The Stack v3 Resets Your Code-Pretraining Floor — and Ships It License-Clean
The dataset that removes a day of blob-resolution plumbing also strips the copyright exposure behind a nine-figure settlement, and vLLM shipped the serving recipe to actually train on it.
The Signal
The number worth planning around is not the 5T headline. It is the lopsided per-language growth. C++ grew 15x over v2, TypeScript 7.5x, Rust 7x. Python only grew 4.8x, because it was already well-covered. A codebase leaning on systems, infra, or web code was starved of exactly those tokens in v2. That asymmetry is what tells you where a continue-pretrain or fine-tune spike actually moves the needle, rather than where the token budget happened to pile up.
| Language | v2 → v3 growth | Who should prioritize it |
|---|---|---|
| C++ | 15x | Systems / perf-critical model teams |
| TypeScript | 7.5x | Frontend / web-agent builders |
| Rust | 7x | Infra / safety-critical code models |
| Python | 4.8x | Everyone (already saturated) |
Under the Microscope
Two operational changes matter more than raw scale. First, contents ship inline instead of Software Heritage IDs, which ends the blob-resolution step that cost a day of preprocessing in v2. Second, the dataset filters restrictively-licensed code — the same class of exposure AINews ties to Anthropic's reported $1.5B copyright settlement, the largest in history. A fresh GitHub recrawl through August 2025, a ready-to-train split, and a full bucket for your own dedup round it out. The license filtering is the cheapest insurance against training-data liability, and it tidies the reproducibility story too.
On the training side, vLLM's prime-rl 0.6.0 is a reference architecture for RL-on-agents at scale: FP8, expert parallelism, prefill/decode disaggregation, KV offload, routing. AINews reports it trains GLM-5 on SWE tasks at 131k context with sub-5-minute steps on 28 H200 nodes. Those are vendor-reported throughput numbers, not independently verified. The thing those step times don't tell you is what they replicate on your hardware. The config patterns — disaggregation plus KV offload as the levers for long-context rollout throughput — are the durable takeaway either way.
The third thread is quieter and points at a real convergence. PRO-LONG treats agent memory as a queryable database of full structured interaction history, and reportedly beats bespoke long-horizon memory harnesses on ARC-AGI-3 with fewer tokens. ARC-AGI-3 is a narrow slice, so the Pareto claim of higher completion at fewer tokens is a hypothesis to falsify, not a result to bank. Paired with the D1 dispatcher and the Harness Handbook, the direction is clear: from context-stuffing toward structured, retrievable memory.
In Your Pipeline
For code-model teams, The Stack v3 is the new floor. Prioritize fine-tune experiments on the C++/TypeScript/Rust gains where v2 was thinnest. That is where the marginal token buys the most. For long-horizon agents, PRO-LONG is a cheap spike with a genuine Pareto claim, worth testing against your own memory harness before committing to a rewrite. What none of these numbers tell you is how much holds on your task distribution. A one-sprint eval settles that.
The Stack v3 and vLLM prime-rl are the two items you can act on — everything else is a benchmark claim waiting for your own harness to confirm.
What to do
Spike a continue-pretrain or fine-tune run on The Stack v3's ready-to-train split this sprint, prioritizing C++/TypeScript/Rust where v2 was thinnest.
Prototype PRO-LONG-style database-backed agent memory against your current long-horizon harness, benchmarking task completion and token spend before any rewrite.