Support latest Vercel AI SDK (LanguageModelV3) in AISdkClient / Stagehand

[PerryFinn]

Is your feature request related to a problem? Please describe.

Yeah,Stagehand’s AISdkClient currently expects an AI SDK model that matches LanguageModelV2, but the latest Vercel AI SDK provider packages (AI SDK v6+) return LanguageModelV3. This causes a TypeScript incompatibility and prevents using Stagehand with up-to-date AI SDK dependencies.
I ran into this while building a demo with these dependencies:

{
  "dependencies": {
    "@ai-sdk/openai": "^3.0.23",
    "@browserbasehq/stagehand": "latest",
    "dotenv": "^16.4.7",
    "zod": "^4.3.6"
  }
}

Minimal repro:

import "dotenv/config";
import { Stagehand, AISdkClient } from "@browserbasehq/stagehand";
import { createOpenAI } from "@ai-sdk/openai";

const openaiProvider = createOpenAI({
  apiKey: "sk-xxxx-xxxx",
});

const llmClient = new AISdkClient({
  model: openaiProvider("gpt-4.1-mini"),
});

async function main() {
  const stagehand = new Stagehand({
    env: "LOCAL",
    verbose: 2,
    logInferenceToFile: true,
    llmClient,
  });

  // ...
}

TypeScript error:

Type 'LanguageModelV3' is not assignable to type 'LanguageModelV2'.
  Types of property 'specificationVersion' are incompatible.
    Type '"v3"' is not assignable to type '"v2"'. ts(2322)
index.d.ts(...): The expected type comes from property 'model' which is declared here on type '{ model: LanguageModelV2; }'

This aligns with the ecosystem shift where AI SDK v6 providers now return LanguageModelV3:
• openai/openai-agents-js#868
• https://ai-sdk.dev/providers/community-providers/custom-providers (Language Model Specification V3)

Describe the solution you'd like

Update Stagehand’s AISdkClient (and any related typings/adapter code paths) to support the latest Vercel AI SDK model interface:
• Accept LanguageModelV3 as the model type (or support both LanguageModelV2 | LanguageModelV3).
• Ideally keep backward compatibility for users still on AI SDK v5/V2.

Concretely, something like:
• AISdkClient constructor: { model: LanguageModelV3 } (or union)
• Any internal calls/adapters updated for V3’s interfaces/options.
• If maintaining both is hard, provide a new client (e.g. AISdkClientV3) or a small compatibility shim.

Describe alternatives you've considered

1. Pin/downgrade AI SDK dependencies to an older major version that still returns LanguageModelV2 (not ideal; blocks using the current AI SDK).
2. Avoid AISdkClient and use Stagehand’s built-in model configuration instead — but this loses the benefits of using the AI SDK provider setup I already use across my codebase.

Are you willing to contribute to implementing this feature or fix?

• Yes, I can submit a PR
• Yes, but I need guidance
• No, I cannot contribute at this time