Definition
A Deep Probe is a real-engine query: the tool actually calls OpenAI/Anthropic/Perplexity APIs using the user's BYOK keys and captures actual citations. Distinct from a simulated probe (like VectorCite's Mirror Engine) which reproduces the retrieval ensemble math but doesn't query the live engines. Deep Probes are paid per-call but give ground-truth citation data.
VectorCite's Mirror Engine simulates: score = α·cosine + β·BM25 + γ·authority + δ·recency. Deep Probe at /app/byok hits POST api.openai.com/v1/responses with web_search_preview, returns actual ChatGPT citations.
How to optimize
Use Mirror Engine for fast, free iterations. Use Deep Probe to ground-truth-verify before client reports. Combine both: Mirror Engine to identify gaps, Deep Probe to confirm citation impact after fixes ship.