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v2.1.90 Claude Code Release Notes

Apr 1, 2026
Claude's Analysisby Sonnet 4.6
Full Analysis

/powerup adds interactive feature lessons; performance gets 3 quadratic-time fixes cutting slowdowns in long sessions; hangs, crashes, and hook bugs resolved.

Changes
19
Total Changes (vs Average)
1.1×
Version Type
Patch
Release Focus
Mixed
Day Since Prior Release
1
Release # This Month
#2 of 26
Bug Fix Ratio
47%
Post-Release Edits
—
Change Category
Ecosystem Impact
MCP has appeared in 8 of the last 10 releases — a sustained extensibility focus. This release's MCP contribution is a performance fix (eliminating per-turn JSON serialization), shifting from earlier functional work toward consolidating long-session reliability.
Key Themes
1New `/powerup` Learning Command|3Three Quadratic-Time Performance Fixes|5Session Stability: Hangs, Crashes & Loops Closed|3Hook & Automation Reliability|4Breaking Changes & Privacy Cleanup
May Help If You've Noticed
Your session crashes or freezes in an infinite loop right after hitting a usage or rate limit
Resuming a session feels sluggish on the first message when you use MCP servers or custom agents
Format-on-save in your editor causes Edit or Write to fail with a 'file content changed' error
Hooks meant to block tool calls are being ignored and the tool runs anyway
The session picker is slow to open when you have many saved projects

Changes in Claude Code v2.1.90

Added3 changes

  • •Added /powerup — interactive lessons teaching Claude Code features with animated demos
  • •Added CLAUDE_CODE_PLUGIN_KEEP_MARKETPLACE_ON_FAILURE env var to keep the existing marketplace cache when git pull fails, useful in offline environments
  • •Added .husky to protected directories (acceptEdits mode)

Improved4 changes

  • •Improved performance: eliminated per-turn JSON.stringify of MCP tool schemas on cache-key lookup
  • •Improved performance: SSE transport now handles large streamed frames in linear time (was quadratic)
  • •Improved performance: SDK sessions with long conversations no longer slow down quadratically on transcript writes
  • •Improved /resume all-projects view to load project sessions in parallel, improving load times for users with many projects

Fixed9 changes

  • •Fixed an infinite loop where the rate-limit options dialog would repeatedly auto-open after hitting your usage limit, eventually crashing the session
  • •Fixed --resume causing a full prompt-cache miss on the first request for users with deferred tools, MCP servers, or custom agents (regression since v2.1.69)
  • •Fixed Edit/Write failing with "File content has changed" when a PostToolUse format-on-save hook rewrites the file between consecutive edits
  • •Fixed PreToolUse hooks that emit JSON to stdout and exit with code 2 not correctly blocking the tool call
  • •Fixed collapsed search/read summary badge appearing multiple times in fullscreen scrollback when a CLAUDE.md file auto-loads during a tool call
  • •Fixed auto mode not respecting explicit user boundaries ("don't push", "wait for X before Y") even when the action would otherwise be allowed
  • •Fixed click-to-expand hover text being nearly invisible on light terminal themes
  • •Fixed UI crash when malformed tool input reached the permission dialog
  • •Fixed headers disappearing when scrolling /model, /config, and other selection screens

Changed1 change

  • •Changed --resume picker to no longer show sessions created by claude -p or SDK invocations

Removed1 change

  • •Removed Get-DnsClientCache and ipconfig /displaydns from auto-allow (DNS cache privacy)

Other1 change

  • •Hardened PowerShell tool permission checks: fixed trailing & background job bypass, -ErrorAction Break debugger hang, archive-extraction TOCTOU, and parse-fail fallback deny-rule degradation

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