diff --git a/open-sse/config/agyModels.ts b/open-sse/config/agyModels.ts
index d43fcc2531..28c1d69f8e 100644
--- a/open-sse/config/agyModels.ts
+++ b/open-sse/config/agyModels.ts
@@ -1,110 +1,22 @@
 // Antigravity CLI (`agy`) model catalog.
 //
-// These models are pinned from the live `:fetchAvailableModels` endpoint
-// (https://daily-cloudcode-pa.googleapis.com/v1internal:fetchAvailableModels) using a
-// real `agy` consumer-OAuth token. The public catalog exposes the upstream Gemini 3.7
-// Flash ids verbatim; the shared Antigravity executor dispatches them unchanged.
+// Models are derived from the shared Antigravity catalog (antigravitySharedModels.ts)
+// which is the single source of truth for both agy and antigravity surfaces.
+// The `agy` provider reuses the `antigravity` executor/translator (identical backend).
 //
-// The `agy` provider reuses the `antigravity` executor/translator (identical backend),
-// but keeps its own catalog so the CLI and IDE model surfaces can evolve independently.
-// Both currently expose the same callable Claude/Gemini/GPT set. Tab-completion models
-// (`tab_flash_lite_preview`, `tab_jump_flash_lite_preview`) are intentionally excluded —
-// they are not chat-callable.
+// To add a model to both surfaces: edit antigravitySharedModels.ts.
+// To add a model to CLI only: add an entry to `add` below.
+// To hide a model from CLI only: add its id to `remove` below.
 
-export const AGY_PUBLIC_MODELS = Object.freeze([
-  // Gemini 3.7 Flash tiers. The live endpoint selects High by default and advertises
-  // all three ids to both the IDE 2.5.5 and CLI 1.1.x clients.
-  {
-    id: "gemini-3.7-flash-high",
-    name: "Gemini 3.7 Flash (High)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gemini-3.7-flash-medium",
-    name: "Gemini 3.7 Flash (Medium)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gemini-3.7-flash-low",
-    name: "Gemini 3.7 Flash (Low)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gemini-3.7-flash-tiered",
-    name: "Gemini 3.7 Flash (Tiered)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  // Gemini 3.1 Pro
-  {
-    id: "gemini-pro-agent",
-    name: "Gemini 3.1 Pro (High)",
-    contextLength: 1048576,
-    maxOutputTokens: 65535,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gemini-3.1-pro-low",
-    name: "Gemini 3.1 Pro (Low)",
-    contextLength: 1048576,
-    maxOutputTokens: 65535,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gemini-3.1-flash-lite",
-    name: "Gemini 3.1 Flash Lite",
-    contextLength: 1048576,
-    maxOutputTokens: 65535,
-    toolCalling: true,
-  },
-  // Claude (Antigravity backend).
-  {
-    id: "claude-opus-4-6-thinking",
-    name: "Claude Opus 4.6 (Thinking)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "claude-sonnet-4-6",
-    name: "Claude Sonnet 4.6 (Thinking)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  // GPT-OSS
-  {
-    id: "gpt-oss-120b-medium",
-    name: "GPT-OSS 120B (Medium)",
-    contextLength: 131072,
-    maxOutputTokens: 32768,
-    supportsReasoning: true,
-    toolCalling: true,
-  },
-]);
+import {
+  ANTIGRAVITY_SHARED_MODELS,
+  buildSurfaceCatalog,
+} from "./antigravitySharedModels.ts";
+
+export const AGY_PUBLIC_MODELS = buildSurfaceCatalog(ANTIGRAVITY_SHARED_MODELS, {
+  add: [], // CLI-only models (currently none)
+  remove: [], // Models hidden from CLI (currently none)
+});
 
 const AGY_PUBLIC_MODEL_IDS = new Set(AGY_PUBLIC_MODELS.map((model) => model.id));
 const AGY_NON_CHAT_MODEL_IDS = new Set(["tab_flash_lite_preview", "tab_jump_flash_lite_preview"]);
diff --git a/open-sse/config/antigravityModelAliases.ts b/open-sse/config/antigravityModelAliases.ts
index 3cf9094cbb..30bdd01c47 100644
--- a/open-sse/config/antigravityModelAliases.ts
+++ b/open-sse/config/antigravityModelAliases.ts
@@ -1,103 +1,12 @@
-export const ANTIGRAVITY_PUBLIC_MODELS = Object.freeze([
-  // Gemini 3.7 Flash tiers listed by the current official Antigravity model catalog.
