diff --git a/backend/internal/pkg/claude/constants.go b/backend/internal/pkg/claude/constants.go
index 22405382..697663a6 100644
--- a/backend/internal/pkg/claude/constants.go
+++ b/backend/internal/pkg/claude/constants.go
@@ -16,7 +16,7 @@ const (
 
 // DroppedBetas 是转发时需要从 anthropic-beta header 中移除的 beta token 列表。
 // 这些 token 是客户端特有的，不应透传给上游 API。
-var DroppedBetas = []string{BetaContext1M, BetaFastMode}
+var DroppedBetas = []string{BetaFastMode}
 
 // DefaultBetaHeader Claude Code 客户端默认的 anthropic-beta header
 const DefaultBetaHeader = BetaClaudeCode + "," + BetaOAuth + "," + BetaInterleavedThinking + "," + BetaFineGrainedToolStreaming
diff --git a/backend/internal/service/gateway_beta_test.go b/backend/internal/service/gateway_beta_test.go
index 21a1faa4..0a66a53d 100644
--- a/backend/internal/service/gateway_beta_test.go
+++ b/backend/internal/service/gateway_beta_test.go
@@ -86,10 +86,10 @@ func TestStripBetaTokens(t *testing.T) {
 			want:   "oauth-2025-04-20,interleaved-thinking-2025-05-14",
 		},
 		{
-			name:   "DroppedBetas removes both context-1m and fast-mode",
+			name:   "DroppedBetas removes fast-mode only",
 			header: "oauth-2025-04-20,context-1m-2025-08-07,fast-mode-2026-02-01,interleaved-thinking-2025-05-14",
 			tokens: claude.DroppedBetas,
-			want:   "oauth-2025-04-20,interleaved-thinking-2025-05-14",
+			want:   "oauth-2025-04-20,context-1m-2025-08-07,interleaved-thinking-2025-05-14",
 		},
 	}
 
@@ -117,21 +117,21 @@ func TestMergeAnthropicBetaDropping_DroppedBetas(t *testing.T) {
 	drop := droppedBetaSet()
 
 	got := mergeAnthropicBetaDropping(required, incoming, drop)
-	require.Equal(t, "oauth-2025-04-20,interleaved-thinking-2025-05-14,foo-beta", got)
-	require.NotContains(t, got, "context-1m-2025-08-07")
+	require.Equal(t, "oauth-2025-04-20,interleaved-thinking-2025-05-14,context-1m-2025-08-07,foo-beta", got)
+	require.Contains(t, got, "context-1m-2025-08-07")
 	require.NotContains(t, got, "fast-mode-2026-02-01")
 }
 
 func TestDroppedBetaSet(t *testing.T) {
 	// Base set contains DroppedBetas
 	base := droppedBetaSet()
-	require.Contains(t, base, claude.BetaContext1M)
+	require.NotContains(t, base, claude.BetaContext1M)
 	require.Contains(t, base, claude.BetaFastMode)
 	require.Len(t, base, len(claude.DroppedBetas))
 
 	// With extra tokens
 	extended := droppedBetaSet(claude.BetaClaudeCode)
-	require.Contains(t, extended, claude.BetaContext1M)
+	require.NotContains(t, extended, claude.BetaContext1M)
 	require.Contains(t, extended, claude.BetaFastMode)
 	require.Contains(t, extended, claude.BetaClaudeCode)
 	require.Len(t, extended, len(claude.DroppedBetas)+1)