Plural

Unified LLM routing with first-class traces, environments, and benchmarks.

Plural is for builders putting AI into products. Start with an OpenRouter-style multi-provider router. Keep going with the thing OpenRouter does not give you: a single Trace object shared by production traffic and RL-style environments — so you can understand prompts, build datasets, run benchmarks, and eventually autoroute to the best model for your data.

flowchart LR
  App[Your app] --> Client[Plural]
  Env[Environment] --> Client
  Client --> Trace[Trace]
  Trace --> TraceDataset[TraceDataset / Dataset]
  TraceDataset --> Training[Training / export]
  TaskDataset[TaskDataset] --> Bench[Benchmark]
  Env --> Bench

Install

pip install plural
# optional OpenTelemetry exporter
pip install "plural[otel]"

Quickstart

Set PLURAL_API_KEY, then use the client like the OpenAI SDK:

export PLURAL_API_KEY=plural-...

from plural import Plural, Message

client = Plural()
response = client.chat(
    model="openai/gpt-4o-mini",
    messages=[Message(role="user", content="Hello from plural")],
    models=["anthropic/claude-sonnet-4"],  # optional fallbacks
)
print(response.text)
client.close()
# Traces → .plural/traces.jsonl

Optional BYOK (pass your own upstream keys explicitly):

import os
from plural import Plural

client = Plural(providers={"openai": os.environ["OPENAI_API_KEY"]})

Four pillars

Environments in 30 seconds

from plural import Environment, TaskData

env = Environment(name="support-triage", version="0.1.0")

@env.tool
def lookup_order(order_id: str) -> dict:
    """Look up an order."""
    return {"status": "shipped"}

@env.scorer(weight=1.0)
def ok(rollout) -> float:
    return 1.0 if "shipped" in (rollout.response.text or "").lower() else 0.0

@env.tasks
def tasks():
    yield TaskData(task_id="1", input="Where is order A?")

rollout = env.rollout(next(env.iter_tasks()), client, model="openai/gpt-4o-mini")
print(rollout.trace.outcome)

Tool environments use the built-in action dispatch. For scalar or custom text actions, override apply_action() and return ActionResult; step() remains framework-owned so lifecycle and trace invariants are always recorded.

Docs

Full documentation: concept pages, guides, and generated API reference.

• Trace schema stability: schemas/trace.v1.json
• Routing walkthrough: examples/routing/ (also under docs → Guides)

Development

uv sync --group dev --group docs
uv run pytest -m "not live"
uv run ruff check .
uv run mypy src/plural
uv run mkdocs build --strict

License

Apache-2.0