-  // Keep the upstream model ids unchanged so discovery and execution address the same
-  // models selected by the native client.
-  {
-    id: "gemini-3.7-flash-high",
-    name: "Gemini 3.7 Flash (High)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gemini-3.7-flash-medium",
-    name: "Gemini 3.7 Flash (Medium)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gemini-3.7-flash-low",
-    name: "Gemini 3.7 Flash (Low)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gemini-3.7-flash-tiered",
-    name: "Gemini 3.7 Flash (Tiered)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  // Gemini 3.1 Pro budget tiers. Live streamGenerateContent validation uses
-  // `gemini-pro-agent` for High; the separately advertised `gemini-3.1-pro-high`
-  // discovery slot currently returns HTTP 400 and is intentionally not public.
-  {
-    id: "gemini-pro-agent",
-    name: "Gemini 3.1 Pro (High)",
-    contextLength: 1048576,
-    maxOutputTokens: 65535,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gemini-3.1-pro-low",
-    name: "Gemini 3.1 Pro (Low)",
-    contextLength: 1048576,
-    maxOutputTokens: 65535,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gemini-3.1-flash-lite",
-    name: "Gemini 3.1 Flash Lite",
-    contextLength: 1048576,
-    maxOutputTokens: 65535,
-    toolCalling: true,
-  },
-  // Claude (Antigravity backend). The `agy` provider already ships these from the live
-  // :fetchAvailableModels probe (see agyModels.ts) and discussion #3184 confirmed they
-  // are user-callable through the `antigravity` OAuth provider too — same backend.
-  // `antigravity/claude-opus-4-6-thinking` and `antigravity/claude-sonnet-4-6` both work.
-  // They are upstream IDs, so no alias remapping is required.
-  {
-    id: "claude-opus-4-6-thinking",
-    name: "Claude Opus 4.6 (Thinking)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "claude-sonnet-4-6",
-    name: "Claude Sonnet 4.6 (Thinking)",
-    contextLength: 1048576,
-    maxOutputTokens: 65536,
-    supportsReasoning: true,
-    supportsVision: true,
-    toolCalling: true,
-  },
-  {
-    id: "gpt-oss-120b-medium",
-    name: "GPT-OSS 120B (Medium)",
-    contextLength: 131072,
-    maxOutputTokens: 32768,
-    supportsReasoning: true,
-    toolCalling: true,
-  },
-]);
+import {
+  ANTIGRAVITY_SHARED_MODELS,
+  buildSurfaceCatalog,
+} from "./antigravitySharedModels.ts";
+
+export const ANTIGRAVITY_PUBLIC_MODELS = buildSurfaceCatalog(ANTIGRAVITY_SHARED_MODELS, {
+  add: [], // IDE-only models (currently none)
+  remove: [], // Models hidden from IDE (currently none)
+});
 
 export const ANTIGRAVITY_MODEL_ALIASES = Object.freeze({
   // Gemini 3.7 Flash tiers map to the upstream tiered endpoint model; the thinking
diff --git a/open-sse/config/antigravitySharedModels.ts b/open-sse/config/antigravitySharedModels.ts
new file mode 100644
index 0000000000..185472ca8b
--- /dev/null
+++ b/open-sse/config/antigravitySharedModels.ts
@@ -0,0 +1,118 @@
+// Shared Antigravity model catalog — single source of truth for both surfaces.
