diff --git a/internal/runtime/executor/claude_executor.go b/internal/runtime/executor/claude_executor.go
index 0845d168..75ea04e1 100644
--- a/internal/runtime/executor/claude_executor.go
+++ b/internal/runtime/executor/claude_executor.go
@@ -13,6 +13,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/textproto"
 	"runtime"
 	"strings"
 	"time"
@@ -783,11 +784,21 @@ func applyClaudeHeaders(r *http.Request, auth *cliproxyauth.Auth, apiKey string,
 		}
 	}
 
-	// Merge extra betas from request body
-	if len(extraBetas) > 0 {
+	hasClaude1MHeader := false
+	if ginHeaders != nil {
+		if _, ok := ginHeaders[textproto.CanonicalMIMEHeaderKey("X-CPA-CLAUDE-1M")]; ok {
+			hasClaude1MHeader = true
+		}
+	}
+
+	// Merge extra betas from request body and request flags.
+	if len(extraBetas) > 0 || hasClaude1MHeader {
 		existingSet := make(map[string]bool)
 		for _, b := range strings.Split(baseBetas, ",") {
-			existingSet[strings.TrimSpace(b)] = true
+			betaName := strings.TrimSpace(b)
+			if betaName != "" {
+				existingSet[betaName] = true
+			}
 		}
 		for _, beta := range extraBetas {
 			beta = strings.TrimSpace(beta)
@@ -796,6 +807,9 @@ func applyClaudeHeaders(r *http.Request, auth *cliproxyauth.Auth, apiKey string,
 				existingSet[beta] = true
 			}
 		}
+		if hasClaude1MHeader && !existingSet["context-1m-2025-08-07"] {
+			baseBetas += ",context-1m-2025-08-07"
+		}
 	}
 	r.Header.Set("Anthropic-Beta", baseBetas)