diff --git a/src/providers/model-discovery.ts b/src/providers/model-discovery.ts
index 78b68e55ef..acf267e29b 100644
--- a/src/providers/model-discovery.ts
+++ b/src/providers/model-discovery.ts
@@ -129,6 +129,14 @@ export function providerModelDiscoverySpecError(spec: ProviderModelDiscoverySpec
   if (queryEntries.some(([key, value]) => !key.trim() || key.length > 128 || typeof value !== "string" || value.length > 512)) {
     return "discovery query keys/values exceed their bounds";
   }
+  for (const [field, value] of [
+    ["envelopeKey", spec.envelopeKey],
+    ["idField", spec.idField],
+  ] as const) {
+    if (value !== undefined && (
+      typeof value !== "string" || !value || value !== value.trim() || value.length > 128
+    )) return `${field} must be a nonblank field name up to 128 characters`;
+  }
   for (const [field, value, hardLimit] of [
     ["maxResponseBytes", spec.maxResponseBytes, MODEL_DISCOVERY_MAX_RESPONSE_BYTES],
     ["maxModels", spec.maxModels, MODEL_DISCOVERY_MAX_MODELS],
@@ -422,7 +430,7 @@ export function extractModelEnvelopeRows(
   return { ok: true, rows };
 }
 
-/** Validate, bound, deduplicate, and declaratively filter OpenAI `{data:[...]}` or top-level arrays (Together `#617`). */
+/** Validate, bound, deduplicate, and filter the declared envelope or a top-level array (Together `#617`). */
 /**
  * Metadata a sibling `models[]` array may contribute to an ALREADY-ADMITTED
  * `data[]` row (#1797).
@@ -501,24 +509,26 @@ export function extractProviderModelItems(
   let data: unknown[];
   let siblings: SiblingIndex | null = null;
   if (Array.isArray(value)) {
-    // Together-style top-level /models arrays. Catalog discovery must not treat a stray
-    // `models` key on openai-chat responses as valid — only `data` envelopes or top-level arrays.
+    // Together-style top-level /models arrays. The default contract must not treat a stray
+    // `models` key on openai-chat responses as valid; only a provider spec may opt into it.
     if (value.length > limit) return { ok: false, reason: "too_many_models" };
     data = value;
   } else {
-    const envelope = extractModelEnvelopeRows(value, discovery.maxModels, ["data"]);
+    const envelopeKey = discovery.spec?.envelopeKey ?? "data";
+    const envelope = extractModelEnvelopeRows(value, discovery.maxModels, [envelopeKey]);
     if (!envelope.ok) return envelope;
     data = envelope.rows;
-    siblings = buildSiblingIndex(value, limit);
+    siblings = envelopeKey === "data" ? buildSiblingIndex(value, limit) : null;
   }
 
