diff --git a/.changeset/automatic-static-querykey-ondemand.md b/.changeset/automatic-static-querykey-ondemand.md
new file mode 100644
index 000000000..f9ae0e33a
--- /dev/null
+++ b/.changeset/automatic-static-querykey-ondemand.md
@@ -0,0 +1,38 @@
+---
+"@tanstack/query-db-collection": patch
+---
+
+Automatically append predicates to static queryKey in on-demand mode.
+
+When using a static `queryKey` with `syncMode: 'on-demand'`, the system now automatically appends serialized LoadSubsetOptions to create unique cache keys for different predicate combinations. This fixes an issue where all live queries with different predicates would share the same TanStack Query cache entry, causing data to be overwritten.
+
+**Before:**
+
+```typescript
+// This would cause conflicts between different queries
+queryCollectionOptions({
+  queryKey: ["products"], // Static key
+  syncMode: "on-demand",
+  queryFn: async (ctx) => {
+    const { where, limit } = ctx.meta.loadSubsetOptions
+    return fetch(`/api/products?...`).then((r) => r.json())
+  },
+})
+```
+
+With different live queries filtering by `category='A'` and `category='B'`, both would share the same cache key `['products']`, causing the last query to overwrite the first.
+
+**After:**
+Static queryKeys now work correctly in on-demand mode! The system automatically creates unique cache keys:
+
+- Query with `category='A'` → `['products', '{"where":{...A...}}']`
+- Query with `category='B'` → `['products', '{"where":{...B...}}']`
+
+**Key behaviors:**
+
+- ✅ Static queryKeys now work correctly with on-demand mode (automatic serialization)
+- ✅ Function-based queryKeys continue to work as before (no change)
+- ✅ Eager mode with static queryKeys unchanged (no automatic serialization)
+- ✅ Identical predicates correctly reuse the same cache entry
+
+This makes the documentation example work correctly without requiring users to manually implement function-based queryKeys for predicate push-down.
diff --git a/packages/query-db-collection/src/query.ts b/packages/query-db-collection/src/query.ts
index ee915aabf..d70128f3b 100644
--- a/packages/query-db-collection/src/query.ts
+++ b/packages/query-db-collection/src/query.ts
@@ -7,6 +7,7 @@ import {
   QueryKeyRequiredError,
 } from "./errors"
 import { createWriteUtils } from "./manual-sync"
+import { serializeLoadSubsetOptions } from "./serialization"
 import type {
   BaseCollectionConfig,
   ChangeMessage,
@@ -627,7 +628,19 @@ export function queryCollectionOptions(
       queryFunction: typeof queryFn = queryFn
     ): true | Promise<void> => {
       // Push the predicates down to the queryKey and queryFn
-      const key = typeof queryKey === `function` ? queryKey(opts) : queryKey
+      let key: QueryKey
+      if (typeof queryKey === `function`) {
+        // Function-based queryKey: use it to build the key from opts
+        key = queryKey(opts)
+      } else if (syncMode === `on-demand`) {
+        // Static queryKey in on-demand mode: automatically append serialized predicates
+        // to create separate cache entries for different predicate combinations
+        const serialized = serializeLoadSubsetOptions(opts)
+        key = serialized !== undefined ? [...queryKey, serialized] : queryKey
+      } else {
+        // Static queryKey in eager mode: use as-is
+        key = queryKey
+      }
       const hashedQueryKey = hashKey(key)
       const extendedMeta = { ...meta, loadSubsetOptions: opts }
 
diff --git a/packages/query-db-collection/src/serialization.ts b/packages/query-db-collection/src/serialization.ts
new file mode 100644
index 000000000..ba22dc75a
--- /dev/null
+++ b/packages/query-db-collection/src/serialization.ts
@@ -0,0 +1,128 @@
+import type { IR, LoadSubsetOptions } from "@tanstack/db"
+
+/**
+ * Serializes LoadSubsetOptions into a stable, hashable format for query keys
+ * @internal
+ */
+export function serializeLoadSubsetOptions(
+  options: LoadSubsetOptions | undefined
+): string | undefined {
+  if (!options) {
+    return undefined
+  }
+
+  const result: Record<string, unknown> = {}
+
+  if (options.where) {
+    result.where = serializeExpression(options.where)
+  }
+
+  if (options.orderBy?.length) {
+    result.orderBy = options.orderBy.map((clause) => {
+      const baseOrderBy = {
+        expression: serializeExpression(clause.expression),
+        direction: clause.compareOptions.direction,
