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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.165

2 entries read diff v2.1.163 → v2.1.165 Markdown

This is a small patch release built one day after v2.1.163. The two notable functional changes are: conversation summarization can now use extended thinking when the active model supports it (controlled by a server-side capability list), and subagent API calls are now tagged in the billing attribution header.

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Extended Thinking Support in Conversation Summarizer#

Previously the summarizer that compresses long conversations always ran with thinkingConfig: { type: "disabled" }, regardless of what model was active. In this version a new capability check is evaluated at summarization time: if the current main-loop model is listed in the server-side cedar_lagoon capability map, the summarizer now inherits the same thinking configuration used by the main conversation loop. For models that are not in the list, the old behavior (thinking disabled) is unchanged.

In practice this means users running a model that supports extended thinking may notice more coherent or accurate conversation compaction when context windows fill up, since the summarizer can now reason before producing the summary.

Evidence

New capability gate function (searches clientDataCache?.cedar_lagoon); summarization call site changed from hardcoded { type: "disabled" } to hM8(K.options.mainLoopModel) ? K.options.thinkingConfig : { type: "disabled" } — search for "cedar_lagoon" to locate the check.

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Subagent Sessions Identified in Billing Attribution Header#

The x-anthropic-billing-header sent with every API request now includes cc_is_subagent=true; when the request originates from a subagent session rather than the top-level interactive session. The main CLI session is tagged isMainSession: true internally; any agent that lacks that flag gets the subagent marker appended.

This is an internal attribution change with no user-visible behavior. It helps Anthropic distinguish API usage generated directly by the user from usage generated by orchestrated subagents, which improves billing analytics and usage reporting.

Evidence

Attribution header builder now appends cc_is_subagent=true; for non-main-session callers (search for "cc_is_subagent=true;" in the source); main session agent config now sets isMainSession: !0.

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Verbatim
Official · Anthropic

Anthropic’s official release notes

Published verbatim by Anthropic for v2.1.165. Text is unmodified from the upstream changelog. Everything else on this page came out of the bundle instead, which is why the two lists don't match.

  • Bug fixes and reliability improvements
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