armos 2.0.1

Automatic PII masking for OpenAI and Anthropic SDKs

Armos

The privacy boundary between regulated workflows and LLM APIs.

Sensitive-data teams want LLM automation — but can't casually send names, IDs, tax records, or health data to external models. Armos is the local detection and reversible token layer that makes it safe.

Built for developers. Drop-in for OpenAI and Anthropic. One line to integrate.

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The problem

Healthtech, fintech, legal, and HR teams are sitting on a specific blocker: they want LLM automation, but they can't casually send names, IDs, tax data, health records, or legal documents into external models.

Every LLM API call sends raw text to a third-party server. If that text contains PII — names, Aadhaar, PAN, SSN, emails, credit cards — that data leaves your infrastructure. Most teams know this is a risk. Few have time to build a proper privacy layer before shipping.

Armos is that layer, pre-built — local detection, reversible tokens, no data sent anywhere during masking.

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How it works

Detection runs entirely on your machine. Presidio + spaCy analyse the text locally. No data is sent to any Armos server — there is no Armos server. The vault (token ↔ real value map) lives in your process memory, or optionally in your own Redis instance.

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Why Armos over alternatives?

vs. building your own: A custom masking layer takes weeks to build correctly and months to handle edge cases. Armos is a pip install.

vs. LLM Guard: LLM Guard focuses on prompt injection and toxicity — not PII masking. Different problem.

vs. Presidio directly: Presidio detects PII but doesn't handle tokenization, vault management, or SDK integration. Armos wraps all of that.

Indian PII first-class: Aadhaar and PAN detection built in. No competitor handles Indian identifiers reliably.

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Quickstart

Install

pip install armos

For Redis-backed persistence across requests:

pip install armos[redis]

Note: On first use, Armos automatically downloads armos-ner-en — our custom-trained NER model (~450 MB). This happens once and is cached at ~/.cache/armos/models/ for all future uses.

OpenAI

# Before
from openai import OpenAI
client = OpenAI()

# After — one import added, one word changed
from openai import OpenAI
from armos import ArmosOpenAI

client = ArmosOpenAI(OpenAI())

# Everything else is identical
response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{
        "role": "user",
        "content": "Summarise the case for patient John Smith, Aadhaar 2345 6789 0123"
    }]
)

# Real values are restored in the response automatically
print(response.choices[0].message.content)

Anthropic

from anthropic import Anthropic
from armos import ArmosAnthropic

client = ArmosAnthropic(Anthropic())

message = client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": "Patient John Smith, DOB 12/04/1982, PAN ABCDE1234F"
    }]
)

print(message.content[0].text)  # real values restored

OpenAI Responses API

response = client.responses.create(
    model="gpt-4o",
    input="Patient John Smith, Aadhaar 2345 6789 0123 — summarise in one line."
)
print(response.output[0].content[0].text)  # real values restored

Embeddings

# PII is masked before the text is sent for embedding
result = client.embeddings.create(
    model="text-embedding-3-small",
    input="John Smith's email is [e-mail]"
)
# Works with list input too
result = client.embeddings.create(
    model="text-embedding-3-small",
    input=["[e-mail]", "no pii here"]
)

With Redis (persistent vault across requests)

# Token mappings survive across processes and requests
client = ArmosOpenAI(OpenAI(), store="redis", redis_url="redis://localhost:6379")
client = ArmosAnthropic(Anthropic(), store="redis", redis_url="redis://localhost:6379")

# Custom TTL (default: 24 hours)
client = ArmosOpenAI(OpenAI(), store="redis", redis_url="redis://localhost:6379", vault_ttl=3600)

Async (OpenAI / Anthropic)

from openai import AsyncOpenAI
from armos import ArmosAsyncOpenAI

client = ArmosAsyncOpenAI(AsyncOpenAI())

response = await client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Patient Priya Sharma, Aadhaar 2345 6789 0123"}]
)

