[BUG] Conversation compaction intermittently fails or deadlocks chats (claude.ai web/mobile, post–Jan 15 regression)

[avrilelvina-web]

Preflight Checklist

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

What's Wrong?

Conversation compaction in the Claude.ai web and mobile chat UI intermittently fails and leaves conversations unusable.

Two failure modes are observed:

A) Hard failure

• Compaction triggers (via /compact or automatic compaction)
• Error banner appears: “Conversation compaction failed”
• After this, the conversation becomes permanently unresponsive:
  • Prompts bounce back to the input box or never complete
  • UI remains stuck in “responding in background”
  • Reloading, logging out, or switching devices does not recover the chat

B) Degraded fallback (incorrect behavior)

• Instead of compacting, Claude returns a “context too large / minimal handover summary”
• This does not compact or reduce the conversation context
• The original conversation remains at or near the context limit and unusable
• User is effectively forced to abandon the chat and start a new one

Additional characteristics:

• Issue reproduces across both web and mobile for the same conversation
• Behavior is intermittent: some conversations compact successfully; others deadlock
• Occurs more frequently in long conversations with many tool calls and uploads
• Once a conversation enters the broken state, it cannot be recovered

This is a post–Jan 15 regression and remains reproducible as of Jan 25, 2026.

What Should Happen?

When a conversation approaches the context limit, compaction should succeed and preserve a usable conversation state.

If compaction cannot succeed, it should fail gracefully without corrupting the conversation or forcing abandonment, and should not present a handover summary as if compaction succeeded.

Error Messages/Logs

"Conversation compaction failed"

OR

No error message displayed; conversation remains stuck in "responding in background".

Steps to Reproduce

1. Start a new conversation on claude.ai (web or mobile)
2. Accumulate a long context (~30–50 messages) with multiple tool calls and uploads
3. Trigger compaction via /compact or allow automatic compaction near the context limit
4. Observe one of the following:
   a) “Conversation compaction failed” error
   b) Silent no-op with conversation stuck in “responding in background”
   c) “Context too large / minimal handover summary” instead of actual compaction
5. After failure, the conversation becomes permanently unusable
6. Reloading, logging out, or switching devices does not recover the chat

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Before Jan 15, 2026 (exact version unknown)

Claude Code Version

N/A – not using Claude Code CLI

Platform

Anthropic API

Operating System

Other

Terminal/Shell

Terminal.app (macOS)

Additional Information

Scope:

• Affects Claude.ai web and mobile chat UI (same conversation breaks across both)
• Not related to Claude Code CLI or terminal usage
• OS/terminal fields are filled only because the template requires them

Observations:

• Issue is intermittent but permanently destructive once triggered
• More frequent in long conversations with many tool calls and uploads

Two distinct failure modes are documented via screenshots:

• Hard failure with explicit compaction error
• Degraded fallback returning a handover summary instead of compacting

Related prior reports (closed due to scope/mixed issues):

• [BUG] Conversation compaction intermittently corrupts conversation state: “Compaction failed unexpectedly” and silent prompt submission failures #18482
• [BUG] Auto-compact not triggering on Claude.ai (web & desktop) despite being marked as fixed #18866

This report isolates the remaining residual failure mode still reproducible as of Jan 25, 2026.

[github-actions]

Found 3 possible duplicate issues:

1. [BUG] Conversation compaction intermittently corrupts conversation state: “Compaction failed unexpectedly” and silent prompt submission failures #18482
2. [BUG] Auto-compact not triggering on Claude.ai (web & desktop) despite being marked as fixed #18866
3. [BUG] [claude.ai] Compaction fails silently on web/desktop/mobile — related to #16349 #19744

This issue will be automatically closed as a duplicate in 3 days.

• If your issue is a duplicate, please close it and 👍 the existing issue instead
• To prevent auto-closure, add a comment or 👎 this comment

🤖 Generated with Claude Code

[avrilelvina-web]

Not a duplicate.

#18482 and #18866 were closed due to scope/mixed-issue reasons and did not track this residual failure mode.

This issue (#20696) isolates a post–Jan 15 regression in claude.ai web/mobile where:

• compaction intermittently fails or deadlocks,
• some chats remain permanently unrecoverable,
• and a degraded “handover summary” is returned instead of actual compaction.

Those behaviors are still reproducible as of Jan 25, 2026 and were not resolved by prior fixes.

Leaving this open to track the remaining failure mode.

[raphaelfontenelle]

I have the same issue here. I usually have long conversations, but now it just stops working and I get the prompt back.
I’m a Max plan subscriber and I’ve been using Claude for months with conversations lasting several days without issues. Since January 14th, auto-compact stopped working completely. This feature was essential for my workflow (academic research).

[rashevzarko-crypto]

Shall we mention here that now Claude compacts every 2-3 messages? This is not normal. That's definitely not 200K context window and once it compacts, you should have more messages before the next compacting. This is in my opinion.

[gretel]

max plan pretty useless without compaction working.

[braidwalkers]

Experienced the "compaction failed unexpectedly" on January 26, 2026.
Sonnet 4.5.
Accessing Claude.ai in a web browser.
Happened twice in a row, both at 95% compaction.
Chat only.
Previously compacted twice successfully in the same chat.
Max plan.

[bkuczabs-arch]

I've been getting it too extremely consistently. I would give steps to reproduce but unfortunately I can't provide steps to NOT reproduce. Whether on mobile app or web UI I consistently get the hard failure. Haven't tried desktop because if I'm on my PC I just use Claude code.

[rashevzarko-crypto]

I just started a new chat and it compacted my first prompt. What kind of nonsense is this???