Deep dive · Training economics · July 16, 2026
A 2.8-trillion-parameter frontier model on export-legal silicon: what the arithmetic of MoE training says about H800 clusters, Huawei superpods, and where the real bottleneck sits. With an interactive datacenter calculator.
Yes — comfortably, even on a frontier data budget. Kimi K3 is 2.8T total parameters with a confirmed 896-expert / 16-active MoE ⇒ ~70B active. On the frontier-rumor data budget from the Reiner Pope / Dwarkesh lecture (~150T tokens), a K3 run is ~9×10²⁵ FLOPs including RL. Here is what it takes to train that in 100 days, chip by chip (same math as the §8 calculator; each chip at its default achievable efficiency, PUE 1.3):
Power spans a single hall (Blackwell) to a ~200 MW campus (Ascend 910C) — large, but China added 429 GW of generation in 2024; energy is ~5% of run cost everywhere. The gating asset is the fleet itself.
The tweet's premise is off: total parameters are not training compute — at ~2.5% activation the dense-2.8T intuition overshoots ~40×. The H800's FLOPs were never nerfed (it is H100 silicon); its interconnect was, and the published DeepSeek/Moonshot systems work routes around that cut. Where China is actually constrained: not power and not one pretraining run, but aggregate compute — RL scaling, serving, experiments per year, trainer restocking — and, on the domestic path, Huawei chip supply (HBM + yield), not physics.
"How is a Chinese lab training an incredible ~3T model (probably same order of magnitude as Fable or GPT-5.6) when they have orders of magnitude less compute than American frontier labs? The best Nvidia chips exportable to China were 66–92% fewer FLOPs/W than B200/B300. Either Huawei caught up big time, labs smuggled Blackwells, they have way bigger power budgets, or Kimi figured out training efficiency."
Kimi K3 launched today: ~2.8T total parameters, 1M-token context, native multimodal, and a new hybrid linear attention scheme ("Kimi Delta Attention"). The tweet assumes a 2.8T-parameter model requires US-frontier-scale compute. This report runs the actual numbers: how much compute a K3-class run plausibly takes, what it costs on export-legal H800s, whether the constraint is FLOPs, interconnect, memory, or power, and whether Huawei's CloudMatrix superpods could carry the same run.
Five relations govern nearly everything below. They follow the roofline style of analysis Reiner Pope laid out on Dwarkesh's blackboard, plus two anchors every practitioner uses.
Each token costs ~2 FLOPs per parameter forward and ~4 backward — but only over the active parameters. For a mixture-of-experts model, total parameter count is nearly irrelevant to compute; what you pay for is the slice of the network each token touches. This single fact does most of the work of answering the tweet. RL costs ~2–6·N·D per generated token (decode-heavy, lower utilization); serving costs 2·N·D.
The correction term is attention: Fattn/token ≈ (6–12)·L·h·S grows with sequence length S. At 4K context it is ~3–5% of the parameter FLOPs; at 1M it would be 6–12× them — which is why 1M-context models (a) need linear/sparse attention like KDA and (b) train almost all tokens at short context, with a staged extension at the end (K2: 15.5T tokens at 4K, only 60B at 32K; DeepSeek-V4 extends 4K → 16K → 64K → 1M). The 6ND rule therefore stays a good estimate of the bulk run.
Model FLOPs utilization is the fraction of peak the training loop sustains end-to-end. Frontier MoE runs on Hopper-class hardware sustain ~17–22% of FP8 peak (equivalently ~35–40% of BF16 peak) — we derive DeepSeek-V3's realized number below, and it anchors every estimate in this report.
Per forward pass you must both do the math on active parameters and fetch all resident weights (plus KV state) from HBM. Equating the two sides gives the critical batch size ≈ 300 × sparsity (the ~300 is the FLOPs:memory-bandwidth ratio, roughly constant across GPU generations). Higher sparsity is nearly free compute-wise but demands bigger batches, more HBM capacity, and more interconnect — which is why sparsity, scale-up domain size, and memory co-evolve.
