# BILL vs Brex

> BILL and Brex score within a point of each other on agent readiness, 60.9 (C) and 60.7 (C). Brex leads on agent ergonomics, security & auth and maintenance & community. Both do spend transactions. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/bill-vs-brex
- Markdown: https://www.anchorterminal.com/compare/bill-vs-brex.md (~2,050 tokens)
- Slim: https://www.anchorterminal.com/compare/bill-vs-brex.min.md (~630 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/bill-vs-brex.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-08

BILL and Brex score within a point of each other on agent readiness, 60.9 (C) and 60.7 (C). Brex leads on agent ergonomics, security & auth and maintenance & community. Both do spend transactions.

- BILL: grade C, 60.9/100, rank #380 of 722. Markdown https://www.anchorterminal.com/tools/bill.md · JSON https://www.anchorterminal.com/api/v1/tools/bill.json
- Brex: grade C, 60.7/100, rank #391 of 722. Markdown https://www.anchorterminal.com/tools/brex.md · JSON https://www.anchorterminal.com/api/v1/tools/brex.json

## Which one, for what

### BILL (C)

Good for: A US company already on BILL that wants an agent to create and read bills, run approvals, schedule vendor payments, raise invoices and manage budgets, vendor cards, card transactions and reimbursements.

Ahead on:
- Reliability, 81 against 60

Also in its favour:
- No incidents deducted, where Brex loses 3 points for them

Watch for: `POST /v3/login` takes a user's username and password with a developer key, and the session carries that user's role with no scopes

### Brex (C)

Good for: A finance team already on Brex that wants an agent to read expenses and transactions, issue and lock cards, set spend limits, upload receipts and pay vendors.

Ahead on:
- Agent ergonomics, 70 against 60
- Security & auth, 72 against 56
- Maintenance & community, 66 against 32

Watch for: The Expenses API update endpoint accepts only `memo`, so an outside agent can't set a category or custom field on an expense through it


## Score by category

| Category | Weight | BILL | Brex | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 81 | 60 | BILL +21 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 83 | 80 | BILL +3 |
| Agent ergonomics | 13% (16.2 this run) | 60 | 70 | Brex +10 |
| Security & auth | 14% (17.5 this run) | 56 | 72 | Brex +16 |
| Payments & pricing | 10% (12.5 this run) | 25 | 25 | even |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 32 | 66 | Brex +34 |
| Transparency & trust | 7% (8.8 this run) | 66 | 67 | Brex +1 |
| Negative events | ≤15 | 0 | -3 | |
| **Total** | | **60.9 · C** | **60.7 · C** | |

## Facts side by side

| Fact | BILL | Brex |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | BILL Holdings, Inc. | Brex LLC |
| Hosted endpoint | `https://gateway.prod.bill.com/connect` | `https://api.brex.com` |
| Transports | HTTP | HTTP |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Proprietary service under the BILL Developer Terms and the BILL General Terms of Service | Proprietary service under the Brex Platform Agreement and the Brex Access Agreement |
| Tools exposed | none | 43 |
| Read-only variant documented | no | yes |
| llms.txt | yes | yes |
| Last release | 2026-05-21 | 2026-10-01 |
| Terms last updated | 2026-03-03 | no date given |
| Privacy policy last updated | 2026-01-30 | no date given |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | not found in the text | not found in the text |
| Terms restrict benchmarking | not found in the text | yes |
| Terms or service can change without notice | not found in the text | not found in the text |
| Arbitration or class-action waiver | not found in the text | yes |

## Verdicts

**BILL.** A public OpenAPI 3.0.1 spec covers 326 operations, a self-serve sandbox moves no money, and payments need a session trusted by multi-factor authentication. The AP and AR API signs in with a user's password and has no scopes, no idempotency key protects payment calls, and no official SDK was found.

**Brex.** User tokens carry per-resource scopes with read-only variants, every POST and PUT accepts an `Idempotency-Key`, and ten OpenAPI specs are public. The Expenses API changes only an expense's memo, there is no customer sandbox or official SDK, and the status page logs API errors lasting over four hours on 4 August 2026.

## Before you call either

### BILL

1. Sign in with `POST /v3/login` and send `sessionId` and `devKey` as headers on every AP and AR call. The session expires after 35 minutes idle
2. Send the `apiToken` header alone on `/v3/spend/` paths. Spend & Expense calls need no login and are limited to 60 a minute per token
3. Complete the MFA challenge before `POST /v3/payments`. An untrusted session fails with `BDC_1361`
4. Read back payments before retrying a failed `POST /v3/payments`. No idempotency key is accepted, so a blind retry can pay twice
5. Keep to three concurrent requests per developer key per organisation and 20,000 an hour. After `BDC_1144`, wait for the next hour

### Brex

1. Ask an account admin or card admin for a user token with only the scopes the task needs, and prefer the `.readonly` variants. A token unused for 90 days expires.
2. Send a stored `Idempotency-Key` on every POST and PUT. Create transfer and Create card reject requests without one.
3. Only settled transactions are returned. Poll card and cash transactions with `posted_at_start` and a lookback of at least one day.
4. Keep under 1,000 requests in 60 seconds per client and account, and back off exponentially with jitter on 429.
5. Send only ASCII in free-text fields, and quote the `X-Brex-Trace-Id` response header when reporting an error.

## Questions

### Which is better for AI agents, BILL or Brex?

BILL and Brex score within a point of each other on agent readiness, 60.9 (C) and 60.7 (C). Brex leads on agent ergonomics, security & auth and maintenance & community.

### Do BILL and Brex need an API key?

Both take an API key or an OAuth sign-in.

### Can an agent call BILL and Brex without installing anything?

Yes. BILL has a hosted endpoint at https://gateway.prod.bill.com/connect and Brex at https://api.brex.com.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/bill-vs-brex.json, and with the fewest tokens: https://www.anchorterminal.com/compare/bill-vs-brex.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "bill", "b": "brex"}`. From a terminal: `anchor compare bill brex`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/bill.json and https://www.anchorterminal.com/api/v1/tools/brex.json

## Other comparisons with BILL or Brex

- [Airwallex Spend and Issuing vs BILL](https://www.anchorterminal.com/compare/airwallex-vs-bill.md)
- [Airwallex Spend and Issuing vs Brex](https://www.anchorterminal.com/compare/airwallex-vs-brex.md)
- [BILL vs Expensify](https://www.anchorterminal.com/compare/bill-vs-expensify.md)
- [BILL vs Mercury API](https://www.anchorterminal.com/compare/bill-vs-mercury.md)
- [BILL vs Pleo API + MCP](https://www.anchorterminal.com/compare/bill-vs-pleo.md)
- [BILL vs Ramp](https://www.anchorterminal.com/compare/bill-vs-ramp.md)
- [BILL vs Spendesk API + MCP](https://www.anchorterminal.com/compare/bill-vs-spendesk.md)
- [Brex vs Expensify](https://www.anchorterminal.com/compare/brex-vs-expensify.md)
- [Brex vs Mercury API](https://www.anchorterminal.com/compare/brex-vs-mercury.md)
- [Brex vs Pleo API + MCP](https://www.anchorterminal.com/compare/brex-vs-pleo.md)
- [Brex vs Ramp](https://www.anchorterminal.com/compare/brex-vs-ramp.md)
- [Brex vs Spendesk API + MCP](https://www.anchorterminal.com/compare/brex-vs-spendesk.md)