diff --git a/zig/src/native/cuda.zig b/zig/src/native/cuda.zig
index 851f919480..eaa977f265 100644
--- a/zig/src/native/cuda.zig
+++ b/zig/src/native/cuda.zig
@@ -7,19 +7,12 @@ const nemotron = @import("nemotron");
 const Allocator = std.mem.Allocator;
 const budget = @import("cuda_memory.zig");
 const lane_backend = @import("cuda_bound.zig");
+const snaps = @import("cuda_snaps.zig");
 const nemotron_slide = @import("nemotron_slide.zig");
 
 /// CUDA families provide metadata, open their lane backend and explain their refusals.
 const registry = .{nemotron.native};
 
-/// Nemotron's prompt-cache copies. A file-level value so the store's pointer stays valid for the process.
-const nemotron_snaps: api.prompt_cache.Snapshots.VTable = .{
-    .bytes = nemotron.native.snap_bytes,
-    .save = nemotron.native.snap_save,
-    .restore = nemotron.native.snap_restore,
-    .drop = nemotron.native.snap_drop,
-};
-
 pub const backends: []const []const u8 = &.{"cuda"};
 pub const families: []const api.Family = blk: {
     var out: [registry.len]api.Family = undefined;
@@ -322,13 +315,18 @@ fn openWith(comptime F: type, a: Allocator, gpa: Allocator, io: std.Io, o: api.O
         },
     };
     const before = try pool(a, io, &g.ctx, problem) orelse return null;
-    const weights = weightBytes(io, o.dir);
+    // a family split over hosts holds only its rank's share (GLM-5.3-Flash's TP)
+    const weights = if (@hasDecl(F, "weightShare")) F.weightShare(weightBytes(io, o.dir)) else weightBytes(io, o.dir);
     const held0 = cuda.usage(false).device;
     if (weights > before.room(held0)) {
         problem.* = try std.fmt.allocPrint(a, "the checkpoint's {d:.1} GiB of weights do not fit the {d:.1} GiB the CUDA memory budget grants ({d:.1} GiB free less a {d:.1} GiB reserve{s}); free device memory or adjust TENSORFOLD_MEMORY_RESERVE_GIB / TENSORFOLD_CUDA_MEMORY_LIMIT_GB", .{ toGib(weights), toGib(before.room(held0)), toGib(before.free), toGib(before.reserve), if (before.limit != null) ", under TENSORFOLD_CUDA_MEMORY_LIMIT_GB" else "" });
         return null;
     }
     const loaded = F.open(gpa, io, &g.ctx, o.dir, kernels, .{ .context = @intCast(window), .drafts = o.drafts, .segments = segments, .slide = o.slide }) catch |e| {
+        if (@hasDecl(F, "explains_open")) if (F.explain(null, e)) |text| {
+            problem.* = text;
+            return null;
+        };
         problem.* = try std.fmt.allocPrint(a, "the native CUDA engine cannot load {s} with {s} glue kernels ({s})", .{ o.dir, kernels orelse "its own", @errorName(e) });
         return null;
     };
@@ -347,24 +345,24 @@ fn openWith(comptime F: type, a: Allocator, gpa: Allocator, io: std.Io, o: api.O
     const h = try gpa.create(Host);
     errdefer gpa.destroy(h);
     h.* = .{ .gpa = gpa, .gpu = g, .family = loaded.ctx, .release = loaded.deinit, .inner = loaded.backend, .vtable = undefined, .cfg = undefined, .clock = undefined, .core = undefined, .host = undefined, .lone = loaded.lone };
-    const cache = budget.cacheBytes(o.prompt_cache_gib, room, loaded.stream_bytes * (streams -| free));
-    h.startup = try std.fmt.allocPrint(gpa, "CUDA sm_{d} device {d} ({s}{s}): model {d:.2} GiB{s}; {d} stream{s} at once, {d:.2} GiB each at a {d}-token window, of {d:.1} GiB left after a {d:.1} GiB reserve; prompts in passes of up to {d} rows{s}{s}; {s}", .{
+    const cache = if (@hasDecl(F, "snap_save")) budget.cacheBytes(o.prompt_cache_gib, room, loaded.stream_bytes * (streams -| free)) else 0;
+    h.startup = try std.fmt.allocPrint(gpa, "CUDA sm_{d} device {d} ({s}{s}): model {d:.2} GiB{s}; {d} stream{s} at once, {d:.2} GiB each at a {d}-token window, of {d:.1} GiB left after a {d:.1} GiB reserve; prompts in {d}-row chunks{s}{s}; {s}", .{
