Claude Opus 5 and Sonnet 5 return empty responses

[cryptonana]

Description

I'm having an issue using Claude Opus 5 and Claude Sonnet 5 with Agent Zero through my own OpenAI-compatible API endpoint.

The API request reaches my API successfully and the requests are being processed/billed, but Agent Zero receives an empty/unusable response.

Interestingly, the exact same Agent Zero setup and API endpoint works correctly with GPT-5.6.

Environment

• Agent Zero: [version]
• OS: Ubuntu 24.04
• Python: 3.12
• LiteLLM: [version]
• Installation: Docker
• API: Custom OpenAI-compatible API
• API mode: OpenAI-compatible / Chat Completions

Models tested

Claude Opus 5

Model:

claude-opus-5

Agent Zero repeatedly shows:

A0: Calling LLM...
WRN: Model returned an empty response (no reasoning, no content, no tool call)