diff --git a/backend/internal/service/billing_service.go b/backend/internal/service/billing_service.go
index 75771f23b9..c4e376fcff 100644
--- a/backend/internal/service/billing_service.go
+++ b/backend/internal/service/billing_service.go
@@ -294,6 +294,24 @@ func (s *BillingService) initFallbackPricing() {
 		CacheReadPricePerTokenPriority: 0.35e-6,
 		SupportsCacheBreakdown:         false,
 	}
+	// DeepSeek V4 Pro
+	// Source: https://api-docs.deepseek.com/quick_start/pricing
+	s.fallbackPrices["deepseek-v4-pro"] = &ModelPricing{
+		InputPricePerToken:     4.35e-7,   // $0.435 per MTok
+		OutputPricePerToken:    8.7e-7,    // $0.87 per MTok
+		CacheReadPricePerToken: 3.625e-9,  // $0.003625 per MTok
+		SupportsCacheBreakdown: false,
+	}
+
+	// DeepSeek V4 Flash
+	// Source: https://api-docs.deepseek.com/quick_start/pricing
+	s.fallbackPrices["deepseek-v4-flash"] = &ModelPricing{
+		InputPricePerToken:     1.4e-7,   // $0.14 per MTok
+		OutputPricePerToken:    2.8e-7,   // $0.28 per MTok
+		CacheReadPricePerToken: 2.8e-9,   // $0.0028 per MTok
+		SupportsCacheBreakdown: false,
+	}
+
 	// Codex 族兜底统一按 GPT-5.3 Codex 价格计费
 	s.fallbackPrices["gpt-5.3-codex"] = &ModelPricing{
 		InputPricePerToken:             1.5e-6, // $1.5 per MTok
@@ -344,6 +362,18 @@ func (s *BillingService) getFallbackPricing(model string) *ModelPricing {
 		return s.fallbackPrices["gemini-3.1-pro"]
 	}
 
+	// DeepSeek V4 系列
+	if strings.Contains(modelLower, "deepseek-v4-flash") {
+		return s.fallbackPrices["deepseek-v4-flash"]
+	}
+	if strings.Contains(modelLower, "deepseek-v4-pro") {
+		return s.fallbackPrices["deepseek-v4-pro"]
+	}
+	// deepseek-chat / deepseek-reasoner → V4 Flash（官方兼容别名）
+	if strings.Contains(modelLower, "deepseek-chat") || strings.Contains(modelLower, "deepseek-reasoner") {
+		return s.fallbackPrices["deepseek-v4-flash"]
+	}
+
 	// OpenAI 仅匹配已知 GPT-5/Codex 族，避免未知 OpenAI 型号误计价。
 	if normalized := normalizeKnownOpenAICodexModel(modelLower); normalized != "" {
 		switch normalized {
diff --git a/backend/internal/service/billing_service_test.go b/backend/internal/service/billing_service_test.go
index 52adc31c85..d75bbfde35 100644
--- a/backend/internal/service/billing_service_test.go
+++ b/backend/internal/service/billing_service_test.go
@@ -352,6 +352,10 @@ func TestGetFallbackPricing_FamilyMatching(t *testing.T) {
 		{name: "openai legacy gpt5.1 codex falls back to gpt5.3 codex", model: "gpt-5.1-codex", expectedInput: 1.5e-6},
 		{name: "openai legacy codex mini latest falls back to gpt5.3 codex", model: "codex-mini-latest", expectedInput: 1.5e-6},
 		{name: "openai unknown no fallback", model: "gpt-unknown-model", expectNilPricing: true},
+		{name: "deepseek v4 pro", model: "deepseek-v4-pro", expectedInput: 4.35e-7},
+		{name: "deepseek v4 flash", model: "deepseek-v4-flash", expectedInput: 1.4e-7},
+		{name: "deepseek chat alias → flash", model: "deepseek-chat", expectedInput: 1.4e-7},
+		{name: "deepseek reasoner alias → flash", model: "deepseek-reasoner", expectedInput: 1.4e-7},
 		{name: "non supported family", model: "qwen-max", expectNilPricing: true},
 	}