feat: auto-detect aiohttp transport for async client

[fern-support]

Summary

• When httpx_aiohttp is installed, the async client automatically uses it as the transport layer, providing native async DNS resolution via aiodns (c-ares) instead of httpx's blocking threadpool-based getaddrinfo. This prevents ConnectError failures under high async concurrency.
• Users opt in with pip install cohere[aiohttp] — no code changes required. Users who want plain httpx can pass httpx_client=DefaultAsyncHttpxClient().
• Adds DefaultAioHttpClient and DefaultAsyncHttpxClient convenience classes exported from the top-level cohere package.

Changes

File	Change
pyproject.toml	Added aiohttp and httpx_aiohttp as optional deps + [aiohttp] extra
src/cohere/_default_clients.py	New — DefaultAioHttpClient, DefaultAsyncHttpxClient, COHERE_DEFAULT_TIMEOUT
src/cohere/base_client.py	Added _make_default_async_client(), updated AsyncBaseCohere.__init__
src/cohere/__init__.py	Exported new convenience classes
tests/test_aiohttp_autodetect.py	New — unit tests for auto-detect logic and convenience classes

Test plan

• pip install -e . — verify httpx_aiohttp is NOT installed, async client uses plain httpx.AsyncClient
• pip install -e ".[aiohttp]" — verify async client auto-uses HttpxAiohttpClient
• Pass explicit httpx_client=DefaultAsyncHttpxClient() with aiohttp installed — verify plain httpx is used
• Pass httpx_client=DefaultAioHttpClient() without aiohttp installed — verify clear RuntimeError
• Run pytest tests/test_aiohttp_autodetect.py

🤖 Generated with Claude Code

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Note

Medium Risk
Changes the default async HTTP transport selection when httpx_aiohttp is installed, which can subtly affect request behavior and dependency resolution. Most logic is isolated and covered by new unit tests, but it impacts all async client users who install the new extra.

Overview
Async client transport auto-detection: the SDK now prefers httpx_aiohttp.HttpxAiohttpClient for AsyncBaseCohere when httpx_aiohttp is available, falling back to plain httpx.AsyncClient otherwise (via new _make_default_async_client).

New opt-in extra + convenience clients: adds optional deps aiohttp/httpx_aiohttp behind a new cohere[aiohttp] extra, and introduces DefaultAioHttpClient (errors with install hint when extra missing) plus DefaultAsyncHttpxClient (applies default timeout/redirect settings), both exported from cohere.

Updates poetry.lock to reflect the new optional dependency group and refreshed lock metadata, and adds tests validating the autodetect and default-client behaviors.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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New entries break alphabetical ordering in lookup dict

Low Severity

"DefaultAioHttpClient" and "DefaultAsyncHttpxClient" are inserted between "DatasetPart" and "DatasetType" in the _dynamic_imports dict, splitting the "Dataset*" group and breaking the alphabetical sort convention maintained throughout the file. Alphabetically, "Default" sorts after "Debug" (since 'b' < 'f'), so these entries belong after "DebugV2ChatStreamResponse". The same misordering occurs in __all__, where the entries are placed before the "Debug*" entries instead of after them.

Additional Locations (1)

• src/cohere/__init__.py#L784-L786