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Anthropic Python SDK 1.0 Switches to httpx2, Potentially Silently Breaking Existing Tracing and Mocks
The new release raises the minimum Python version to 3.10 and removes Text Completions, several sampling parameters, and the client-side compaction interface. Most standard API calls require no changes, but monitoring, testing, and custom transport layers that depend directly on httpx must be migrated.
Anthropic released version 1.0 of its Python SDK on August 20. The most significant underlying change is the replacement of the `httpx` HTTP client with `httpx2`, a compatible fork maintained by the Pydantic team. Applications that only pass ordinary values such as numeric timeouts and retry counts should generally continue to work. Code that constructs its own `Client`, `Timeout`, transport, proxy, or event hooks must instead use `httpx2` classes. Passing a legacy `httpx.Client` to the SDK immediately raises a `TypeError`. However, tools such as OpenTelemetry, Sentry, RESPX, pytest-httpx, or VCR that intercept traffic by patching `httpx` may continue running without seeing any Claude requests, creating a harder-to-detect observability gap. The official compatibility option is `httpx2.alias_httpx()`, which applies process-wide, but it must be called before any module imports `httpx`, and libraries should not enable it on behalf of downstream applications.
This major release also removes several legacy interfaces. The minimum supported runtime has been raised from Python 3.9 to 3.10. `client.completions.create()`, the legacy Text Completions types, `HUMAN_PROMPT`, and `AI_PROMPT` have all been removed. The `temperature`, `top_p`, and `top_k` parameters no longer appear in the formal signatures of Messages methods; when these controls are still required for older models, they can only be sent through `extra_body`. For asynchronous `.with_raw_response` calls, `parse()`, `text()`, and `read()` must now be awaited. The tool runner’s client-side `compaction_control` has also been replaced by server-side context management. Bedrock users who do not configure an AWS Region will now receive an error instead of defaulting to `us-east-1`.
Engineering teams should not treat this upgrade as a routine dependency update. A safer approach is to remain pinned to 0.x initially, upgrade on a separate branch, and then run type checking, HTTP mock tests, APM trace verification, proxy tests, and enterprise CA tests before validating structured outputs and asynchronous raw-response paths. The official migration guide is comprehensive, but support for `httpx2` must still be verified individually across third-party monitoring packages.