langchain - 💡(How to fix) Fix feat(exa): add integration header and instant search type

Submission checklist

• This is a feature request, not a bug report or usage question.
• I added a clear and descriptive title that summarizes the feature request.
• I used the GitHub search to find a similar feature request and didn't find it.
• I checked the LangChain documentation and API reference to see if this feature already exists.
• This is not related to the langchain-community package.

Package (Required)

• langchain
• langchain-openai
• langchain-anthropic
• langchain-classic
• langchain-core
• langchain-model-profiles
• langchain-tests
• langchain-text-splitters
• langchain-chroma

Feature Description

Two small additive changes to the langchain-exa partner package:

1. Integration header — adds x-exa-integration: langchain-integration header to all Exa API requests via client.headers.set(). This is for Exa's internal usage analytics and has no effect on request/response behavior.

2. instant search type — Exa now supports 4 search types: auto, deep, fast, instant. The current Literal only has 3 (auto, deep, fast). Adding instant so users can pass it without type errors.

Use Case

These changes come from the Exa team to keep the LangChain integration aligned with the current Exa API.

• The integration header lets Exa track usage from different integrations for analytics.
• The instant search type is already live in the Exa API and users who try type="instant" currently get a type error from the Literal.

Proposed Solution

PR #37496 is ready with the implementation:

# 1. Integration header (in _utilities.py)
client.headers.set("x-exa-integration", "langchain-integration")

# 2. Add instant to type Literal (in retrievers.py and tools.py)
type: Optional[Literal["auto", "deep", "fast", "instant"]] = None

No function signatures changed, no defaults changed, no breaking changes. Both changes are additive only. CI passes.

Alternatives Considered

No alternatives — these are straightforward additive changes requested by the API provider.

Additional Context

I'm from the Exa team. Happy to answer any questions.