Feature Request: Expose Gemini 3 thinking/reasoning via includeThoughts in providerOptions

[hoverlover]

Summary

When using Gemini 3 models with stream: true, reasoning/thinking output is never available in the onChunk callback or reasoningText field. This is because Stagehand hardcodes providerOptions for Gemini 3 and doesn't include thinkingConfig: { includeThoughts: true }.

Current Behavior

With stream: true and a Gemini 3 model, the onChunk callback only receives tool-related chunks:

• tool-input-start
• tool-input-delta
• tool-call
• tool-result

No text-delta or reasoning-delta chunks are ever emitted. In onStepFinish, reasoning is always an empty array and reasoningText is always undefined.

Expected Behavior

Gemini 3's thinking/reasoning should be accessible via streaming when enabled. According to Google's documentation, this requires setting includeThoughts: true in the thinking config.

Root Cause

In dist/index.js, Stagehand hardcodes providerOptions for Gemini 3 models:

providerOptions: wrappedModel.modelId.includes("gemini-3") ? {
  google: {
    mediaResolution: "MEDIA_RESOLUTION_HIGH"
  }
} : void 0

This appears in two places (for streaming and non-streaming execution). The thinkingConfig with includeThoughts: true is not included.

Proposed Solution

Allow users to pass custom providerOptions through AgentModelConfig, or add thinkingConfig support:

Option A: Extend AgentModelConfig

  const agent = stagehand.agent({
    model: {
      modelName: "google/gemini-3-flash-preview",
      providerOptions: {
        google: {
          thinkingConfig: {
            includeThoughts: true,
            thinkingLevel: "medium"
          }
        }
      }
    },
    stream: true,
    mode: "hybrid",
  });

Option B: Add dedicated thinking config

  const agent = stagehand.agent({
    model: { modelName: "google/gemini-3-flash-preview" },
    stream: true,
    thinking: {
      includeThoughts: true,
      thinkingLevel: "medium"  // or thinkingBudget for Gemini 2.5
    }
  });

Option C: Merge user-provided providerOptions with defaults

Update the hardcoded providerOptions to merge with any user-provided options from AgentModelConfig:

  providerOptions: wrappedModel.modelId.includes("gemini-3") ? {
    google: {
      mediaResolution: "MEDIA_RESOLUTION_HIGH",
      ...userProvidedGoogleOptions,  // from AgentModelConfig
      thinkingConfig: {
        ...userProvidedThinkingConfig
      }
    }
  } : userProvidedProviderOptions

Environment

• Stagehand version: 3.0.7
• Model: google/gemini-3-flash-preview
• Mode: hybrid with stream: true

References

• https://ai.google.dev/gemini-api/docs/thinking

• https://ai-sdk.dev/providers/ai-sdk-providers/google-generative-ai

• Is there a way to set thinking config for vertex/google gemini? vercel/ai#5460

• Yes, I can submit a PR

• Yes, but I need guidance

• No, I cannot contribute at this time

[tkattkat]

this is good idea. we will add.