[changed] /skill-doctor is treated as on by default in current releases. When it is missing, Claude explains realistic causes (older client, Bedrock/Vertex/Foundry, telemetry or non-essential traffic disabled, first launch before settings fetch, or admin policy) and suggests updating or asking an administrator — without telling you to run it in a session where it is unavailable.
[fixed] Terminal output can run in a non-blocking mode with backpressure handling, reducing stalls when large amounts of stdout are produced.
[changed] Auto mode more carefully tracks context pressure (over ceiling, static over budget, withheld context) so long autonomous runs degrade more predictably instead of blowing the window.
[new] Clients that are too far behind can be detected via a dedicated “version too old” path, so outdated installs surface a clearer upgrade signal.
[changed] Auto mode can probe git state when deciding how to proceed, improving decisions that depend on the working tree.
[changed] Stricter prefix-lock failures (HTTP 400) are surfaced more clearly when they occur.
[changed] SDK compatibility testing drops wrapper versions 0.3.219 and 0.3.220; 0.3.221+ remain in the tested set.
Models & prompts
Built-in guidance for /skill-doctor no longer frames it as early access; it matches the “default on, absent only in specific environments” behavior above.
Agent, subagent, focus-mode, corrections/memory, connector, and user-messaging prompt text is otherwise carried forward with light internal consolidation (no broad behavior rewrite).
Under the hood
New environment knobs: CLAUDE_CODE_NONBLOCKING_STDOUT, CLAUDE_CODE_COMPILED_ACORN, and CLAUDE_AUTO_BACKGROUND_TASKS2 for stdout behavior, a compiled Acorn path, and background-task iteration.
API beta header dangerous-tool-use-2026-09-03 added for gated tool-use work.
CCR work continues: v2 bridge create-CLI wiring and a killswitch to exclude dynamic restore.
Telemetry and experimentation hooks for context usage bulk counts, tool CPU by phase, plugin hint tracking, prefix-break hashes, and several named feature gates (including compiled Acorn and stdout backpressure).
Removed stale env names CLAUDE_CODE_ASSUME_FIRST_PARTY_BASE_URLI and CLAUDE_CODE_MAX_WEB_SEARCHES_PER_SESSIONN.
Upgrade notes
If you pin the Claude Code SDK/wrapper, use 0.3.221 or newer; 0.3.219 and 0.3.220 are no longer in the tested compat list.
If /skill-doctor is missing after upgrade, check release age, cloud provider path (Bedrock/Vertex/Foundry), telemetry/non-essential traffic settings, or admin feature policy before assuming a product regression.
Optional: CLAUDE_CODE_NONBLOCKING_STDOUT if you hit terminal backpressure on heavy command output.
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