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 v2.1.252 ·

Context/cost breakdown now counts tool descriptions from a recorded prompt snapshot

Context/cost breakdowns like /context now reuse the exact tool description text actually sent, for accuracy.

TierUnder the hoodhow much it should matter to you
Useful2my rating, 1 to 5
Signal2worth watching, 1 to 5
AreaElsewherewhat it touches
KindInternal Changesin v2.1.252,
Under the hood

Context/cost breakdowns like /context now reuse the exact tool description text actually sent, for accuracy.

The token-counting helpers for MCP tools, built-in tools, skills, and slash commands (dA, formerly TA) now accept a recordedDescription map sourced from the last prompt snapshot, so re-analysis of context usage (e.g. /context) reuses the exact tool description text actually sent to the model instead of recomputing it.

Read from
Names in the bundle/context
Feature flag
tengu_carved_slate Off in both readings

The flag server returned off for the account this site reads and for the anonymous baseline. A reading of off cannot rule out a rollout these two readings sit outside of.

This account: off · anonymous baseline: off · compiled default in v2.1.252: not a boolean we can read

Read once, for one account on one subscription tier, against v2.1.252. It isn't a statement about your account. What a flag value here can and cannot tell you

Since it was published

The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.

Added since A small documentation edit on whats-new-fable-5-1 touched a line naming /context after this was published. To keep thinking valid across a long session, treat the conversation as append-only. Add instructions with a [mid-conversation system message](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages) ([turn-s… models/fable-5-1/whats-new-fable-5-1 see the edit
Confirmed since Anthropic's documentation has since written up /context, on How Claude Code uses prompt caching. [Compaction](/docs/en/context-window#what-survives-compaction) replaces your message history with a summary. By design, this invalidates the conversation layer, since the next request has a new, shorter history that doesn't share a prefix … prompt-caching see the edit
What has happened since
Flag reading moved The flag server now returns on for tengu_carved_slate, 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 nothing at all, having stopped carrying it for tengu_carved_slate, 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
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agreesAnthropic's documentation has since written up /context, on How Claude Code uses prompt caching.

See this entry in the whole of v2.1.252 →