diff --git a/internal/translator/antigravity/claude/antigravity_claude_request.go b/internal/translator/antigravity/claude/antigravity_claude_request.go
index 0af039f6..2287bccc 100644
--- a/internal/translator/antigravity/claude/antigravity_claude_request.go
+++ b/internal/translator/antigravity/claude/antigravity_claude_request.go
@@ -86,6 +86,10 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 				hasSystemInstruction = true
 			}
 		}
+	} else if systemResult.Type == gjson.String {
+		systemInstructionJSON = `{"role":"user","parts":[{"text":""}]}`
+		systemInstructionJSON, _ = sjson.Set(systemInstructionJSON, "parts.0.text", systemResult.String())
+		hasSystemInstruction = true
 	}
 
 	// contents
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 c421d22f..66e0385f 100644
--- a/internal/translator/gemini-cli/claude/gemini-cli_claude_request.go
+++ b/internal/translator/gemini-cli/claude/gemini-cli_claude_request.go
@@ -62,6 +62,8 @@ func ConvertClaudeRequestToCLI(modelName string, inputRawJSON []byte, _ bool) []
 		if hasSystemParts {
 			out, _ = sjson.SetRaw(out, "request.systemInstruction", systemInstruction)
 		}
+	} else if systemResult.Type == gjson.String {
+		out, _ = sjson.Set(out, "request.systemInstruction.parts.-1.text", systemResult.String())
 	}
 
 	// contents
diff --git a/internal/translator/gemini/claude/gemini_claude_request.go b/internal/translator/gemini/claude/gemini_claude_request.go
index 8c95b6ea..4ab6ab97 100644
--- a/internal/translator/gemini/claude/gemini_claude_request.go
+++ b/internal/translator/gemini/claude/gemini_claude_request.go
@@ -55,6 +55,8 @@ func ConvertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 		if hasSystemParts {
 			out, _ = sjson.SetRaw(out, "system_instruction", systemInstruction)
 		}
+	} else if systemResult.Type == gjson.String {
+		out, _ = sjson.Set(out, "request.system_instruction.parts.-1.text", systemResult.String())
 	}
 
 	// contents