# Contrastive Language Models: A Fast, Generalizable System One Model > Source: > Published: 2026-09-25 18:34:21+00:00 *A System One Model for Fast and Generalizable Decision-Making* | πŸ“„ [**Blog**](https://contrastive-lm.notion.site) | πŸ—£οΈ [** Discord**](https://discord.gg/5dAQEDJBs) | πŸ€— [** Data & Models**](https://huggingface.co/Contrastive-LM) | πŸ“š [** API Reference**](#api-reference) | πŸ› οΈ [** Fine-Tuning Tutorial**](#fine-tuning-clm-on-your-own-data) | πŸ”₯ **Contrastive Language Models (CLMs)** are a new class of **System One model** trained with a **contrastive learning** objective that connects **states and actions**. This repo serves **CLM-8B** behind a TypeSafe-compatible API. - **CLM-8B** is pre-trained on**60M Nemotron Q&A pairs** , mid-trained on**30M synthetic hard negatives** , and post-trained on**1M agentic trajectories** . - It performs on par with **Jev** across computer-use, gaming and tool-calling tasks with up to**9Γ— lower latency** . With lightweight fine-tuning it sets a new SOTA as a verifier on agentic coding benchmarks:**Terminal-Bench 2.1 (87.6%)** and**DeepSWE (81.6%)** . - **States and actions are disaggregated** , so their embeddings are cached and reused independently, which makes training and serving cheap and blazing fast! We invite the community to plug it into their own agents and benchmarks! ``` pip install contrastive-lm ``` To install the latest from a clone: ``` pip install -e . # 1. encoder (Qwen3-8B embeddings) vllm serve Qwen/Qwen3-8B --served-model-name qwen3-8b --runner pooling --max-model-len 2048 --port 8090 & # 2. CLM API on :8700 (downloads the 75 MB reference head on first run) clm-serve ``` States longer than 2048 tokens are truncated. For longer states, raise both limits together, e.g. `--max-model-len 8192` on `vllm serve` and `clm-serve --max-tokens 8192` (needs more GPU memory). ``` python from clm import CLMClient, Choice, Noul, Score client = CLMClient() # CLM_BASE_URL (default http://127.0.0.1:8700), CLM_API_KEY r = client.system_one( state="Customer: my invoice was charged twice and nobody answers the phone!", questions={ "urgency": Noul(instructions="Is this urgent?"), "department": Choice(instructions="Which team should handle this?", criteria={"billing": "Charges, invoices, refunds", "technical": "Bugs and outages"}), "frustration": Score(instructions="How frustrated is the customer?", criteria=["Calm", "Frustrated", "Very angry"]), }, ) print(r.answers["urgency"].noul) # 0.41022 probability the statement is true print(r.answers["department"].choice) # billing print(r.answers["department"].probabilities) # {'billing': 0.93878, 'technical': 0.06122} print(r.answers["frustration"].score) # 1.98386 expected level, 0..2 print(r.usage.input_tokens, r.latency_ms) # 38 58.1 (106 tokens on a cold cache: option texts are embedded once) ``` Questions may be `Noul` / `Choice` / `Score` objects or plain wire-format dicts, so a request written for TypeSafe replays as `client.system_one(state, questions)`. `system_one` is built on one primitive: score a candidate against a state. For free-form candidates (best-of-N answers, tool names, next moves) use the in-process engine's `rank`: ``` python from clm import Engine engine = Engine(emb_url="http://127.0.0.1:8090/v1/embeddings") # reference head, downloaded if missing engine.rank("What causes tides on Earth?", ["The Moon's gravitational pull.", "Photosynthesis in plants.", "Because the Earth is round."]) # [{'rank': 1, 'candidate': "The Moon's gravitational pull.", 'prob': 0.997}, ...] engine.answer(state, questions) # the same dict the HTTP endpoint returns, no server needed ``` `clm-serve` also serves a web UI at `/` (`http://localhost:8700/` by default). Write a state, add typed questions, and see CLM's answer distributions; every request is also shown as JSON, `curl` and Python. A **Rank** tab ranks any candidate set, and links are shareable. Captured against a real `clm-serve` (`clm-latest`, Qwen3-8B encoder on one RTX 4090). Remote server? `ssh -L 8700:localhost:8700 `. API only: `clm-serve --no-ui`. Across **computer-use, gaming and tool-calling tasks**, CLM-8B performs on par with Jev while running **up to 9Γ— faster**. The speedups are largest when the number of candidate actions is large (WikiRacing) or when actions are reused across states (the T-Rex game). The T-Rex benchmark ships in this repo: see [examples/t_rex](https://github.com/Contrastive-LM/CLM/blob/main/examples/t_rex/README.md). For