# get_network_system_change

Get Network System Change · v0.2.0 · medicare

Which health systems (or specialties) Medicare Advantage networks gained and lost between 2026 and 2027, from the plans' own published directories: for a contract, every health system with the clinicians listed in each year, how many stayed, left and joined, and an exit or join signal where a system's listing collapsed while the rest of the network held; or search one health system by name across every contract.

Use cases: 'Did Humana drop Ohio State for 2027?'; 'Which systems left H5216's network?'; 'Which contracts lost cardiologists for 2027?'.

Like for like: only each contract's own-year lists (no stand-ins), only ZIP3 areas it lists in both years, members only. A signal is a DIRECTORY SIGNAL to verify with the system or plan, never proof a contract ended; a contract whose source changed between years carries no signal. The publish is pinned by dataset_id.

SOURCE: medicare_silver.ma_network_change_v1 (the Data Tracker's directory table x CMS Doctors and Clinicians facility affiliation x the hospital system map).

**Inputs.**
- `contract_id`: CMS contract id (H5216). One of contract_id / system.
- `system`: Health system name (contains match, e.g. 'Ohio State'); searches every contract.
- `rollup`: 'system' (default; health systems) or 'specialty' (CMS network-adequacy types).
- `signals_only`: Return only system rows flagged as an exit or join signal.
- `limit`: Rows to return (default 50, max 500).

**Known limits.**
- Only contracts with an own-year list in both 2026 and 2027 are compared; the 40 contracts whose 2027 list is their 2026 directory standing in have no change rows.
- A clinician affiliated with several systems counts in each; system membership is CMS's hospital affiliation (2026-05-29) through the hospital system map.
- A publisher that moved from a thin API snapshot to a full one reads as a high joined rate; joined rates above 20% are flagged unverified.

**A real answer** (customer seat, 1.74 s, args `{"system":"Ohio State","signals_only":true}`):

```json
{
 "value": {
  "found": false,
  "not_found_reason": "no_row_matches_filters",
  "query": {
   "system": "Ohio State",
   "rollup": "system",
   "signals_only": true,
   "limit": 50
  },
  "dataset_id": "7bceef45cc9e5910e64caa428a1f3e40869f91d149c4e19f08cc55f5e468ba7c",
  "rows": [],
  "query_ids": [
   "ea97bac2-35ac-4b91-b429-8702a0116670"
  ]
 },
 "unit": "network_system_change",
 "vintage": null,
 "source": {
  "dataset": "MA plan networks, 2026 and 2027 (Data Tracker): plan year x CMS plan x NPI x listed location",
  "publisher": "vlada",
  "catalog_updated_at": "2026-11-02"
 },
 "caveats": [],
 "response_hash": "b0a9e1372c71a7a58b43c717b8ca93424efc0f83f0199cc2e4bb52a380e3e533",
 "semantic_version": 1,
 "tool_version": "get_network_system_change@0.2.0",
 "explanation": null,
 "status": "complete",
 "audience": "customer",
 "answer": {
  "value_ref": "value",
  "unit": "network_system_change",
  "scope": {
   "tool": "get_network_system_change",
   "filters": {
    "system": "Ohio State",
    "rollup": "system",
    "signals_only": true
   }
  }
 },
 "method": "Computed over the filters shown in this answer's scope, from the sources listed in its evidence. Nothing outside those filters was included. You did not specify rollup; system was used.",
 "evidence": {
  "sources": [
   {
    "dataset": "MA plan networks, 2026 and 2027 (Data Tracker): plan year x CMS plan x NPI x listed location",
    "publisher": "vlada",
    "catalog_updated_at": "2026-11-02"
   }
  ],
  "response_hash": "b0a9e1372c71a7a58b43c717b8ca93424efc0f83f0199cc2e4bb52a380e3e533"
 },
 "defaults_applied": [
  {
   "param": "rollup",
   "used": "system",
   "reason": "'system' (default"
  }
 ],
 "freshness": {
  "state": "unknown",
  "why": "This tool does not report an edition for its answer, and the door could not derive one from what the answer reads. Treat the result as current to no stated date."
 }
}
```

REST: `POST https://api.vladahealth.com/v1/tools/get_network_system_change` with the inputs as the JSON body. MCP: the tool by name.