         capability,                                                                                                        device,                                                                                                       name, if (after.unified) ", memory shared with the host" else "", toGib(model), if (loaded.learn_bytes > 0) try std.fmt.allocPrint(a, " and {d:.2} GiB kept for --slide's trainer", .{toGib(loaded.learn_bytes)}) else "", streams, if (streams == 1) "" else "s", toGib(loaded.stream_bytes), window, toGib(room), toGib(after.reserve), F.prompt_rows, if (segments > 1) try std.fmt.allocPrint(a, ", {d} staggered segments a call", .{segments}) else "",
         if (cache > 0) try std.fmt.allocPrint(a, ", a {d:.1} GiB prompt cache", .{toGib(cache)}) else ", no prompt cache", if (kernels) |dir| try std.fmt.allocPrint(a, "glue kernels captured at {s}", .{dir}) else "own glue kernels",
     });
     errdefer gpa.free(h.startup);
-    if (cache > 0) {
+    if (@hasDecl(F, "snap_save") and cache > 0) {
         const pc = api.prompt_cache;
         const store = try gpa.create(pc.Store);
-        // states keep at any row at no prompt call (the head reads one token on); replies prefill when it is quiet
-        store.* = pc.Store.init(gpa, .{ .ptr = loaded.target, .vtable = &nemotron_snaps }, .{ .lookahead = 1, .min_prompt = 0, .warm = .waits }, cache - try nemotron.native.snap_ready(loaded.target, cache));
+        // rules and budget from the family's snap_* declarations (cuda_snaps.zig)
+        store.* = pc.Store.init(gpa, .{ .ptr = loaded.target, .vtable = &snaps.Snaps(F).vtable }, snaps.cacheRules(F), try snaps.cacheBudget(F, loaded.target, cache));
         h.store = store;
     }
     errdefer if (h.store) |store| {
         store.deinit();
         gpa.destroy(store);
     };
-    if (loaded.learns != null) {
+    if (@hasDecl(F, "slide")) if (loaded.learns != null) {
         const Slide = nemotron_slide.Adapter(F.slide);
         h.dir = try gpa.dupe(u8, o.dir);
         const s = try gpa.create(Slide);
@@ -378,13 +376,13 @@ fn openWith(comptime F: type, a: Allocator, gpa: Allocator, io: std.Io, o: api.O
             }
         }.f;
         h.learn = s.hook();
-    }
+    };
     errdefer if (h.slide) |s| {
         h.slide_free.?(gpa, s);
         gpa.free(h.dir);
     };
     // the family cuts its own prompt grid from position 0, as `tensorfold run` does: prefill_step 0
-    try h.serve(io, loaded.facts, loaded.rows, .{ .lanes = streams, .context_window = @intCast(window), .startup = h.startup, .prompt_cache = h.store != null, .warm_turns = h.store != null, .logprobs = loaded.backend.vtable.first_row != null, .prompt_logprobs = loaded.backend.vtable.prompt_rows, .structures = loaded.backend.vtable.first_masked != null }, .{ .ctx = loaded.ctx, .text = F.explain });
+    try h.serve(io, loaded.facts, loaded.rows, .{ .lanes = streams, .context_window = @intCast(window), .startup = h.startup, .prompt_cache = h.store != null, .warm_turns = h.store != null and @hasDecl(F, "warm_quiet"), .logprobs = loaded.backend.vtable.first_row != null, .prompt_logprobs = loaded.backend.vtable.prompt_rows, .structures = loaded.backend.vtable.first_masked != null }, .{ .ctx = loaded.ctx, .text = F.explain });
     opened = true;
     return .{ .engine = h.host.engine(), .close = Host.close, .ctx = h };
 }
@@ -397,6 +395,7 @@ test {
     _ = budget; // cuda_memory.zig's own tests, which no other test binary reaches
     _ = refusals;
     _ = lane_backend;
+    _ = snaps;
 }
 
 test "the lane core sees a family's prefill_step through the lane backend, so a served prompt can step" {
diff --git a/zig/src/native/cuda_snaps.zig b/zig/src/native/cuda_snaps.zig
new file mode 100644
index 0000000000..961ab866ac
--- /dev/null
+++ b/zig/src/native/cuda_snaps.zig
@@ -0,0 +1,62 @@
+//! A CUDA family's prompt cache in the native server: rules, budget and copies from the family's `snap_*` decls.
