Configure model fallback and reconcile blocked-request billing

Goal

Verify in low-risk test requests that fallback triggers only for configured stop reasons and produce a billing-reconciliation record.

Steps

1. Use the notebook to distinguish stop reasons and record intended fallback path and retained prompt-cache prefix. [src10-anthropic-configure-classifier-model-fallback-and-reconcile-billing]
2. Configure server-side fallback on the supported Claude API path; with SDK helpers, call the backup only for documented classifier-block conditions. [src10-anthropic-configure-classifier-model-fallback-and-reconcile-billing]
3. Test output-bearing blocks, no-output blocks, and normal stops separately; compare usage with billing without replaying sensitive prompts. [src10-anthropic-configure-classifier-model-fallback-and-reconcile-billing]

How to verify

Each stop reason follows the planned path; fallback calls, usage, and invoice/console line items reconcile.

Troubleshooting

If backup runs for every error, narrow stop-reason conditions; for billing deltas, check whether blocked requests were billed before output and whether cache prefixes persisted.