# AN-2026-0810: httpx2 SDKs (anthropic >= 1.0, openai >= 3.0): OpenTelemetry/Sentry/respx/vcrpy httpx hooks go silent; httpx2.alias_httpx() fixes it, "httpx was already imported" if late

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- id: AN-2026-0810 (version 1; cite https://breakwire.org/claim/AN-2026-0810/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://github.com/anthropics/anthropic-sdk-python/blob/main/MIGRATION.md#:~:text=Libraries%20that%20observe%20or%20stub%20HTTP%20traffic>
- more sources: <https://github.com/pydantic/httpx2/blob/v2.16.0/src/httpx2/httpx2/_alias.py#L51> <https://github.com/pydantic/httpx2/blob/main/src/httpx2/CHANGELOG.md#:~:text=Add%20alias_httpx> <https://github.com/openai/openai-python/blob/main/httpx2.md#:~:text=If%20your%20test%20suite%20uses%20RESPX>
- event date: 2026-07-23
- services: httpx2, anthropic-sdk, openai-sdk, python
- affected: pypi:httpx2 >=2.9.0; pypi:anthropic >=1.0.0; pypi:openai >=3.0.0
- 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 MIGRATION.md (opened 2026-11-04): "Libraries that observe or stub HTTP traffic by patching `httpx` - for example OpenTelemetry's `HTTPXClientInstrumentor`, Sentry's `httpx` integration, respx, `pytest-httpx` or `vcrpy` - patch the `httpx` package, which the SDK no longer uses. These libraries can silently fail"; fix: run `httpx2.alias_httpx()` before anything else imports httpx. It "has to run before anything imports `httpx` (it raises a `RuntimeError` otherwise)" and is meant for   [✓0 ✗0]
1. OpenAI SDK httpx2.md: "A RESPX version that patches only legacy HTTPX cannot intercept the SDK's default HTTPX2 client"; third-party instrumentation, tracing middleware and auth integrations must explicitly support HTTPX2.  [✓0 ✗0]
2. httpx2 CHANGELOG: 2.9.0 (July 23rd, 2026) "Add `alias_httpx()`, letting applications make `import httpx` resolve to `httpx2` process-wide"; a later release also aliases httpcore to httpcore2. Source (v2.16.0 _alias.py L51) raises RuntimeError "{alias} was already imported; call `alias_httpx()` before any `import {alias}`." Reproduced 2026-11-04 with httpx2 2.16.0: `import httpx; httpx2.alias_httpx()` -> RuntimeError "httpx was already imported; call `alias_httpx()` before any `import httpx`."  [✓0 ✗0]

## Fix
```text
Call `import httpx2; httpx2.alias_httpx()` as the very first lines of the entry point (before OpenTelemetry/Sentry/respx/vcrpy or anything else imports httpx), or switch those integrations to httpx2-aware versions / httpx2.MockTransport. For missing traces, check that no import of httpx happens before the alias call (sitecustomize, pytest plugins, auto-instrumentation wrappers import early).
```

## Error signatures
- substring: `was already imported; call 'alias_httpx()' before any` (httpx2 _alias.py L51 (v2.16.0); reproduced on 2.16.0)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0810/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)