MoE layers route every token to experts scattered across GPUs — an all-to-all traffic pattern. Scale-up fabric (NVLink, in-rack) is ~8× faster than scale-out (NIC, cross-rack), so the all-to-all wants to stay inside the scale-up domain; whatever crosses nodes must fit through the NIC within the compute time it overlaps:
The DeepSeek-V4 report reduces this to one clean criterion. Per token-expert pair, an expert of hidden width de in a model of width h costs Vcomp = 6·h·de FLOPs but moves only Vcomm = 3h bytes (FP8 dispatch + BF16 combine). Expert count and top-k cancel from the ratio, so all-to-all can hide behind compute exactly when the chip's arithmetic intensity per byte of network clears 2·de:
Note the shape: the faster the chip and the narrower the expert, the more network each chip needs — a slower chip is actually easier to feed. At the V3-calibrated 343 useful TF/s, an H800 worst-cases to ~84 GB/s (de=2048) against a 50 GB/s NIC — which is exactly why DeepSeek invented node-limited routing and Moonshot keeps EP at 16: locality brings it under the line. An H20 at 50–148 TF/s needs only 8–24 GB/s (trivially fits); a B200 at ~1 PF/s needs ~160+ GB/s, which is why its expert parallelism lives inside the NVL72 scale-up domain. Nerfing NVLink (the H800's actual handicap) attacks exactly this term — and both DeepSeek and Moonshot's infrastructure papers are, at heart, engineering around it.
A 2.8T-parameter model carries ~45 TB of sharded training state — a memory-capacity floor on cluster size (~600+ chips at 80 GB each just to hold state, more for activations). The last line is the power bound: at fixed site power PIT, adding less-efficient chips cannot beat F/(P·η) — more chips only buy time while unused electrical and cooling capacity remains. Power cost, as we'll see, is economically trivial for a single run; power delivery (racks, cooling) is the real constraint on substituting many slow chips for few fast ones.
We don't need to speculate about whether frontier-quality training works on export-grade silicon — it's documented in two technical reports.
| Quantity | Value | Source |
|---|---|---|
| Architecture | 671B total / 37B active, 256 experts (top-8), MLA | V3 report §2 |
| Data | 14.8T tokens | V3 report §4 |
| Cluster | 2,048 × H800, 8-GPU nodes, IB scale-out | V3 report §3.1 |
| Pretraining cost | 2.664M H800-hours (180K hrs / T tokens; 3.7 days / T) | V3 report Table 1 |
| Full run incl. context ext. + post-train | 2.788M H800-hours ≈ $5.576M @ $2/hr | V3 report Table 1 |
| Implied 6ND FLOPs | 6 × 37e9 × 14.8e12 ≈ 3.3×10²⁴ | derived |
| Implied sustained throughput | ≈ 343 TFLOP/s per H800 ⇒ ~17% of FP8 peak / ~35% of BF16 peak | derived |
The systems work that made this possible on nerfed-interconnect hardware: FP8 mixed-precision GEMMs, the DualPipe schedule hiding all-to-all behind compute, ~20 SMs per GPU dedicated to communication, and node-limited routing (each token dispatched to ≤ 4 nodes) to economize the slow cross-node hop. DeepSeek's "suggestions to hardware vendors" section is a list of complaints about communication, not FLOPs.
| Quantity | Value | Source |
|---|---|---|
| Architecture | 1.04T total / 32.6B active, 384 experts (top-8 + 1 shared), 61 layers, d=7168 | K2 report §2.3 |
| Data / optimizer | 15.5T tokens, MuonClip, zero loss spikes | K2 report §2.1 |
| Cluster | H800 nodes (8 GPU + 2TB RAM), 8×400 Gbps RoCE scale-out | K2 report §2.4.1 |
| Parallelism | PP=16 (virtual stages) × EP=16 × ZeRO-1 DP; runs on any multiple of 32 nodes; 67M-token global batch | K2 report §2.4.2, §3 |
| Memory | BF16 weights + FP32 grad-accum ≈ 6 TB over a 256-GPU model-parallel group; activations offloaded to CPU RAM; FP8 for storage only, not compute | K2 report §2.4.2–2.4.3 |
| Implied 6ND FLOPs | 6 × 32.6e9 × 15.5e12 ≈ 3.0×10²⁴ | derived |
| At V3-anchored efficiency | ≈ 2.5M H800-hours ≈ $5M rental | derived |
K2's sparsity scaling law is the strategic tell: holding active parameters fixed, Moonshot found more total experts monotonically improves quality — sparsity 48 saves 1.7× FLOPs vs sparsity 8 at equal loss. The gradient for a compute-constrained lab points exactly where K3 went: grow total parameters, hold active parameters down, spend the savings on tokens.