+const std = @import("std");
+const api = @import("engine_api");
+
+/// Any row, the head one token on (Nemotron's); `snap_grid`'s chunk starts and `warm_quiet`'s warm turns if declared.
+pub fn cacheRules(comptime F: type) api.prompt_cache.Rules {
+    var rules: api.prompt_cache.Rules = .{ .lookahead = 1, .min_prompt = 0 };
+    if (@hasDecl(F, "warm_quiet")) rules.warm = .waits;
+    if (@hasDecl(F, "snap_grid")) {
+        rules.planned = true;
+        rules.grid = F.snap_grid;
+    }
+    return rules;
+}
+
+/// The cache's bytes less what the family sets aside for its states (`snap_ready`, as Nemotron's spare buffers).
+pub fn cacheBudget(comptime F: type, target: anytype, cache: u64) !u64 {
+    return if (@hasDecl(F, "snap_ready")) cache - try F.snap_ready(target, cache) else cache;
+}
+
+/// The family's `snap_*` copies (none: no prompt cache), a container-level value so the store's pointer stays valid.
+pub fn Snaps(comptime F: type) type {
+    return struct {
+        pub const vtable: api.prompt_cache.Snapshots.VTable = .{
+            .bytes = F.snap_bytes,
+            .save = F.snap_save,
+            .restore = F.snap_restore,
+            .drop = F.snap_drop,
+        };
+    };
+}
+
+test "a family with snap_grid keeps on its chunk starts, any other at any row as Nemotron does" {
+    const Glm = struct {
+        pub const snap_grid: u32 = 2048;
+    };
+    const Other = struct {};
+    const Warm = struct {
+        pub const warm_quiet: u64 = 1;
+    };
+    const any = cacheRules(Other);
+    try std.testing.expect(!any.planned and any.min_prompt == 0 and any.lookahead == 1 and any.warm == .off);
+    try std.testing.expect(cacheRules(Warm).warm == .waits and cacheRules(Glm).warm == .off);
+    const Stub = struct {
+        fn bytes(_: *anyopaque, _: u32) u64 {
+            return 0;
+        }
+        fn save(_: *anyopaque, _: ?*anyopaque, _: u32) anyerror!api.prompt_cache.Saved {
+            return error.Unused;
+        }
+        fn restore(_: *anyopaque, _: ?*anyopaque, _: api.prompt_cache.Saved) anyerror!void {}
+        fn drop(_: *anyopaque, _: api.prompt_cache.Saved) void {}
+    };
+    var unused: u8 = 0;
+    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
+    defer arena.deinit();
+    const prompt = try arena.allocator().alloc(u32, 3547);
+    for (prompt, 0..) |*t, i| t.* = @intCast(i);
+    var store = api.prompt_cache.Store.init(std.testing.allocator, .{ .ptr = &unused, .vtable = &.{ .bytes = Stub.bytes, .save = Stub.save, .restore = Stub.restore, .drop = Stub.drop } }, cacheRules(Glm), 1 << 30);
+    defer store.deinit();
+    try std.testing.expectEqualSlices(u32, &[_]u32{2048}, try store.marks(arena.allocator(), prompt, 0, 3540, &.{}, &.{}, &.{}));
+}