+			toolChoiceName = toolChoiceResult.Get("name").String()
+		} else if toolChoiceResult.Type == gjson.String {
+			toolChoiceType = toolChoiceResult.String()
+		}
+
+		switch toolChoiceType {
+		case "auto":
+			out, _ = sjson.Set(out, "request.toolConfig.functionCallingConfig.mode", "AUTO")
+		case "none":
+			out, _ = sjson.Set(out, "request.toolConfig.functionCallingConfig.mode", "NONE")
+		case "any":
+			out, _ = sjson.Set(out, "request.toolConfig.functionCallingConfig.mode", "ANY")
+		case "tool":
+			out, _ = sjson.Set(out, "request.toolConfig.functionCallingConfig.mode", "ANY")
+			if toolChoiceName != "" {
+				out, _ = sjson.Set(out, "request.toolConfig.functionCallingConfig.allowedFunctionNames", []string{toolChoiceName})
+			}
+		}
+	}
+
 	// Map Anthropic thinking -> Gemini thinkingBudget/include_thoughts when type==enabled
 	if t := gjson.GetBytes(rawJSON, "thinking"); enableThoughtTranslate && t.Exists() && t.IsObject() {
 		switch t.Get("type").String() {
diff --git a/internal/translator/antigravity/claude/antigravity_claude_request_test.go b/internal/translator/antigravity/claude/antigravity_claude_request_test.go
index 53a24339..39dc493d 100644
--- a/internal/translator/antigravity/claude/antigravity_claude_request_test.go
+++ b/internal/translator/antigravity/claude/antigravity_claude_request_test.go
@@ -193,6 +193,42 @@ func TestConvertClaudeRequestToAntigravity_ToolDeclarations(t *testing.T) {
 	}
 }
 
+func TestConvertClaudeRequestToAntigravity_ToolChoice_SpecificTool(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "gemini-3-flash-preview",
+		"messages": [
+			{
+				"role": "user",
+				"content": [
+					{"type": "text", "text": "hi"}
+				]
+			}
+		],
+		"tools": [
+			{
+				"name": "json",
+				"description": "A JSON tool",
+				"input_schema": {
+					"type": "object",
+					"properties": {}
+				}
+			}
+		],
+		"tool_choice": {"type": "tool", "name": "json"}
+	}`)
+
+	output := ConvertClaudeRequestToAntigravity("gemini-3-flash-preview", inputJSON, false)
+	outputStr := string(output)
+
+	if got := gjson.Get(outputStr, "request.toolConfig.functionCallingConfig.mode").String(); got != "ANY" {
+		t.Fatalf("Expected toolConfig.functionCallingConfig.mode 'ANY', got '%s'", got)
+	}
+	allowed := gjson.Get(outputStr, "request.toolConfig.functionCallingConfig.allowedFunctionNames").Array()
+	if len(allowed) != 1 || allowed[0].String() != "json" {
+		t.Fatalf("Expected allowedFunctionNames ['json'], got %s", gjson.Get(outputStr, "request.toolConfig.functionCallingConfig.allowedFunctionNames").Raw)
+	}
+}
+
 func TestConvertClaudeRequestToAntigravity_ToolUse(t *testing.T) {
 	inputJSON := []byte(`{
 		"model": "claude-3-5-sonnet-20240620",
diff --git a/internal/translator/gemini-cli/claude/gemini-cli_claude_request.go b/internal/translator/gemini-cli/claude/gemini-cli_claude_request.go
index 076e09db..e3753b03 100644
--- a/internal/translator/gemini-cli/claude/gemini-cli_claude_request.go
+++ b/internal/translator/gemini-cli/claude/gemini-cli_claude_request.go
@@ -172,6 +172,33 @@ func ConvertClaudeRequestToCLI(modelName string, inputRawJSON []byte, _ bool) []
 		}
 	}
 
