diff --git a/internal/translator/antigravity/claude/antigravity_claude_request.go b/internal/translator/antigravity/claude/antigravity_claude_request.go
index 7f36b11cc..456475f1f 100644
--- a/internal/translator/antigravity/claude/antigravity_claude_request.go
+++ b/internal/translator/antigravity/claude/antigravity_claude_request.go
@@ -101,7 +101,7 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 			systemTypePromptResult := systemPromptResult.Get("type")
 			if systemTypePromptResult.Type == gjson.String && systemTypePromptResult.String() == "text" {
 				systemPrompt := systemPromptResult.Get("text").String()
-				if strings.HasPrefix(systemPrompt, "x-anthropic-billing-header:") {
+				if util.IsClaudeCodeAttributionSystemText(systemPrompt) {
 					continue
 				}
 				partJSON := []byte(`{}`)
@@ -112,7 +112,7 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 				hasSystemInstruction = true
 			}
 		}
-	} else if systemResult.Type == gjson.String {
+	} else if systemResult.Type == gjson.String && !util.IsClaudeCodeAttributionSystemText(systemResult.String()) {
 		systemInstructionJSON = []byte(`{"role":"user","parts":[{"text":""}]}`)
 		systemInstructionJSON, _ = sjson.SetBytes(systemInstructionJSON, "parts.0.text", systemResult.String())
 		hasSystemInstruction = true
diff --git a/internal/translator/antigravity/claude/antigravity_claude_request_test.go b/internal/translator/antigravity/claude/antigravity_claude_request_test.go
index bb3cdf4f3..f4ffa3e41 100644
--- a/internal/translator/antigravity/claude/antigravity_claude_request_test.go
+++ b/internal/translator/antigravity/claude/antigravity_claude_request_test.go
@@ -70,6 +70,28 @@ func uint64Ptr(v uint64) *uint64 {
 	return &v
 }
 
+func TestConvertClaudeRequestToAntigravity_StripsClaudeCodeAttribution(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "claude-sonnet-4-5",
+		"messages": [{"role": "user", "content": [{"type": "text", "text": "Hello"}]}],
+		"system": [
+			{"type": "text", "text": "x-anthropic-billing-header: cc_version=2.1.63.abc; cc_entrypoint=cli; cch=12345;"},
+			{"type": "text", "text": "Antigravity system prompt"}
+		]
+	}`)
+
+	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5", inputJSON, false)
+	outputStr := string(output)
+
+	parts := gjson.Get(outputStr, "request.systemInstruction.parts").Array()
+	if len(parts) != 1 {
+		t.Fatalf("Expected 1 system part after attribution strip, got %d: %s", len(parts), gjson.Get(outputStr, "request.systemInstruction.parts").Raw)
+	}
+	if got := parts[0].Get("text").String(); got != "Antigravity system prompt" {
+		t.Fatalf("Unexpected system part: %q", got)
+	}
+}
+
 func testNonAnthropicRawSignature(t *testing.T) string {
 	t.Helper()
 
diff --git a/internal/translator/codex/claude/codex_claude_request.go b/internal/translator/codex/claude/codex_claude_request.go
index 029db14e7..b74f35c90 100644
--- a/internal/translator/codex/claude/codex_claude_request.go
+++ b/internal/translator/codex/claude/codex_claude_request.go
@@ -12,6 +12,7 @@ import (
 	"strings"
 
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
 )
@@ -50,7 +51,7 @@ func ConvertClaudeRequestToCodex(modelName string, inputRawJSON []byte, _ bool)
 		contentIndex := 0
 
 		appendSystemText := func(text string) {
-			if text == "" || strings.HasPrefix(text, "x-anthropic-billing-header: ") {
+			if text == "" || util.IsClaudeCodeAttributionSystemText(text) {
 				return
 			}
 
