async-batch-llm 0.14.0

Provider-agnostic framework for high-throughput LLM processing with async workers, automatic retries, rate limiting, and intelligent validation recovery.

async-batch-llm

async-batch-llm is an asyncio toolkit for latency-sensitive LLM workloads made of independent calls: bulk prompt runs you want back during the current workflow, plus single-call and service request paths that need the same retry/rate-limit behavior. It provides provider-agnostic execution surfaces — a bounded worker pool for bulk runs, plus queue-less single-call and gateway helpers for request paths — with coordinated cooldowns for rate limits, error-type-aware retries, bounded streaming, and token/cost accounting, including failed attempts.

Use it when provider batch APIs are too slow for the job; use those batch APIs when a cheaper 24-hour turnaround is acceptable.

Provider-agnostic (OpenAI, Anthropic, Google, DeepSeek, OpenRouter, PydanticAI, or your own) through a simple strategy pattern; built on asyncio for I/O-bound throughput.

📚 Read the Documentation

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A sense of scale

One concrete GSM8K test-split run is more useful than an abstract "fast". Treat these as order-of-magnitude examples, not promises: model latency, account limits, pricing, and network all move the numbers.

• Thirty independent calls: seconds instead of a minute. The serial race took 39–65 s. With a worker pool it finished in 2.1–4.2 s on the uncapped providers (15.6–19.1× faster). The throttle-capped Gemini 2.5 run used 5 workers and landed at 8.1 s (5.0×).
• A thousand-call pool actually fills. At equal concurrency on 1,000 prompts, async-batch-llm processed 72 items/s on DeepSeek and 108 items/s on Gemini 3.1, versus 58 and 55 items/s for a fair Semaphore pool. The exact multiple is run-specific; the durable point is bounded workers and backpressure without scheduling every coroutine up front.
• The full 1,319-item split made provider tradeoffs visible. DeepSeek Flash completed for $0.054 at 97.0% accuracy; Gemini 3.1 cost $0.433 at 96.6%; Gemini 2.5 cost $0.261 at 95.4% but took ~21.5 minutes because it was capped at 5 workers. The package does not make provider calls cheaper; it makes the cost/latency/accuracy tradeoffs visible and keeps the provider swap small.
• Retries are part of the run, not an afterthought. DeepSeek recovered 9 parse failures; the rough Gemini 2.5 run recorded 120 retries, 41 model escalations, and transient 503s/timeouts, finishing at 95.4% accuracy with 2 permanent errors. A bare gather loop would make that error handling and cost accounting your problem.

See the benchmarks for methodology and the full tables.

vs. rolling your own

The 90% version is a semaphore and a gather. Here's what those few lines don't handle:

import asyncio

sem = asyncio.Semaphore(20)  # cap concurrency

async def call_one(prompt: str) -> str:
    async with sem:
        resp = await client.chat.completions.create(
            model="gpt-4o-mini", messages=[{"role": "user", "content": prompt}]
        )
        return resp.choices[0].message.content

results = await asyncio.gather(*(call_one(p) for p in prompts))

• 429 / rate limits — no coordinated cooldown; every task keeps hammering a throttled endpoint.
• Validation failures — a malformed/unparseable response is just returned; no retry, no "escalate to a smarter or thinking model when the output is bad".
• Transient errors — one raised exception loses the whole batch; return_exceptions=True only trades that for Exception objects salted through your results to hand-filter.
• Cost — no idea what you spent, and zero accounting for tokens burned on failed attempts.
• Memory — gather() materializes every coroutine up front; you can't stream a million prompts through constant memory.

async-batch-llm is that loop with the operational layer filled in — coordinated cooldowns, error-type-aware retries, token/cost accounting (including failures), bounded-memory streaming, and a one-line provider swap.

