stream.get_final_message() does not return the correct usage of output_tokens

The problem

Issue anthropics/anthropic-sdk-python#424 (closed, 9 comments): After streaming, stream.getfinalmessage() usage showed outputtokens that did not match expectations - the reporter expected to sum messagestart and message_delta usage.

The verified resolution

Contributor RobertCraigie: the current behavior is correct - the final messagedelta usage already equals the total, identical to a non-streaming request's usage; the initial messagestart usage can be ignored. Reporter confirmed understanding.

Rule of thumb

for streamed Anthropic requests, use the final usage block as the total; do not sum messagestart + messagedelta.

Asked in gh:anthropics/anthropic-sdk-python#424 (https://github.com/anthropics/anthropic-sdk-python/issues/424): stream.getfinalmessage() does not return the correct usage of outputtokens. The issue report: Issue anthropics/anthropic-sdk-python#424 (closed, 9 comments): After streaming, stream.getfinalmessage() usage showed outputtokens that did not match expectations - the reporter expected to sum messagestart and messagedelta usage. The verified answer: Contributor RobertCraigie: the current behavior is correct - the final messagedelta usage already equals the total, identical to a non-streaming request's usage; the initial messagestart usage can be ignored. Reporter confirmed understanding. Lesson: for streamed Anthropic requests, use the final usage block as the total; do not sum messagestart + messagedelta.