[Bug] VS Code extension: Tool use concurrency error after Jan 23-24 update

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/20555
2. https://github.com/anthropics/claude-code/issues/20532
3. https://github.com/anthropics/claude-code/issues/20539

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🤖 Generated with Claude Code

Same! I literally can't work

same

+1

same here 1+

downgrade to vscode extension version 2.1.17 fixed the issue
uninstall the extension --> restart vscode --> install extension with 2.1.17 version -> fixed

Additional data point:

• CLI version 2.1.19 works fine after removing a PreToolUse hook
• VS Code extension 2.1.19 still errors with the same configuration

My setup had a PreToolUse hook (running a Python script on every tool call via "matcher": ".*"). Removing the hook fixed the CLI, but the VS Code extension continues to throw API Error: 400 due to tool use concurrency issues on simple operations like echo "__tool_test__".

This suggests the extension has a separate code path triggering the concurrency issue, independent of user hooks.

Environment:

• macOS Darwin 25.2.0 (Apple Silicon)
• Claude Code CLI: 2.1.19 ✅ works
• Claude Code VS Code Extension: 2.1.19 ❌ still errors

Screenshot attached shows the error occurring on a basic echo command in the extension.

+1 vs code extension literally become unusable

✅ WORKAROUND FOUND

The fix: Install VS Code extension version 2.1.17 while keeping CLI at 2.1.19

Steps:

1. In VS Code, go to Extensions
2. Find "Claude Code for VS Code"
3. Click the dropdown arrow next to Uninstall → "Install Specific Version" → Select 2.1.17
4. Uncheck "Auto Update" to prevent it from upgrading
5. Restart VS Code

Result:

• Extension shows: 2.1.17
• claude --version shows: 2.1.19
• It works! No more concurrency errors

What this tells us:
The bug is in the VS Code extension code (2.1.18 or 2.1.19), NOT in the CLI or API. The extension's tool call orchestration is broken in newer versions.

| Configuration | Status |
|---------------|--------|
| Extension 2.1.19 + CLI 2.1.19 | ❌ Broken |
| Extension 2.1.17 + CLI 2.1.19 | ✅ Works |

Hope this helps others!

I'm also getting this

Add me to the pile.

Also experiencing this on Linux (Garuda/Arch) with VSCodium + CLI
Environment:

Platform: linux (Garuda Linux / Arch-based)
IDE: VSCodium with Claude Code extension
CLI Version: 2.1.19
Subscription: Claude Pro (just subscribed today, Jan 24 2026)

Key finding: Unlike some reports, the CLI is also failing for me with the same thinking block error—not just the extension.
Error (both CLI and extension):
API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0: If an assistant message contains any thinking blocks, the first block must be thinking or redacted_thinking. Found text."},"request_id":"req_011CXTLk88zU9yYdVULufFFg"}
Reproduction:

Open Claude Code (CLI or VSCodium extension)
Ask any question that triggers a tool call (e.g., "can you see the files here?")
Error occurs on first tool use

Notes:

Fresh install, first day using the product
Error is immediate (not a long conversation / context corruption issue)
Restarting session doesn't help
Session is unrecoverable once the error occurs

in cursor extension happened too much. even i reset the session

API Error: 400 due to tool use concurrency issues.

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.3.content.1: tool_use ids must be unique"},"request_id":"req_011CXTZGHjg2Y12XDSgmR3oE"

problem solved when i disable extension auto update and install specific version 2.1.17 plugin

Cmd + Shift + X > extensions > claude code > setting > Install Another Version... > 2.1.17 > restart

same error

same

Same for me too

can confirm this too. v2.1.19 of the extension and get a lot of

<img width="438" height="120" alt="Image" src="https://github.com/user-attachments/assets/09754ebb-5faa-47b2-a8f6-d37ae216741d" />

same here....

same

same

Nice work on triaging this. I can confirm the exact same 400 error in the VS Code extension logs.

Env:

• Windows 10.0.26100.7623
• VS Code 1.108.2
• Claude Code VS Code extension 2.1.19 (embedded claude.exe reports 2.1.19)
• CLI 2.0.37 (separate)

Error (repeated):
invalid_request_error: tool_use ids were found without tool_result blocks immediately after
Occurs in non‑streaming fallback, multiple times.

