fix(streaming): preserve BetaCompactionBlock type during streaming accumulation#1200
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bledden wants to merge 1 commit intoanthropics:mainfrom
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fix(streaming): preserve BetaCompactionBlock type during streaming accumulation#1200bledden wants to merge 1 commit intoanthropics:mainfrom
bledden wants to merge 1 commit intoanthropics:mainfrom
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…cumulation When the beta streaming accumulator builds the final message snapshot, it reconstructs each content block by converting it to a dict and passing it through construct_type with the ParsedBetaContentBlock discriminated union. On some Python versions, the generic ParsedBetaTextBlock[T] variant in that union breaks Pydantic's discriminator resolution, causing all non-text blocks (including BetaCompactionBlock) to be incorrectly deserialized as ParsedBetaTextBlock. The fix: only text blocks need reconstruction through construct_type (to wrap them in ParsedBetaTextBlock which adds the parsed_output field). Non-text blocks are already the correct type from the event and can be appended directly to the snapshot. Fixes anthropics#1175
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Summary
When using the beta streaming API with compaction enabled, the final message from
get_final_message()incorrectly typesBetaCompactionBlockcontent blocks asParsedBetaTextBlock. The block hastype='compaction'butisinstance(block, BetaCompactionBlock)returns False, and parasitic fields liketext,citations, andparsed_outputappear as None.The issue is in the streaming accumulator's
content_block_starthandling. It converts every content block to a dict and reconstructs it through theParsedBetaContentBlockdiscriminated union viaconstruct_type(). On some Python versions (reported on 3.12), the genericParsedBetaTextBlock[ResponseFormatT]variant in that union breaks Pydantic's discriminator resolution, causing all blocks to fall through to the first union variant (ParsedBetaTextBlock).The fix: only text blocks need reconstruction through
construct_type(they're the only type that needs wrapping inParsedBetaTextBlockto add theparsed_outputfield). Non-text blocks likeBetaCompactionBlock,BetaToolUseBlock,BetaThinkingBlock, etc. are already the correct type from the streaming event and can be appended directly.Added a test fixture simulating a compaction streaming response and two tests (sync + async) that verify
BetaCompactionBlockinstances are preserved in the final message. All 14 beta streaming tests pass.Fixes #1175