Anthropic Python SDK 1.0 Migration Guide: Upgrading to httpx2

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Anthropic Python SDK 1.0 Migration Guide: Upgrading to httpx2

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A complete guide to migrating to Anthropic Python SDK 1.0: switching the underlying layer to httpx2, requiring Python 3.10+, removing temperature and Text Completions, with environment checks, dependency replacement, and upgrade verification steps.

Article Content

Anthropic has officially released Python SDK 1.0, a major version leap for the library. The core changes include switching the underlying HTTP client from httpx to httpx2, raising the minimum Python version to 3.10, and removing the temperature parameter and the Text Completions interface. For developers building applications with the Anthropic API, this upgrade brings gains in performance and type safety, but it also means existing code needs to be actively adjusted.

Why This Upgrade Matters

SDK 1.0 is not just a simple version number bump. The introduction of httpx2 replaces the original network request layer, with the official rationale being better async support and connection management. On the other side, the Python 3.10+ requirement allows the SDK to use more modern type annotations and language features. The cost is that older projects still on Python 3.9 or earlier must first upgrade their runtime environment.

Another breaking change to face squarely is the removal of the Text Completions interface. Anthropic has fully consolidated conversational capabilities into the Messages API, and the old text completion endpoint is no longer supported. At the same time, the temperature parameter has also been removed, which means calls that rely on this parameter to adjust output randomness need to redesign their prompting strategy.

The Difference Between the Messages API and Text Completions

Text Completions was a text completion interface provided by Anthropic in its early days. It accepted a single prompt and returned continuation content, similar to traditional language model calls. The Messages API is an interface designed for conversational scenarios. The request body consists of a system prompt and a messages array, where each message contains role (user or assistant) and content. This structure naturally supports multi-turn conversations, separation of system prompts, and advanced capabilities such as tool calling. Anthropic's consolidation of conversational capabilities into the Messages API means developers need to break down old single prompts into system instructions and user messages, and consider whether to retain assistant turns to guide model behavior.

The Role of the temperature Parameter and Why It Was Removed

temperature is a sampling parameter that controls the randomness of model output. Lower values make output more deterministic, while higher values make it more diverse. Many teams use it to stabilize tasks such as summarization and classification. Anthropic's removal of this parameter may be related to the model's own alignment strategy and output stability optimizations, guiding developers to control output variance through prompt engineering (such as explicit instructions, few-shot examples, and output format constraints) rather than relying on sampling parameters.

Environment Checks Before Migration

Before changing any code, confirm three things: whether the Python version is 3.10, whether the project directly or indirectly depends on an old version of httpx, and whether any code calls Text Completions.

You can quickly check the interpreter version with python --version. For the dependency tree, it is recommended to use pip list | grep httpx or pipdeptree to check for version conflicts. If other libraries in the project pin an older version of httpx, upgrading the Anthropic SDK may cause dependency resolution failures, so it should be verified separately in a virtual environment.

Steps for Replacing Dependencies and the Client

Upgrading the SDK itself requires only one command, but the real work lies in replacing direct references. First run pip install --upgrade anthropic to update the package to version 1.0. Then search the code for all import httpx call sites—if these calls are used to configure timeouts, proxies, or custom transport layers for the Anthropic client, they need to be changed to use the corresponding httpx2 interfaces.

The construction of the Anthropic client itself remains fairly consistent, but the type of the underlying transport has changed. Scenarios with a custom http_client are the most error-prone part of migration. It is recommended to check parameter names and type signatures item by item against the official migration documentation.

The Relationship Between httpx and httpx2

httpx is a widely used synchronous/asynchronous HTTP client in the Python ecosystem, supporting HTTP/2, connection pooling, and custom transport layers. httpx2 is its subsequent evolved version, with improvements in async support, connection management, and type annotations. Anthropic SDK 1.0 switches the underlying network layer to httpx2, which means that when passing a custom http_client, the transport type, timeout configuration, and proxy settings need to correspond to the httpx2 interfaces. If other libraries in the project still pin the old version of httpx, two packages may coexist or dependency resolution conflicts may occur, so it is recommended to verify separately in a virtual environment.

Impact of Removing temperature and Text Completions

The removal of temperature has a broader impact than one might imagine. Many teams lower temperature when generating summaries, classifications, or structured outputs to obtain more stable results. Once the SDK no longer accepts this parameter, such control needs to move to the prompt level—for example, reducing variance through clearer instructions, few-shot examples, or output format constraints.

The removal of Text Completions requires rewriting old calls entirely to the Messages API. The two differ fundamentally in message structure: the former is single-prompt completion, while the latter is based on a list of role/content messages. During migration, do not simply stuff the old prompt into a single user message; instead, redesign the division between system prompts and conversation structure.

Post-Upgrade Verification Checklist

After completing code changes, it is recommended to verify in the following order: first run unit tests in an isolated environment, focusing on all paths that make API requests; then check whether timeout and retry logic still work, because httpx2's default behavior may differ from the old version; finally, use small-traffic requests in a pre-release environment to verify real responses and confirm that nothing has silently degraded due to parameter removal.

For production systems, it is recommended to keep a rollback path to the old SDK version until the new version has been running stably for some time. Version lock files should explicitly record the anthropic version number to avoid inconsistencies in CI environments.

Changes in Timeout and Retry Logic

httpx2's default timeout behavior and retry strategy may differ from the old httpx. For example, the default values for connection timeout and read timeout may be adjusted, and the conditions for automatic retries may also change. After upgrading, explicitly check whether the timeout parameter still takes effect when constructing the client, and whether custom retry logic relies on old-version behavior. It is recommended to use small-traffic requests in a pre-release environment to verify real responses and confirm that nothing has silently degraded due to parameter removal.

Is It Worth Upgrading Now

If the project is just getting started, adopting 1.0 directly is a reasonable choice and can avoid a second migration later. For systems already running stably, the urgency of upgrading depends on whether they rely on removed features: if Text Completions or temperature are heavily used, migration costs are higher, and it may be better to wait for a more complete transition plan; if only standard Messages API calls are used, the upgrade path is relatively smooth, and the main work is adapting the environment and dependencies.

In either case, doing a trial migration on a branch in advance is safer than reacting passively in production.

One-line Summary

Anthropic Python SDK 1.0 upgrade guide: key migration points and impact assessment

Paragraph Summary

Anthropic has released Python SDK 1.0, switching the underlying HTTP client from httpx to httpx2, raising the minimum Python version to 3.10, and removing the temperature parameter and Text Completions interface. The article systematically covers pre-migration environment checks, dependency and client replacement steps, the impact of removed features, and a post-upgrade verification checklist. The core point is that whether to upgrade immediately depends on how much the project relies on removed features, and it is recommended to trial the migration on a branch and keep a rollback path to avoid reacting passively in production.