+        nulls: clause.compareOptions.nulls,
+        stringSort: clause.compareOptions.stringSort,
+      }
+
+      // Handle locale-specific options when stringSort is 'locale'
+      if (clause.compareOptions.stringSort === `locale`) {
+        return {
+          ...baseOrderBy,
+          locale: clause.compareOptions.locale,
+          localeOptions: clause.compareOptions.localeOptions,
+        }
+      }
+
+      return baseOrderBy
+    })
+  }
+
+  if (options.limit !== undefined) {
+    result.limit = options.limit
+  }
+
+  return Object.keys(result).length === 0 ? undefined : JSON.stringify(result)
+}
+
+/**
+ * Recursively serializes an IR expression for stable hashing
+ * @internal
+ */
+function serializeExpression(expr: IR.BasicExpression | undefined): unknown {
+  if (!expr) {
+    return null
+  }
+
+  switch (expr.type) {
+    case `val`:
+      return {
+        type: `val`,
+        value: serializeValue(expr.value),
+      }
+    case `ref`:
+      return {
+        type: `ref`,
+        path: [...expr.path],
+      }
+    case `func`:
+      return {
+        type: `func`,
+        name: expr.name,
+        args: expr.args.map((arg) => serializeExpression(arg)),
+      }
+    default:
+      return null
+  }
+}
+
+/**
+ * Serializes special JavaScript values (undefined, NaN, Infinity, Date)
+ * @internal
+ */
+function serializeValue(value: unknown): unknown {
+  if (value === undefined) {
+    return { __type: `undefined` }
+  }
+
+  if (typeof value === `number`) {
+    if (Number.isNaN(value)) {
+      return { __type: `nan` }
+    }
+    if (value === Number.POSITIVE_INFINITY) {
+      return { __type: `infinity`, sign: 1 }
+    }
+    if (value === Number.NEGATIVE_INFINITY) {
+      return { __type: `infinity`, sign: -1 }
+    }
+  }
+
+  if (
+    value === null ||
+    typeof value === `string` ||
+    typeof value === `number` ||
+    typeof value === `boolean`
+  ) {
+    return value
+  }
+
+  if (value instanceof Date) {
+    return { __type: `date`, value: value.toJSON() }
+  }
+
+  if (Array.isArray(value)) {
+    return value.map((item) => serializeValue(item))
+  }
+
+  if (typeof value === `object`) {
+    return Object.fromEntries(
+      Object.entries(value as Record<string, unknown>).map(([key, val]) => [
+        key,
+        serializeValue(val),
+      ])
+    )
+  }
+
+  return value
+}
diff --git a/packages/query-db-collection/tests/query.test.ts b/packages/query-db-collection/tests/query.test.ts
index 2f218d73a..a909d7c0e 100644
--- a/packages/query-db-collection/tests/query.test.ts
+++ b/packages/query-db-collection/tests/query.test.ts
@@ -12,6 +12,7 @@ import type {
   Collection,
   DeleteMutationFnParams,
   InsertMutationFnParams,
+  LoadSubsetOptions,
   TransactionWithMutations,
   UpdateMutationFnParams,
 } from "@tanstack/db"
@@ -3538,4 +3539,180 @@ describe(`QueryCollection`, () => {
       expect(collection.size).toBe(0)
     })
   })
+
+  describe(`Static queryKey with on-demand mode`, () => {
+    it(`should automatically append serialized predicates to static queryKey in on-demand mode`, async () => {
+      const items: Array<CategorisedItem> = [
+        { id: `1`, name: `Item 1`, category: `A` },
+        { id: `2`, name: `Item 2`, category: `A` },
+        { id: `3`, name: `Item 3`, category: `B` },
+        { id: `4`, name: `Item 4`, category: `B` },
+      ]
+
+      const queryFn = vi.fn((ctx: QueryFunctionContext) => {
+        const loadSubsetOptions = ctx.meta?.loadSubsetOptions as
+          | LoadSubsetOptions
+          | undefined
+        // Filter items based on the where clause if present
+        if (loadSubsetOptions?.where) {
+          // Simple mock filtering - in real use, you'd use parseLoadSubsetOptions
+          return Promise.resolve(items)
+        }
+        return Promise.resolve(items)
+      })
+
+      const staticQueryKey = [`static-on-demand-test`]
+
+      const config: QueryCollectionConfig<CategorisedItem> = {
+        id: `static-on-demand-test`,
+        queryClient,
+        queryKey: staticQueryKey, // Static queryKey (not a function)
+        queryFn,
+        getKey: (item: CategorisedItem) => item.id,
+        syncMode: `on-demand`,
+        startSync: true,
+      }
+
+      const options = queryCollectionOptions(config)
+      const collection = createCollection(options)
+
+      // Collection should start empty with on-demand sync mode
