lenz-io

Official Python SDK for the Lenz Claim Verification API for AI Product Teams.

Two API primitives for AI product teams. extract pulls verifiable claims out of any text — free, 1000 calls/key/day. verify checks one with a 7-model panel and citations, ~90s. Use them together or alone.

Built for teams whose AI output is async or document-shaped: legal-memo generators, deep-research products, due-diligence platforms, vertical agents producing structured deliverables. Not chat AI, not voice AI, not real-time copilots — pipeline runs are the wrong shape for those.

pip install lenz-io

Quickstart — the canonical integration

from lenz_io import Lenz

client = Lenz(api_key="lenz_...")

# 1. Pull factual claims out of your model output (free, instant)
claims = client.extract(text=llm_output).claims

# 2. Verify the ones that matter (~90s each, 7-model panel)
for claim in claims:
    v = client.verify_and_wait(claim=claim).verdict
    print(v.label, v.score, v.confidence)

How verification works

Frame → Collect Evidence → Debate (2 models, 2 rounds) → Adjudicate (3 models: sources, logic, context) → Conclude. ~90 seconds wall-clock per claim.

Magical-moment demo

from lenz_io import Lenz

client = Lenz(api_key="lenz_...")

v = client.verify_and_wait(claim="Sharks don't get cancer")
print(v.verdict.label, v.verdict.score)
# false 2.0

for source in v.sources[:3]:
    print(" -", source.title, source.url)

The demo claim is pre-cached so this returns in ~1.5s. Your own claims hit the full pipeline (~60-90s) — use webhooks for production async flows.

Get your webhook secret here → lenz.io/api-integration

What you get

• client.verify_and_wait(...) — submit + poll until the pipeline lands. Returns a typed Verification.
• client.verify(...) — async submit; returns a task_id. Use webhooks for the callback.
• client.extract(text=...) — pull verifiable claims out of any text (free, capped at 1000/key/day).
• client.verify_batch(claims=[...]) — fan-out for multi-claim LLM outputs.
• client.verifications.{list,get,delete,set_visibility}(...) — manage past verifications.
• client.followup.{history,send,reset}(verification_id) — Q&A on a verification.
• client.library.{list,get}(...) — browse the public catalog (no API key needed).
• client.usage() — credits and rate-limit remaining.

Webhooks

from lenz_io import LenzWebhooks, VerificationCompleted, VerificationNeedsInput

webhooks = LenzWebhooks(secret="whsec_...")

# In your web handler:
event = webhooks.parse(raw_body=request.body, headers=request.headers)
if isinstance(event, VerificationCompleted):
    vid, result = event.verification_id, event.result
    ...
elif isinstance(event, VerificationNeedsInput):
    tid, ni = event.task_id, event.needs_input
    ...

If you're on Python 3.10+ a match statement reads even cleaner — events are plain dataclasses, so structural pattern matching works.

Signature verification is HMAC-SHA256 over the raw body; the SDK does it for you and rejects tampered or replayed payloads.

See examples/core/fastapi_webhook.py for a runnable FastAPI receiver, and examples/core/verify_llm_output.py for the headline extract-and-verify integration pattern.

Errors

Every error subclass is typed and carries a request_id you can quote on support tickets:

from lenz_io import LenzAuthError, LenzRateLimitError, LenzValidationError

try:
    client.verify_and_wait(claim="...")
except LenzAuthError as exc:
    print(exc)
    # Unauthorized
    #   Cause:  Invalid api key
    #   Fix:    Generate a new key at https://lenz.io/api-integration.
    #   Docs:   https://lenz.io/docs/auth
    #   Request ID: req_abc123
except LenzRateLimitError as exc:
    time.sleep(exc.retry_after)
except LenzValidationError as exc:
    for field_err in exc.errors:
        print(field_err["loc"], field_err["msg"])

Resuming a verification

If a verify_and_wait call exceeds its timeout (default 120s) or your process dies mid-poll, the pipeline keeps running. The exception carries the task_id:

from lenz_io import LenzTimeoutError

try:
    client.verify_and_wait(claim="...", timeout=30)
except LenzTimeoutError as exc:
    print("resume later via:", exc.task_id)

# Later (different process / restart):
status = client.get_status("tsk_abc123")
if status.status == "completed":
    print(status.result.verdict.label)

Idempotency

verify_and_wait sends an auto-generated Idempotency-Key on every call by default, so a network drop after submit doesn't spawn a duplicate verification or charge a second credit. Override with idempotency_key="..." to pin a specific key, or idempotency=False to opt out.

Configuration

Lenz(
    api_key="lenz_...",                  # or set LENZ_API_KEY env var
    base_url="https://lenz.io/api/v1",   # override for staging / local
    timeout=30.0,
    max_retries=3,
)

Environment variables:

• LENZ_API_KEY — read if api_key= is not passed
• LENZ_BASE_URL — read if base_url= is not passed

Compatibility

• Python 3.9, 3.10, 3.11, 3.12
• Works in CI/CD (no interactive prompts, no global state)
• Mockable for tests: every HTTP call goes through httpx; use respx or inject your own httpx.Client via Lenz(..., http_client=...)

Bug reports + feature requests

github.com/lenzhq/lenz-io-python/issues

For commercial use, volume pricing, or onboarding support, get in touch.

License

MIT. See LICENSE.