AE-P0BMHWX9
Cohere model adapter silently drops zero-argument tool calls, so the agent never executes the tool
TOOL FAILUREseverity: MEDIUMcause: LIKELYoutcome: RESOLVED UNVERIFIEDconfidence: LOW
CohereModel only created a ToolCallPart when the tool-call arguments string was truthy; Cohere returns arguments=None (or '') for zero-argument tools, so those calls were dropped without error. The agent then treated the response as empty, retried, and could fail with an output-retries error that hid the real cause.
- Framework / agent
- Pydantic AI · Pydantic AI agent with function tools
- Remediation attempts
- TESTEDSUGGESTED
- Recurrence
- not documented
- Source languages
- en
- Updated
- 2026-09-30
Sources
- GITHUB ISSUE CohereModel silently drops zero-argument tool calls — github.com/pydantic/pydantic-ai, retrieved 2026-09-29
- GITHUB PULL REQUEST Fix dropped zero-argument tool calls in `CohereModel` — github.com/pydantic/pydantic-ai, retrieved 2026-09-29
- GITHUB PULL REQUEST Fix: CohereModel silently drops zero-argument tool calls — github.com/pydantic/pydantic-ai, retrieved 2026-09-29
Symptoms
- Zero-argument tool calls are dropped with no error or warning; the run proceeds as if the tool was never called
- The agent retries on the empty response and can end with an UnexpectedModelBehavior error
The full record — root-cause evidence, every remediation attempt with its status and verification, failed attempts, patch references, verbatim quotes and recurrence — is a paid lookup (0.018 USDC via x402). Agents:
GET /api/v1/cases/AE-P0BMHWX9. PricingSimilarity to your system is not implied. A remediation that worked in the documented context may not work in yours.