stagehand
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browserbase
Act with Model Option fails
Stagehand:
- Language/SDK: Typescript
- Stagehand version: 3.0.1
AI Provider:
- Provider:Google
- Model: Any model
Issue Description
See code below. To reproduce as well as results
/**
* Bug: stagehand.act() fails when passing model override parameter
*
* Expected: act() should work with model override, like observe() does
* Actual: act() throws "An unexpected error occurred"
*/
const { Stagehand } = require("@browserbasehq/stagehand");
async function reproduceActBug() {
const stagehand = new Stagehand({
env: "BROWSERBASE",
apiKey: process.env.BROWSERBASE_API_KEY,
projectId: process.env.BROWSERBASE_PROJECT_ID,
model: {
modelName: "google/gemini-2.5-pro",
apiKey: process.env.GOOGLE_API_KEY,
},
});
await stagehand.init();
const page = stagehand.context.pages()[0];
await page.goto("https://example.com");
// ✅ This works - observe() with model override
console.log("Testing observe() with model override...");
const observations = await stagehand.observe("Find the first link", {
model: { modelName: "google/gemini-2.5-pro" },
});
console.log("✅ observe() SUCCESS -", observations.length, "elements found");
// ❌ This fails - act() with model override
console.log("\nTesting act() with model override...");
try {
await stagehand.act(observations[0], {
model: { modelName: "google/gemini-2.5-pro" },
});
console.log("✅ act() SUCCESS");
} catch (error) {
console.log("❌ act() FAILED:", error.message);
}
await stagehand.close();
}
reproduceActBug().catch(console.error);
Results
[[email protected]] injecting env (3) from .env -- tip: 👥 sync secrets across teammates & machines: https://dotenvx.com/ops
[[email protected]] injecting env (0) from .env -- tip: 🛠️ run anywhere with `dotenvx run -- yourcommand`
[2025-11-13 12:29:50.853 -0800] INFO: Using Browserbase credentials
category: "init"
[2025-11-13 12:29:50.854 -0800] INFO: Starting browserbase session
category: "init"
[2025-11-13 12:29:50.854 -0800] INFO: Creating new browserbase session...
category: "init"
[2025-11-13 12:29:52.961 -0800] INFO: Browserbase session started [REDUCTED]
[2025-11-13 12:29:53.327 -0800] INFO: Connecting to local browser
category: "init"
Testing observe() with model override...
[2025-11-13 12:29:54.301 -0800] INFO: starting observation
category: "observation"
instruction: "Find the first link"
[2025-11-13 12:29:54.317 -0800] INFO: Got accessibility tree data
category: "observation"
[2025-11-13 12:29:54.317 -0800] DEBUG: creating chat completion
category: "aisdk"
options: {
"messages": [
{
"role": "system",
"content": " You are helping the user automate the browser by finding elements based on what the user wants to observe in the page. You will be given: 1. a instruction of elements to observe 2. a hierarchical accessibility tree showing the semantic structure of the page. The tree is a hybrid of the DOM and the accessibility tree. Return an array of elements that match the instruction if they exist, otherwise return an empty array."
},
{
"role": "user",
"content": "instruction: Find the first link\nAccessibility Tree: \n[2-2] RootWebArea: Example Domain\n [2-3] scrollable, html\n [2-16] div\n [2-17] heading: Example Domain\n [2-19] paragraph\n [2-20] StaticText: This domain is for use in documentation examples without needing permission. Avoid use in operations.\n [2-21] paragraph\n [2-22] link: Learn more\n"
}
],
"response_model": {
"schema": {
"_def": {
"unknownKeys": "strip",
"catchall": {
"_def": {
"typeName": "ZodNever"
},
"~standard": {
"version": 1,
"vendor": "zod"
}
},
"typeName": "ZodObject"
},
"~standard": {
"version": 1,
"vendor": "zod"
},
"_cached": null
},
"name": "Observation"
},
"temperature": 0.1,
"top_p": 1,
"frequency_penalty": 0,
"presence_penalty": 0
}
modelName: "gemini-2.5-pro"
✅ observe() SUCCESS - 1 elements found
Testing act() with model override...
[2025-11-13 12:29:58.175 -0800] INFO: response
category: "aisdk"
response: {
"object": {
"elements": [
{
"elementId": "2-22",
"description": "A link with the text 'Learn more'.",
"method": "click",
"arguments": []
}
]
},
"usage": {
"inputTokens": 199,
"outputTokens": 60,
"totalTokens": 401,
"reasoningTokens": 142
},
"finishReason": "stop"
}
[2025-11-13 12:29:58.175 -0800] INFO: found elements
category: "observation"
elements: [
{
"description": "A link with the text 'Learn more'.",
"method": "click",
"arguments": [],
"selector": "xpath=/html[1]/body[1]/div[1]/p[2]/a[1]"
}
]
❌ act() FAILED: An unexpected error occurred
[2025-11-13 12:29:58.961 -0800] ERROR: No known environment variable for provider 'gpt-4o'
category: "init"
Act with an Action parameter doesn't take in model options, for self-healing it reuses the model configuration passed on the stagehand constructor (docs link)
@miguelg719 @JerryWu1234 That's unrelated. See below example that uses Act with an instruction
/**
* Bug: stagehand.act() fails when passing model override parameter
*
* Expected: act() should work with model override, like observe() does
* Actual: act() throws "An unexpected error occurred"
*/
const { Stagehand } = require("@browserbasehq/stagehand");
async function reproduceActBug() {
const stagehand = new Stagehand({
env: "BROWSERBASE",
apiKey: process.env.BROWSERBASE_API_KEY,
projectId: process.env.BROWSERBASE_PROJECT_ID,
verbose: 1,
model: {
modelName: "google/gemini-2.5-pro",
apiKey: process.env.GOOGLE_API_KEY,
},
});
await stagehand.init();
const page = stagehand.context.pages()[0];
await page.goto("https://example.com");
// ✅ This works - observe() with model override
console.log("Testing observe() with model override...");
const observations = await stagehand.observe("Find the first link", {
model: { modelName: "google/gemini-2.5-pro" },
});
console.log("✅ observe() SUCCESS -", observations.length, "elements found");
// ❌ This fails - act() with model override
console.log("\nTesting act() with model override...");
try {
await stagehand.act("Click on the first link", {
model: { modelName: "anthropic/claude-sonnet-4-5" },
});
console.log("✅ act() SUCCESS");
} catch (error) {
console.log("❌ act() FAILED:", error.message);
}
await stagehand.close();
}
reproduceActBug().catch(console.error);