yuullm

Unified streaming LLM interface with provider-agnostic reasoning / tool-call abstraction.

What It Does

yuullm normalises the streaming differences across LLM providers (OpenAI, Anthropic, and any OpenAI-compatible API) into a uniform AsyncIterator[Reasoning | ToolCall | Response]. It also collects Usage and Cost after the stream ends.

yuullm is stateless — no session, no history management. You own the message list.

Design in One Sentence

Messages and output items are typed structs, tools and content blocks are plain dicts — minimal abstraction, maximum interop.

Installation

pip install yuullm

Quick Start

import yuullm

client = yuullm.YLLMClient(
    provider=yuullm.providers.OpenAIProvider(api_key="sk-..."),
    default_model="gpt-4o",
)

messages = [
    yuullm.system("You are a helpful assistant."),
    yuullm.user("What is 2+2?"),
]

stream, store = await client.stream(messages)
async for item in stream:
    match item:
        case yuullm.Reasoning(text=t):
            print(f"[thinking] {t}", end="")
        case yuullm.Response(text=t):
            print(t, end="")

# After stream ends
usage = store["usage"]
cost = store["cost"]  # Cost | None

Best Practice: Tool-Call Round-Trip

When you give tools to an LLM, the model may respond with ToolCall items instead of (or alongside) text. You need to execute those calls and feed results back. Here's the idiomatic pattern:

import json
import yuullm

messages = [yuullm.user("What's the weather in Paris?")]

while True:
    stream, store = await client.stream(messages, tools=tools)

    tool_calls: list[yuullm.ToolCall] = []
    async for item in stream:
        match item:
            case yuullm.Reasoning(item=text) if isinstance(text, str):
                print(f"[thinking] {text}", end="")
            case yuullm.ToolCall() as tc:
                tool_calls.append(tc)
            case yuullm.Response(item=text) if isinstance(text, str):
                print(text, end="")
            case yuullm.Tick():
                pass  # heartbeat during tool-call streaming, safe to ignore

    if not tool_calls:
        break  # model replied with text, done

    # Append assistant message containing tool calls
    messages.append(yuullm.assistant(
        *[{"type": "tool_call", "id": tc.id,
           "name": tc.name, "arguments": tc.arguments}
          for tc in tool_calls]
    ))

    # Execute each tool and append results
    for tc in tool_calls:
        result = execute_tool(tc.name, json.loads(tc.arguments))
        messages.append(yuullm.tool(tc.id, json.dumps(result)))

Key points:

• Use match/case to dispatch all four stream item types. Tick carries no payload — ignore it unless you have a reason not to.
• The while True loop handles multi-round tool use (the model may chain multiple tool calls before producing a final text response).
• yuullm.assistant(...) and yuullm.tool(...) are helpers that build Message structs with the right role and content.

Hooks: Provider-Level Visibility

Motivation

yuullm abstracts away raw provider chunks into Reasoning | ToolCall | Response. But sometimes you need the raw chunks — for example, to forward SSE events to a frontend in real time, or to detect a specific tool call name before the full arguments finish streaming.

The on_raw_chunk hook gives you provider-level visibility without abandoning the streaming abstraction.

on_raw_chunk

Pass a callback to client.stream(). It fires on every raw provider chunk before yuullm processes it:

def forward_to_frontend(chunk):
    # chunk type depends on provider:
    #   OpenAI:    openai.types.chat.ChatCompletionChunk
    #   Anthropic: event object with .type attribute
    sse_queue.put(chunk)

stream, store = await client.stream(
    messages,
    on_raw_chunk=forward_to_frontend,
)

Tick Heartbeat

Problem: During tool-call streaming, the provider accumulates argument deltas internally and yields nothing to the async-for loop. If your on_raw_chunk hook pushes SSE events into a queue, the consumer loop never gets a chance to flush them until the tool call finishes — SSE events arrive in a burst instead of in real time.

Solution: When on_raw_chunk is registered, yuullm yields Tick() items during tool-call argument accumulation. Tick carries no data; it just keeps your async-for loop spinning so side-channel work (like flushing an SSE queue) can proceed promptly.

If you don't use on_raw_chunk, no Tick is ever emitted — fully backward compatible.

on_tool_call_name Helper

Fires a callback when a specific tool call name is detected in the raw stream, useful for early UI feedback (e.g., showing a "Searching..." indicator before arguments finish streaming):

def on_search_start(index: int):
    notify_ui("search_started")

stream, store = await client.stream(
    messages,
    on_raw_chunk=yuullm.on_tool_call_name("search", on_search_start),
)

Providers

OpenAI / OpenAI-compatible

provider = yuullm.providers.OpenAIProvider(
    api_key="sk-...",
    base_url="https://api.openai.com/v1",  # or any compatible endpoint
    provider_name="openai",                 # used for price lookup
)

Works with any OpenAI-compatible API (DeepSeek, OpenRouter, vLLM, etc.) by setting base_url and provider_name:

# DeepSeek
provider = yuullm.providers.OpenAIProvider(
    api_key="sk-...",
    base_url="https://api.deepseek.com/v1",
    provider_name="deepseek",
)

Anthropic

provider = yuullm.providers.AnthropicProvider(
    api_key="sk-ant-...",
    provider_name="anthropic",
)

Pricing

Cost is calculated using a three-level fallback:

If none match, store["cost"] is None — never blocks.

client = yuullm.YLLMClient(
    provider=...,
    default_model="gpt-4o",
    price_calculator=yuullm.PriceCalculator(
        yaml_path="./custom_prices.yaml",  # optional
    ),
)

- provider: openai
  models:
    - id: gpt-4o
      prices:
        input_mtok: 2.5        # USD per million input tokens
        output_mtok: 10
        cache_read_mtok: 1.25   # optional

- provider: anthropic
  models:
    - id: claude-sonnet-4-20250514
      prices:
        input_mtok: 3
        output_mtok: 15
        cache_read_mtok: 0.3
        cache_write_mtok: 3.75

API Reference

Messages

ContentItem = TextItem | ImageItem | AudioItem | FileItem
ProtocolItem = ToolCallItem | ToolResultItem
MessageItem = ContentItem | ProtocolItem

Content = list[ContentItem]
MessageContent = list[MessageItem]

class Message:
    role: Role
    content: MessageContent
    provider_extra: dict[str, Any]

Helper functions: system(content), user(*items), assistant(*items), tool(tool_call_id, content).

Provider-specific message options can be passed through helper keyword arguments and are stored in provider_extra.

Stream Items

YLLMClient

YLLMClient(
    provider: Provider,
    default_model: str,
    tools: list[dict] | None = None,
    price_calculator: PriceCalculator | None = None,
)

client.stream(messages, *, model=None, tools=None, on_raw_chunk=None, **kwargs)

Returns (AsyncIterator[StreamItem], store). model and tools override the defaults. After the iterator is exhausted, store["usage"] is a Usage and store["cost"] is Cost | None.

Usage & Cost

Usage(provider, model, request_id, input_tokens, output_tokens, cache_read_tokens, cache_write_tokens, total_tokens)
Cost(input_cost, output_cost, total_cost, cache_read_cost, cache_write_cost, source)

Development Setup

./scripts/setup-dev.sh

Installs git hooks (currently: pre-push tag/version validation).