openclaw/docs/concepts/streaming.md

summary, read_when, title

summary	read_when	title
Streaming + chunking behavior (block replies, channel preview streaming, mode mapping)	Explaining how streaming or chunking works on channels Changing block streaming or channel chunking behavior Debugging duplicate/early block replies or channel preview streaming	Streaming and Chunking

Streaming + chunking

OpenClaw has two separate streaming layers:

• Block streaming (channels): emit completed blocks as the assistant writes. These are normal channel messages (not token deltas).
• Preview streaming (Telegram/Discord/Slack): update a temporary preview message while generating.

There is no true token-delta streaming to channel messages today. Preview streaming is message-based (send + edits/appends).

Block streaming (channel messages)

Block streaming sends assistant output in coarse chunks as it becomes available.

Model output
  └─ text_delta/events
       ├─ (blockStreamingBreak=text_end)
       │    └─ chunker emits blocks as buffer grows
       └─ (blockStreamingBreak=message_end)
            └─ chunker flushes at message_end
                   └─ channel send (block replies)

Legend:

• text_delta/events: model stream events (may be sparse for non-streaming models).
• chunker: EmbeddedBlockChunker applying min/max bounds + break preference.
• channel send: actual outbound messages (block replies).

Controls:

• agents.defaults.blockStreamingDefault: "on"/"off" (default off).
• Channel overrides: *.blockStreaming (and per-account variants) to force "on"/"off" per channel.
• agents.defaults.blockStreamingBreak: "text_end" or "message_end".
• agents.defaults.blockStreamingChunk: { minChars, maxChars, breakPreference? }.
• agents.defaults.blockStreamingCoalesce: { minChars?, maxChars?, idleMs? } (merge streamed blocks before send).
• Channel hard cap: *.textChunkLimit (e.g., channels.whatsapp.textChunkLimit).
• Channel chunk mode: *.chunkMode (length default, newline splits on blank lines (paragraph boundaries) before length chunking).
• Discord soft cap: channels.discord.maxLinesPerMessage (default 17) splits tall replies to avoid UI clipping.

Boundary semantics:

• text_end: stream blocks as soon as chunker emits; flush on each text_end.
• message_end: wait until assistant message finishes, then flush buffered output.

message_end still uses the chunker if the buffered text exceeds maxChars, so it can emit multiple chunks at the end.

Chunking algorithm (low/high bounds)

Block chunking is implemented by EmbeddedBlockChunker:

• Low bound: don’t emit until buffer >= minChars (unless forced).
• High bound: prefer splits before maxChars; if forced, split at maxChars.
• Break preference: paragraph → newline → sentence → whitespace → hard break.
• Code fences: never split inside fences; when forced at maxChars, close + reopen the fence to keep Markdown valid.

maxChars is clamped to the channel textChunkLimit, so you can’t exceed per-channel caps.

Coalescing (merge streamed blocks)

When block streaming is enabled, OpenClaw can merge consecutive block chunks before sending them out. This reduces “single-line spam” while still providing progressive output.

• Coalescing waits for idle gaps (idleMs) before flushing.
• Buffers are capped by maxChars and will flush if they exceed it.
• minChars prevents tiny fragments from sending until enough text accumulates (final flush always sends remaining text).
• Joiner is derived from blockStreamingChunk.breakPreference (paragraph → \n\n, newline → \n, sentence → space).
• Channel overrides are available via *.blockStreamingCoalesce (including per-account configs).
• Default coalesce minChars is bumped to 1500 for Signal/Slack/Discord unless overridden.

Human-like pacing between blocks

When block streaming is enabled, you can add a randomized pause between block replies (after the first block). This makes multi-bubble responses feel more natural.

• Config: agents.defaults.humanDelay (override per agent via agents.list[].humanDelay).
• Modes: off (default), natural (800–2500ms), custom (minMs/maxMs).
• Applies only to block replies, not final replies or tool summaries.

"Stream chunks or everything"

This maps to:

• Stream chunks: blockStreamingDefault: "on" + blockStreamingBreak: "text_end" (emit as you go). Non-Telegram channels also need *.blockStreaming: true.
• Stream everything at end: blockStreamingBreak: "message_end" (flush once, possibly multiple chunks if very long).
• No block streaming: blockStreamingDefault: "off" (only final reply).

Channel note: Block streaming is off unless *.blockStreaming is explicitly set to true. Channels can stream a live preview (channels.<channel>.streaming) without block replies.

Config location reminder: the blockStreaming* defaults live under agents.defaults, not the root config.

Preview streaming modes

Canonical key: channels.<channel>.streaming

Modes:

• off: disable preview streaming.
• partial: single preview that is replaced with latest text.
• block: preview updates in chunked/appended steps.
• progress: progress/status preview during generation, final answer at completion.

Channel mapping

Channel	off	partial	block	progress
Telegram	✅	✅	✅	maps to partial
Discord	✅	✅	✅	maps to partial
Slack	✅	✅	✅	✅

Slack-only:

• channels.slack.streaming.nativeTransport toggles Slack native streaming API calls when channels.slack.streaming.mode="partial" (default: true).
• Slack native streaming and Slack assistant thread status require a reply thread target; top-level DMs do not show that thread-style preview.

Legacy key migration:

• Telegram: streamMode + boolean streaming auto-migrate to streaming enum.
• Discord: streamMode + boolean streaming auto-migrate to streaming enum.
• Slack: streamMode auto-migrates to streaming.mode; boolean streaming auto-migrates to streaming.mode plus streaming.nativeTransport; legacy nativeStreaming auto-migrates to streaming.nativeTransport.

Runtime behavior

Telegram:

• Uses sendMessage + editMessageText preview updates across DMs and group/topics.
• Preview streaming is skipped when Telegram block streaming is explicitly enabled (to avoid double-streaming).
• /reasoning stream can write reasoning to preview.

Discord:

• Uses send + edit preview messages.
• block mode uses draft chunking (draftChunk).
• Preview streaming is skipped when Discord block streaming is explicitly enabled.

Slack:

• partial can use Slack native streaming (chat.startStream/append/stop) when available.
• block uses append-style draft previews.
• progress uses status preview text, then final answer.

Related

• Messages — message lifecycle and delivery
• Retry — retry behavior on delivery failure
• Channels — per-channel streaming support