+      expect(collection.size).toBe(0)
+
+      // Create first live query with category A filter
+      const queryA = createLiveQueryCollection({
+        query: (q) =>
+          q
+            .from({ item: collection })
+            .where(({ item }) => eq(item.category, `A`))
+            .select(({ item }) => item),
+      })
+
+      await queryA.preload()
+
+      // Wait for first query to load
+      await vi.waitFor(() => {
+        expect(collection.size).toBeGreaterThan(0)
+      })
+
+      // Verify queryFn was called
+      expect(queryFn).toHaveBeenCalledTimes(1)
+      const firstCall = queryFn.mock.calls[0]?.[0]
+      expect(firstCall?.meta?.loadSubsetOptions).toBeDefined()
+
+      // Create second live query with category B filter
+      const queryB = createLiveQueryCollection({
+        query: (q) =>
+          q
+            .from({ item: collection })
+            .where(({ item }) => eq(item.category, `B`))
+            .select(({ item }) => item),
+      })
+
+      await queryB.preload()
+
+      // Wait for second query to trigger another queryFn call
+      await vi.waitFor(() => {
+        expect(queryFn).toHaveBeenCalledTimes(2)
+      })
+
+      // Verify the second call has different loadSubsetOptions
+      const secondCall = queryFn.mock.calls[1]?.[0]
+      expect(secondCall?.meta?.loadSubsetOptions).toBeDefined()
+
+      // The two queries should have triggered separate cache entries
+      // because the static queryKey was automatically extended with serialized predicates
+      expect(queryFn).toHaveBeenCalledTimes(2)
+
+      // Cleanup
+      await queryA.cleanup()
+      await queryB.cleanup()
+    })
+
+    it(`should create same cache key for identical predicates with static queryKey`, async () => {
+      const items: Array<CategorisedItem> = [
+        { id: `1`, name: `Item 1`, category: `A` },
+        { id: `2`, name: `Item 2`, category: `A` },
+      ]
+
+      const queryFn = vi.fn().mockResolvedValue(items)
+
+      const config: QueryCollectionConfig<CategorisedItem> = {
+        id: `static-identical-predicates-test`,
+        queryClient,
+        queryKey: [`identical-test`],
+        queryFn,
+        getKey: (item: CategorisedItem) => item.id,
+        syncMode: `on-demand`,
+        startSync: true,
+      }
+
+      const options = queryCollectionOptions(config)
+      const collection = createCollection(options)
+
+      // Create two live queries with identical predicates
+      const query1 = createLiveQueryCollection({
+        query: (q) =>
+          q
+            .from({ item: collection })
+            .where(({ item }) => eq(item.category, `A`))
+            .select(({ item }) => item),
+      })
+
+      const query2 = createLiveQueryCollection({
+        query: (q) =>
+          q
+            .from({ item: collection })
+            .where(({ item }) => eq(item.category, `A`))
+            .select(({ item }) => item),
+      })
+
+      await query1.preload()
+      await query2.preload()
+
+      await vi.waitFor(() => {
+        expect(collection.size).toBeGreaterThan(0)
+      })
+
+      // Should only call queryFn once because identical predicates
+      // should produce the same serialized cache key
+      expect(queryFn).toHaveBeenCalledTimes(1)
+
+      // Cleanup
+      await query1.cleanup()
+      await query2.cleanup()
+    })
+
+    it(`should work correctly in eager mode with static queryKey (no automatic serialization)`, async () => {
+      const items: Array<TestItem> = [
+        { id: `1`, name: `Item 1` },
+        { id: `2`, name: `Item 2` },
+      ]
+
+      const queryFn = vi.fn().mockResolvedValue(items)
+
+      const config: QueryCollectionConfig<TestItem> = {
+        id: `static-eager-test`,
+        queryClient,
+        queryKey: [`eager-test`],
+        queryFn,
+        getKey,
+        syncMode: `eager`, // Eager mode should NOT append predicates
+        startSync: true,
+      }
+
+      const options = queryCollectionOptions(config)
+      const collection = createCollection(options)
+
+      // Wait for initial load
+      await vi.waitFor(() => {
+        expect(collection.size).toBe(items.length)
+      })
+
+      // Should call queryFn once with empty predicates
+      expect(queryFn).toHaveBeenCalledTimes(1)
+      const call = queryFn.mock.calls[0]?.[0]
+      expect(call?.meta?.loadSubsetOptions).toEqual({})
+    })
+  })
 })