diff --git a/relay/channel/deepseek/adaptor.go b/relay/channel/deepseek/adaptor.go
index 60eaf22be568..0c4d2937a5ac 100644
--- a/relay/channel/deepseek/adaptor.go
+++ b/relay/channel/deepseek/adaptor.go
@@ -37,6 +37,7 @@ func (a *Adaptor) ConvertClaudeRequest(c *gin.Context, info *relaycommon.RelayIn
 	if !ok {
 		return convertedRequest, nil
 	}
+	normalizeClaudeSystemMessagesForNonNativeUpstream(claudeRequest)
 	if err := applyDeepSeekV4ClaudeThinkingSuffix(info, claudeRequest); err != nil {
 		return nil, err
 	}
diff --git a/relay/channel/deepseek/adaptor_test.go b/relay/channel/deepseek/adaptor_test.go
new file mode 100644
index 000000000000..58c1752cae92
--- /dev/null
+++ b/relay/channel/deepseek/adaptor_test.go
@@ -0,0 +1,71 @@
+package deepseek
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/QuantumNous/new-api/dto"
+	relaycommon "github.com/QuantumNous/new-api/relay/common"
+)
+
+func TestConvertClaudeRequestMergesTrailingSystemIntoPreviousUser(t *testing.T) {
+	req := &dto.ClaudeRequest{
+		Model: "deepseek-v4-pro",
+		Messages: []dto.ClaudeMessage{
+			{Role: "user", Content: "Why did the skill stop?"},
+			{Role: "system", Content: "Ultracode is on: keep working."},
+		},
+	}
+
+	converted, err := (&Adaptor{}).ConvertClaudeRequest(nil, &relaycommon.RelayInfo{}, req)
+	if err != nil {
+		t.Fatalf("ConvertClaudeRequest returned error: %v", err)
+	}
+	claudeReq := converted.(*dto.ClaudeRequest)
+
+	if len(claudeReq.Messages) != 1 {
+		t.Fatalf("expected 1 message after normalization, got %d", len(claudeReq.Messages))
+	}
+	if claudeReq.Messages[0].Role != "user" {
+		t.Fatalf("expected normalized message to remain user, got %q", claudeReq.Messages[0].Role)
+	}
+	content := claudeReq.Messages[0].GetStringContent()
+	if !strings.Contains(content, "Why did the skill stop?") {
+		t.Fatalf("expected user content to be preserved, got %q", content)
+	}
+	if !strings.Contains(content, "Ultracode is on: keep working.") {
+		t.Fatalf("expected trailing system content to be merged into user content, got %q", content)
+	}
+}
+
+func TestConvertClaudeRequestMergesInterleavedSystemIntoNextUser(t *testing.T) {
+	req := &dto.ClaudeRequest{
+		Model: "deepseek-v4-pro",
+		Messages: []dto.ClaudeMessage{
+			{Role: "user", Content: "First request"},
+			{Role: "assistant", Content: "First response"},
+			{Role: "system", Content: "Apply this reminder before the next answer."},
+			{Role: "user", Content: "Second request"},
+		},
+	}
+
+	converted, err := (&Adaptor{}).ConvertClaudeRequest(nil, &relaycommon.RelayInfo{}, req)
+	if err != nil {
+		t.Fatalf("ConvertClaudeRequest returned error: %v", err)
+	}
+	claudeReq := converted.(*dto.ClaudeRequest)
+
+	if len(claudeReq.Messages) != 3 {
+		t.Fatalf("expected 3 messages after normalization, got %d", len(claudeReq.Messages))
+	}
+	if claudeReq.Messages[2].Role != "user" {
+		t.Fatalf("expected interleaved system to be merged into next user, got role %q", claudeReq.Messages[2].Role)
+	}
+	content := claudeReq.Messages[2].GetStringContent()
+	if !strings.Contains(content, "Apply this reminder before the next answer.") {
+		t.Fatalf("expected interleaved system content in next user message, got %q", content)
+	}
+	if !strings.Contains(content, "Second request") {
+		t.Fatalf("expected next user content to be preserved, got %q", content)
+	}
+}
diff --git a/relay/channel/deepseek/claude_system_normalize.go b/relay/channel/deepseek/claude_system_normalize.go