each task we sample several candidate solutions (**Opus 5** for DeepSWE, **Fable 5** for Terminal-Bench 2.1), and CLM or Jev acts as the verifier that picks the best one. Evaluated on **38 held-out DeepSWE tasks** and **30 held-out Terminal-Bench 2.1 tasks**; latency on an H100. Jev fails to serve as a verifier for these long-horizon tasks, scoring below pass@1. With lightweight fine-tuning, CLM reaches SOTA on both (**81.6%** and **87.6%**) while running **4.1–5.7Γ— faster than Jev**. See [docs/FINETUNING.md](https://github.com/Contrastive-LM/CLM/blob/main/docs/FINETUNING.md). ``` # reproduce the task-disjoint DeepSWE heldout-38 result (31/38 = 81.6%) hf download Contrastive-LM/deepswe-clm-heads-8k --local-dir heads/deepswe python evaluation/bon_eval.py --hf-dataset Contrastive-LM/deepswe-clm-embeddings-8k \ --checkpoint heads/deepswe/best_head.pt \ --tasks-file heads/deepswe/heldout_tasks.json --n 4 --window 12 # fine-tune the matching DeepSWE head python train/finetune.py --task clm --init-ckpt "$(clm-download)" --out-dir runs/deepswe \ --holdout-tasks heads/deepswe/heldout_tasks.json --batch 512 # typed decisions python train/finetune.py --task choice --data LocalLLaMA/typed-decisions --workflow all \ --init-ckpt "$(clm-download)" --out-dir runs/typed ``` CLM first trains a **state encoder** and an **action encoder** on a large-scale dataset with a contrastive objective (InfoNCE), so that each state is pulled toward the ground-truth action that was taken and pushed away from all others. The two encoders then serve directly as a zero-shot action classifier: at deployment, given the current state and a set of candidate actions, CLM scores each action by how well its embedding aligns with the state embedding and selects the highest-scoring action. That is what this package serves. A typed question is a state plus a closed set of candidate actions (the options and their descriptions); a softmax over CLM's scores *is* the answer distribution, and the same call ranks best-of-N trajectories, routes tools, shortlists retrieval pools and answers typed decisions with no per-task setup. **Architecture, data recipe and scaling laws:** - Each encoder is a frozen LLM backbone plus a 20M-parameter trainable projection head, so inference is one embedding per fresh text and a dot product per cached candidate. - CLM is **pre-trained** on internet-scale Q&A,**mid-trained** on synthetic hard negatives,**post-trained** on agentic traces, and can be easily fine-tuned on downstream tasks ([data recipe](#data-recipe) ). - The InfoNCE loss **decreases predictably as a power law** in training compute, model size and dataset size ([details](#scaling-laws-for-verification) ). ``` browser ──► clm-serve (CPU, :8700) GET / (playground) client ──► POST /v1/systemone Β· GET /v1/models Β· GET /health β”‚ state head + action head (20M params, hot-reloaded), embedding cache β–Ό vLLM Qwen3-8B pooling server (GPU, :8090) /v1/embeddings ``` CLM is trained with a bidirectional InfoNCE loss. Given a batch of For mid-training, the objective is extended with hard negatives. Let The test InfoNCE loss where [blog post](https://contrastive-lm.notion.site). **Data vs. optimal model size.** At a fixed compute budget, each iso-FLOP curve of test loss against head size is well approximated by a parabola in log-parameter space, and its minimum gives the optimal head size for that data budget. The optimum grows almost exactly linearly with the number of training tokens, **310 tokens per parameter**. CLM is trained in three stages, each a progressively harder form of state–action alignment: 1. **Pre-training** on**~60M Nemotron DQA question–answer pairs** , each question the state and its answer the action. This learns broad semantic representations. 2. **Mid-training** on**~30M synthetic hard negatives** generated by Gemini 2.5 Flash-Lite: semantically similar but incorrect answers to Nemotron DQA questions, added to the InfoNCE loss as above. This develops fine-grained discrimination between plausible actions. 3. **Post-training** on**~1M agent trajectories** from the Agent Data Protocol (ADP) dataset, plus terminal traces from Endless-Terminals and LiteCoder-Terminal-SFT. Each trajectory step is a state–action pair: the agent's current context and the decision it took. **Replay during post-training.