When NOT to use this

• You can wait hours. If the job is latency-tolerant, the providers' own batch APIs (OpenAI / Anthropic / Gemini Batch) run ~50% cheaper with results in up to 24 h. This library is for real-time bulk — results now, at full price.
• It's a handful of calls. For a one-off script over a few dozen prompts, a bare asyncio.gather (optionally with a semaphore) is fine — don't take the dependency. That said, if you want this library's resilience (error-aware retries, a coordinated rate-limit cooldown, token accounting) for a single call or a web service's request path without the batch machinery, reach for call() / LLMGateway instead.

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Quick Start

Installation

# Basic installation
pip install async-batch-llm

# With PydanticAI support (recommended for structured output)
pip install 'async-batch-llm[pydantic-ai]'

# With Google Gemini support
pip install 'async-batch-llm[gemini]'

# With OpenAI support
pip install 'async-batch-llm[openai]'

# With OpenRouter support (multi-provider via one OpenAI-compatible API)
pip install 'async-batch-llm[openrouter]'

# With DeepSeek support (direct DeepSeek API, native cache-hit tracking)
pip install 'async-batch-llm[deepseek]'

# With everything
pip install 'async-batch-llm[all]'

# Alternatively, using the uv workflow from this repo's Makefile:
uv venv && uv sync

Once dependencies are installed, run the pinned tooling via make check-all so your local Ruff/mypy versions match CI (all Makefile targets call uv run to use the synced environment).

Basic Example

The fastest way in is process_prompts — hand it a strategy and an iterable of prompts, get a BatchResult back. Item ids are auto-generated for bare strings:

import asyncio
from async_batch_llm import OpenAIModel, OpenAIStrategy, ProcessorConfig, process_prompts

documents = ["Document 1 text...", "Document 2 text..."]

async def main():
    strategy = OpenAIStrategy(OpenAIModel.from_api_key("gpt-4o-mini"))  # reads OPENAI_API_KEY

    result = await process_prompts(
        strategy,
        [f"Summarize: {doc}" for doc in documents],
        config=ProcessorConfig(max_workers=10),  # up to 10 calls in flight
    )

    print(f"Succeeded: {result.succeeded}/{result.total_items}")
    for r in result.successes:
        print(r.item_id, "->", r.output)

asyncio.run(main())

Want results as they finish (e.g. to write each to disk)? Stream them. With a bounded max_queue_size, the producer applies backpressure — so you can stream a million prompts (or an unbounded source) through constant memory, since work isn't all buffered up front:

from async_batch_llm import process_stream, ProcessorConfig

config = ProcessorConfig(max_workers=50, max_queue_size=200)  # ~constant memory

async for result in process_stream(strategy, huge_prompt_source, config=config):
    if result.success:
        await save(result.item_id, result.output)   # results arrive in completion order

prompts can be any sync or async iterable. Pass (item_id, prompt) pairs instead of bare strings to control ids — or (item_id, prompt, context) triples to carry per-item data through to the result — and forward any processor option (post_processor, observers, error_classifier, …) as a keyword argument. The error classifier is auto-selected from the strategy when you don't pass one.

Need the low-level controls? processor.start() / add_work() / finish() / results() is the streaming mode process_stream is built on (workers run while you add work — a bounded queue is backpressure, not a deadlock).

Full control (advanced)

For custom queueing, per-item context, or fine-grained lifecycle control, drive the ParallelBatchProcessor directly — process_prompts is a thin wrapper over it:

import asyncio
from async_batch_llm import (
    LLMWorkItem,
    OpenAIModel,
    OpenAIStrategy,
    ParallelBatchProcessor,
    ProcessorConfig,
)

documents = ["Document 1 text...", "Document 2 text..."]

async def main():
    model = OpenAIModel.from_api_key("gpt-4o-mini")   # reads OPENAI_API_KEY
    strategy = OpenAIStrategy(model)
    config = ProcessorConfig(max_workers=10)          # up to 10 calls in flight at once

    async with ParallelBatchProcessor(config=config) as processor:
        for i, doc in enumerate(documents):
            await processor.add_work(
                LLMWorkItem(item_id=f"doc_{i}", strategy=strategy, prompt=f"Summarize: {doc}")
            )
        result = await processor.process_all()

    print(f"Succeeded: {result.succeeded}/{result.total_items}")
    print(f"Tokens used: {result.total_input_tokens + result.total_output_tokens}")

asyncio.run(main())

Switching providers is a one-line change (DeepSeekModel / GeminiModel / OpenRouterModel, or a custom strategy). For structured output pass a response_parser (or use PydanticAIStrategy); for smart retries, caching, and observability, see Core Features below and the examples/ directory.

