Function/tool calling never resolves

Description

When using the inference client with function calling, models seem to never resolve their calls.

As we know, typically, with the OpenAI pattern, the simplest function/tool call is a series of messages of various roles (system, user, assistant, tool) organized like this:

system → user ("what's the weather?") → assistant (tool_calls) → tool (result: "4ºC") → assistant (content: "it's 4ºC")

The HF docs seem to indicate this is the same pattern, although the messages have some minor differences (e.g. description: null, which never happens with OpenAI). When using the Python inference client, these tool_calls never resolve even after functions are called and their return values are included and seemingly properly referenced. Instead, they look like this:

system → user ("what's the weather?") → assistant (tool_calls) → tool (result: "4ºC") → assistant (tool_calls) …

Instead of returning a text completion, the HF inference client returns the same "assistant" message specifying a required tool_calls. In OpenAI, they resolve to a typical "assistant" message with token content if the function calls have been satisfied and no further calls are required.

Models used that exhibit this behavior:

• NousResearch/Hermes-3-Llama-3.1-8B
• Qwen/Qwen2.5-72B-Instruct
• meta-llama/Meta-Llama-3-8B-Instruct

It's worth noting that Mistral models also error out, specifying that a 9-character alphanumeric string is required for the tool_call_id. Now, the models themselves don't provide such IDs, so we need to supply them ourselves. But even when doing so, the same error occurs, that 9-char identifiers are missing. (e.g. mistralai/Mistral-7B-Instruct-v0.3)

The JavaScript client also fails with the above errors, and also a third: "An error occurred while fetching the blob".

System Info

• macOS 15.2
• Python 3.13.1
• huggingface_hub 0.28.1

Information

• Docker
• The CLI directly

Tasks

• An officially supported command
• My own modifications

Reproduction

Gist of sample error code is here: https://gist.github.com/awmartin/c64c84fbbdc3a9f0c2ce6e5ae0dab3dc

1. Provide API token
2. python inference-tool-calls.py

A message results that's unexpected. I expected this to be a typical message with a string content, something like, "It's 4 degrees today." Instead, it just repeats the assistant message with the original tool_call message:

[ChatCompletionOutputComplete(finish_reason='stop', index=0, message=ChatCompletionOutputMessage(role='assistant', content=None, tool_calls=[ChatCompletionOutputToolCall(function=ChatCompletionOutputFunctionDefinition(arguments={'unit': 'Celsius', 'location': 'Philadelphia, PA, US'}, name='get_current_temperature', description=None), id='0', type='function')]), logprobs=None)]

Expected behavior

I expected a message that resolved to something similar to "It's 4 degrees Celsius today" rather than the tool_call message repeated.