DeepSeek's V4 report (arXiv:2606.19348, June 2026; cited here via the ChatGPT-Pro bottleneck analysis) extends the same lineage: 1.6T total / 49B active, 33T tokens ⇒ ~9.7×10²⁴ FLOPs, with context extended in stages 4K → 16K → 64K → 1M. Two systems findings matter for this report: it derives the C/B ≤ 2·de criterion of §2.4 and concludes interconnect no longer needs to grow with this design — and it reports that once fused kernels drive tensor cores, HBM, and network engines simultaneously, chip-level power throttling itself becomes a performance limiter. The bottleneck discourse has moved from "can the network keep up?" to "can the chip's power envelope?".
Officially confirmed at launch: ~2.8T total parameters (largest open-weights model to date), 1M native context, native multimodal, and 896 experts with 16 active per token (~1.8% activation, under a scheme Moonshot calls "Stable LatentMoE" — the pre-launch rumor was exactly right). The attention stack is Kimi Delta Attention: per the published Kimi Linear paper (arXiv 2510.26692), three linear-attention KDA layers per full-attention layer, cutting KV cache up to 75% and delivering the headline 6.3× faster decoding at 1M context; "Attention Residuals" claim ~25% higher training efficiency at <2% extra cost. Weights ship in MXFP4 with MXFP8 activations. Still undisclosed: active parameters, token count, cluster, and cost.
The clean way to size a MoE's active parameters (h/t the ChatGPT-Pro cross-check) splits the model into a trunk C that every token pays (attention, shared expert, embeddings) plus routed experts:
The blog's naive 16/896 × 2.8T ≈ 50.6B is the C=0 lower bound. Allowing C = 15–25B for a larger trunk, Attention Residuals, and native vision gives 65–75B: we take 70B active as central (60–80B as the interval — the same range the ChatGPT-Pro analysis lands on).
Moonshot has not disclosed the token count. Two reference points bracket it. The conservative one is lineage: K2 used 15.5T, DeepSeek-V4-Pro used 33T — so 20–35T is the "same-playbook" band. The aggressive one comes from the Reiner Pope / Dwarkesh lecture: working back from deployment economics (pretraining ≈ RL ≈ inference tokens at the cost-balanced optimum), Pope cites the rumor that current frontier models train on ~150T tokens, with ~100B active parameters — a deliberately speculative 6 × 100B × 150T ≈ 9×10²⁵ FLOPs frontier scenario. If K3's near-frontier benchmark position is taken at face value, the 150T-class data budget is the reading consistent with it, and Moonshot's rephrasing / synthetic-data pipeline (documented in the K2 report) is exactly the machinery you'd use to get there. We adopt 150T as the central scenario per this report's brief, keeping 20–30T rows as the conservative alternative.
Kimi's launch blog states: "these structural changes yield an approximate 2.5× improvement in overall scaling efficiency compared to Kimi K2" (KDA + Attention Residuals + Stable LatentMoE). Read literally, that is a claim about converting FLOPs into capability, not about GPU throughput — so it does not reduce the 6ND bill; it multiplies what the bill buys. We report it as effective compute = 2.5 × physical FLOPs (K2-architecture-equivalent). Note the blog says MXFP4/MXFP8 quantization-aware training starts only at the SFT stage, so the bulk pretrain was not FP4-cheap.