Same pattern for Anthropic:

from anthropic import AsyncAnthropic
from armos import ArmosAsyncAnthropic

client = ArmosAsyncAnthropic(AsyncAnthropic())

response = await client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=100,
    messages=[{"role": "user", "content": "Employee Rahul Mehta, PAN ABCDE1234F"}]
)

Standalone (any LLM or framework)

from armos import Armos

guard = Armos()

result = guard.mask("Patient John Smith, Aadhaar 2345 6789 0123, email [e-mail]")
print(result.text)
# → "Patient [PII:NAME:a1b2c3d4], Aadhaar [PII:AADHAAR:b2c3d4e5], email [PII:EMAIL:e5f6g7h8]"

print(result.has_pii)  # True

restored = guard.demask(result.text)
print(restored)
# → "Patient John Smith, Aadhaar 2345 6789 0123, email [e-mail]"

Async variants are also available on the standalone guard:

result = await guard.amask("Patient John Smith, Aadhaar 2345 6789 0123")
restored = await guard.ademask(result.text)

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What gets detected

Entity	Token	Example
Person name	[PII:NAME:…]	John Smith
Email address	[PII:EMAIL:…]	[e-mail]
Phone number	[PII:PHONE:…]	[phone]
Aadhaar number	[PII:AADHAAR:…]	2345 6789 0123
PAN card	[PII:PAN:…]	ABCDE1234F
SSN	[PII:SSN:…]	371-53-1234
IBAN	[PII:IBAN:…]	GB29NWBK60161331926819
Credit / debit card	[PII:CARD:…]	4111 1111 1111 1111
IP address	[PII:IP:…]	192.168.1.100
API keys & secrets	[PII:APIKEY:…]	sk-abc123… / AKIA… / ghp_…
Physical address	[PII:ADDRESS:…]	123 Oak Ave, Chicago, IL 60601 / Flat 4B, Koramangala, Bangalore

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Token design

Tokens are deterministic and normalisation-aware:

"john smith"  →  [PII:NAME:a1b2c3d4]  ← stored: "john smith"
"John Smith"  →  [PII:NAME:a1b2c3d4]  ← same token, vault unchanged
"JOHN SMITH"  →  [PII:NAME:a1b2c3d4]  ← same token, vault unchanged

All casing variants of the same name map to one token. The LLM sees one consistent entity across a conversation — not three different people. De-masking restores the first-seen value.

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Vault options

Option	Default	Use when
In-memory	Armos()	Single request or single process
Redis	Armos(store="redis", redis_url="redis://…")	Multi-turn conversations, multiple workers, or across requests

In-memory vault is zero configuration and the default. Redis vault persists token mappings so a token created in request 1 can be de-masked in request 5.

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Token overhead

Masking replaces PII values with tokens like [PII:NAME:a1b2c3d4]. These are longer than the original values, adding a small number of tokens to each request. Measured with GPT-4 tokenization (cl100k_base):

Entity type	Example	Original tokens	Masked tokens	Overhead
NAME	John Smith	2	10	+8
EMAIL	[e-mail]	3	13	+10
AADHAAR	2345 6789 0123	8	13	+5
PAN	ABCDE1234F	4	11	+7
PHONE	[phone]	8	12	+4
IP	192.168.1.100	7	11	+4
Average		6	11	+5

In practice: a message with 4 PII entities adds ~20 tokens to the request, plus a one-time 13-token system hint injected when PII is detected. For a typical 200-token prompt this is a ~15% increase — negligible against LLM pricing at scale.

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Performance

Detection and masking run entirely in-process with no network calls. Benchmarked on Apple M-series (50 runs, median / p95):

Text size	Memory — p50	Memory — p95	Redis — p50	Redis — p95
Short (~20 tokens)	2.5 ms	2.7 ms	3.6 ms	3.9 ms
Medium (~60 tokens)	6.0 ms	6.4 ms	8.6 ms	9.0 ms
Long (~150 tokens)	13.3 ms	13.9 ms	19.4 ms	20.5 ms

Redis overhead is the localhost round-trip cost (~1–2 ms per vault operation). Both are negligible relative to LLM response times (typically 500 ms–5 s).

