diff --git a/src/agents/types.ts b/src/agents/types.ts
index 92834883..4ee1b3a6 100644
--- a/src/agents/types.ts
+++ b/src/agents/types.ts
@@ -100,6 +100,7 @@ export type AgentName = BuiltinAgentName
 export type AgentOverrideConfig = Partial<AgentConfig> & {
   prompt_append?: string
   variant?: string
+  fallback_models?: string | string[]
 }
 
 export type AgentOverrides = Partial<Record<OverridableAgentName, AgentOverrideConfig>>
diff --git a/src/shared/index.ts b/src/shared/index.ts
index 263d50ba..09187602 100644
--- a/src/shared/index.ts
+++ b/src/shared/index.ts
@@ -34,6 +34,7 @@ export * from "./system-directive"
 export * from "./agent-tool-restrictions"
 export * from "./model-requirements"
 export * from "./model-resolver"
+export { normalizeFallbackModels } from "./model-resolver"
 export { resolveModelPipeline } from "./model-resolution-pipeline"
 export type {
   ModelResolutionRequest,
diff --git a/src/shared/model-resolver.ts b/src/shared/model-resolver.ts
index 84cbcbe2..a9e450fb 100644
--- a/src/shared/model-resolver.ts
+++ b/src/shared/model-resolver.ts
@@ -7,6 +7,17 @@ export type ModelResolutionInput = {
 	systemDefault?: string
 }
 
+/**
+ * Normalizes fallback_models to an array.
+ * Handles single string or array input, returns undefined for falsy values.
+ */
+export function normalizeFallbackModels(
+	fallbackModels: string | string[] | undefined | null
+): string[] | undefined {
+	if (!fallbackModels) return undefined
+	return Array.isArray(fallbackModels) ? fallbackModels : [fallbackModels]
+}
+
 export type ModelSource =
 	| "override"
 	| "category-default"