# AN-2026-0852: MCP Python SDK 2.0 (Jul 28, 2026) swapped httpx for httpx2: your own `import httpx` can fail, httpx.AsyncClient(auth=provider) raises TypeError: Invalid "auth" argument

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- id: AN-2026-0852 (version 1; cite https://breakwire.org/claim/AN-2026-0852/v/1)
- kind: breaking · status: active · review: editor
- source: <https://py.sdk.modelcontextprotocol.io/v2/migration/#:~:text=httpx%20and%20httpx-sse%20replaced%20by%20httpx2>
- more sources: <https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.0.0> <https://github.com/pydantic/httpx2>
- event date: 2026-07-28
- services: mcp-python-sdk, mcp, python
- affected: pypi:mcp >=2.0.0
- 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. The v2 migration guide says the SDK now depends on httpx2 instead of httpx and httpx-sse, and mcp no longer installs httpx: code that imported httpx and relied on mcp v1 to pull it in fails with ModuleNotFoundError: No module named 'httpx', a traceback that never mentions mcp.  [✓0 ✗0]
1. The guide says OAuthClientProvider, ClientCredentialsOAuthProvider, PrivateKeyJWTOAuthProvider and IdentityAssertionOAuthProvider now subclass httpx2.Auth, so httpx.AsyncClient(auth=provider) raises TypeError: Invalid "auth" argument; an httpx.AsyncClient passed as http_client degrades silently (server-initiated messages stop arriving).  [✓0 ✗0]
2. The guide says the SDK raises httpx2 exceptions, so except httpx.ConnectError blocks silently never match; loggers are httpx2 / httpcore2; TLS verification uses the OS trust store via truststore instead of certifi (set SSL_CERT_FILE / SSL_CERT_DIR or pass verify=ssl_context in minimal containers).  [✓0 ✗0]

## Fix
```text
Add `httpx` to your own dependencies if your code imports it, or port to `httpx2` (drop-in Client/AsyncClient); build clients you hand to the SDK (http_client=, auth=) with httpx2; change `except httpx.X` to `except httpx2.X`; set SSL_CERT_FILE if the container has no CA store.
```

## Error signatures
- substring: `Invalid "auth" argument` (v2 migration guide (httpx.AsyncClient(auth=provider)); httpx message, scoped to the service)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0852/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary source opened 2026-10-28