Log evidence:
C:\Users\user\AppData\Roaming\Code\logs\20260126T133640\window2\exthost\Anthropic.claude-code\Claude VSCode.log
lines 371, 639, 940, 1120, 1499

Additional (possibly separate) issue I also see:
ENOENT for missing skills dirs:
C:\ProgramData\ClaudeCode\.claude\skills
C:\Users\User\.claude\skills

Log:
C:\Users\User\AppData\Roaming\Code\logs\20260126T140056\window1\exthost\Anthropic.claude-code\Claude VSCode.log
lines 33, 44, 161, 173, 299, 310, 385, 396

Also saw:
MCP server "claude-vscode" Failed to fetch tools: MCP error -32601: Method not found
(same log file, lines 265, 451)

I created empty skills dirs locally to see if it suppresses the ENOENTs; happy to update after a clean restart.

Update: After full restart, ENOENT still appears, and 400 persists.

me also !!!

+1

+1

Same error here!

Same error

Same over here. Downgrading to 2.1.17 fixes it.

Same here

This also affects the VS Code extension on macOS.

same

same!

How the eff is this not assigned or something? Is this github unmonitored or something? The new version of no reply emails?

Same

+1 Experiencing the same issue.

Environment:

• Platform: Linux (Ubuntu, kernel 6.14.0-37-generic)
• VS Code Extension: 2.1.19
• Subscription: Claude Max

Behavior:

• Frequent API Error: 400 due to tool use concurrency issues errors during normal tool operations
• Error occurs on file reads, edits, and other standard tool calls
• Never experienced this issue before the recent extension update

Will try the 2.1.17 downgrade workaround.

+1

yupp +1

Until Anthropic devs fix this issue, the best workaround is to disable Auto Update and install specific version 2.1.17
This has fixed the issue for me for now.

<img width="1017" height="290" alt="Image" src="https://github.com/user-attachments/assets/8a7aa2a0-051b-44f9-ad7b-d4b949052f86" />

Affected on MacOS, followed downgrade instructions and completely restarted vs code, Claude Code Chat works but another product I love using Chat for Claude Code is not :(

+1

+1, but downgrading to 2.1.17 fixed it for me (on Windows)

same...happened out of nothing, 1 minute is working another minute is not :(

+1

+1, will try the dowgrade

Another one here

Impacts me as well - Just downgraded to 2.1.17

Same issue - I'm downgrading to 2.1.17

Having this issue as well

😢

Same 🪳

Having this issue as well

Same issue - I'm downgrading to 2.1.17

same

Facing the same issue on both versions:

1. CLI 2.1.19 - on mac
2. docker sandbox claude cli with 2.1.17

same

Facing same issue

I'm having this issue too starting in the last few days

same, 2.1.17 works 2.1.19 doesn't

Claude is broken for me too

Same and I downgraded to 2.1.17 and it is still happening.

Same and I downgraded to 2.1.17 and it is still happening.

Exact same boat here.

Same here... it is useless to try to get any work done in VS code..

Yup same, downgrading to 2.1.17 worked for me. Happening in local VSCode on MacOS and SSH'd remote connection VSCode on debian.

Same here. Hitting this error every 3 seconds. Can't work like this.

Downgrading to 2.1.17 fixed it for me.

Same issue on linux, downgrading to 2.1.17 and restart IDE fixed it for me.

Same Issue. MacOS/VS Code

+1

+1

+1

+1

Same. Claude Code basically useless now.

+1

+1, downgrading to 2.1.17 worked for me

+1

+1

+1

Same issue, 100% of my calls are hitting this

Same, Affects 100% of my calls +1

+1

+1

+1

+1

Same, affects 100% of my calls

<img width="376" height="378" alt="Image" src="https://github.com/user-attachments/assets/0833433d-3df0-4fb7-9174-5c9c82a99a5d" />

+1, downgraded to 2.1.17

+1

+1 here, will donwgrade soon

+1 blocking me

+1. all my calls are affected. why am i paying for this? (owngrading to 2.1.17 also fixes)

+1, confirmed the CLI is fine and downgrading to 2.1.17 also fixes

+1

+1

+1

+1

+1 Had to downgrade to get it to work... Really annoying

+1

+1

We've implemented a fix for this, and errors should be going down. Please tag if it's still present

Saw this just now. I am using the json-sdk so this isn't just a VSCode issue

{"type":"assistant","message":{"id":"5647d532-dc96-4eba-aaf7-d7ba078838d8","container":null,"model":"<synthetic>","role":"assistant","stop_reason":"stop_sequence","stop_sequence":"","type":"message","usage":{"input_tokens":0,"output_tokens":0,"cache_creation_input_tokens":0,"cache_read_input_tokens":0,"server_tool_use":{"web_search_requests":0,"web_fetch_requests":0},"service_tier":null,"cache_creation":{"ephemeral_1h_input_tokens":0,"ephemeral_5m_input_tokens":0}},"content":[{"type":"text","text":"API Error: 400 due to tool use concurrency issues."}],"context_management":null},"parent_tool_use_id":null,"session_id":"6bfc6ec2-94cd-4ca3-8568-9db6507d5239","uuid":"db081a88-7f8d-41c8-9ead-6f16e0a38bcf","error":"invalid_request"}

The problematic experiment has been disabled, no upgrade needed.

