The Anthropic→Responses streaming converter omits two things the OpenAI
Responses wire format requires, which breaks clients that reconstruct the
response from the event stream (rather than just reading deltas).
1. response.content_part.added is never emitted.
A message item is opened with content: [], and the OpenAI SDK's
accumulating stream helper (client.responses.stream) only appends a
content part when it sees content_part.added. Without it, the next
output_text.delta indexes output.content[content_index] and raises:
File "openai/lib/streaming/responses/_responses.py", line 352,
in accumulate_event
content = output.content[event.content_index]
IndexError: list index out of range
Raw iteration (responses.create(stream=True)) does not accumulate and is
unaffected, which is why this went unnoticed.
2. response.completed carries Output: []ResponsesOutput{}.
get_final_response() and tracing integrations parse the terminal event's
response directly, so callers see an empty output_text even though the
deltas streamed correctly. This one is invisible when only watching the
stream render.
Also carries the full text on output_text.done / content_part.done (deltas
carry increments only, done events carry the whole part) and fills in
content/arguments/summary on output_item.done, which had the same
empty-payload issue.
Reproduced against a live Anthropic-platform group with the openai Python
SDK 2.46.0; Arize Phoenix's playground hits the same path. Verified before
(IndexError) and after (full text via get_final_response()).
Adds regression tests covering event ordering, done-event payloads, and the
terminal event's output for both text and tool calls.
docooler
26b5e87457