> For the complete documentation index, see [llms.txt](https://docs.layerlens.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.layerlens.ai/12.-support/billing-faq.md).

# Billing FAQ

Billing FAQ — ECU, invoices, plans, upgrades.

## How is ECU charged?

Per compute-intensive operation (model inference, judge calls, GEPA, trace evaluations). See [ECU concept](/11.-admin/concepts-ecu-credits.md).

## When does ECU expire?

Free tier starter ECU expires per the terms; PAYG ECU does not expire while your account is active.

## Where do I see invoices?

**Settings → Billing → Invoices**.

## Can I upgrade or downgrade?

Yes. Free → Premium PAYG is self-serve. Premium → Enterprise is sales-led.

## What if I run out of ECU?

New compute-intensive operations are blocked until you top up. Catalog browsing and saved configs continue to work.

## See also

* [Pricing](/12.-support/12-support.md)
* [ECU credits](/11.-admin/ecu-credits-billing.md)