feat: add --model flag (#32)

README.md

@@ -83,9 +83,13 @@ Join our [Discord](https://discord.gg/letta) to share feedback on persistence pa
 letta                    # Auto-resume project agent (or create new if first time)
 letta --new              # Force create new agent
 letta --agent <id>       # Use specific agent ID
+letta --model <model>    # Specify model (e.g., claude-sonnet-4.5, gpt-4o)
+letta -m <model>         # Short form of --model
 letta --continue         # Resume global last agent (deprecated, use project-based)
 ```
 
+> **Note:** The `--model` flag is inconsistent when resuming sessions. We recommend using the `/model` command instead to change models in interactive mode.
+
 ### Headless Mode
 ```bash
 letta -p "Run bun lint and correct errors"              # Auto-resumes project agent
@@ -93,6 +97,7 @@ letta -p "Pick up where you left off"                   # Same - auto-resumes by
 letta -p "Start fresh" --new                            # Force new agent
 letta -p "Run all the test" --allowedTools "Bash"       # Control tool permissions
 letta -p "Just read the code" --disallowedTools "Bash"  # Control tool permissions
+letta -p "Explain this code" -m gpt-4o                  # Use specific model
 
 # Pipe input from stdin
 echo "Explain this code" | letta -p

src/agent/create.ts

@@ -7,6 +7,7 @@ import type {
   Block,
   CreateBlock,
 } from "@letta-ai/letta-client/resources/agents/agents";
+import { formatAvailableModels, resolveModel } from "../model";
 import {
   loadProjectSettings,
   updateProjectSettings,
@@ -19,9 +20,25 @@ import { SYSTEM_PROMPT } from "./promptAssets";
 
 export async function createAgent(
   name = "letta-cli-agent",
-  model = "anthropic/claude-sonnet-4-5-20250929",
+  model?: string,
   embeddingModel = "openai/text-embedding-3-small",
 ) {
+  // Resolve model identifier to handle
+  let modelHandle: string;
+  if (model) {
+    const resolved = resolveModel(model);
+    if (!resolved) {
+      console.error(`Error: Unknown model "${model}"`);
+      console.error("Available models:");
+      console.error(formatAvailableModels());
+      process.exit(1);
+    }
+    modelHandle = resolved;
+  } else {
+    // Use default model
+    modelHandle = "anthropic/claude-sonnet-4-5-20250929";
+  }
+
   const client = await getClient();
 
   // Get loaded tool names (tools are already registered with Letta)
@@ -141,7 +158,7 @@ export async function createAgent(
     system: SYSTEM_PROMPT,
     name,
     embedding: embeddingModel,
-    model,
+    model: modelHandle,
     context_window_limit: 200_000,
     tools: toolNames,
     block_ids: blockIds,

src/cli/App.tsx

@@ -989,8 +989,7 @@ export default function App({
 
       try {
         // Find the selected model from models.json first (for loading message)
-        const modelsModule = await import("../models.json");
-        const models = modelsModule.default;
+        const { models } = await import("../model");
         const selectedModel = models.find((m) => m.id === modelId);
 
         if (!selectedModel) {

src/cli/components/ModelSelector.tsx

@@ -1,7 +1,7 @@
 // Import useInput from vendored Ink for bracketed paste support
 import { Box, Text, useInput } from "ink";
 import { useState } from "react";
-import models from "../../models.json";
+import { models } from "../../model";
 import { colors } from "./colors";
 
 interface ModelSelectorProps {

src/headless.ts

@@ -15,7 +15,7 @@ import { drainStream } from "./cli/helpers/stream";
 import { loadSettings, updateSettings } from "./settings";
 import { checkToolPermission, executeTool } from "./tools/manager";
 
-export async function handleHeadlessCommand(argv: string[]) {
+export async function handleHeadlessCommand(argv: string[], model?: string) {
   const settings = await loadSettings();
 
   // Parse CLI args
@@ -70,7 +70,7 @@ export async function handleHeadlessCommand(argv: string[]) {
 
   // Priority 2: Check if --new flag was passed (skip all resume logic)
   if (!agent && forceNew) {
-    agent = await createAgent();
+    agent = await createAgent(undefined, model);
   }
 
   // Priority 3: Try to resume from project settings (.letta/settings.local.json)
@@ -101,7 +101,7 @@ export async function handleHeadlessCommand(argv: string[]) {
 
   // Priority 5: Create a new agent
   if (!agent) {
-    agent = await createAgent();
+    agent = await createAgent(undefined, model);
   }
 
