diff --git a/drift-proposals/openai-gpt-6.1-terra-new-family.md b/drift-proposals/openai-gpt-6.1-terra-new-family.md
new file mode 100644
index 00000000..13f75db9
--- /dev/null
+++ b/drift-proposals/openai-gpt-6.1-terra-new-family.md
@@ -0,0 +1,45 @@
+# New / unclassified model family: gpt-6.1-terra
+
+Provider: openai
+Detected: 2026-10-26
+Status: RESOLVED — decision recorded below and applied to the registry
+
+This model family appeared in a live /models listing but matches no classification rule (include, exclude, -preview, gemma). drift-sync never silently classifies a new family.
+
+## Decision
+<!-- drift-sync never auto-classifies a new family. A HUMAN decides, by
+     changing the line below to either:
+
+       Decision: include   — aimock mocks this family on the chat surface
+       Decision: exclude   — wrong modality / retired / preview; not ours
+
+     The NEXT drift-sync run then applies the mechanical registry edit to
+     includeFamilies or excludeFamilies respectively, and re-pins that
+     set's membership checksum in the same commit (still zero-LLM: this
+     is a human-authored decision, not generated code).
+
+     ONE EXCEPTION, and it is the common one for `exclude`: a VOICE/AUDIO
+     family (realtime / audio / live / transcribe / whisper / voice / tts)
+     is watched by a SECOND canary whose seed set — knownVoiceModelFamilies
+     in src/__tests__/drift/voice-models.ts — is a deliberately disjoint
+     surface drift-sync does not write. Classifying such a family in the
+     registry alone leaves that canary red, so the run would gate-fail and
+     revert, nightly, forever. drift-sync therefore does NOT auto-apply it:
+     it drops a `-voice-seed-set.md` note and a human makes both edits in
+     one reviewed commit. -->
+Decision: INCLUDE (applied 2026-10-26 — includeFamilies.openai in
+`src/__tests__/drift/model-registry.ts`, with the `includeFamilies.openai`
+re-pin in `src/__tests__/drift/logic-pin.test.ts`, plus the static OpenAI
+/models wave in `src/__tests__/drift/models.drift.ts`).
+
+Rationale: gpt-6.1 point release of the included `gpt-5.6-terra` line and
+sibling of the included `gpt-6.1-sol`. The normalizer keeps the `.1` version
+token, so it is its own family and must be enumerated.
+
+Evidence (live, 2026-10-26): `GET /v1/models/gpt-6.1-terra` returned 200 with
+`id`, `object`, `created: 1791908780`, `owned_by: "system"`,
+`shutdown_date: null` — no capability field, the same shape as `gpt-6.1-sol`.
+A minimal `POST /v1/chat/completions` with `model: "gpt-6.1-terra"` returned
+200, `object: "chat.completion"`, `finish_reason: "stop"`, and a real assistant
+text turn. It is text chat on the surface aimock mocks. Not a voice/audio
+family, so no `knownVoiceModelFamilies` edit is needed.
diff --git a/src/__tests__/drift/logic-pin.test.ts b/src/__tests__/drift/logic-pin.test.ts
index 3151ca1f..13429a5d 100644
--- a/src/__tests__/drift/logic-pin.test.ts
+++ b/src/__tests__/drift/logic-pin.test.ts
@@ -456,7 +456,7 @@ describe("classification-logic checksum freeze (Phase-0 anti-silence guard)", ()
 const DATA_FROZEN: Record<string, { members: () => string[]; pin: string }> = {
   "includeFamilies.openai": {
     members: () => [...includeFamilies.openai].sort(),
-    pin: "7c28e670d7ce3a5903b47aa605f3af391ba816529eaefbb4f81ac4f60c30ec0a",
+    pin: "d62f65955c9b867171e8889381bb818c724a3b5f9c3a60fcdf51716f82ee05ca",
   },
   "includeFamilies.anthropic": {
     members: () => [...includeFamilies.anthropic].sort(),
diff --git a/src/__tests__/drift/model-registry.ts b/src/__tests__/drift/model-registry.ts
index e4c36097..b84df9bb 100644
--- a/src/__tests__/drift/model-registry.ts
+++ b/src/__tests__/drift/model-registry.ts
@@ -144,6 +144,23 @@ export const includeFamilies: Record<Provider, Set<string>> = {
     // Decision: INCLUDE, recorded in
     // drift-proposals/openai-gpt-6.1-sol-new-family.md.
     "gpt-6.1-sol",
+    // gpt-6.1 point release of the included `gpt-5.6-terra` line, sibling of
+    // `gpt-6.1-sol` above. First listed by drift run 40422235776 (2026-10-26;
+    // `created: 1791908780`). The normalizer keeps the `.1` version token, so
+    // it is its own family and must be enumerated.
+    //
+    // Classified on a LIVE PROBE (2026-10-26), not on lineage alone.
+    // `GET /v1/models/gpt-6.1-terra` returns only `id` / `object` / `created` /
+    // `owned_by: "system"` / `shutdown_date: null`, the same shape as
+    // `gpt-6.1-sol`. A minimal /v1/chat/completions call returned 200,
+    // `object: "chat.completion"`, `finish_reason: "stop"` and a real assistant
+    // text turn, the same shape `gpt-6.1-sol` returned. No name token places it
+    // in an excluded cluster, and it is not a voice/audio family, so no
+    // knownVoiceModelFamilies pairing.
+    //
+    // Decision: INCLUDE, recorded in
+    // drift-proposals/openai-gpt-6.1-terra-new-family.md.
+    "gpt-6.1-terra",
     // Codex line (coding chat; text output)
     "gpt-5-codex",
     "gpt-5.1-codex",
diff --git a/src/__tests__/drift/models.drift.ts b/src/__tests__/drift/models.drift.ts
index 83ef4dfa..14eb8475 100644
--- a/src/__tests__/drift/models.drift.ts
+++ b/src/__tests__/drift/models.drift.ts
@@ -1040,6 +1040,8 @@ describe("recorded /models family waves are classified", () => {
       // gpt-6.1 point release (2026-09-24..30 wave, first listed 09-30; its own
       // normalized family)
       "gpt-6.1-sol",
+      // gpt-6.1-terra (2026-10-26 wave, drift run 40422235776; probe-verified text chat)
+      "gpt-6.1-terra",
       // o-series reasoning
       "o1",
       "o1-pro",
diff --git a/src/__tests__/drift/text-drift.test.ts b/src/__tests__/drift/text-drift.test.ts
index 608e2526..eca6c4a4 100644
--- a/src/__tests__/drift/text-drift.test.ts
+++ b/src/__tests__/drift/text-drift.test.ts
@@ -11,7 +11,7 @@
 
