lm-sys / lm-sys/FastChat

Session Hang on Long Conversations - No Error Feedback

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Description

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Bug Report: Session Hang on Long Conversations (Cache/Context Management Issue)
Reporter: Community Tester
Platform: lmarena.ai / lmarena.direct
Model affected: claude-sonnet-4-6 (primarily), others affected intermittently
Date: April 2026
Browser: Chrome 147
OS: Windows 10

Summary
When continuing a long conversation session (20+ exchanges), the model enters an infinite "Generating..." state and never returns a response. This appears to be related to improper cache/context management on the frontend side.

Steps to Reproduce
Open lmarena.direct or lmarena.ai
Select claude-sonnet-4-6 in Direct Chat mode
Send 25-35 messages in the same session (complex prompts with context)
On one of the subsequent messages, the model shows "Generating..." indefinitely
Page refresh restores the session but immediately resumes "Generating..." state (stuck)

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the hang on lmarena.direct or lmarena.ai in Direct Chat with claude-sonnet-4-6 after 20–35 messages, using the reported Chrome and Windows setup. Compare behavior before and after refresh; done means the session returns a response instead of remaining indefinitely in “Generating...”.

Written by the indexing model from the issue text.

Assessment

Domain
frontend
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Needs clarification
Newbie friendliness
35/100

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