# AN-2026-0809: Anthropic Python SDK >= 1.4.0 (Sep 4, 2026) rejects httpx objects: "`httpx.Client` is from the `httpx` package, but this SDK uses `httpx2`" (http_client/timeout/transport)

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- id: AN-2026-0809 (version 1; cite https://breakwire.org/claim/AN-2026-0809/v/1)
- kind: breaking · status: active · review: editor
- source: <https://github.com/anthropics/anthropic-sdk-python/blob/main/CHANGELOG.md#:~:text=raise%20a%20clear%20error%20when%20an%20httpx%20object%20is%20passed>
- more sources: <https://github.com/anthropics/anthropic-sdk-python/blob/v2.4.0/src/anthropic/_base_client.py#L160-L167> <https://github.com/anthropics/anthropic-sdk-python/blob/main/MIGRATION.md#the-sdk-is-built-on-httpx2> <https://pypi.org/project/anthropic/1.4.0/>
- event date: 2026-09-04
- services: anthropic-sdk, httpx2, httpx, python
- affected: pypi:anthropic >=1.4.0
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. anthropic-sdk-python CHANGELOG (opened 2026-11-04): 1.0.0 (2026-08-20) "upgrade to httpx2 and some minor breaking changes"; 1.4.0 (2026-09-04) Bug Fixes: "client: raise a clear error when an httpx object is passed instead of an httpx2 one". MIGRATION.md: "Passing an `httpx.Client` / `httpx.AsyncClient` (from the old package) as `http_client=` raises a `TypeError` at construction time".  [✓0 ✗0]
1. Source (v2.4.0 src/anthropic/_base_client.py `_reject_httpx_object`) raises TypeError "Invalid `{name}` argument; `httpx.{cls}` is from the `httpx` package, but this SDK uses `httpx2`. Use `httpx2.{cls}` instead." for `http_client`, `timeout` and `transport` values whose class comes from the httpx package.  [✓0 ✗0]
2. Reproduced 2026-11-04 with anthropic 2.4.0 + httpx 0.28.1 + httpx2 2.16.0: Anthropic(http_client=httpx.Client()) -> "Invalid `http_client` argument; `httpx.Client` is from the `httpx` package, but this SDK uses `httpx2`. Use `httpx2.Client` instead."; AsyncAnthropic with httpx.AsyncClient() and Anthropic(timeout=httpx.Timeout(5.0)) give the AsyncClient / `timeout` + httpx.Timeout variants.  [✓0 ✗0]

## Fix
```text
Build the objects from httpx2: `import httpx2` and use `httpx2.Client` / `httpx2.AsyncClient` / `httpx2.Timeout` / `httpx2.HTTPTransport`, or the SDK re-exports `anthropic.DefaultHttpxClient`, `anthropic.DefaultAsyncHttpxClient`, `anthropic.Timeout` (they already point at httpx2). The quickest edit is `import httpx2 as httpx`; or call `httpx2.alias_httpx()` at the very start of the process so `import httpx` resolves to httpx2. Pinning `anthropic<1.0` keeps httpx.
```

## Error signatures
- substring: `is from the 'httpx' package, but this SDK uses 'httpx2'` (anthropic _base_client.py _reject_httpx_object (1.4.0+; v2.4.0 L160-167); reproduced on 2.4.0 for http_client, AsyncClient and timeout)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0809/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary sources opened 2026-11-04 (httpx/httpx2/openai-python/anthropic-sdk-python changelogs + source, reproduced locally)