Conversation history shows duplicate 'Warmup' titles and loads wrong conversations

I'd submitted a duplicate here. I can add that:

• The issue occurs with the extension 2.0.19 as well
• The issue occurs on Windows as well
• The issue occurs whether the Haiku model is 3.5 or 4.5
• When I launch the CLI that is bundled with the extension, the issue doesn't appear (or at least titles that are NOT "Warmup" show up for the conversations). Thus, perhaps the issue is specific to the extension and doesn't even apply to the CLI that is bundled with the extension.
• I think the issue occurred for me without me using "Warmup" as the prompt, but that prompt somehow ended up replacing the prompts that I did use (at least for one-prompt conversations).

I have this issue too and imo I think some kind of agent setting is being overriden when haiku model got triggered. This also happens when I use agent sdk with fork_session=true, resume={session_id}

It's not that users start conversations with "Warmup"

It looks like Claude Code itself started sending a "Warmup" message from user side. Which in turn triggers assistant response of the sorts of "Hi, I'm Claude Code, ready to work on your project ..."

started happening on the day of haiku 4.5 release

My conversation history has been flooded by sessions named "Warmup" as well

This is happening for me as well. VSCode Plugin v2.0.21

Numerous conversations all starting with "Warmup" and then a confused Claude trying to figure out what you want to do. Completely wiped out a bunch of conversations.

Same problem here, I'm building a script to remove this files until they fixed.

Same issue on macOS

Environment:

macOS (Darwin 24.4.0)
Claude Agent SDK: 2.0.19, 2.0.21, 2.0.22 (all affected)
Last working version: 2.0.13 (October 16, 2025)
First broken session: October 17, 2025 @ 3:16 PM (SDK 2.0.19)

我也遇到了，这个影响很大

Same issue here. All my past conversations were deleted

Same here! MacOS.
First broken session: October 20, 2025
I saw the session, closed VS Code and opened another file and wanted to continue with the session and suddenly saw "Warmup" in all!

I "hot fixed" my issue by just asking another question inside the session. Not sure at what point exactly, but afterwards I was able to see the previous conversations. Just asked "Can you summarize our session so far?".

赶紧解决啊

Sorry for the inconvenience, this should be fixed in the latest release! Please update and give it a spin (and let us know if you continue to see if afterwards!)

Sorry for the inconvenience, this should be fixed in the latest release! Please update and give it a spin (and let us know if you continue to see if afterwards!)

no, not fixed! still going!

应该

还没改好，很严重这个问题

Can you please let us know the version you're seeing this in?

2.0.24 (Claude Code)

Can you please let us know the version you're seeing this in?

2.0.24

2.0.25 and this warmup still exists.

raw jsonl of an example chat:

{"type": "summary"}
{"type": "summary"}
{"uuid": "1", "parentUuid": null, "sessionId": "2", "timestamp": "2025-10-22T10:50:15.112Z", "type": "user", "message": {"role": "user", "content": "Warmup"}}
{"uuid": "3", "parentUuid": "1", "sessionId": "2", "timestamp": "2025-10-22T10:50:20.158Z", "type": "assistant", "message": {"role": "assistant", "content": [{"type": "text", "text": "I'm ready to assist you with the Conare project. I've reviewed the system instructions and understand:\n\n**Key principles I'll follow:**\n- Minimal, elegant code changes\n- Nuxt 4 pre-release structure (app/ for frontend, root for backend)\n- [TRUNCATED: 1170 chars total]"}]}}
{"type": "file-history-snapshot"}
{"uuid": "4", "parentUuid": null, "sessionId": "2", "timestamp": "2025-10-22T10:50:30.921Z", "type": "user", "message": {"role": "user", "content": "tf"}}

my first actual message was "tf"

Found the issue, fix inbound!

Found the issue, fix inbound!

thanks!

We just shipped a hotfix for this in v2.0.27. Apologies for the inconvenience. Let us know if you still run into it with the new update!

not sure if this fix was intended for VSCode extension only. but Claude still sends the same warmup messages

raw jsonl of the chat in 2.0.27:

{"type": "summary"}
{"type": "summary"}
{"type": "summary"}
{"uuid": "1", "parentUuid": null, "sessionId": "2", "timestamp": "2025-10-25T08:25:52.590Z", "type": "user", "message": {"role": "user", "content": "Warmup"}}
{"uuid": "3", "parentUuid": "1", "sessionId": "2", "timestamp": "2025-10-25T08:25:57.256Z", "type": "assistant", "message": {"role": "assistant", "content": [{"type": "text", "text": "I'm Claude Code, Anthropic's official CLI for Claude. I'm ready to help you navigate and explore this codebase efficiently.\n\n [TRUNCATED]"}]}}
{"type": "file-history-snapshot"}
{"uuid": "4", "parentUuid": null, "sessionId": "2", "timestamp": "2025-10-25T08:25:58.043Z", "type": "user", "message": {"role": "user", "content": "hello54321"}}
{"uuid": "5", "parentUuid": "4", "sessionId": "2", "timestamp": "2025-10-25T08:26:01.967Z", "type": "assistant", "message": {"role": "assistant", "content": [{"type": "text", "text": "Hello! I see your test message. The vibe-rules are loading correctly (I can see \"test1234\" and \"hello54321\" in the context).\n\nHow can I help you today?"}]}}

This keeps happening. would you guys open the issue please

This keeps happening. would you guys open the issue please

same to me

@hackyon-anthropic can we get the issue re-opened please?

Can you check that you have updated and post screenshots of your issue?

@FutureExcited this gets sent but it shouldn't show up in your message history.

Double Warmup Sessions + No Summaries Generated

Just discovered that SDK v2.0.28 is creating TWO warmup phantom sessions on every initialization, not just one:

1. agent-{id1}.jsonl - Haiku 4.5 warmup
2. agent-{id2}.jsonl - Sonnet 4.5 warmup

Both created simultaneously (1ms apart) with isSidechain: true and marked with the same parent sessionId.

Impact during development:

• Every app restart = 2 phantom sessions
• Every hot reload = 2 more phantom sessions
• After a few hours of dev work = hundreds of agent-*.jsonl files cluttering the sessions directory

Additional Impact - No Summaries:
Sessions initiated through the SDK are no longer generating conversation summaries. This breaks the ability to quickly identify and /resume conversations when switching between Claude CLI, VSCode extension, and SDK-based applications. All sessions just show as "New Session", <ide_opened_file>, or display the warmup message instead of meaningful summaries.

Workaround:
Auto-delete files matching agent-*.jsonl pattern when loading sessions:

// Filter and delete warmup phantom sessions
for (const file of files) {
  if (file.startsWith('agent-')) {
    fs.unlinkSync(path.join(sessionsDir, file));
  }
}

This matches the CLI's behavior of hiding warmup messages from users, but at the filesystem level.

Related: This appears to be related to Anthropic's fix for keeping warmup out of real conversations (from #9671), but creating separate phantom sessions causes its own problems - especially for SDK-based applications with frequent restarts during development.

This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.