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 3e77b3f75..b21936a95 100644
--- a/internal/translator/gemini-cli/claude/gemini-cli_claude_request.go
+++ b/internal/translator/gemini-cli/claude/gemini-cli_claude_request.go
@@ -49,6 +49,9 @@ func ConvertClaudeRequestToCLI(modelName string, inputRawJSON []byte, _ bool) []
 			if systemPromptResult.Get("type").String() == "text" {
 				textResult := systemPromptResult.Get("text")
 				if textResult.Type == gjson.String {
+					if util.IsClaudeCodeAttributionSystemText(textResult.String()) {
+						return true
+					}
 					part := []byte(`{"text":""}`)
 					part, _ = sjson.SetBytes(part, "text", textResult.String())
 					systemInstruction, _ = sjson.SetRawBytes(systemInstruction, "parts.-1", part)
@@ -60,7 +63,7 @@ func ConvertClaudeRequestToCLI(modelName string, inputRawJSON []byte, _ bool) []
 		if hasSystemParts {
 			out, _ = sjson.SetRawBytes(out, "request.systemInstruction", systemInstruction)
 		}
-	} else if systemResult.Type == gjson.String {
+	} else if systemResult.Type == gjson.String && !util.IsClaudeCodeAttributionSystemText(systemResult.String()) {
 		out, _ = sjson.SetBytes(out, "request.systemInstruction.parts.-1.text", systemResult.String())
 	}
 
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
index 10364e751..ff0cea657 100644
--- a/internal/translator/gemini-cli/claude/gemini-cli_claude_request_test.go
+++ b/internal/translator/gemini-cli/claude/gemini-cli_claude_request_test.go
@@ -40,3 +40,24 @@ func TestConvertClaudeRequestToCLI_ToolChoice_SpecificTool(t *testing.T) {
 		t.Fatalf("Expected allowedFunctionNames ['json'], got %s", gjson.GetBytes(output, "request.toolConfig.functionCallingConfig.allowedFunctionNames").Raw)
 	}
 }
+
+func TestConvertClaudeRequestToCLI_StripsClaudeCodeAttribution(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "claude-sonnet-4-5",
+		"system": [
+			{"type": "text", "text": "x-anthropic-billing-header: cc_version=2.1.63.abc; cc_entrypoint=cli; cch=12345;"},
+			{"type": "text", "text": "User system prompt"}
+		],
+		"messages": [{"role": "user", "content": [{"type": "text", "text": "hi"}]}]
+	}`)
+
+	output := ConvertClaudeRequestToCLI("gemini-3-flash-preview", inputJSON, false)
+
+	parts := gjson.GetBytes(output, "request.systemInstruction.parts").Array()
+	if len(parts) != 1 {
+		t.Fatalf("Expected 1 system part after attribution strip, got %d: %s", len(parts), gjson.GetBytes(output, "request.systemInstruction.parts").Raw)
+	}
+	if got := parts[0].Get("text").String(); got != "User system prompt" {
+		t.Fatalf("Unexpected system part: %q", got)
+	}
+}
diff --git a/internal/translator/gemini/claude/gemini_claude_request.go b/internal/translator/gemini/claude/gemini_claude_request.go
index 454668cbc..3beadea18 100644
--- a/internal/translator/gemini/claude/gemini_claude_request.go
+++ b/internal/translator/gemini/claude/gemini_claude_request.go
@@ -43,6 +43,9 @@ func ConvertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 			if systemPromptResult.Get("type").String() == "text" {
 				textResult := systemPromptResult.Get("text")
 				if textResult.Type == gjson.String {
+					if util.IsClaudeCodeAttributionSystemText(textResult.String()) {
+						return true
+					}
 					part := []byte(`{"text":""}`)
 					part, _ = sjson.SetBytes(part, "text", textResult.String())
 					systemInstruction, _ = sjson.SetRawBytes(systemInstruction, "parts.-1", part)
@@ -54,7 +57,7 @@ func ConvertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 		if hasSystemParts {
 			out, _ = sjson.SetRawBytes(out, "system_instruction", systemInstruction)
 		}
-	} else if systemResult.Type == gjson.String {
+	} else if systemResult.Type == gjson.String && !util.IsClaudeCodeAttributionSystemText(systemResult.String()) {
 		out, _ = sjson.SetBytes(out, "system_instruction.parts.-1.text", systemResult.String())
 	}
 