| Scenario | N_active | Tokens | Pretrain FLOPs | ×2.5 effective | Comparable (physical) |
|---|---|---|---|---|---|
| Conservative (K2-style data) | 50B | 20T | 6.0×10²⁴ | 1.5×10²⁵ | ≈ 2× K2; ~⅔ V4-Pro |
| Moderate (V4-Pro-style) | 70B | 30T | 1.3×10²⁵ | 3.2×10²⁵ | ≈ ½ GPT-4; ChatGPT-Pro's central |
| Central — frontier data (Reiner 150T) | 70B | 150T | 6.3×10²⁵ | 1.6×10²⁶ | ≈ GPT-4.5-class physical; frontier-band effective |
Apply the V3-anchored efficiency (343 sustained TFLOP/s per H800, i.e. 180K H800-hours per trillion tokens at 37B active, scaled by active parameters). This empirical number already absorbs bubbles, communication, and non-GEMM overheads for a V3-like short-context workload:
| Scenario | Pretrain H800-hrs | + 1M-ctx ext & RL (×1.4–1.8) | Rental @ $2/hr | On 10k H800s | On 30k H800s |
|---|---|---|---|---|---|
| Conservative (50B × 20T) | 4.9M | 7.0M | $14M | 29 days | 10 days |
| Moderate (70B × 30T) | 10.2M | 15M | $30M | 62 days | 21 days |
| Central — 150T tokens | 51M | 74M | $148M | ~10 months | 103 days |
The conservative and moderate runs are DeepSeek-V3-class events: a mid-two-digit-million bill on a 10k-GPU cluster (even V3's own 2,048-GPU cluster could grind out the moderate run in ~7 months). The 150T central is a different animal — a ~$150M, ~3-month occupation of a 30k-H800 fleet — yet still: Moonshot has raised ~$3.9B, including a Jan 2026 $500M round explicitly earmarked for K3 compute, and was reportedly raising at a ~$31.5B valuation at launch. The run is ~4% of funds raised. For context, the H800s themselves (≈$1–2B of capex for 30–50k units at China market prices) dwarf the marginal cost of any single run — the fleet is the moat, the run is cheap. What the 150T scenario really prices is fleet size: it only fits a training season if Moonshot controls DeepSeek-scale (~50k Hopper-class) compute, which its funding implies it does.
The H800 is H100 silicon: ~990 dense BF16 / ~1979 dense FP8 TFLOPs, 80 GB HBM3 at 3.35 TB/s — identical to the H100 SXM. Export rules cut its NVLink from 900 to 400 GB/s and its FP64 (34 → ~1 TFLOPs); neither touches transformer arithmetic. The tweet's chip list is also off: the H100 was never legally exportable — the actual sequence is A800/H800 (2022–Oct 2023), H20 (2024–Apr 2025 ban, licensed again mid-2025, ~1.46M installed), and since January 2026 the H200 (capped at 50% of US volumes with a 25% surcharge — likely the "few days ago" policy backdrop, alongside the May 2026 rule closing the offshore-Blackwell loophole). "66–92% fewer FLOPs/W than B200/B300" fits the H20, a deliberately compute-gutted inference part — not the H800 fleet these models train on, and per-chip FLOPs/W was never the binding term anyway: what binds is chips × time × engineering.
Apply the §2.4 criterion to an H800 at the V3-calibrated 343 useful TF/s with K2-width experts (de = 2048): worst-case Brequired = C/(2·de) ≈ 84 GB/s per chip — against a 50 GB/s NIC. Naively routed, the run is comms-bound. It fits only because of the tricks now standard in Chinese labs — all documented in the reports: DeepSeek's node-limited routing (each token confined to ≤4 of its 16 target slots cuts cross-node traffic ~4×, to ~21 GB/s sustained), 20 of 132 SMs dedicated to communication, DualPipe hiding the all-to-all (the V3 paper measures NVLink's effective 160 GB/s against InfiniBand's 50 GB/s — a 3.2× cliff every token must negotiate); Kimi's small EP=16, halved attention heads, and interleaved-1F1B overlap — and K3's launch material advertises "balanced expert-parallel training with static shapes and no host synchronization on the critical path," i.e. the 896-expert straggler problem got its own engineering. DeepSeek's "suggestions to hardware vendors" is explicit that burning SMs on communication "limits computational throughput" — the 400 GB/s NVLink cut costs real efficiency (V3's ~17% FP8 MFU vs ~25%+ achievable on full-NVLink hardware). Call it a 20–40% tax, not a wall — and note DeepSeek-V4's conclusion that with these designs, interconnect no longer needs to grow with the model.
2.8T parameters ≈ 16.8 TB of BF16 weights + FP32 grad-accum (K2's recipe): 65.6 GB/GPU sharded over a 256-GPU model-parallel group, or 32.8 GB/GPU over 512 — feasible even on 96 GB H20s with ZeRO, recomputation, and K2-style CPU offload; ~45 TB all-in with master weights and Muon momentum. Gradient synchronization is equally tame: a 512-GPU group leaves a ~5.5B-parameter shard per rank, whose ~22 GB ring all-reduce takes ~0.4 s at 400G — hidden inside multi-second training steps on tens-of-millions-token batches. Practical floor: a few thousand GPUs for healthy activation headroom, comfortably below the 10k+ any such lab would use anyway. KDA is the memory-bandwidth play: linear attention holds per-token state constant, exactly the term (§2.3) that otherwise explodes at 1M context.
