[BUG] 2.1.159: autocompact silently disabled for non-remote sessions unless `autoCompactWindow` is set

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Starting in 2.1.159, automatic context compaction no longer fires by default for local (non-Remote-Control) sessions, regardless of how full the context is. The 2.1.159
changelog describes the release as "Internal infrastructure improvements (no user-facing changes)", but a runtime guard was added that gates autocompact behind
CLAUDE_CODE_REMOTE, an experiment flag, or an explicit autoCompactWindow / CLAUDE_CODE_AUTO_COMPACT_WINDOW setting.

For users who relied on autocompact firing automatically (the documented behaviour since 0.2.47), conversations now silently exceed the documented ~80% trigger and continue
running until the model itself errors with "Prompt is too long". There is no warning, no log line, and no /status indicator that autocompact has been short-circuited — the
failure mode is silent.

Root cause (from the JS bundle): a new early-return guard was added to the autocompact-decision function in 2.1.159:

``js
// Present in 2.1.159, absent in 2.1.156
if (EDH() && !uc() && !K__(model, autoCompactWindow)) return false;
``

Where EDH() is true for non-remote sessions, uc() requires the tengu_amber_redwood3 experiment, and K__ is true only when autoCompactWindow came from settings.json
or the CLAUDE_CODE_AUTO_COMPACT_WINDOW env var. For a typical local user with none of those set, the function short-circuits to return false regardless of context fill.

Verifiable from any user's local binary cache:

``sh
$ strings ~/.local/share/claude/versions/2.1.156 | grep -c "if(EDH()&&!uc()&&!K__"
0
$ strings ~/.local/share/claude/versions/2.1.159 | grep -c "if(EDH()&&!uc()&&!K__"
1
``

Related: #42149 asked for a way to disable autocompact and was closed as not planned. 2.1.159 effectively grants that, but as a default rather than an opt-in, and without
documenting it.

What Should Happen?

With autoCompactEnabled: true (the default), autocompact should fire automatically when the context approaches the threshold, as it has since 0.2.47. The 1.0.51 changelog set
this trigger to ~80%.

If gating autocompact behind explicit configuration is intentional, then at minimum:

1. Document autoCompactWindow, CLAUDE_CODE_AUTO_COMPACT_WINDOW, DISABLE_AUTO_COMPACT, and DISABLE_COMPACT in the public settings/env-var reference.
2. Add a 2.1.159 changelog entry naming the behavioural change.
3. Surface the gate at startup or in /status (e.g. "Autocompact is configured but inactive — set autoCompactWindow to enable").

Error Messages/Logs

(none — failure is silent; no warning, no log entry, no /status indicator)

Steps to Reproduce

1. Use Claude Code 2.1.159 in a normal local session (not Remote Control; CLAUDE_CODE_REMOTE unset).
2. Confirm ~/.claude/settings.json does not contain autoCompactWindow, and CLAUDE_CODE_AUTO_COMPACT_WINDOW is unset.
3. Confirm autoCompactEnabled is true (default).
4. Have a long conversation. Watch /context climb past the documented ~80% trigger.
5. Observed: no compaction fires. /context keeps climbing past 100%. Eventually the model itself returns "Prompt is too long".
6. Add "autoCompactWindow": 160000 to ~/.claude/settings.json. Restart Claude Code. Repeat steps 4–5.
7. Observed: autocompact now fires as it did pre-2.1.159.

Reproducing the binary diff (any machine with both versions cached):

``sh
strings ~/.local/share/claude/versions/2.1.156 | grep -c "if(EDH()&&!uc()&&!K__" # 0
strings ~/.local/share/claude/versions/2.1.159 | grep -c "if(EDH()&&!uc()&&!K__" # 1
``

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.156

Claude Code Version

2.1.159 (Claude Code)

Platform

AWS Bedrock

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Workarounds (any one re-enables previous behaviour):

• Add to ~/.claude/settings.json: "autoCompactWindow": 160000 (range accepted by the schema is 100000–1000000; 160000 ≈ legacy ~80% trigger on a 200K window).
• Or env: export CLAUDE_CODE_AUTO_COMPACT_WINDOW=160000.
• Or roll back: ln -sf ~/.local/share/claude/versions/2.1.156 ~/.local/bin/claude (until next auto-update).

Timeline of autocompact in the public CHANGELOG (for context):

| Version | Entry |
|---|---|
| 0.2.47 | "Automatic conversation compaction for infinite conversation length (toggle with /config)" |
| 1.0.51 | "Increased auto-compact warning threshold from 60% to 80%" |
| 2.1.128 | First public mention of "autocompact window" (in a bugfix) |
| 2.1.149 | Bugfix for /config reporting phantom changes to auto-compact (confirms /config exposes a toggle) |
| 2.1.156 | Last version where the guard is absent — autocompact fires by default |
| 2.1.159 | Guard introduced; changelog reads only "Internal infrastructure improvements (no user-facing changes)" |

autoCompactWindow and CLAUDE_CODE_AUTO_COMPACT_WINDOW are not in the public docs at code.claude.com/docs and not in the changelog. Discovering the workaround required
disassembling the JS bundle.