Sweep 19 Sep 2026 · 02:36Z Build v2.1.278 500 read Stable v2.1.267 Latest v2.1.278 Next v2.1.278 Feeds RSS JSON llms.txt Unofficial
Claude Code v2.1.265 ·

Tool-use IDs with a reserved prefix are now classified as underivable_excluded

Tool calls with a special reserved ID prefix are now excluded from resume history reconstruction

TierUnder the hoodhow much it should matter to you
Useful1my rating, 1 to 5
Signal1worth watching, 1 to 5
AreaSessionswhat it touches
KindInternal Changesin v2.1.265,
Under the hood No documentation found

Tool calls with a special reserved ID prefix are now excluded from resume history reconstruction

What

When Claude Code resumes a session and figures out which prior tool calls can be reconstructed, a tool call whose ID starts with a specific reserved prefix is now immediately classified as "underivable_excluded", before the normal checks for whether it was superseded or mismatched even run.

Why

This ensures tool calls carrying that reserved ID prefix are never mistakenly reconstructed during resume, treating them as excluded from the start rather than relying on the standard classification logic to catch them.

Read from
Names in the bundleunderivable_excluded
How sure we are
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubtWhat the reserved ID prefix specifically identifies is not shown by the evidence.

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