[jeffdupont]

Jira: https://launchdarkly.atlassian.net/browse/AIC-3735
Spec: launchdarkly/ai-sdks-monorepo#125

What broke

Every claude-messages call whose AI Config set temperature (or top_p / top_k) failed with anthropic 1.x installed:

AsyncMessages.create() got an unexpected keyword argument 'temperature'

anthropic 1.0.0 (2026-08-20) removed temperature, top_p and top_k from messages.create(), messages.stream() and messages.parse(). Passing them is now a TypeError. stop_sequences is still accepted. anthropic-sdk-python MIGRATION.md, "Removed: deprecated request parameters", says to remove them or, for a model that still honours them, pass them through extra_body. It also says: "The sampling parameters are only gone from the method signatures, not from the API."

The handler forwarded them as keyword arguments since #107. CI didn't catch it: pyproject.toml allowed anthropic>=0.113, but every job syncs from uv.lock, which pins 0.113.0, so nothing ever ran against 1.x. The mock-based handler tests passed anyway, because a MagicMock client accepts any kwarg.

The fix

• _forwarded_parameters moves temperature / top_p / top_k (_MESSAGES_SAMPLING_KEYS) into extra_body. extra_body is merged into the request JSON on every anthropic release, so the wire body is unchanged on 0.113 and works on 1.x. Both invoke and stream read this function. A config-supplied extra_body is still dropped.
• claude-messages now requires anthropic>=0.113,<2 (that package only; uv.lock updated, and it still pins 0.113.0). anthropic 2.x sends API version 2026-10-21 (anthropic/_constants.py in 2.3.0: ANTHROPIC_API_VERSION = "2026-10-21"). On that version, the API returns 400 for temperature, top_p and top_k, "even at the parameter's default value" (https://platform.claude.com/docs/en/api/migration-2026-10-21, "Sampling parameters are removed"). So the extra_body route only holds for anthropic 0.x and 1.x, which send 2023-06-01. Support for anthropic 2 is a follow-up that decides the 2026-10-21 behaviour: AIC-3736.
• The drift tests in test_parameter_forwarding.py now cover the whole allowed range. The sampling keys are no longer required in the SDK signatures, and keys added in 1.x aren't flagged as stale on 0.113.
• Tests:
  • New test_forwarded_parameters_bind_to_the_installed_sdk[create|stream] binds the handler's kwargs to the installed SDK's real signatures.
  • The wire test now sets temperature and asserts it reaches the HTTP body. It picks httpx/httpx2 from what anthropic's own client imports, because 1.x rejects an httpx client.

New CI job: test-latest-anthropic

The lock keeps 0.113.0 (the lowest supported version). The new job:

1. syncs from the lock,
2. runs uv pip install --upgrade-package anthropic -r packages/claude-messages/pyproject.toml,
3. prints the installed version,
4. runs the full suite (uv run --no-sync pytest).

The requirement is read from claude-messages' own pyproject.toml because uv pip install anthropic ignores the installed package's <2 cap: I checked, and it installed 2.3.0. --upgrade-package moves only anthropic. The job's first version used --upgrade, which also upgraded opentelemetry-api and pydantic and broke the OTel imports in the full suite. Today the job resolves anthropic 1.17.0, and compared with the lock, only anthropic changes.

main has no required status checks, so this job is advisory unless someone adds it.

Other SDKs

SDK	Exposed?	Why
Python (this PR)	Yes on anthropic 1.x	kwargs to messages.create/.stream. Fixed here, and capped below 2.x.
JS (js-ai-sdk claude-messages)	Not yet	@anthropic-ai/sdk is pinned ^0.103.0 (resolves below 0.104.0), which sends API 2023-06-01. A 1.x bump moves it to 2026-10-21 (client.js in 1.3.0), where these keys are a 400, so that bump needs the same decision.
Go (go-ai-sdk claudemessages)	No	Forwards model.parameters with params.SetExtraFields (raw JSON), and go.mod pins v1.80.0. The latest v1 is v1.84.0, which still has Temperature/TopK/TopP. v2 (v2.4.0) is a separate /v2 module on API 2026-10-21.

This PR doesn't change which keys are forwarded (only how they're sent), so the Claude Messages list still matches JS. Go's list already differed before this PR (it forwards container, inference_geo, metadata, and output_config whole), and that is out of scope here.

Policy decisions for reviewers

• Excluded, not forwarded: diagnostics, workspace_id and speed, which arrived in anthropic 1.x after 1.0.0. None of them shapes what the model generates: a diagnostics opt-in, a workspace-selection header, and a price/latency mode. Forwarding one later is additive. JS and Go don't forward them either.
• thinking: {"type": "between_tools"} is not forwarded. It also arrived in 1.x after 1.0.0. A config that sets it is dropped, not an error. test_the_shapes_match_the_sdk_types lists it as a known gap. To forward it, add it to _TYPED_OBJECT_SHAPES and remove it from that list. The spec PR names it as not forwarded.

Test output

Before the fix (original handler.py), wire test:

anthropic 0.113.0: 1 passed
anthropic 1.9.0:   TypeError: AsyncMessages.create() got an unexpected keyword argument 'top_p'

After (head 7a54bf0), full repo pytest:

lock, anthropic 0.113.0:                     3848 passed, 18 skipped
newest allowed (CI job's install), 1.17.0:   3848 passed, 18 skipped

make lint and make format-check are clean, and make typecheck reports no issues in 106 source files. The cap fires: resolving claude-messages with anthropic==2.3.0 fails with "depends on anthropic>=0.113,<2 … unsatisfiable".

Not run against the live Anthropic API.

🤖 Generated with Claude Code

---

Note

Overview
Fixes AIC-3735: AI Configs that set temperature, top_p, or top_k no longer crash on anthropic 1.x, which removed those keys from messages.create / .stream kwargs.

Handler: _forwarded_parameters now strips _MESSAGES_SAMPLING_KEYS and sends them in extra_body so the request JSON stays the same on 0.113 and binds cleanly on 1.x. Newer SDK-only params (diagnostics, speed, workspace_id) are documented as excluded, not forwarded.

Dependency: claude-messages requires anthropic>=0.113,<2 (anthropic 2.x API rejects sampling params even via extra_body).

CI & tests: Adds test-latest-anthropic (upgrade anthropic within the cap, full pytest). Drift tests treat sampling keys as signature-optional; new test binds handler output to the installed SDK. Handler tests assert extra_body and wire-level sampling; wire tests use anthropic’s httpx2 when present.

^{Reviewed by Cursor Bugbot for commit 7a54bf0. Bugbot is set up for automated code reviews on this repo. Configure here.}