   // Save agent ID to both project and global settings

src/index.ts

@@ -28,6 +28,7 @@ OPTIONS
   --new                 Force create new agent (skip auto-resume)
   -c, --continue        Resume previous session (uses global lastAgent, deprecated)
   -a, --agent <id>      Use a specific agent ID
+  -m, --model <id>      Model ID or handle (e.g., "opus" or "anthropic/claude-opus-4-1-20250805")
   -p, --prompt          Headless prompt mode
   --output-format <fmt> Output format for headless mode (text, json, stream-json)
                         Default: text
@@ -65,6 +66,7 @@ async function main() {
         continue: { type: "boolean", short: "c" },
         new: { type: "boolean" },
         agent: { type: "string", short: "a" },
+        model: { type: "string", short: "m" },
         prompt: { type: "boolean", short: "p" },
         run: { type: "boolean" },
         tools: { type: "string" },
@@ -109,6 +111,7 @@ async function main() {
   const shouldContinue = (values.continue as boolean | undefined) ?? false;
   const forceNew = (values.new as boolean | undefined) ?? false;
   const specifiedAgentId = (values.agent as string | undefined) ?? null;
+  const specifiedModel = (values.model as string | undefined) ?? undefined;
   const isHeadless = values.prompt || values.run || !process.stdin.isTTY;
 
   // Validate API key early before any UI rendering
@@ -174,7 +177,7 @@ async function main() {
     await upsertToolsToServer(client);
 
     const { handleHeadlessCommand } = await import("./headless");
-    await handleHeadlessCommand(process.argv);
+    await handleHeadlessCommand(process.argv, specifiedModel);
     return;
   }
 
@@ -189,10 +192,12 @@ async function main() {
     continueSession,
     forceNew,
     agentIdArg,
+    model,
   }: {
     continueSession: boolean;
     forceNew: boolean;
     agentIdArg: string | null;
+    model?: string;
   }) {
     const [loadingState, setLoadingState] = useState<
       "assembling" | "upserting" | "initializing" | "checking" | "ready"
@@ -233,7 +238,7 @@ async function main() {
         // Priority 2: Check if --new flag was passed (skip all resume logic)
         if (!agent && forceNew) {
           // Create new agent, don't check any lastAgent fields
-          agent = await createAgent();
+          agent = await createAgent(undefined, model);
         }
 
         // Priority 3: Try to resume from project settings (.letta/settings.local.json)
@@ -265,7 +270,7 @@ async function main() {
 
         // Priority 5: Create a new agent
         if (!agent) {
-          agent = await createAgent();
+          agent = await createAgent(undefined, model);
         }
 
         // Save agent ID to both project and global settings
@@ -294,7 +299,7 @@ async function main() {
       }
 
       init();
-    }, [continueSession, forceNew, agentIdArg]);
+    }, [continueSession, forceNew, agentIdArg, model]);
 
     if (!agentId) {
       return React.createElement(App, {
@@ -323,6 +328,7 @@ async function main() {
       continueSession: shouldContinue,
       forceNew: forceNew,
       agentIdArg: specifiedAgentId,
+      model: specifiedModel,
     }),
     {
       exitOnCtrlC: false, // We handle CTRL-C manually with double-press guard

src/model.ts

@@ -0,0 +1,36 @@
+/**
+ * Model resolution and handling utilities
+ */
+import modelsData from "./models.json";
+
+export const models = modelsData;
+
+/**
+ * Resolve a model by ID or handle
+ * @param modelIdentifier - Can be either a model ID (e.g., "opus") or a full handle (e.g., "anthropic/claude-opus-4-1-20250805")
+ * @returns The model handle if found, null otherwise
+ */
+export function resolveModel(modelIdentifier: string): string | null {
+  const byId = models.find((m) => m.id === modelIdentifier);
+  if (byId) return byId.handle;
+
+  const byHandle = models.find((m) => m.handle === modelIdentifier);
+  if (byHandle) return byHandle.handle;
+
+  return null;
+}
+
+/**
+ * Get the default model handle
+ */
+export function getDefaultModel(): string {
+  const defaultModel = models.find((m) => m.isDefault);
+  return defaultModel?.handle || models[0].handle;
+}
+
+/**
+ * Format available models for error messages
+ */
+export function formatAvailableModels(): string {
+  return models.map((m) => `  ${m.id.padEnd(20)} ${m.handle}`).join("\n");
+}

src/tests/tools/bash.test.ts

@@ -80,7 +80,7 @@ describe("Bash tool", () => {
   });
 
   test("throws error when command is missing", async () => {
-    await expect(bash({} as any)).rejects.toThrow(
+    await expect(bash({} as Parameters<typeof bash>[0])).rejects.toThrow(
       /missing required parameter.*command/,
     );
   });

src/tests/tools/edit.test.ts

@@ -71,7 +71,7 @@ describe("Edit tool", () => {
       edit({
         old_string: "foo",
         new_string: "bar",
-      } as any),
+      } as Parameters<typeof edit>[0]),
     ).rejects.toThrow(/missing required parameter.*file_path/);
   });
 
