Your Model Isn’t Bad at Tool Calling. Your Serving Stack Is.
Blog post from LiveKit
In the context of tool-calling in AI models, the text outlines a common issue where open models, despite having excellent benchmarks, fail to call tools correctly when integrated with voice agents. This failure is not due to the model itself but rather to the assumption that tool-calling capability resides solely within the model; it actually depends on the interaction between the model and the serving stack. The text explains that the model's native syntax must be correctly parsed by the serving stack, which varies between providers, resulting in discrepancies in tool-calling ability. OpenAI models succeed universally because their native syntax does not require translation on OpenAI-compatible endpoints, whereas the tool-calling success of open models depends on whether the provider has configured a parser for the model's syntax. Additionally, hybrid reasoning models like Nemotron 3 introduce complexity by requiring multiple parsers, which can lead to silent failures in tool calling. The key takeaway is that model capability and endpoint parsing are distinct elements, and teams should conduct a simple diagnostic test to determine whether the issue lies with the endpoint's parsing capabilities rather than the agent or model itself.
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