 import { describe, it, expect } from "vitest";
 
-import { isClassifiedFamily, excludeFamilies } from "./model-registry.js";
+import { isClassifiedFamily, excludeFamilies, includeFamilies } from "./model-registry.js";
 import { normalizeModelFamily } from "./model-family.js";
 import { unclassifiedFamilies } from "./text-drift.js";
 
@@ -562,3 +562,27 @@ describe("the 2026-10-14..18 model-family waves are classified", () => {
     ]);
   });
 });
+
+// ---------------------------------------------------------------------------
+// The 2026-10-26 wave — BEHAVIOURAL coverage of `gpt-6.1-terra` (INCLUDE), in
+// the same shape as the blocks above. Evidence sits beside the entry in
+// model-registry.ts and in drift-proposals/.
+// ---------------------------------------------------------------------------
+
+describe("the 2026-10-26 model-family wave is classified", () => {
+  it("gpt-6.1-terra is INCLUDED in a /models-shaped payload", () => {
+    expect(includeFamilies.openai.has("gpt-6.1-terra")).toBe(true);
+    expect(isClassifiedFamily("gpt-6.1-terra", "openai")).toBe(true);
+    expect(excludeFamilies.openai.has("gpt-6.1-terra")).toBe(false);
+    expect(unclassifiedFamilies(["gpt-6.1-sol", "gpt-6.1-terra"], "openai")).toEqual([]);
+  });
+
+  it("the new key does not classify a neighbouring family", () => {
+    // NEGATIVE CONTROLS: without these, `toEqual([])` above is also what a
+    // neutered `unclassifiedFamilies` would produce.
+    expect(normalizeModelFamily("gpt-6.1-terra", "openai")).toBe("gpt-6.1-terra");
+    expect(unclassifiedFamilies(["gpt-6.1-luna"], "openai")).toEqual(["gpt-6.1-luna"]);
+    expect(unclassifiedFamilies(["gpt-6.2-terra"], "openai")).toEqual(["gpt-6.2-terra"]);
+    expect(unclassifiedFamilies(["gpt-6.1-terra-tts"], "openai")).toEqual(["gpt-6.1-terra-tts"]);
+  });
+});