diff --git a/src/headless.ts b/src/headless.ts
index 018e4b0..fed441c 100644
--- a/src/headless.ts
+++ b/src/headless.ts
@@ -259,17 +259,25 @@ export async function handleHeadlessCommand(
   // If resuming and a model or system prompt was specified, apply those changes
   if (isResumingAgent && (model || specifiedSystem)) {
     if (model) {
-      const { updateAgentLLMConfig } = await import("./agent/modify");
       const { resolveModel } = await import("./agent/model");
       const modelHandle = resolveModel(model);
       if (!modelHandle) {
         console.error(`Error: Invalid model "${model}"`);
         process.exit(1);
       }
-      const updateArgs = getModelUpdateArgs(model);
-      await updateAgentLLMConfig(agent.id, modelHandle, updateArgs);
-      // Refresh agent state after model update
-      agent = await client.agents.retrieve(agent.id);
+
+      // Optimization: Skip update if agent is already using the specified model
+      const currentModel = agent.llm_config?.model;
+      const currentEndpointType = agent.llm_config?.model_endpoint_type;
+      const currentHandle = `${currentEndpointType}/${currentModel}`;
+
+      if (currentHandle !== modelHandle) {
+        const { updateAgentLLMConfig } = await import("./agent/modify");
+        const updateArgs = getModelUpdateArgs(model);
+        await updateAgentLLMConfig(agent.id, modelHandle, updateArgs);
+        // Refresh agent state after model update
+        agent = await client.agents.retrieve(agent.id);
+      }
     }
 
     if (specifiedSystem) {
diff --git a/src/index.ts b/src/index.ts
index 6ee5b2d..609e68f 100755
--- a/src/index.ts
+++ b/src/index.ts
@@ -200,6 +200,13 @@ async function main() {
   const fromAfFile = values["from-af"] as string | undefined;
   const isHeadless = values.prompt || values.run || !process.stdin.isTTY;
 
+  // Fail if an unknown command/argument is passed (and we're not in headless mode where it might be a prompt)
+  if (command && !isHeadless) {
+    console.error(`Error: Unknown command or argument "${command}"`);
+    console.error("Run 'letta --help' for usage information.");
+    process.exit(1);
+  }
+
   // --init-blocks only makes sense when creating a brand new agent
   if (initBlocksRaw && !forceNew) {
     console.error(
@@ -785,19 +792,26 @@ async function main() {
         // If resuming and a model or system prompt was specified, apply those changes
         if (resuming && (model || system)) {
           if (model) {
-            const { updateAgentLLMConfig } = await import("./agent/modify");
-            const { getModelUpdateArgs, resolveModel } = await import(
-              "./agent/model"
-            );
+            const { resolveModel } = await import("./agent/model");
             const modelHandle = resolveModel(model);
             if (!modelHandle) {
               console.error(`Error: Invalid model "${model}"`);
               process.exit(1);
             }
-            const updateArgs = getModelUpdateArgs(model);
-            await updateAgentLLMConfig(agent.id, modelHandle, updateArgs);
-            // Refresh agent state after model update
-            agent = await client.agents.retrieve(agent.id);
+
+            // Optimization: Skip update if agent is already using the specified model
+            const currentModel = agent.llm_config?.model;
+            const currentEndpointType = agent.llm_config?.model_endpoint_type;
+            const currentHandle = `${currentEndpointType}/${currentModel}`;
+
+            if (currentHandle !== modelHandle) {
+              const { updateAgentLLMConfig } = await import("./agent/modify");
+              const { getModelUpdateArgs } = await import("./agent/model");
+              const updateArgs = getModelUpdateArgs(model);
+              await updateAgentLLMConfig(agent.id, modelHandle, updateArgs);
+              // Refresh agent state after model update
+              agent = await client.agents.retrieve(agent.id);
+            }
           }
 
           if (system) {