Python SDK: _transform_recursive blocking event loop on large message payloads

We profiled our FastAPI gateway (which runs an agent orchestration loop using the Anthropic Python SDK) and found that _transform_recursive in anthropic/_utils/_transform.py consumes ~6.6% of total CPU time during heavy workloads.

The function recursively walks the entire messages + tools payload doing type introspection (get_type_hints, is_typeddict, is_union_type) at every level of nesting. For Messages API types, this produces zero changes — no key renames, no date formatting. The transform allocates new dicts at every level and copies every key-value pair, producing an identical structure.

Additionally, AsyncMessages.stream() calls the synchronous maybe_transform (not async_maybe_transform), so the entire recursive walk blocks the event loop.

We're currently working around this by passing messages and tools via extra_body so the transform only runs on empty placeholders. Has this been reported as a known issue? Is there a better recommended approach?