Didn't they allow using oauth in custom harnesses for personal use (e.g. pi.dev)?

That changes every 2-3 days. The current stance is that only interactive mode of first party harnesses is covered under monthly plans, everything else is pay-as-you-go with monthly credit allowance equal to the plan price.

	▲	popcorncowboy 11 minutes ago \| parent [-]
		Though this is how it will stay, and it won't be changing back. Anthropic has understood clearly for a while that they need to capture the stack. They will subsidise Max for as long as they need to do this. All other off-stack usage will get pushed into per-token billing.