+//
+// `agy` (CLI) and `antigravity` (IDE) share the same backend. Adding a model
+// to both surfaces = one edit here. Each surface can still diverge via an
+// explicit add/remove delta in its own file (currently both deltas are empty).
+
+export const ANTIGRAVITY_SHARED_MODELS = Object.freeze([
+  // Gemini 3.7 Flash tiers. The live endpoint selects High by default and advertises
+  // all three ids to both the IDE 2.5.5 and CLI 1.1.x clients.
+  {
+    id: "gemini-3.7-flash-high",
+    name: "Gemini 3.7 Flash (High)",
+    contextLength: 1048576,
+    maxOutputTokens: 65536,
+    supportsReasoning: true,
+    supportsVision: true,
+    toolCalling: true,
+  },
+  {
+    id: "gemini-3.7-flash-medium",
+    name: "Gemini 3.7 Flash (Medium)",
+    contextLength: 1048576,
+    maxOutputTokens: 65536,
+    supportsReasoning: true,
+    supportsVision: true,
+    toolCalling: true,
+  },
+  {
+    id: "gemini-3.7-flash-low",
+    name: "Gemini 3.7 Flash (Low)",
+    contextLength: 1048576,
+    maxOutputTokens: 65536,
+    supportsReasoning: true,
+    supportsVision: true,
+    toolCalling: true,
+  },
+  {
+    id: "gemini-3.7-flash-tiered",
+    name: "Gemini 3.7 Flash (Tiered)",
+    contextLength: 1048576,
+    maxOutputTokens: 65536,
+    supportsReasoning: true,
+    supportsVision: true,
+    toolCalling: true,
+  },
+  // Gemini 3.1 Pro budget tiers. Live streamGenerateContent validation uses
+  // `gemini-pro-agent` for High; the separately advertised `gemini-3.1-pro-high`
+  // discovery slot currently returns HTTP 400 and is intentionally not public.
+  {
+    id: "gemini-pro-agent",
+    name: "Gemini 3.1 Pro (High)",
+    contextLength: 1048576,
+    maxOutputTokens: 65535,
+    supportsReasoning: true,
+    supportsVision: true,
+    toolCalling: true,
+  },
+  {
+    id: "gemini-3.1-pro-low",
+    name: "Gemini 3.1 Pro (Low)",
+    contextLength: 1048576,
+    maxOutputTokens: 65535,
+    supportsReasoning: true,
+    supportsVision: true,
+    toolCalling: true,
+  },
+  {
+    id: "gemini-3.1-flash-lite",
+    name: "Gemini 3.1 Flash Lite",
+    contextLength: 1048576,
+    maxOutputTokens: 65535,
+    toolCalling: true,
+  },
+  // Claude (Antigravity backend). Discussion #3184 confirmed these are
+  // user-callable through both the agy and antigravity OAuth providers.
+  {
+    id: "claude-opus-4-6-thinking",
+    name: "Claude Opus 4.6 (Thinking)",
+    contextLength: 1048576,
+    maxOutputTokens: 65536,
+    supportsReasoning: true,
+    supportsVision: true,
+    toolCalling: true,
+  },
+  {
+    id: "claude-sonnet-4-6",
+    name: "Claude Sonnet 4.6 (Thinking)",
+    contextLength: 1048576,
+    maxOutputTokens: 65536,
+    supportsReasoning: true,
+    supportsVision: true,
+    toolCalling: true,
+  },
+  // GPT-OSS
+  {
+    id: "gpt-oss-120b-medium",
+    name: "GPT-OSS 120B (Medium)",
+    contextLength: 131072,
+    maxOutputTokens: 32768,
+    supportsReasoning: true,
+    toolCalling: true,
+  },
+]);
+
+/**
+ * Build a surface-specific catalog from the shared base plus an explicit delta.
+ * This preserves the ability for agy/antigravity to diverge in the future while
+ * keeping today's single-edit maintenance path.
