# Active Embedding Model is global, not an Experiment axis

**Status:** Superseded by [ADR-0024](0024-boundary-vs-corpus-embedding-models.md) — single Active Embedding Model replaced by **Boundary** + **Corpus** roles (query locked to Corpus).

Original decision retained for history:

The platform compares **Strategies** under controlled conditions. Embedding Model is a confounder, not a second experiment dimension: one **Active Embedding Model** applies to process, query, and new Experiments. The operator switches it from Admin among entries in a static **Embedding Model Registry** (Provider, stable id, vector dimension). Selection persists across restarts (config supplies the default only when unset). Every Experiment records which Embedding Model produced it; historical rows without provenance are treated as the default cloud model. A process, query, or Experiment **snapshots** the Active Embedding Model at start so a mid-flight Admin switch cannot mix models inside one operation.

## Considered Options

- **Global Active Embedding Model** — chosen; fair Strategy comparisons; A/B models via separate Experiments
- **Embedding Model as Experiment axis** — Strategy × model cross-product; richer science, much heavier data model/UI
- **Per-run choice with no Experiment coupling** — flexible, invites silent unfair comparisons

Switcher: **Admin UI** (not env-only, not read-only status). Catalog: **static registry** (not live Ollama discovery, not free-form). Local Provider host: **`OLLAMA_BASE_URL` in config only**. Cost Estimator: **$0 embedding line when Active Embedding Model is Local**; LLM costs unchanged. This carve-out does not reopen general `/admin/config` (ADR-0007 deferred).

## Consequences

- Introduce Provider adapters (Cloud OpenAI, Local Ollama) behind one embed API; callers bind a registry entry for the operation
- Dashboard Admin gains an Embedding Model switcher; Benchmarks/reports must show Experiment provenance
- `docs/out-of-scope-v1.md` “no embedding model from dashboard” is superseded for this focused control only
- Local Nomic registry entries use task prefixes (`search_document` / `search_query`); Cloud OpenAI entries do not