@meawoppl yes- VSCode is built on the SDK and the issue was in the SDK.

we can we now use the latest version of the vscode extension ? all fixed ?

we can we now use the latest version of the vscode extension ? all fixed ?

i changed nothing and it's working now, but i'm a newb so, maybe? XD

It worked for awhile, and it's broken again now. Latest extension version. Going back to 2.1.17 @km-anthropic

@blois - Unfortunately, this issue was not resolved in VS Code extension version 2.1.20.
I think the text of the error referencing "concurrency" is misleading. The issue appears to have nothing to do with concurrency. Even the prompt "What's in my home directory?" which results in a single tool call "ls -la ~/" leads to this error:

API Error: 400 due to tool use concurrency issues.

I'm still having this issue on 2.1.20.

I have this issue right now, since last night. in Cursor:
Version: 2.4.21 (Universal)
VSCode Version: 1.105.1

I'm still having this issue on 2.1.20.

Ditto, still having this issue on 2.1.20.

+1 having the issue.

@blois , not sure if you already saw this, but there is still people experiencing this issue, including me.

same. still having this issue.

+1

same, still happening :/

Identificateur : anthropic.claude-code
Version : 2.1.20

yup
Version : 2.1.20

downgrading to 2.1.17 worked to fix for now

Oh wow is this annoying! Hoping a fix is implemented soon

yup Version : 2.1.20 downgrading to 2.1.17 worked to fix for now

thanks, you're right, seems to be good for me for the moment

Identifier
anthropic.claude-code
Version
2.1.20

same here

Same issue as yesterday, errors should be recovering with no upgrade/downgrade needed.

Same issue as yesterday, errors should be recovering with no upgrade/downgrade needed.

Might be a coincidence then, but downgrading to .17 immediately resolved it.

+1 with the same issue

Just upgraded my subscription, can't use the latest version 🥲 . Downgrade for now folks

+1

+1

+1

+1

+1

+1

reopening this to take a look!

was on 2.1.27 and it worked for a half day before it started throwing errors again

Error rates for latest versions (>2.1.20) are much better, even than much older versions. If you are seeing this on newer versions, please make sure that the new version is actually running- may need to reload the VSCode window for an upgrade to take effect.

The issue is specific to the VS Code extension version, not the CLI -- the bug was introduced in a recent SDK experiment. Rolling back to a specific extension version fixes it while keeping your CLI up to date. You can find the full verified solution at https://cacheoverflow.dev/blog/Hx2IdZyg

I see this in the Android Claude app too, in Code. version 1.260223.17, com.anthropic.claude.

Once a conversation gets into this state, it keeps outputting new versions of this error, regardless of what I say. Eg:

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.3.content.1: tool_use ids must be unique"},"request_id":"req_011CYUyp2DwLs4M7GE7u7WWh"}

Getting it as well

I am also getting it since March 5, 2026
<img width="1117" height="389" alt="Image" src="https://github.com/user-attachments/assets/555bec8d-c707-47aa-a596-727554483ee6" />

This "tool_use ids found without tool_result blocks" error typically means the extension's message handling is out of sync with the API — tool calls are being sent but their results aren't being properly paired.
Workaround 1 — Use the integrated terminal instead of Native UI:
Open VS Code's terminal (Ctrl+`) and run claude` directly. The CLI handles tool use sequencing correctly and doesn't have this issue.
Workaround 2 — Update both the extension and CLI:

claude --update

Make sure both are on the same version. Version mismatches between the CLI and extension can cause serialization issues.
Workaround 3 — Clear extension state:

1. Open Command Palette (Ctrl+Shift+P)
2. Run "Claude Code: Reset State" (if available)
3. Or manually: close VS Code, delete ~/.vscode/extensions/anthropic.claude-code-*/ cache files, reopen

Workaround 4 — Reduce concurrent tool calls:
Add to your CLAUDE.md:

Execute tool calls sequentially, not in parallel. Wait for each tool result before making the next tool call.

This is a performance tradeoff but may avoid the concurrency race condition in the extension's message handler.
The ENOENT error in your logs (scandir 'C:\ProgramData\ClaudeCode\.claude\skills') suggests the extension is looking for skills in an unexpected path. This may be contributing — the extension may be erroring during skill discovery and corrupting the tool call sequence. Creating the missing directory might help:

mkdir "C:\ProgramData\ClaudeCode\.claude\skills"