+ */
+export function buildSurfaceCatalog<T extends { id: string }>(
+  base: readonly T[],
+  delta: { add?: readonly T[]; remove?: readonly string[] } = {}
+): readonly T[] {
+  const removed = new Set(delta.remove ?? []);
+  const added = delta.add ?? [];
+  const filtered = base.filter((m) => !removed.has(m.id));
+  return Object.freeze([...filtered, ...added]);
+}
diff --git a/tests/unit/agy-antigravity-shared-catalog-12724.test.ts b/tests/unit/agy-antigravity-shared-catalog-12724.test.ts
new file mode 100644
index 0000000000..8402be0834
--- /dev/null
+++ b/tests/unit/agy-antigravity-shared-catalog-12724.test.ts
@@ -0,0 +1,61 @@
+// #12724 — agy and antigravity catalogs must be derived from the shared base
+// and stay identical until a per-surface delta is introduced.
+
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import {
+  ANTIGRAVITY_SHARED_MODELS,
+  buildSurfaceCatalog,
+} from "../../open-sse/config/antigravitySharedModels.ts";
+import { AGY_PUBLIC_MODELS } from "../../open-sse/config/agyModels.ts";
+import { ANTIGRAVITY_PUBLIC_MODELS } from "../../open-sse/config/antigravityModelAliases.ts";
+
+const serial = { concurrency: false };
+
+test("#12724 — shared base has exactly 10 models", serial, () => {
+  assert.equal(ANTIGRAVITY_SHARED_MODELS.length, 10);
+});
+
+test("#12724 — agy catalog equals shared base (empty deltas)", serial, () => {
+  assert.deepEqual([...AGY_PUBLIC_MODELS], [...ANTIGRAVITY_SHARED_MODELS]);
+});
+
+test("#12724 — antigravity catalog equals shared base (empty deltas)", serial, () => {
+  assert.deepEqual([...ANTIGRAVITY_PUBLIC_MODELS], [...ANTIGRAVITY_SHARED_MODELS]);
+});
+
+test("#12724 — agy and antigravity catalogs are byte-identical", serial, () => {
+  assert.deepEqual([...AGY_PUBLIC_MODELS], [...ANTIGRAVITY_PUBLIC_MODELS]);
+});
+
+test("#12724 — buildSurfaceCatalog remove delta works", serial, () => {
+  const subset = buildSurfaceCatalog(ANTIGRAVITY_SHARED_MODELS, {
+    remove: ["gemini-3.7-flash-high"],
+  });
+  assert.equal(subset.length, 9);
+  assert.ok(!subset.some((m) => m.id === "gemini-3.7-flash-high"));
+});
+
+test("#12724 — buildSurfaceCatalog add delta works", serial, () => {
+  const extended = buildSurfaceCatalog(ANTIGRAVITY_SHARED_MODELS, {
+    add: [{ id: "custom-model-v1", name: "Custom Model" }],
+  });
+  assert.equal(extended.length, 11);
+  assert.ok(extended.some((m) => m.id === "custom-model-v1"));
+});
+
+test("#12724 — buildSurfaceCatalog with both add and remove", serial, () => {
+  const mixed = buildSurfaceCatalog(ANTIGRAVITY_SHARED_MODELS, {
+    add: [{ id: "custom-model-v1", name: "Custom Model" }],
+    remove: ["gemini-3.7-flash-high", "gemini-3.7-flash-medium"],
+  });
+  assert.equal(mixed.length, 9); // 10 - 2 + 1
+  assert.ok(!mixed.some((m) => m.id === "gemini-3.7-flash-high"));
+  assert.ok(mixed.some((m) => m.id === "custom-model-v1"));
+});
+
+test("#12724 — buildSurfaceCatalog returns frozen array", serial, () => {
+  const result = buildSurfaceCatalog(ANTIGRAVITY_SHARED_MODELS);
+  assert.ok(Object.isFrozen(result));
+});