10k H800s draw ≈ 18 MW at ~1.4 kW/GPU all-in IT load (SemiAnalysis's H100-cluster figure) and PUE 1.3 — Chinese policy requires ≤1.25 for new large datacenters. The central run consumes ~20 GWh ≈ $1.2M at Chinese datacenter-hub rates (~$0.04–0.06/kWh vs ~$0.086 US industrial average) — about 5% of the rental cost, matching Epoch AI's finding that energy is 2–6% of frontier training cost. China added 429 GW of generation capacity in 2024 — roughly a third of the entire installed US grid — while US interconnection queues average ~5 years. Power constrains US buildouts, not an 18 MW Chinese training hall. The tweet's "way bigger power budgets" guess is true but backwards: power headroom is why aggregate Chinese compute can scale despite worse FLOPs/W silicon, but a single K3 run never gets near a power limit — and being ~30–40% cheaper on an input that is ~5% of run cost moves nothing.
Where power does bite is delivery density, not economics. Per Uptime Institute, 82% of operators run no racks above 30 kW, while four DGX-B200 boxes already draw ~57 kW in one rack — frontier campuses are purpose-built for densities ordinary datacenters can't host. And DeepSeek-V4 reports the same wall at chip level: with fused kernels driving tensor cores, HBM, and network engines at once, power throttling itself becomes the performance limiter. "Power is not the constraint" is true of the grid; it is decidedly not true of the rack or the die.
The tweet's implicit question — and the H20 question — deserves its own answer. For the bulk 4–16K portion of MoE pretraining, the arithmetic says yes, nearly linearly: the §2.4 criterion shows a slower chip is easier to feed per chip (an H20 needs only 8–24 GB/s of all-to-all), its HBM and NVLink were never cut, and extra chips slot in through data and pipeline parallelism while expert-parallel groups stay local. The V4-Pro report makes the same point from the other side: interconnect stopped being the term that has to grow. The limits are physical and organizational:
So: H800 scaling is proven (V3, K2, and by every indication K3); H20 scaling is technically viable for pretraining but pays ~6× power per useful FLOP; the hard ceiling is neither FLOPs nor networking but power delivery, fleet reliability, and experiments-per-year.
| Constraint | H800 cluster | Status |
|---|---|---|
| Per-chip FLOPs | H100-class; FP8 supported | Non-issue |
| Scale-up interconnect | 400 GB/s (½ of H100) — the actual nerf | 20–40% MFU tax, engineered around |
| Scale-out network | 400 Gbps NIC/GPU (IB or RoCE) — unrestricted; worst-case EP need ~84 GB/s vs 50 GB/s available | Fits with routing locality + overlap |
| HBM capacity/bandwidth | 80 GB / 3.35 TB/s per chip | Floor ≈ few thousand chips |
| Power & energy | ~18 MW / ~$1.2M per run | Trivial in China |
| Chip count (fleet) | Fixed pre-2023 H800/A800 stock + H20s; trainer restock only via capped H200 (Jan 2026) or gray market | The real constraint — for RL & serving |
Could K3 have been trained without Nvidia at all? On paper, nearly. The Ascend 910C delivers roughly 0.8 dense BF16 PFLOPs (about ⅓ of a B200, ~80% of an H800's BF16), and Huawei's CloudMatrix 384 supernode lashes 384 of them into one all-optical, fully peer-to-peer scale-up domain — more total FLOPs, HBM, and scale-up bandwidth than a GB200 NVL72, bought with ~4× the chips and ~2.3× the power per FLOP. For MoE all-to-all, a 384-chip scale-up domain is architecturally exactly what you want (§2.4): Huawei's answer to worse chips is a bigger, flatter network — and inside China, power and floor space are the cheap inputs.
| Metric | GB200 NVL72 | CloudMatrix 384 | ratio |
|---|---|---|---|
| Chips per domain | 72 | 384 | 5.3× |
| Dense BF16 PFLOPs | ~180 | ~300 | 1.7× |
| Total HBM | 13.8 TB | 49 TB | 3.6× |
| Power (all-in) | ~145 kW | ~560 kW | 3.9× |
| Power per FLOP | — | — | ~2.3× worse |
A central-scenario K3 on 910Cs at a (generous) 20% BF16 MFU needs ~16M chip-hours of pretraining — e.g. ~40 CloudMatrix pods (15k chips, ~22 MW of pod power) for ~six weeks, or ~nine weeks with the RL phase. Feasible on paper; the binding constraints are upstream and organizational, not physical:
There is meanwhile direct evidence the CloudMatrix system concept works for MoE serving: at EP=256, published CM384 tests sustain ~54 GB/s dispatch and ~103 GB/s combine per rank, and its 910C MLA kernels hit ~246 TF/s per die vs ~660 TF/s for the same kernel on H800 — the same utilization percentage on a much slower die, kept fed by the huge optical all-to-all domain. That validates Huawei's system-over-silicon approach for inference; it is not evidence K3 trained there.