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Detection accuracy

Tested across 10,000 random samples per entity type, each embedded in a realistic sentence context. Name and address detection uses armos-ner-en — a custom-trained NER model built specifically for Indian and Western PII, not a generic off-the-shelf model.

Entity	Method	Samples	Detected	Rate
Person name (Indian)	armos-ner-en	10,000	9,920	99.2%
Person name (Western)	armos-ner-en	10,000	9,970	99.7%
Physical address (Indian)	armos-ner-en	10,000	10,000	100%
Physical address (US/UK)	armos-ner-en	10,000	10,000	100%
Email address	Regex	10,000	10,000	100%
Phone number	Regex	10,000	10,000	100%
Aadhaar	Regex	10,000	10,000	100%
PAN	Regex	10,000	10,000	100%
SSN	Regex	10,000	10,000	100%
IBAN	Regex + checksum	10,000	10,000	100%
Credit / debit card	Regex + Luhn	10,000	10,000	100%
IP address	Regex	10,000	9,980	99.8%
API keys	Regex	10,000	10,000	100%

vs. en_core_web_lg baseline: armos-ner-en improves Indian name detection by +9.1% and adds ADDRESS detection from 0% to 100% — a capability the baseline model has none of.

Address detection covers full US/UK addresses, street-only, P.O. Box, and Indian formats (flat, house, plot, named locality) across 8 sub-categories. False positive rate across all entity types: 0%.

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Failure modes — what Armos catches and what it doesn't

Armos is designed to be transparent about its boundaries. Use this to decide whether a given use case is a fit.

Reliably caught (99%+)

Case	Example
Full name in sentence context	Patient Priya Sharma was admitted...
Indian address with flat/locality/PIN	Flat 4B, Koramangala, Bangalore 560095
US/UK address with street and postcode	123 Oak Ave, Chicago, IL 60601
All structured identifiers	Aadhaar, PAN, SSN, IBAN, card, email, phone, IP, API key

Intentionally not caught (out of scope today)

Case	Why
Passport numbers, voter ID, driving licence	Not yet supported — on the roadmap
Names in non-Latin scripts	प्रिया शर्मा — English model only
Dates of birth	Ambiguous — 12/04/1982 could be a date, not PII in all contexts
Company / organisation names	ORG detection not enabled
Custom internal identifiers	Employee IDs, account codes — use custom model for these

Known gaps (miss rate < 1%)

Case	Notes
Single-word names without context	"Contact Priya" — too ambiguous, skipped intentionally
Very long or uncommon South Indian names	e.g. Venkataraman Subramaniam — trained on these but rarely missed
Heavily abbreviated addresses	B-42, MG Rd with no city or PIN — incomplete format
Names embedded in long lists	CC: Ananya, Vikram, Neha, Rahul — sometimes boundary detection slips
Partial / truncated numbers	4111 1111... — regex requires complete format

If your data looks like a specific case here, open an issue or reach out — we train on real-world gaps.

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Known limitations

1. Token length — [PII:NAME:a1b2c3d4] is 18 chars vs John (4 chars). Near context-window limits this may push content over. Rare in practice.
2. Casing: first-seen wins — De-masking always restores the first-seen casing of an entity. Use consistent casing in your prompts for exact restoration.
3. Streaming not supported — stream=True passes through without masking. (planned)

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Contributing

Armos is open source and MIT licensed. Issues and pull requests welcome.

git clone https://github.com/armos-ai/armos-python
cd armos-python
pip install -e ".[dev,all]"
python -m spacy download en_core_web_lg
pytest tests/ -v

License

MIT