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Core Features

Any LLM Provider

Built-in strategies for common providers:

• PydanticAIStrategy - PydanticAI agents with structured output
• GeminiStrategy - Google Gemini; returns response text by default or accepts a response_parser for structured output. Wrap a GeminiCachedModel for context caching.
• OpenAIStrategy - OpenAI (OpenAIModel.from_api_key(...))
• OpenRouterStrategy - OpenRouter, a single OpenAI-compatible API in front of Anthropic, Google, DeepSeek, etc. (OpenRouterModel.from_api_key(...))
• DeepSeekStrategy - DeepSeek direct, with native cache-hit token tracking (DeepSeekModel.from_api_key(...))

OpenAIStrategy/OpenRouterStrategy/DeepSeekStrategy are thin subclasses of ModelStrategy; their models all extend OpenAICompatibleModel, so any OpenAI-compatible endpoint (Together, Fireworks, vLLM, …) works by subclassing it. Built-in usage is a two-liner:

from async_batch_llm import OpenAIModel, OpenAIStrategy

model = OpenAIModel.from_api_key("gpt-4o-mini")  # reads OPENAI_API_KEY
strategy = OpenAIStrategy(model)

For a provider without a built-in, write a custom strategy:

from async_batch_llm import LLMCallStrategy, TokenUsage

class MyProviderStrategy(LLMCallStrategy[str]):
    def __init__(self, client, model: str):
        self.client = client
        self.model = model

    async def execute(self, prompt: str, attempt: int, timeout: float, state=None):
        response = await self.client.generate(prompt, model=self.model)
        tokens: TokenUsage = {
            "input_tokens": response.usage.input_tokens,
            "output_tokens": response.usage.output_tokens,
            "total_tokens": response.usage.total_tokens,
        }
        # 3-tuple (output, tokens, metadata); metadata may be None.
        return response.text, tokens, None

See the examples/ directory for OpenAI, OpenRouter, DeepSeek, Anthropic, LangChain, and more.

DeepSeek quickstart

DeepSeek allows thousands of concurrent connections — far more than most providers — so one asyncio batch can drive very high throughput. The footgun: the openai SDK defaults to httpx's ~100-connection pool, so raising max_workers past that gives no extra throughput (workers just block on the pool). Size max_connections to match max_workers:

from async_batch_llm import DeepSeekModel, DeepSeekStrategy

model = DeepSeekModel.from_api_key(
    "deepseek-v4-flash",   # reads DEEPSEEK_API_KEY; V4 defaults thinking ON (pricey for batch)
    thinking=False,        # turn it off for classification/extraction
    max_connections=150,   # size the httpx pool to your max_workers
)
strategy = DeepSeekStrategy(model)

examples/example_deepseek.py has the full version: JSON mode with markdown-fence-tolerant parsing (pydantic_json_parser), 402 Insufficient Balance handling, and cache-hit token accounting (CachedTokenRates.DEEPSEEK).

Automatic Retries

Configure retry behavior with exponential backoff and jitter:

from async_batch_llm import RetryConfig

config = ProcessorConfig(
    max_workers=5,
    timeout_per_item=30.0,
    retry=RetryConfig(
        max_attempts=3,             # budget for content/transport failures
        initial_wait=1.0,
        exponential_base=2.0,
        jitter=True,                # Prevents thundering herd
        max_rate_limit_retries=20,  # rate-limit retries are budgeted separately
    ),
)

The framework automatically retries on validation errors, network errors, and other transient failures.

