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Sweep 22 Sep 2026 · 17:19Z Build v2.1.280 501 read Stable v2.1.267 Latest v2.1.280 Next v2.1.280 Feeds RSS JSON llms.txt Unofficial
Claude Code v2.1.261 ·

Subagent "harness tail" size accounting behind tengu_swift_whistle

Subagent report truncation accounting for a 'harness tail' section stays inert behind a flag.

TierNothing to try yethow much it should matter to you
Useful2my rating, 1 to 5
Signal3worth watching, 1 to 5
AreaSubagentswhat it touches
KindIn Developmentin v2.1.261,
Nothing to try yet No documentation found

Subagent report truncation accounting for a 'harness tail' section stays inert behind a flag.

New code paths, gated behind tengu_swift_whistle, control whether subagent SendMessage report truncation reserves extra budget for a harnessTail/inlineHandback section, and whether a telemetry counter fires when that path is taken. The logic is reachable from report formatting on agent completion and from mapToolResultToToolResultBlockParam for SendMessage, but the whole branch stays inert until the gate is enabled.

Read from
Names in the bundletengu_swift_whistle
Feature flag
tengu_swift_whistle Not enough to say

Nothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.

This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.261: off

These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.

Read once, for one account on one subscription tier, against v2.1.261. It isn't a statement about your account. What a flag value here can and cannot tell you

What has happened since
Flag reading moved The flag server now returns on for tengu_swift_whistle, read as this account. A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
Flag reading moved The flag server now returns off for tengu_swift_whistle, read as this account. A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
Flag reading moved The flag server now returns on for tengu_swift_whistle, read as this account. A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.

See this across every release →

How sure we are
Two sources agreeTwo things we can check say the same as this entry.
Anthropic's release notes agreeFixed SendMessage to an offline Remote Control session on another machine reading as delivered; the result now says delivery is queued until…
The name it cites is new in this buildNew in this build: tengu_swift_whistle

See this entry in the whole of v2.1.261 →

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