@@ -83,7 +83,7 @@ describe("Edit tool", () => {
       edit({
         file_path: file,
         new_string: "bar",
-      } as any),
+      } as Parameters<typeof edit>[0]),
     ).rejects.toThrow(/missing required parameter.*old_string/);
   });
 
@@ -95,7 +95,7 @@ describe("Edit tool", () => {
       edit({
         file_path: file,
         old_string: "foo",
-      } as any),
+      } as Parameters<typeof edit>[0]),
     ).rejects.toThrow(/missing required parameter.*new_string/);
   });
 
@@ -108,7 +108,7 @@ describe("Edit tool", () => {
         file_path: file,
         old_string: "World",
         new_str: "Bun",
-      } as any),
+      } as Parameters<typeof edit>[0]),
     ).rejects.toThrow(/missing required parameter.*new_string/);
   });
 });

src/tests/tools/grep.test.ts

@@ -58,7 +58,7 @@ describe("Grep tool", () => {
   });
 
   test("throws error when pattern is missing", async () => {
-    await expect(grep({} as any)).rejects.toThrow(
+    await expect(grep({} as Parameters<typeof grep>[0])).rejects.toThrow(
       /missing required parameter.*pattern/,
     );
   });

src/tests/tools/ls.test.ts

@@ -47,7 +47,7 @@ describe("LS tool", () => {
   });
 
   test("throws error when path is missing", async () => {
-    await expect(ls({} as any)).rejects.toThrow(
+    await expect(ls({} as Parameters<typeof ls>[0])).rejects.toThrow(
       /missing required parameter.*path/,
     );
   });

src/tests/tools/multiedit.test.ts

@@ -45,7 +45,7 @@ describe("MultiEdit tool", () => {
     await expect(
       multi_edit({
         edits: [{ old_string: "foo", new_string: "bar" }],
-      } as any),
+      } as Parameters<typeof multi_edit>[0]),
     ).rejects.toThrow(/missing required parameter.*file_path/);
   });
 
@@ -56,7 +56,7 @@ describe("MultiEdit tool", () => {
     await expect(
       multi_edit({
         file_path: file,
-      } as any),
+      } as Parameters<typeof multi_edit>[0]),
     ).rejects.toThrow(/missing required parameter.*edits/);
   });
 
@@ -67,7 +67,9 @@ describe("MultiEdit tool", () => {
     await expect(
       multi_edit({
         file_path: file,
-        edits: [{ new_string: "bar" } as any],
+        edits: [
+          { new_string: "bar" } as Parameters<typeof multi_edit>[0]["edits"][0],
+        ],
       }),
     ).rejects.toThrow(/missing required parameter.*old_string/);
   });
@@ -79,7 +81,9 @@ describe("MultiEdit tool", () => {
     await expect(
       multi_edit({
         file_path: file,
-        edits: [{ old_string: "foo" } as any],
+        edits: [
+          { old_string: "foo" } as Parameters<typeof multi_edit>[0]["edits"][0],
+        ],
       }),
     ).rejects.toThrow(/missing required parameter.*new_string/);
   });
@@ -91,7 +95,11 @@ describe("MultiEdit tool", () => {
     await expect(
       multi_edit({
         file_path: file,
-        edits: [{ old_string: "foo", new_str: "baz" } as any],
+        edits: [
+          { old_string: "foo", new_str: "baz" } as Parameters<
+            typeof multi_edit
+          >[0]["edits"][0],
+        ],
       }),
     ).rejects.toThrow(/missing required parameter.*new_string/);
   });

src/tests/tools/read.test.ts

@@ -104,7 +104,7 @@ export default box;
   });
 
   test("throws error when file_path is missing", async () => {
-    await expect(read({} as any)).rejects.toThrow(
+    await expect(read({} as Parameters<typeof read>[0])).rejects.toThrow(
       /missing required parameter.*file_path/,
     );
   });

src/tests/tools/write.test.ts

@@ -53,7 +53,7 @@ describe("Write tool", () => {
     await expect(
       write({
         content: "Hello",
-      } as any),
+      } as Parameters<typeof write>[0]),
     ).rejects.toThrow(/missing required parameter.*file_path/);
   });
 
@@ -64,7 +64,7 @@ describe("Write tool", () => {
     await expect(
       write({
         file_path: filePath,
-      } as any),
+      } as Parameters<typeof write>[0]),
     ).rejects.toThrow(/missing required parameter.*content/);
   });
 });