Why does listener config for Claude Code Router demo specify message_format: openai?

[l2dy]

demos/use_cases/claude_code_router contains the following configuration:

listeners:
  egress_traffic:
    address: 0.0.0.0
    port: 12000
    message_format: openai
    timeout: 30s

But AFAIK, Claude Code doesn't accept OpenAI-format responses. Is message_format used at all?

[failable]

Same question