new file mode 100644
index 000000000000..85778174d73a
--- /dev/null
+++ b/relay/channel/deepseek/claude_system_normalize.go
@@ -0,0 +1,112 @@
+package deepseek
+
+import (
+	"strings"
+
+	"github.com/QuantumNous/new-api/dto"
+)
+
+func normalizeClaudeSystemMessagesForNonNativeUpstream(request *dto.ClaudeRequest) {
+	if request == nil || len(request.Messages) == 0 {
+		return
+	}
+
+	normalizedMessages := make([]dto.ClaudeMessage, 0, len(request.Messages))
+	var pendingSystems []string
+
+	for _, message := range request.Messages {
+		if message.Role != "system" {
+			if message.Role == "user" && len(pendingSystems) > 0 {
+				mergeSystemTextIntoUserMessage(&message, strings.Join(pendingSystems, "\n\n"), true)
+				pendingSystems = nil
+			}
+			normalizedMessages = append(normalizedMessages, message)
+			continue
+		}
+
+		systemText := claudeSystemMessageText(message)
+		if systemText == "" {
+			continue
+		}
+		if len(normalizedMessages) > 0 && normalizedMessages[len(normalizedMessages)-1].Role == "user" {
+			mergeSystemTextIntoUserMessage(&normalizedMessages[len(normalizedMessages)-1], systemText, false)
+			continue
+		}
+		pendingSystems = append(pendingSystems, systemText)
+	}
+
+	if len(pendingSystems) > 0 {
+		mergePendingSystemTextIntoLastUser(normalizedMessages, strings.Join(pendingSystems, "\n\n"))
+	}
+	request.Messages = normalizedMessages
+}
+
+func mergePendingSystemTextIntoLastUser(messages []dto.ClaudeMessage, systemText string) {
+	for i := len(messages) - 1; i >= 0; i-- {
+		if messages[i].Role == "user" {
+			mergeSystemTextIntoUserMessage(&messages[i], systemText, false)
+			return
+		}
+	}
+}
+
+func claudeSystemMessageText(message dto.ClaudeMessage) string {
+	if message.IsStringContent() {
+		return strings.TrimSpace(message.GetStringContent())
+	}
+	contents, err := message.ParseContent()
+	if err != nil {
+		return strings.TrimSpace(message.GetStringContent())
+	}
+	var builder strings.Builder
+	for _, content := range contents {
+		if content.Type == dto.ContentTypeText {
+			builder.WriteString(content.GetText())
+		}
+	}
+	return strings.TrimSpace(builder.String())
+}
+
+func mergeSystemTextIntoUserMessage(message *dto.ClaudeMessage, systemText string, prepend bool) {
+	if systemText == "" {
+		return
+	}
+	if message.IsStringContent() {
+		userText := message.GetStringContent()
+		if prepend {
+			message.SetStringContent(joinClaudeText(systemText, userText))
+		} else {
+			message.SetStringContent(joinClaudeText(userText, systemText))
+		}
+		return
+	}
+
+	systemTextBlock := dto.ClaudeMediaMessage{Type: dto.ContentTypeText}
+	systemTextBlock.SetText(systemText)
+	contents, err := message.ParseContent()
+	if err != nil || len(contents) == 0 {
+		if prepend {
+			message.SetStringContent(joinClaudeText(systemText, message.GetStringContent()))
+		} else {
+			message.SetStringContent(joinClaudeText(message.GetStringContent(), systemText))
+		}
+		return
+	}
+	if prepend {
+		message.SetContent(append([]dto.ClaudeMediaMessage{systemTextBlock}, contents...))
+	} else {
+		message.SetContent(append(contents, systemTextBlock))
+	}
+}
+
+func joinClaudeText(first string, second string) string {
+	first = strings.TrimSpace(first)
+	second = strings.TrimSpace(second)
+	if first == "" {
+		return second
+	}
+	if second == "" {
+		return first
+	}
+	return first + "\n\n" + second
+}