lenz-io 1.0.2

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

lenz-io

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

Four API primitives, one research-depth ladder.

• extract — pull verifiable claims out of any text. Free, 1000 calls/key/day.
• assess — fast 3-model panel verdict in ~5-10s. Sync, paid.
• verify — full 7-model pipeline with citations in ~90s. Async, paid.
• ask — follow-up questions grounded on a verification.

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. extract — pull verifiable claims out of any text (free)
out = client.extract(text=llm_output)

# 2. assess — fast 3-model verdict on each (~5-10s, sync)
quick = client.assess(text=llm_output)
for c in quick.claims:
    print(c.verdict, c.confidence, c.claim)

# 3. verify — escalate low-confidence claims to the full panel + citations
for c in quick.claims:
    if c.confidence == "low":
        v = client.verify_and_wait(claim=c.claim)
        print(v.verdict, v.lenz_score, v.executive_summary)

# 4. ask — follow-up grounded on a verification
reply = client.ask.send(v.verification_id, message="Which source is strongest?")
print(reply.reply)

assess and verify share a result cache server-side: if a claim already has a deep verification, assess returns it via verification_url and you can skip the escalation.

How verification works

Frame → Collect Evidence → Debate (2 models, 2 rounds) → Adjudicate (3 models: sources, logic, context) → Conclude. ~90 seconds wall-clock per claim. assess runs a leaner 3-model panel against the same framing for the ~5-10s pass.

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, v.lenz_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 on the client

• client.extract(text=...) → ExtractedClaims. Free, capped at 1000/key/day.
• client.assess(text=...) → AssessResponse. Sync, ~5-10s, returns one entry per identified claim.
• client.verify(...) → TaskAccepted. Async submit; returns a task_id. Pair with a webhook for the callback.
• client.verify_and_wait(...) → Verification. Submit + poll until the pipeline lands (sync ergonomic).
• client.verify_batch(claims=[...]) → BatchAccepted. Fan-out for multi-claim LLM outputs.
• client.ask.{history,send,reset}(verification_id, ...) → Q&A on a verification.
• client.verifications.{list,get,delete,set_visibility,related}(...) → manage past verifications. get accepts anon callers and returns any non-hidden public claim.
• client.library.list(...) → browse the public catalog (no API key needed).
• client.usage() → credits and rate-limit remaining.

Response shape — the unified vocabulary

Every claim-shaped response shares these fields at top level:

Field	Type	Notes
claim	str	The framed claim text.
verdict	str	"True" | "Mostly True" | "Misleading" | "False" | "Error".
confidence	str	Categorical: "high" | "medium" | "low".
lenz_score	int | None	Integer 0–10 (deep verdicts and list endpoints; assess omits it).

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
    # result["verdict"], result["lenz_score"], result["confidence"], ...
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 assess-then-escalate 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, status.result.lenz_score)

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.

Multi-language output

The Lenz API returns prose fields (atomic claim, executive summary, debate, panel reasoning) in any of 12 languages. Pass language= on verify, verify_and_wait, verify_batch, assess, extract, or ask.send. Verdict labels stay English regardless of language.

v = client.verify_and_wait(
    claim="La Tierra es plana",
    language="es",                 # Spanish output
)
print(v.verdict, v.language)
# False es

Supported codes: en (default), es, de, fr, it, pt, nl, sv, da, no, fi, bg. Per-item override on verify_batch:

batch = client.verify_batch(
    claims=[
        {"text": "Coffee causes cancer."},                    # en (batch default)
        {"text": "El café causa cáncer.", "language": "es"},  # overrides
    ],
    language="en",
)

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=...)

Contributing

git clone https://github.com/lenzhq/lenz-io-python && cd lenz-io-python
uv sync --extra dev
git config core.hooksPath scripts/hooks   # one-time: enables pre-commit

The pre-commit hook mirrors CI exactly (ruff check, ruff format --check, mypy, pytest). Runs ~10s per commit on a warm cache. Skip once with git commit --no-verify when you must.

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.