** 40% of the post-training mixture is Nemotron DQA replay and 60% agentic trajectories. With replay, Nemotron hard-negative top-1 accuracy only moves from 69% to 68.5%; training on agentic data alone for the same number of agentic steps drops it to 56.2%. **Why not train on hard negatives from the start?** On ~100K held-out questions (one gold answer, 10 hard negatives each), pre-training alone reaches **52.1%** top-1 without seeing a hard negative, and a short mid-training stage lifts it to **69.2%**. Training with hard negatives from the start improves quickly but peaks at **62.4%** before overfitting, so the two-stage recipe is **7 points better** at a fixed budget: hard negatives work best as a refinement on top of pre-training, not a substitute for it. The reference head served as `clm-latest` is [Contrastive-LM/CLM-v0.1-8B](https://huggingface.co/Contrastive-LM/CLM-v0.1-8B) (`CLM_v0.1-8B.pt`, Qwen3-8B backbone, last-token pooling). Any head in the same checkpoint format β€” a `torch.save` dict with `state_head` / `action_head` state dicts, `logit_scale` and `cfg` (`width`, `depth`, `projection_dim`, `activation`, `layernorm`, `residual`) β€” can be served with `--ckpt`; a head only makes sense with the encoder and pooling it was trained against. 1. **Scaling experiments:** larger backbones, and how far verification performance keeps scaling. 2. **Vision and multimodal support:** images, video and other modalities for robotics and computer-use tasks. 3. **Scaling the data recipe:** more pre-training, hard-negative mining and agentic post-training. If you find CLM useful, please consider citing it: ``` @misc{kwok2026contrastivelanguagemodels, title={Contrastive Language Models: A System One Model for Fast and Generalizable Decision-Making}, author={Jacky Kwok and Hangoo Kang and Tarun Suresh and Jon Saad-Falcon and Marco Pavone and Christopher RΓ© and Azalia Mirhoseini}, year={2026}, note={Notion Blog}, url={https://contrastive-lm.notion.site} } ``` The code in this repository is released under the [Apache 2.0 License](https://github.com/Contrastive-LM/CLM/blob/main/LICENSE). The CLM-8B weights are released under Apache 2.0 on [Hugging Face](https://huggingface.co/Contrastive-LM/CLM-v0.1-8B). ``` . β”œβ”€β”€ pyproject.toml # the clm package (installed editable by requirements.txt) β”œβ”€β”€ serve_qwen3_8b.sh # launch the Qwen3-8B pooling encoder on a GPU β”œβ”€β”€ download_head.sh # fetch the released head (`clm-download` does the same) β”œβ”€β”€ assets/ # logo + the playground screenshot used above β”œβ”€β”€ src/clm/ # inference: the package `clm-serve` and `clm` ship β”‚ β”œβ”€β”€ __init__.py # from clm import CLMClient, Noul, Choice, Score, Engine β”‚ β”œβ”€β”€ client.py # CLMClient + question / answer types (no torch needed) β”‚ β”œβ”€β”€ schema.py # question -> (state text, candidate texts); logits -> Answer β”‚ β”œβ”€β”€ engine.py # Engine.answer(...) / Engine.rank(...): the inference engine β”‚ β”œβ”€β”€ heads.py # head architecture, checkpoint load / hot-reload / download β”‚ β”œβ”€β”€ embedder.py # /v1/embeddings client + LRU cache of normalised embeddings β”‚ β”œβ”€β”€ cache.py # the reserved vector arena behind --action-cache β”‚ β”œβ”€β”€ server.py # FastAPI app, `clm-serve` β”‚ └── static/ # the playground: index.html + app.css + app.js, no build step β”œβ”€β”€ tools/playground_mock.py # serve the playground without a GPU (fake encoder) β”œβ”€β”€ train/ # fine-tuning β”‚ β”œβ”€β”€ finetune.py # trains the projection heads on a frozen encoder β”‚ β”œβ”€β”€ adapters.py # dataset adapters: agentic traces, typed decisions β”‚ └── embed_utils.py # encoder embeddings with the training token recipe β”œβ”€β”€ evaluation/bon_eval.py # unified best-of-N evaluation β”œβ”€β”€ preprocessing/hf_embeddings.py # embedding dir <-> Hugging Face dataset β”œβ”€β”€ requirements.txt # pip install -r requirements.txt (clm + torch + vLLM + example deps) β”œβ”€β”€ examples/ # CLM vs Jev on the T-Rex runner (examples/t_rex/README.md) β”‚ β”œβ”€β”€ common.py # one client for both endpoints: retries, latency, cache β”‚ └── t_rex/ # Chrome dinosaur game in real time (run.py --model clm|jev) └── docs/FINETUNING.md # the fine-tuning guide ``` This branch carries the inference package, the playground, the fine-tuning script, the T-Rex example. The scaling experiments, data pipelines and paper figures live in the research repo's `main` branch. | field | | |---|---| | `state` | string, object or array (objects are rendered as `key: value` text, arrays as`- item` lines; never JSON, the heads are trained on