diff --git a/src/resources/extensions/sf/preferences-models.ts b/src/resources/extensions/sf/preferences-models.ts
index 2cb031a1c..57a9faadd 100644
--- a/src/resources/extensions/sf/preferences-models.ts
+++ b/src/resources/extensions/sf/preferences-models.ts
@@ -429,7 +429,17 @@ export function resolveModelWithFallbacksForUnit(
 
 	// Normalize: string -> { model, fallbacks: [] }
 	if (typeof phaseConfig === "string") {
-		return { primary: phaseConfig, fallbacks: [] };
+		const auto = autoBenchmark
+			? resolveAutoBenchmarkPickForUnit(unitType, prefs?.preferences)
+			: undefined;
+		const autoFallbacks = (auto?.fallbacks ?? []).filter(
+			(id) => id !== phaseConfig,
+		);
+		// Don't double-include the user's primary if benchmarks picked it as #1.
+		if (auto && auto.primary !== phaseConfig) {
+			autoFallbacks.unshift(auto.primary);
+		}
+		return { primary: phaseConfig, fallbacks: autoFallbacks };
 	}
 
 	// When provider is explicitly set, prepend it to the model ID so the
@@ -439,10 +449,24 @@ export function resolveModelWithFallbacksForUnit(
 			? `${phaseConfig.provider}/${phaseConfig.model}`
 			: phaseConfig.model;
 
-	return {
-		primary,
-		fallbacks: phaseConfig.fallbacks ?? [],
-	};
+	const userFallbacks = phaseConfig.fallbacks ?? [];
+	if (userFallbacks.length > 0) {
+		// Explicit fallbacks: respect them as-is, no auto-fill.
+		return { primary, fallbacks: userFallbacks };
+	}
+
+	// Auto-fill empty/missing fallbacks from the benchmark picker so a user
+	// who only pinned a primary still gets rate-limit auto-switch behavior
+	// out of the box. The auto-pick may include the user's primary as its #1
+	// — drop it to avoid `primary == fallbacks[0]` no-op switches.
+	const auto = autoBenchmark
+		? resolveAutoBenchmarkPickForUnit(unitType, prefs?.preferences)
+		: undefined;
+	const autoFallbacks = (auto?.fallbacks ?? []).filter((id) => id !== primary);
+	if (auto && auto.primary !== primary) {
+		autoFallbacks.unshift(auto.primary);
+	}
+	return { primary, fallbacks: autoFallbacks };
 }
 
 /**