Rate limits don't consume your retry budget. max_attempts bounds content and transport failures (bad/invalid output, timeouts, connection errors, 5xx). A 429 / quota / coordinated-cooldown signal is a "wait and try again", not a failed attempt — so it's retried at the same logical attempt number after the cooldown and is bounded separately by max_rate_limit_retries (default 20; set to 0 to make rate limits fail immediately). When that separate budget is exceeded the item fails with a RateLimitRetriesExceeded error (token usage included, like any other exhausted failure).

This keeps the attempt number that execute() sees meaningful: a model-escalation strategy (escalate to a smarter/thinking model on attempt ≥ 2) escalates because the output was bad over max_attempts tries — never just because the endpoint was busy.

For error-type-aware retries — retry the cheap model on transient/rate-limit errors, but escalate to a smarter or thinking model only when the output is bad — see examples/example_smart_model_escalation.py.

Rate Limiting

Coordinated rate limit handling across all workers:

from async_batch_llm import RateLimitConfig

config = ProcessorConfig(
    rate_limit=RateLimitConfig(
        cooldown_seconds=60.0,        # Pause after rate limit
        backoff_multiplier=2.0,       # Increase cooldown on repeated limits
        slow_start_items=50,          # Gradual ramp-up over 50 items
        slow_start_initial_delay=2.0, # Start slow
        slow_start_final_delay=0.1,   # Ramp to full speed
    ),
)

When any worker hits a rate limit (429 error), all workers pause during cooldown, then gradually resume to prevent immediate re-limiting.

Single calls and a shared gateway

The resilience layer above — error-aware retries, the coordinated cooldown, token accounting — is also reachable without the batch processor, for the cases where parallelism isn't the point:

from async_batch_llm import OpenAIModel, OpenAIStrategy, call, LLMGateway

strategy = OpenAIStrategy(OpenAIModel.from_api_key("gpt-4o-mini"))

# One prompt through the full pipeline — no queue, workers, or result stream.
summary = await call(strategy, "Summarize: ...")          # returns output, or raises

# A long-lived, shared entry point for a web service's request path. Many
# concurrent callers share one cooldown (one caller's 429 throttles everyone,
# then slow-starts); a semaphore bounds global concurrency. Opt into
# load-shedding with max_pending (admission cap) and submit_timeout (latency budget).
async with LLMGateway(
    strategy, config=ProcessorConfig(max_workers=5), max_pending=100, submit_timeout=30
) as gw:
    reply = await gw.submit("Answer this one request")

On failure, call() / gw.submit() re-raise the provider's own exception (preserving its type; LLMCallError only when none was preserved). call_result() / gw.submit_result() instead return the full WorkItemResult — success, error, token_usage, metadata, and the originating exception — without raising. See examples/example_single_call.py and examples/example_gateway.py.

Cost Optimization with Caching

Share a single cached strategy across all work items to avoid paying for the same context repeatedly:

from async_batch_llm import GeminiCachedModel, GeminiStrategy
from google import genai

client = genai.Client(api_key="your-api-key")

# v0.6.0+: wrap a cached model in GeminiStrategy. Create ONE cached
# model and share it across all work items — constructing a new model
# per item would defeat caching and can cost 10x more.
cached_model = GeminiCachedModel(
    model="gemini-2.0-flash",
    client=client,
    cached_content=[
        genai.types.Content(
            role="user",
            parts=[genai.types.Part(text="Large document context...")],
        )
    ],
    cache_ttl_seconds=3600,  # 1 hour
    auto_renew=True,         # Automatic renewal for long pipelines
)
strategy = GeminiStrategy(model=cached_model)

async with ParallelBatchProcessor(config=config) as processor:
    for item in items:
        await processor.add_work(
            LLMWorkItem(
                item_id=item.id,
                strategy=strategy,  # Shared instance
                prompt=format_prompt(item),
            )
        )

    result = await processor.process_all()

# Framework calls prepare() once per shared strategy (creates cache).
# All items share the cache (cached tokens are billed at 10% of the normal rate).
# Cleanup runs once when the processor context exits; the Gemini cache stays
# alive until TTL expiry unless you call cached_model.delete_cache().

