Timestamp and anchor¶

Prove when an audit existed with OpenTimestamps or the Ethereum Attestation Service, and commit to private suites.

pip install "modeldiffr[anchor]"

Anchors are optional. Only statement_sha256 is published, which reveals nothing about the models or prompts.

OpenTimestamps on Bitcoin¶

modeldiffr anchor ots audit/report.json

wrote audit/statement.sha256
the Bitcoin attestation completes in a few hours: modeldiffr anchor upgrade REPORT

This writes statement.sha256 (the hash as text) and statement.sha256.ots (the pending proof). Public calendars batch many submissions into one Bitcoin transaction, so it is free. A few hours later:

modeldiffr anchor upgrade audit/report.json
modeldiffr verify audit/report.json

PASS  opentimestamps             anchored in a Bitcoin block

Before the upgrade the check passes with submitted to calendars, waiting for a Bitcoin block.

Ethereum Attestation Service¶

One attestation per audit on an L2, readable by anyone and by contracts.

Register the schema once on easscan.org:

bytes32 auditId,bytes32 resultsRoot,bytes32 statementSha256,string verdict

Note the schema UID it returns.

Fund an account with a little ETH on the chain and export its key:
```
export MODELDIFFR_ETH_KEY=0x...
```

Attest:

modeldiffr anchor eas audit/report.json \
  --schema 0xSCHEMA_UID \
  --rpc https://mainnet.base.org

attestation 0x5c2e... in transaction 0x8a91...

The record is appended to anchors.json. Anyone can check it:

modeldiffr verify audit/report.json --rpc https://mainnet.base.org

PASS  eas                        attested on chain 8453 by 0x3F1a...

The check reads the attestation from the EAS contract at 0x4200000000000000000000000000000000000021, fails if it was revoked, and compares all three hashes with the report.

Chain	Chain id	RPC example
Base	8453	`https://mainnet.base.org`
Base Sepolia	84532	`https://sepolia.base.org`
Optimism	10	`https://mainnet.optimism.io`

Warning

The private key never leaves your machine, and Modeldiffr never writes it to disk. Use an account that holds only enough for fees.

Commit and reveal private suites¶

Keep a holdout suite private while proving it existed before a model was trained.

modeldiffr commit holdout.jsonl

root sha256:4be1... over 500 items, wrote holdout.jsonl.commitment.json
publish the commitment now and keep the file private until you reveal it

Publish the commitment (and timestamp it with ots stamp holdout.jsonl.commitment.json). Later, publish the file and anyone can check it:

modeldiffr reveal holdout.jsonl --commitment holdout.jsonl.commitment.json

PASS 500 items match the commitment made at 2026-10-22T10:31:02+00:00

Each row is hashed as canonical JSON with its index, so reordering keys does not change the root and changing any value or the order of rows does. reveal exits with 4 on a mismatch.