Qwen 3.5 tool calling requires XML

The Qwen 3.5 27B release introduced a major hurdle for the local agent ecosystem by diverging from standard JSON tool-calling formats in favor of a specialized XML-based syntax.

• –**Format Mismatch:** Qwen 3.5 was trained on `<function=name>` XML tags; sending JSON results in the model outputting raw commands as text instead of executing them.
• –**Backend Solutions:** Ollama v0.17.5+ and recent vLLM versions (using the `--tool-call-parser hermes` flag) correctly handle this format translation.
• –**Agent Friction:** Integration frameworks like OpenClaw and Hermes Agent require specific SDK patches to ensure tool definitions are correctly surfaced in the system prompt.
• –**Performance Tweaks:** Users on RTX 3090 setups should prioritize 8k+ context windows and full GPU offloading to maintain reasoning stability during complex tool chains.