v2.1.92 regression: autocompact threshold reduced to 400k on Opus 4.6 (1M context)

Summary

Claude Code v2.1.92 reduces the autocompact window to ~400k tokens on Opus 4.6 (1M context), down from the full ~1M available in v2.1.91 and earlier. This is an undocumented regression — the v2.1.92 release notes contain no mention of autocompact threshold changes.

Evidence

v2.1.91 and earlier: /context shows 24k/1000k tokens — full 1M window available. Sessions routinely ran to 600k+ tokens without compaction. 32MB session transcripts with zero compaction events.

v2.1.92: /context shows 25.7k/400k tokens — autocompact window capped at 400k. Sessions trigger compaction at ~400k, wasting 60% of the context window. Confirmed on two separate machines (Ubuntu 22.04) with the same Claude Max subscription and Opus 4.6 model.

Rollback confirms: Downgrading to v2.1.91 on one machine immediately restored the full 1M window. Upgrading back to v2.1.92 re-introduced the 400k limit.

Visual comparison

v2.1.91 — full 1M context available

 ▐▛███▜▌   Claude Code v2.1.91
▝▜█████▛▘  Opus 4.6 (1M context) · Claude Max
  ▘▘ ▝▝    ~/Projects/cairn

❯ /context
  ⎿  Context Usage
     ⛁ ⛁ ⛁ ⛁ ⛀ ⛀ ⛀ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   Opus 4.6 (1M context)
                                               claude-opus-4-6[1m]
     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   23.8k/1m tokens (2%)

     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   Estimated usage by category
                                               ⛁ System prompt: 6.3k tokens (0.6%)
     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   ⛁ System tools: 8.6k tokens (0.9%)
                                               ⛁ Memory files: 8.3k tokens (0.8%)
     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   ⛁ Skills: 493 tokens (0.0%)
                                               ⛁ Messages: 8 tokens (0.0%)
     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   ⛶ Free space: 955.2k (95.5%)
                                               ⛝ Autocompact buffer: 21k tokens
     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶                         (2.1%)

v2.1.92 — capped at 400k

 ▐▛███▜▌   Claude Code v2.1.92
▝▜█████▛▘  Opus 4.6 (1M context) · Claude Max
  ▘▘ ▝▝    ~/Projects/cairn

❯ /context
  ⎿  Context Usage
     ⛁ ⛀ ⛁ ⛁ ⛁ ⛁ ⛀ ⛀ ⛶ ⛶   Opus 4.6 (1M context)
                           claude-opus-4-6[1m]
     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   23.8k/400k tokens (6%)

     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   Estimated usage by category
                           ⛁ System prompt: 6.3k tokens (1.6%)
     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   ⛁ System tools: 8.6k tokens (2.2%)
                           ⛁ Memory files: 8.3k tokens (2.1%)
     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   ⛁ Skills: 493 tokens (0.1%)
                           ⛁ Messages: 8 tokens (0.0%)
     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶   ⛶ Free space: 355.2k (88.8%)
                           ⛝ Autocompact buffer: 21k tokens (5.3%)
     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶

     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶

     ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶ ⛶

     ⛶ ⛶ ⛶ ⛶ ⛶ ⛝ ⛝ ⛝ ⛝ ⛝

     Auto-compact window: 400k tokens · /autocompact

Note: the bar shrinks from 20 columns to 10 columns, and the denominator drops from 1m to 400k.

Environment

• Claude Code v2.1.92 (npm and native builds)
• Model: Opus 4.6 (1M context) via Claude Max
• Ubuntu 22.04 (tested on two machines)
• No custom autocompact configuration

Impact

Users paying for 1M context are getting 400k. Long-form development sessions that previously worked without compaction now lose context mid-task.

Related

• #34332 — Autocompact triggers too early on Opus 4.6 (1M context)
• #31806 — CLAUDE_AUTOCOMPACT_PCT_OVERRIDE capped by Math.min
• #24079, #19485 — Earlier premature autocompact reports