Cline hits OpenAI native model reasoning/function_call pairing error during MCP tool use

What this error means

reasoning/function_call pairing error during MCP/tool use on gpt-5.3-codex, gpt-5.4, gpt-5.5 is a Cline (Claude Code) failure pattern reported for developers trying to fix reasoning/function_call pairing errors when using gpt-5 series models through cline mcp integration. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issue #10656 in cline/cline (opened May 12, 2026). Latest Cline versions encounter errors combining reasoning capabilities with function calls when using new GPT-5 models via MCP. Multiple comments indicate active user frustration with paid model features failing. Maps to ‘AI Coding Tools’.

Common causes

• GitHub issue #10656 in cline/cline (opened May 12, 2026). Latest Cline versions encounter errors combining reasoning capabilities with function calls when using new GPT-5 models via MCP. Multiple comments indicate active user frustration with paid model features failing. Maps to ‘AI Coding Tools’.

Quick fixes

1. Confirm the exact error signature matches reasoning/function_call pairing error during MCP/tool use on gpt-5.3-codex, gpt-5.4, gpt-5.5.
2. Check the Cline (Claude Code) account, local tool state, and provider configuration involved in the failing workflow.
3. Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

• Verify the command, editor, extension, or API client that produced the error.
• Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
• Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. Keep the working fix documented for the team or deployment environment.

How to prevent it

• Keep provider/tool configuration documented.
• Record non-secret diagnostics such as tool version, provider name, model name, and command path.
• Add a lightweight check before CI or production workflows depend on the tool.

Sources checked

• https://github.com/cline/cline/issues/10656

Evidence note: GitHub issue #10656 in cline/cline (opened May 12, 2026). Latest Cline versions encounter errors combining reasoning capabilities with function calls when using new GPT-5 models via MCP. Multiple comments indicate active user frustration with paid model features failing. Maps to ‘AI Coding Tools’.

Related errors

• AI Coding Tools

FAQ

What should I check first?

Start with the exact reasoning/function_call pairing error during MCP/tool use on gpt-5.3-codex, gpt-5.4, gpt-5.5 text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Cline (Claude Code) workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without reasoning/function_call pairing error during MCP/tool use on gpt-5.3-codex, gpt-5.4, gpt-5.5.