diff --git a/internal/translator/gemini/claude/gemini_claude_request_test.go b/internal/translator/gemini/claude/gemini_claude_request_test.go
index 10ad2d3af..0fd515e59 100644
--- a/internal/translator/gemini/claude/gemini_claude_request_test.go
+++ b/internal/translator/gemini/claude/gemini_claude_request_test.go
@@ -78,3 +78,31 @@ func TestConvertClaudeRequestToGemini_ImageContent(t *testing.T) {
 		t.Fatalf("Expected image data 'aGVsbG8=', got '%s'", got)
 	}
 }
+
+func TestConvertClaudeRequestToGemini_StripsClaudeCodeAttribution(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "claude-sonnet-4-5",
+		"system": [
+			{"type": "text", "text": "x-anthropic-billing-header: cc_version=2.1.63.abc; cc_entrypoint=cli; cch=12345;"},
+			{"type": "text", "text": "You are a Claude agent, built on Anthropic's Claude Agent SDK."},
+			{"type": "text", "text": "User system prompt"}
+		],
+		"messages": [{"role": "user", "content": [{"type": "text", "text": "hi"}]}]
+	}`)
+
+	output := ConvertClaudeRequestToGemini("gemini-3-flash-preview", inputJSON, false)
+
+	parts := gjson.GetBytes(output, "system_instruction.parts").Array()
+	if len(parts) != 2 {
+		t.Fatalf("Expected 2 system parts after attribution strip, got %d: %s", len(parts), gjson.GetBytes(output, "system_instruction.parts").Raw)
+	}
+	if got := parts[0].Get("text").String(); got != "You are a Claude agent, built on Anthropic's Claude Agent SDK." {
+		t.Fatalf("Unexpected first system part: %q", got)
+	}
+	if got := parts[1].Get("text").String(); got != "User system prompt" {
+		t.Fatalf("Unexpected second system part: %q", got)
+	}
+	if gjson.GetBytes(output, `system_instruction.parts.#(text%"x-anthropic-billing-header:*")`).Exists() {
+		t.Fatalf("Claude Code attribution block was forwarded: %s", gjson.GetBytes(output, "system_instruction.parts").Raw)
+	}
+}
diff --git a/internal/translator/openai/claude/openai_claude_request.go b/internal/translator/openai/claude/openai_claude_request.go
index 99fc2763f..98954b383 100644
--- a/internal/translator/openai/claude/openai_claude_request.go
+++ b/internal/translator/openai/claude/openai_claude_request.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
 )
@@ -103,7 +104,7 @@ func ConvertClaudeRequestToOpenAI(modelName string, inputRawJSON []byte, stream
 	hasSystemContent := false
 	if system := root.Get("system"); system.Exists() {
 		if system.Type == gjson.String {
-			if system.String() != "" {
+			if system.String() != "" && !util.IsClaudeCodeAttributionSystemText(system.String()) {
 				oldSystem := []byte(`{"type":"text","text":""}`)
 				oldSystem, _ = sjson.SetBytes(oldSystem, "text", system.String())
 				systemMsgJSON, _ = sjson.SetRawBytes(systemMsgJSON, "content.-1", oldSystem)
@@ -334,7 +335,7 @@ func convertClaudeContentPart(part gjson.Result) (string, bool) {
 	switch partType {
 	case "text":
 		text := part.Get("text").String()
-		if strings.TrimSpace(text) == "" {
+		if strings.TrimSpace(text) == "" || util.IsClaudeCodeAttributionSystemText(text) {
 			return "", false
 		}
 		textContent := []byte(`{"type":"text","text":""}`)
diff --git a/internal/translator/openai/claude/openai_claude_request_test.go b/internal/translator/openai/claude/openai_claude_request_test.go