Most likely reading of K3 specifically: pretrained on the existing Nvidia (H800-era) fleet with the K2 software stack; Ascend increasingly carries inference — Moonshot hasn't disclosed its infrastructure, and its provable lineage (K2) is H800. A full-Huawei frontier pretrain is plausible in 2026–27 but still carries schedule risk that a lab racing to a launch date avoids.
All the math above, live. Pick a chip, set the model and cluster, and see cost, wall-clock, power, and which constraint trips first. Presets reproduce the published anchors (choose "DeepSeek-V3 replay" to sanity-check against Table 1 of the V3 report).
Roofline estimates — right to ~±30%, like every number in this business.
| Constraint | This configuration | Status |
|---|
Model: FLOPs = 6·N_active·D·(1+overhead). Chip-hours = FLOPs ÷ (MFU·peak). Cost = chip-hours × price + energy (chips × all-in kW × PUE × time × tariff). Memory floor = training state (16 B/param, ZeRO-sharded) + 30% activation headroom vs. cluster HBM. Interconnect check = DeepSeek-V4 criterion (§2.4): worst-case B = C/(2·d_e), d_e = 2048, ×¼ for node-limited routing (≤4 of 16 slots off-node), vs. NIC bandwidth — waived when the scale-up domain holds ≥64 chips (NVL72, CloudMatrix). Effective compute = physical FLOPs × claimed architecture efficiency (Kimi blog: ~2.5× vs K2). Anchors: DeepSeek-V3 Table 1; Kimi K2 §2.4; specs from vendor sheets and SemiAnalysis CloudMatrix analysis.
"How is a Chinese lab training a 3T model with orders of magnitude less compute?" Because a 3T-parameter MoE is not a 3T-compute model. At ~2.5% activation (70B of 2.8T), K3's pretraining is ~40× cheaper than the dense model the tweet is picturing: even on a frontier-rumor 150T-token data budget it is ~6×10²⁵ physical FLOPs — a GPT-4.5-class budget, roughly an eighth of the largest known run — executed as ~3 months on ~30k of the H800s China legally imported by the hundred thousand before October 2023; on a K2-style 20–30T budget it drops to ~10²⁵ and six weeks on 10k. Stack Kimi's claimed 2.5× architecture efficiency on top and the effective scale (~1.6×10²⁶ K2-equivalent) sits in the frontier band — which is exactly what its benchmarks show. The published Chinese systems innovations — extreme sparsity, FP8 pipelines, communication-hiding schedules, and now KDA/AttnRes — exist precisely to make that arithmetic work on nerfed interconnect.
Taking the tweet's hypotheses in order:
Where the compute gap is real: aggregate capacity and its growth rate. The largest known run (Grok 4) is ~5×10²⁶ FLOPs — still ~8× our 150T central — and Epoch pegs US lab fleets at 1.7M H100-equivalents (OpenAI), >1M (Anthropic, on Trainium), 4–5M (Google), each headed to 5–6 GW during 2026; one analysis puts the US advantage in 2026-produced AI compute at 21–49×. More decisively, that surplus pours into RL post-training, reasoning-heavy serving, and — the quiet advantage — parallel experiments: published "final-run" hours exclude the ablations, and a lab with 10× compute runs 10 candidate architectures while its rival runs one. Export controls, on this evidence, impose an economic and iteration-speed tax rather than a feasibility ceiling: China's constraint shows up after pretraining, in RL scaling, long-thinking inference economics, experiments per year, and the ceiling on restocking trainers. That's the honest version of the tweet's concern — not whether Kimi can train K3, but whether anyone can serve and RL-scale it against B300 economics. Sparsity, ironically, is also the right hedge there: 16-of-896 experts is exactly what makes serving a 2.8T model on H20s and Ascends viable.