diff --git a/packages/cli/src/nodehost.ts b/packages/cli/src/nodehost.ts
index 6e628b22d8..f7edd750ee 100644
--- a/packages/cli/src/nodehost.ts
+++ b/packages/cli/src/nodehost.ts
@@ -196,8 +196,9 @@ export class NodeHost implements RuntimeHost {
         if (typeof value === "string") value = { model: value }
         const aliases = this._modelAliases[source]
         const c = aliases[id] || (aliases[id] = {})
-        c.model = value.model
-        c.temperature = value.temperature
+        if (value.model !== undefined) (c as any).model = value.model
+        if (!isNaN(value.temperature))
+            (c as any).temperature = value.temperature
     }
 
     async readConfig(): Promise<HostConfiguration> {
diff --git a/packages/cli/src/run.ts b/packages/cli/src/run.ts
index 233a0d0843..e1d9095946 100644
--- a/packages/cli/src/run.ts
+++ b/packages/cli/src/run.ts
@@ -212,11 +212,9 @@ export async function runScriptInternal(
     const fenceFormat = options.fenceFormat
 
     if (options.json || options.yaml) overrideStdoutWithStdErr()
-    if (options.model) runtimeHost.modelAliases.large.model = options.model
-    if (options.smallModel)
-        runtimeHost.modelAliases.small.model = options.smallModel
-    if (options.visionModel)
-        runtimeHost.modelAliases.vision.model = options.visionModel
+    if (options.model) runtimeHost.setModelAlias("cli", "large", options.model)
+    if (options.smallModel) runtimeHost.setModelAlias("cli", "small", options.smallModel)
+    if (options.visionModel) runtimeHost.setModelAlias("cli", "vision", options.visionModel)
     for (const kv of options.modelAlias || []) {
         const aliases = parseKeyValuePair(kv)
         for (const [key, value] of Object.entries(aliases))
diff --git a/packages/cli/src/test.ts b/packages/cli/src/test.ts
index 5803c103c7..a91e661e6e 100644
--- a/packages/cli/src/test.ts
+++ b/packages/cli/src/test.ts
@@ -109,11 +109,11 @@ export async function runPromptScriptTests(
         testDelay?: string
     }
 ): Promise<PromptScriptTestRunResponse> {
-    if (options.model) runtimeHost.modelAliases.large.model = options.model
+    if (options.model) runtimeHost.setModelAlias("cli", "large", options.model)
     if (options.smallModel)
-        runtimeHost.modelAliases.small.model = options.smallModel
+        runtimeHost.setModelAlias("cli", "small", options.smallModel)
     if (options.visionModel)
-        runtimeHost.modelAliases.vision.model = options.visionModel
+    runtimeHost.setModelAlias("cli", "vision", options.visionModel)
     Object.entries(runtimeHost.modelAliases).forEach(([key, value]) =>
         logVerbose(` ${key}: ${value.model}`)
     )
diff --git a/packages/cli/src/worker.ts b/packages/cli/src/worker.ts
index edfca60a76..d05960bb2e 100644
--- a/packages/cli/src/worker.ts
+++ b/packages/cli/src/worker.ts
@@ -10,10 +10,11 @@ export async function worker() {
     } & object
     switch (type) {
         case "run": {
-            const { scriptId, files, ...options } = data as {
+            const { scriptId, files, options } = data as {
                 scriptId: string
-                files: string[]
-            } & object
+                files: string[],
+                options: object
+            }
             const { result } = await runScriptInternal(scriptId, files, options)
             parentPort.postMessage(result)
             break
diff --git a/packages/core/src/connection.ts b/packages/core/src/connection.ts
index da07249a82..21d183f79f 100644
--- a/packages/core/src/connection.ts
+++ b/packages/core/src/connection.ts
@@ -76,7 +76,7 @@ export function findEnvVar(
 export async function parseDefaultsFromEnv(env: Record<string, string>) {
     // legacy
     if (env.GENAISCRIPT_DEFAULT_MODEL)
-        runtimeHost.modelAliases.large.model = env.GENAISCRIPT_DEFAULT_MODEL
+        runtimeHost.setModelAlias("env", "large", env.GENAISCRIPT_DEFAULT_MODEL)
 
     const rx =
         /^GENAISCRIPT(_DEFAULT)?_((?<id>[A-Z0-9_\-]+)_MODEL|MODEL_(?<id2>[A-Z0-9_\-]+))$/i
@@ -88,7 +88,7 @@ export async function parseDefaultsFromEnv(env: Record<string, string>) {
         runtimeHost.setModelAlias("env", id, v)
     }
     const t = normalizeFloat(env.GENAISCRIPT_DEFAULT_TEMPERATURE)
-    if (!isNaN(t)) runtimeHost.modelAliases.large.temperature = t
+    if (!isNaN(t)) runtimeHost.setModelAlias("env", "large", { temperature: t })
 }
 
 export async function parseTokenFromEnv(
diff --git a/packages/core/src/host.ts b/packages/core/src/host.ts
index f126842bf5..df6e4d1829 100644
--- a/packages/core/src/host.ts
+++ b/packages/core/src/host.ts
@@ -113,7 +113,7 @@ export interface AzureTokenResolver {
     ): Promise<AuthenticationToken>
 }
 
-export type ModelConfiguration = Pick<ModelOptions, "model" | "temperature">
+export type ModelConfiguration = Readonly<Pick<ModelOptions, "model" | "temperature">>
 
 export type ModelConfigurations = {
     large: ModelConfiguration