prose) | | `model` | `clm-latest` (default),`clm-raw` , or any model from`GET /v1/models` | | `questions` | `{id: Question}` , at least one | | `temperature` | optional, `(0, 100]` , default 1; divides the logits before the softmax | | question | required | answer | |---|---|---| | `noul` | `instructions` ; optional`criteria: {"true": …, "false": …}` | `{"noul": p_true}` | | `choice` | `instructions` (the question),`criteria: {option: description}` (each option is embedded as its description, or its key when the description is empty) | `{"choice", "confidence", "probabilities"}` | | `score` | `instructions` ,`criteria: [level0, level1, …]` (ordered, β‰₯2) | `{"score", "confidence", "legend", "probabilities"}` | - `confidence` = top probability minus the mean of the others. - `score` = expected level index;`legend` maps indices back to the rubric. - `usage.input_tokens` counts encoder tokens spent on cache misses;`billing_units` is the number of questions. - Errors: `401` bad key Β·`422` malformed request or unknown model Β·`502` embedder unreachable.`X-CLM-Latency-Ms` carries the server-side time. The same primitive in its plain form: `{"context": ..., "question": ..., "answers": [...]}` returns `{"model", "ranked": [{"rank", "candidate", "prob"}, ...]}`, best first. The state head sees `context + question`, the action head sees each answer verbatim. `CLMClient.rank(context, question, answers)` and `Engine.rank(context, answers, question)` are the client and in-process forms. The playground (see [above](#playground)), unless `clm-serve --no-ui`. Static files only; every API route above shadows it. ``` {"models": [{"name": "clm-latest", "description": "...", "release_date": "2026-09-19"}, {"name": "clm-raw", "description": "Ablation: cosine in the raw encoder space", ...}]} clm-serve [--port 8700] [--emb-url http://127.0.0.1:8090/v1/embeddings] [--emb-model qwen3-8b] [--max-tokens 2048] [--ckpt PATH] [--ckpt-dir DIR] [--model NAME=PATH ...] [--device cpu|cuda] [--action-cache 0.02|512MiB|0] [--no-ui] [--cors] ``` `--ckpt PATH` serves your own head as `clm-latest` (default: the reference head in `~/.cache/clm/`, downloaded if missing); `--ckpt-dir DIR` serves every `*.pt` there under its file stem; `--model NAME=PATH` adds one more. The heads run on the GPU when torch sees one, else on the CPU; `--device` (or `CLM_DEVICE`) forces one. Checkpoints hot-reload when the file changes. Set `CLM_API_KEY` to require `Authorization: Bearer ` (the playground has a field for it). Environment equivalents: `CLM_PORT`, `CLM_EMB_URL`, `CLM_EMB_MODEL`, `CLM_CKPT`, `CLM_DEVICE`, `CLM_ACTION_CACHE`. `--no-ui` drops the playground and serves the API alone. `--cors` allows browser requests from any origin and is off by default, because an API key otherwise travels in a header any page would then be free to send. An agent asks about a changing state but a mostly fixed set of actions, and it revisits states it has already seen. Neither their embeddings nor their projections change while the head does not, so `clm-serve` reserves a slab of device memory at start-up β€” the way vLLM claims its KV cache β€” and keeps them in it: ``` [clm] vector cache 505.0 MB reserved on cuda (215,764x512d + 3,852x4096d) ``` `--action-cache` takes a fraction of the device (`0.02`, the default), an absolute size (`512MiB`), or `0` to switch it off; `CLM_ACTION_CACHE` does the same. It covers states and actions on every served head, and `clm-raw` in the encoder's own space β€” the two widths are pools carved from the one allocation, which never grows, so a long-running server cannot drift into an out-of-memory kill. Entries are keyed by head and generation, so several heads share the arena and a hot-reloaded head stops matching rows its previous weights produced; eviction is least-recently-used. `GET /health` reports occupancy and hit rate. A hit skips the encoder call, the host-to-device copy and the head's forward pass. Measured on one RTX 4090, server-side p50, against a fixed action set: | | 3 actions | 50 actions | |---|---|---| | new state every call | 28.6 β†’ 28.0 ms | 28.8 β†’ 28.1 ms | | revisited states (20 rooms) | 1.7 β†’ 0.6 ms | 2.0 β†’ 0.7 ms | | one repeated state | 1.7 β†’ 0.6 ms | 2.0 β†’ 0.7 ms | So a loop that revisits states answers about 2.8x faster, and a loop that never repeats itself pays the encoder either way. A cached vector costs no encoder tokens, so `usage.input_tokens` counts only what the encoder actually did.