feat(models): add BlockChunk type to chat.{start,append,stop}Stream methods

[srtaalej]

Summary

This PR adds BlocksChunk model class to support the new blocks chunk type in the streaming API (chat.startStream, chat.appendStream, chat.stopStream). Follows the April 16, 2026 changelog which notes updates to the text-streaming API methods to support streaming blocks.

Testing

Sample app.py

fromslack_sdk.models.blocksimportCardBlock, CarouselBlockfromslack_sdk.models.messages.chunkimportBlocksChunkstreamer=client.chat_stream( channel="C0123456789", thread_ts="1700000001.123456", recipient_team_id="T0123456789", recipient_user_id="U0123456789", ) streamer.append(markdown_text="Here's a **card** streamed via `BlocksChunk`:\n\n") streamer.append( chunks=[ BlocksChunk( blocks=[ CardBlock( title="Streaming Card", subtitle="Sent via BlocksChunk", body="This card was streamed inside a chunks array.", ), ] ), ] ) streamer.stop( chunks=[
BlocksChunk( blocks=[ CarouselBlock( elements=[ CardBlock(title="Card 1", subtitle="First", body="First card in carousel."), CardBlock(title="Card 2", subtitle="Second", body="Second card in carousel."), CardBlock(title="Card 3", subtitle="Third", body="Third card in carousel."), ] ), ] ), ] ) 

Category

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.signature (Request Signature Verifier)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.models (UI component builders)
• slack_sdk.scim (SCIM API client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.rtm_v2 (RTM client)
• /docs (Documents)
• /tutorial (PythOnBoardingBot tutorial)
• tests/integration_tests (Automated tests for this library)

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes.

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 84.13%. Comparing base (73d255a) to head (8b8ab8b).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
slack_sdk/models/messages/chunk.py	92.30%	1 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #1872 +/- ##
==========================================
+ Coverage 84.09% 84.13% +0.04% 
==========================================
Files 117 117 Lines 13325 13337 +12 ==========================================
+ Hits 11205 11221 +16 + Misses 2120 2116 -4 

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[zimeg]

@srtaalej Nice! LGTM with a note on alphabetics I'd like us to keep pattern for since it makes later finding and additions less difficult I think!

[zimeg]

🧮 quibble: Might this be alright to move up for alphabetical ordering to match other entries?