   const items: ProviderModelsApiItem[] = [];
   const seen = new Set<string>();
+  const idField = discovery.spec?.idField ?? "id";
   for (const raw of data) {
     if (raw === null || typeof raw !== "object" || Array.isArray(raw)) {
       return { ok: false, reason: "invalid_shape" };
     }
-    const id = (raw as { id?: unknown }).id;
+    const id = (raw as Record<string, unknown>)[idField];
     if (!isValidModelDiscoveryModelId(id)) return { ok: false, reason: "invalid_shape" };
     const prefix = discovery.spec?.stripIdPrefix;
     let finalId = id;
@@ -526,7 +536,9 @@ export function extractProviderModelItems(
       finalId = finalId.slice(prefix.length);
       if (!isValidModelDiscoveryModelId(finalId)) continue;
     }
-    const item = finalId === id ? raw as ProviderModelsApiItem : { ...(raw as ProviderModelsApiItem), id: finalId };
+    const item = finalId === id && idField === "id"
+      ? raw as ProviderModelsApiItem
+      : { ...(raw as Record<string, unknown>), id: finalId };
     // Admission is decided on the ORIGINAL `data[]` row, before any sibling
     // enrichment. Merging first let a `models[]` entry supply the very field a
     // provider filter requires — reproduced against the real Chutes policy,
diff --git a/src/providers/registry/entries-extended.ts b/src/providers/registry/entries-extended.ts
index 1791659615..9c5991c42c 100644
--- a/src/providers/registry/entries-extended.ts
+++ b/src/providers/registry/entries-extended.ts
@@ -427,6 +427,7 @@ export const PROVIDER_REGISTRY_EXTENDED: readonly ProviderRegistryEntry[] = [
     // model_access_denied, which is why the Chat path cannot simply hang off the new base.
     responsesPath: "/api/v1/responses",
     chatCompletionsPath: "/api/coding/paas/v4/chat/completions",
+    modelDiscovery: { path: "/api/v1/models", envelopeKey: "models", idField: "slug" },
     // The address this row occupied before the move. A saved custom provider still pointing
     // at the Chat endpoint keeps receiving this row's metadata (#1100).
     destinationAliases: [{ baseUrl: "https://api.z.ai/api/coding/paas/v4", adapter: "openai-chat" }],
diff --git a/src/providers/registry/types.ts b/src/providers/registry/types.ts
index f71c0fafe4..5192149cf4 100644
--- a/src/providers/registry/types.ts
+++ b/src/providers/registry/types.ts
@@ -64,6 +64,10 @@ export interface ProviderModelDiscoveryFilter {
 interface ProviderModelDiscoverySharedSpec {
   /** Query parameters applied to the resolved discovery URL. */
   query?: Readonly<Record<string, string>>;
+  /** Top-level response key containing model rows; defaults to `data`. */
+  envelopeKey?: string;
+  /** Model-row field containing the provider-native identifier; defaults to `id`. */
+  idField?: string;
   /** Declarative eligibility rules evaluated against each untrusted model row. */
   filter?: ProviderModelDiscoveryFilter;
   /** Optional lower byte ceiling; the process-wide hard ceiling still wins. */
diff --git a/structure/runtime.md b/structure/runtime.md
index 17a3ccbf95..808b5774a8 100644
--- a/structure/runtime.md
+++ b/structure/runtime.md
@@ -234,9 +234,10 @@ Custom providers keep the conventional `${baseUrl}/models` request, normalized b
 whitespace and trailing slashes are trimmed and an already-pasted `/models` is not doubled, so a
 `baseUrl` written with or without a trailing slash yields the identical discovery URL and an
 existing path prefix is preserved. Canonical presets may select a
-trusted URL/path/query and declarative eligibility filter without persisting that policy into user
-config. A response is rejected before caching when it exceeds 4 MiB, contains more than 2,000 raw
-rows, has a malformed OpenAI list envelope, or includes an invalid model id. Tests use fixtures and
+trusted URL/path/query, response envelope key, model identifier field, and declarative eligibility
+filter without persisting that policy into user config. A response is rejected before caching when
+it exceeds 4 MiB, contains more than 2,000 raw rows, has a malformed declared list envelope, or
+includes an invalid model id. Tests use fixtures and
 must never depend on live provider endpoints. Newly promoted fixed key presets opt into
 `preserveCustomDestination`, so an older same-named custom provider keeps its configured adapter,
 destination, and key boundary instead of being silently canonicalized onto the new host. Fixed
diff --git a/tests/providers/provider-model-discovery-contract.test.ts b/tests/providers/provider-model-discovery-contract.test.ts
index 9a4a6fae25..3a7cf8aa30 100644
--- a/tests/providers/provider-model-discovery-contract.test.ts
+++ b/tests/providers/provider-model-discovery-contract.test.ts
@@ -148,6 +148,44 @@ describe("registry-owned provider model discovery", () => {
       path: "models",
     } as unknown as ProviderModelDiscoverySpec)).toContain("mutually exclusive");
     expect(providerModelDiscoverySpecError({ maxModels: 25 })).toBeNull();
+    expect(providerModelDiscoverySpecError({ envelopeKey: " models ", idField: "slug" }))
+      .toContain("envelopeKey");
+    expect(providerModelDiscoverySpecError({ envelopeKey: "models", idField: "" }))
+      .toContain("idField");
+  });
+
+  test("zai uses its provider-specific discovery endpoint and response shape (#4822)", () => {
+    const entry = PROVIDER_REGISTRY.find(row => row.id === "zai");
+    if (!entry?.modelDiscovery) throw new Error("zai must declare modelDiscovery");
+    const seed = providerConfigSeed(entry);
+    const canonical = "https://api.z.ai/api/v1/models";
+
+    expect(resolveProviderModelDiscoveryUrl(
+      entry.id,
+      seed,
+      entry.baseUrl,
+      providerModelsUrl(entry.baseUrl),
+    )).toBe(canonical);
+    expect(isRegistryModelDiscoveryUrl(entry.id, canonical)).toBe(true);
+    expect(isRegistryModelDiscoveryUrl(entry.id, "https://api.z.ai/models")).toBe(false);
+
+    const discovery = resolveProviderModelDiscovery(entry.id, seed);
+    expect(extractProviderModelItems({ models: [{ slug: "glm-5.3" }] }, discovery)).toEqual({
+      ok: true,
+      rawCount: 1,
+      items: [{ slug: "glm-5.3", id: "glm-5.3" }],
+    });
+    expect(extractProviderModelItems(
+      { models: [{ slug: "glm-5.3" }] },
+      { maxResponseBytes: discovery.maxResponseBytes, maxModels: discovery.maxModels },
+    )).toEqual({ ok: false, reason: "invalid_shape" });
+
+    expect(entry.baseUrl).toBe("https://api.z.ai");
+    expect(entry.responsesPath).toBe("/api/v1/responses");
+    expect(entry.chatCompletionsPath).toBe("/api/coding/paas/v4/chat/completions");
+    expect(entry.destinationAliases).toEqual([
+      { baseUrl: "https://api.z.ai/api/coding/paas/v4", adapter: "openai-chat" },
+    ]);
   });
 
   test("clears cached rows before applying a temporary registry discovery policy", async () => {