+	// tool_choice
+	toolChoiceResult := gjson.GetBytes(rawJSON, "tool_choice")
+	if toolChoiceResult.Exists() {
+		toolChoiceType := ""
+		toolChoiceName := ""
+		if toolChoiceResult.IsObject() {
+			toolChoiceType = toolChoiceResult.Get("type").String()
+			toolChoiceName = toolChoiceResult.Get("name").String()
+		} else if toolChoiceResult.Type == gjson.String {
+			toolChoiceType = toolChoiceResult.String()
+		}
+
+		switch toolChoiceType {
+		case "auto":
+			out, _ = sjson.Set(out, "request.toolConfig.functionCallingConfig.mode", "AUTO")
+		case "none":
+			out, _ = sjson.Set(out, "request.toolConfig.functionCallingConfig.mode", "NONE")
+		case "any":
+			out, _ = sjson.Set(out, "request.toolConfig.functionCallingConfig.mode", "ANY")
+		case "tool":
+			out, _ = sjson.Set(out, "request.toolConfig.functionCallingConfig.mode", "ANY")
+			if toolChoiceName != "" {
+				out, _ = sjson.Set(out, "request.toolConfig.functionCallingConfig.allowedFunctionNames", []string{toolChoiceName})
+			}
+		}
+	}
+
 	// Map Anthropic thinking -> Gemini CLI thinkingConfig when enabled
 	// Translator only does format conversion, ApplyThinking handles model capability validation.
 	if t := gjson.GetBytes(rawJSON, "thinking"); t.Exists() && t.IsObject() {
diff --git a/internal/translator/gemini-cli/claude/gemini-cli_claude_request_test.go b/internal/translator/gemini-cli/claude/gemini-cli_claude_request_test.go
new file mode 100644
index 00000000..10364e75
--- /dev/null
+++ b/internal/translator/gemini-cli/claude/gemini-cli_claude_request_test.go
@@ -0,0 +1,42 @@
+package claude
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertClaudeRequestToCLI_ToolChoice_SpecificTool(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "gemini-3-flash-preview",
+		"messages": [
+			{
+				"role": "user",
+				"content": [
+					{"type": "text", "text": "hi"}
+				]
+			}
+		],
+		"tools": [
+			{
+				"name": "json",
+				"description": "A JSON tool",
+				"input_schema": {
+					"type": "object",
+					"properties": {}
+				}
+			}
+		],
+		"tool_choice": {"type": "tool", "name": "json"}
+	}`)
+
+	output := ConvertClaudeRequestToCLI("gemini-3-flash-preview", inputJSON, false)
+
+	if got := gjson.GetBytes(output, "request.toolConfig.functionCallingConfig.mode").String(); got != "ANY" {
+		t.Fatalf("Expected request.toolConfig.functionCallingConfig.mode 'ANY', got '%s'", got)
+	}
+	allowed := gjson.GetBytes(output, "request.toolConfig.functionCallingConfig.allowedFunctionNames").Array()
+	if len(allowed) != 1 || allowed[0].String() != "json" {
+		t.Fatalf("Expected allowedFunctionNames ['json'], got %s", gjson.GetBytes(output, "request.toolConfig.functionCallingConfig.allowedFunctionNames").Raw)
+	}
+}
diff --git a/internal/translator/gemini/claude/gemini_claude_request.go b/internal/translator/gemini/claude/gemini_claude_request.go
index 0e367c0d..ff276ce3 100644
--- a/internal/translator/gemini/claude/gemini_claude_request.go
+++ b/internal/translator/gemini/claude/gemini_claude_request.go
@@ -153,6 +153,33 @@ func ConvertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 		}
 	}
 
+	// tool_choice
+	toolChoiceResult := gjson.GetBytes(rawJSON, "tool_choice")
+	if toolChoiceResult.Exists() {
+		toolChoiceType := ""
+		toolChoiceName := ""
+		if toolChoiceResult.IsObject() {
+			toolChoiceType = toolChoiceResult.Get("type").String()
+			toolChoiceName = toolChoiceResult.Get("name").String()
+		} else if toolChoiceResult.Type == gjson.String {
+			toolChoiceType = toolChoiceResult.String()
+		}
+
+		switch toolChoiceType {
+		case "auto":
+			out, _ = sjson.Set(out, "toolConfig.functionCallingConfig.mode", "AUTO")
+		case "none":
+			out, _ = sjson.Set(out, "toolConfig.functionCallingConfig.mode", "NONE")
+		case "any":
+			out, _ = sjson.Set(out, "toolConfig.functionCallingConfig.mode", "ANY")
+		case "tool":
+			out, _ = sjson.Set(out, "toolConfig.functionCallingConfig.mode", "ANY")
+			if toolChoiceName != "" {
+				out, _ = sjson.Set(out, "toolConfig.functionCallingConfig.allowedFunctionNames", []string{toolChoiceName})
+			}
+		}
+	}
+
 	// Map Anthropic thinking -> Gemini thinking config when enabled
 	// Translator only does format conversion, ApplyThinking handles model capability validation.
 	if t := gjson.GetBytes(rawJSON, "thinking"); t.Exists() && t.IsObject() {
diff --git a/internal/translator/gemini/claude/gemini_claude_request_test.go b/internal/translator/gemini/claude/gemini_claude_request_test.go
new file mode 100644
index 00000000..e242c42c
--- /dev/null
+++ b/internal/translator/gemini/claude/gemini_claude_request_test.go
@@ -0,0 +1,42 @@
+package claude
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertClaudeRequestToGemini_ToolChoice_SpecificTool(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "gemini-3-flash-preview",
+		"messages": [
+			{
+				"role": "user",
+				"content": [
+					{"type": "text", "text": "hi"}
+				]
+			}
+		],
+		"tools": [
+			{
+				"name": "json",
+				"description": "A JSON tool",
+				"input_schema": {
+					"type": "object",
+					"properties": {}
+				}
+			}
+		],
+		"tool_choice": {"type": "tool", "name": "json"}
+	}`)
+
+	output := ConvertClaudeRequestToGemini("gemini-3-flash-preview", inputJSON, false)
+
+	if got := gjson.GetBytes(output, "toolConfig.functionCallingConfig.mode").String(); got != "ANY" {
+		t.Fatalf("Expected toolConfig.functionCallingConfig.mode 'ANY', got '%s'", got)
+	}
+	allowed := gjson.GetBytes(output, "toolConfig.functionCallingConfig.allowedFunctionNames").Array()
+	if len(allowed) != 1 || allowed[0].String() != "json" {
+		t.Fatalf("Expected allowedFunctionNames ['json'], got %s", gjson.GetBytes(output, "toolConfig.functionCallingConfig.allowedFunctionNames").Raw)
+	}
+}