GitHub Copilot CLI error
Copilot CLI: CAPIError: 400 ... Duplicate item found with id
Execution failed: CAPIError: 400 {"error":{"code":"bad_request","type":"websocket_error","message":"Duplicate item found with id fc_call_ikBrgmi06fcJeO6uIpJJEQbJ. Remove duplicate items from your input and try again."}}Status: OpenLast verified 0 documented fixes2 sources
What it means
On the turn after a tool or function call, the API rejected the request because the same function-call item ID appeared twice in the input.
Causes
- The reporter said it fails "only ... on the turn after a tool/function call" and suspected a server-side regression. No maintainer has confirmed a cause.
How to fix it
No fix or workaround is documented yet. Follow the linked issues under Sources for updates.
More Copilot CLI errors
All 12 Copilot CLI errors✗ No model available. Check policy enablement under GitHub Settings > CopilotStatus: Fixed in releaseYou are not authorized to use this Copilot feature, it requires an enterprise or organization policy to be enabled.Status: By designRequest failed due to a transient API error. Retrying...Status: Open✗ Execution failed: Error: Failed to get response from the AI model; retried 5 times (total retry wait time: 5.927545045390875 seconds) Last error: Unknown errorStatus: Fixed in releaseCAPIError: 400 {"message":"","code":"invalid_request_body"}Status: Open✗ Model call failed: "Connection error." ✗ Execution failed: CAPIError: Connection error.Status: Fixed in releaseposix_spawnp failureStatus: Fixed in releaseServer failed to connectStatus: Fixed in release
Related reading
- Claude Code vs Codex vs Copilot CLI: Local Sandboxes ComparedCopilot CLI local sandboxing is GA. How it compares with Claude Code and Codex on defaults, network, credentials, Windows, and what still runs outside.
- GitHub Copilot CLI With Ollama: Local Models and the New SandboxCopilot CLI 1.0.94 finds local Ollama models from /model and ships an OS-level sandbox. Setup, the 4k context trap, and why local is not offline.
- Claude Sonnet 5.5 Developer Guide: Pricing and API ChangesClaude Sonnet 5.5 costs $2/$10 per million tokens, and cache reads fell to $0.10 on October 7 - half of Opus 5.5 on every line. Pricing math and API changes.
- GitHub Copilot's September Reset: Prepaid Seats, One Unified Agent Experience, Balanced Reviews by DefaultGitHub Copilot September changes: prepaid Business and Enterprise seats, one unified agent experience and Balanced reviews by default. What it means for teams.
- GitHub's August 17 Outage: Agent Fleets Need a 4-Hour Local FallbackGitHub's August 17 outage ran 7 hours 47 minutes across PRs, Actions, APIs and Copilot. Why coding agent fleets need a four-hour local fallback.
- GitHub Copilot for JetBrains Gains Persistent Memory and Ollama BYOKGitHub Copilot for JetBrains adds memory across chat sessions, Ollama as a BYOK provider, and enterprise settings for MCP access. What each feature does.
FAQ
What does "CAPIError: 400 ... Duplicate item found with id" mean in Copilot CLI?
On the turn after a tool or function call, the API rejected the request because the same function-call item ID appeared twice in the input.
How do I fix "CAPIError: 400 ... Duplicate item found with id"?
No fix is documented yet. The reporter said it fails "only ... on the turn after a tool/function call" and suspected a server-side regression. No maintainer has confirmed a cause.
Is this Copilot CLI error fixed?
Status: Open. Still open upstream. Any documented fixes are workarounds so far. Affected versions: Reported on 1.0.54 and 1.0.55 (May 2026). Still reported in later comments.
Sources
Last verified against 2 sources: official docs, maintainer replies and release notes.
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