index 3fd4707f5..9c6ba77c3 100644
--- a/internal/translator/openai/claude/openai_claude_request_test.go
+++ b/internal/translator/openai/claude/openai_claude_request_test.go
@@ -696,3 +696,28 @@ func TestConvertClaudeRequestToOpenAI_AssistantThinkingToolUseThinkingSplit(t *t
 		t.Fatalf("Expected reasoning_content %q, got %q", "t1\n\nt2", got)
 	}
 }
+
+func TestConvertClaudeRequestToOpenAI_StripsClaudeCodeAttribution(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "claude-sonnet-4-5",
+		"system": [
+			{"type": "text", "text": "x-anthropic-billing-header: cc_version=2.1.63.abc; cc_entrypoint=cli; cch=12345;"},
+			{"type": "text", "text": "User system prompt"}
+		],
+		"messages": [{"role": "user", "content": [{"type": "text", "text": "hi"}]}]
+	}`)
+
+	output := ConvertClaudeRequestToOpenAI("gpt-5", inputJSON, false)
+	messages := gjson.GetBytes(output, "messages").Array()
+	if len(messages) == 0 || messages[0].Get("role").String() != "system" {
+		t.Fatalf("Expected first message to be system, got: %s", gjson.GetBytes(output, "messages").Raw)
+	}
+
+	content := messages[0].Get("content").Array()
+	if len(content) != 1 {
+		t.Fatalf("Expected 1 system content item after attribution strip, got %d: %s", len(content), messages[0].Get("content").Raw)
+	}
+	if got := content[0].Get("text").String(); got != "User system prompt" {
+		t.Fatalf("Unexpected system content: %q", got)
+	}
+}
diff --git a/internal/util/claude_attribution.go b/internal/util/claude_attribution.go
new file mode 100644
index 000000000..ddfa1da58
--- /dev/null
+++ b/internal/util/claude_attribution.go
@@ -0,0 +1,15 @@
+package util
+
+import (
+	"strings"
+	"unicode"
+)
+
+const claudeCodeAttributionSystemPrefix = "x-anthropic-billing-header:"
+
+// IsClaudeCodeAttributionSystemText reports whether text is the Claude Code
+// attribution block that carries per-request billing and prompt fingerprint data.
+func IsClaudeCodeAttributionSystemText(text string) bool {
+	text = strings.TrimLeftFunc(text, unicode.IsSpace)
+	return strings.HasPrefix(text, claudeCodeAttributionSystemPrefix)
+}
diff --git a/internal/util/claude_attribution_test.go b/internal/util/claude_attribution_test.go
new file mode 100644
index 000000000..02817ee1d
--- /dev/null
+++ b/internal/util/claude_attribution_test.go
@@ -0,0 +1,40 @@
+package util
+
+import "testing"
+
+func TestIsClaudeCodeAttributionSystemText(t *testing.T) {
+	tests := []struct {
+		name string
+		text string
+		want bool
+	}{
+		{
+			name: "Claude Code attribution block",
+			text: "x-anthropic-billing-header: cc_version=2.1.63.abc; cc_entrypoint=cli; cch=12345;",
+			want: true,
+		},
+		{
+			name: "leading whitespace",
+			text: "\n\t x-anthropic-billing-header: cc_version=2.1.63.abc; cch=12345;",
+			want: true,
+		},
+		{
+			name: "regular system prompt",
+			text: "You are helpful.",
+			want: false,
+		},
+		{
+			name: "empty text",
+			text: "",
+			want: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := IsClaudeCodeAttributionSystemText(tt.text); got != tt.want {
+				t.Fatalf("IsClaudeCodeAttributionSystemText(%q) = %v, want %v", tt.text, got, tt.want)
+			}
+		})
+	}
+}