Cost Example:

• Without caching: 100 items × $0.10 = $10.00
• With shared caching: 100 items × $0.03 = $3.00 (assuming cached tokens are billed at 10% of the original rate)

Token & cost accounting

Every BatchResult aggregates input / cached / output tokens — across retries, and recovered from failed attempts. Turn them into money with estimated_cost, which applies the per-provider cache discount:

from async_batch_llm import CachedTokenRates

print(f"Cache hit rate: {result.cache_hit_rate():.1f}%")
cost = result.estimated_cost(
    input_per_mtok=0.15, output_per_mtok=0.60,   # $ per 1M tokens
    cached_token_rate=CachedTokenRates.OPENAI,   # per-provider cache rate
)
print(f"Estimated cost: ${cost:.4f}")

Observability

Metrics observers, lifecycle events (ITEM_*, RATE_LIMIT_HIT, COOLDOWN_*, …) with JSON / Prometheus export, plus middleware and progress callbacks. See Advanced Patterns → Custom Observers / Middleware.

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Common Use Cases

Worked, runnable versions of the usual jobs — structured extraction with validation retry, document summarization, RAG with shared context caching, and saving results to a DB via a post_processor — live in examples/ and the Basic Usage guide.

Advanced Patterns

RetryState persists across an item's attempts, which unlocks error-type-aware strategies — progressive temperature, smart model escalation (cheap model first, escalate to a smarter/thinking model only on bad output — typically 60–80% cheaper), and partial-field recovery. Because rate limits don't advance the attempt number, escalation tracks genuine quality failures, not throttling.

→ Full walkthroughs in Advanced Patterns, runnable in examples/example_smart_model_escalation.py and examples/example_gemini_smart_retry.py.

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Configuration & tuning

ProcessorConfig (with nested RetryConfig / RateLimitConfig) controls workers, per-attempt timeout, retry budgets (max_attempts, plus max_rate_limit_retries — rate limits don't burn your retry budget), rate-limit cooldown + slow-start, proactive limiting, progress reporting, and queueing. Full field reference: API reference → ProcessorConfig.

For the operational decisions — worker count per provider, sizing max_connections to max_workers, the RLIMIT_NOFILE footgun, timeout-vs-retry-budget interaction, rate-limit tuning, and the constant-memory streaming pattern — see the Production Checklist.

Testing

Test without spending on API calls — dry-run mode, MockAgent (simulates latency, rate limits, and errors), and small-batch integration tests. See the Testing guide.

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Examples

Check out the examples/ directory for complete working examples:

• example_llm_strategies.py - All built-in strategies
• example_single_call.py - One resilient call, no batch machinery
• example_gateway.py - Shared rate-limited gateway for a request path
• example_openai.py - OpenAI integration
• example_openrouter.py - OpenRouter (multi-provider)
• example_deepseek.py - DeepSeek with native cache-hit tracking
• example_anthropic.py - Anthropic Claude
• example_langchain.py - LangChain & RAG
• example_gemini_direct.py - Direct Gemini API
• example_gemini_smart_retry.py - Smart retry patterns
• example_smart_model_escalation.py - Cost optimization
• example_context_manager.py - Resource management
• example_batch_benchmark.py - Flagship bulk-benchmark demo

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Documentation

• Full Documentation - Getting started, examples, and API reference
• API Reference - Complete API documentation
• Migration Guides - Version upgrade guides

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Contributing

Contributions welcome! Areas of interest:

• Additional provider strategies (AWS Bedrock, Azure OpenAI, etc.)
• Improved error classification
• Performance optimizations
• Documentation improvements

Development Setup

# Clone and install
git clone https://github.com/geoff-davis/async-batch-llm.git
cd async-batch-llm
uv sync --all-extras

# Run tests
uv run pytest

# Run all checks (lint + typecheck + test + markdown-lint)
make ci

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License

MIT License - see LICENSE file for details.

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Questions? Open an issue on GitHub or check the documentation.