SuperApriel-15b-Base

SuperApriel-15b-Base

<img src="assets/super-apriel.png" width="120" alt="thumbnail"/> /ˈɑː.pri.əl/

A 15B-parameter token-mixer supernet derived from Apriel-1.6 via stochastic distillation. Every decoder layer exposes four trained mixer options—Full Attention, Sliding Window Attention, Gated DeltaNet, and Kimi Delta Attention—enabling flexible architecture selection from a single checkpoint.

• Model Size: 15B parameters
• Layers: 48 decoder layers, each with 4 mixer variants
• Context Length: 262K positions (runtime dependent)
• Languages: English (best)

Highlights

• Supernet architecture: Single checkpoint containing 4 mixer types at every layer, yielding 4⁴⁸ ≈ 7.9 × 10²⁸ possible architectures
• Four mixer types: Full Attention (FA), Sliding Window Attention (SWA, window=4096), Gated DeltaNet (GDN), Kimi Delta Attention (KDA)
• Stage 1 distillation checkpoint: Trained via stochastic distillation from frozen Apriel-1.6 teacher on 266B tokens
• Foundation for fine-tuning: Use this checkpoint to fine-tune on your own data with targeted placement strategies

Model Overview

SuperApriel-15b-Base is the Stage 1 (distillation) checkpoint of the Super Apriel supernet. During training, all four mixer types at each layer were trained simultaneously using stochastic local sampling—each layer's mixer was drawn uniformly from the four types at each training step. Only mixer weights were trained; all shared parameters (FFNs, embeddings, layer norms, vision encoder) remain frozen from the Apriel-1.6 teacher.

This checkpoint is intended as a foundation for downstream fine-tuning. For a ready-to-use model with optimized deployment presets, see SuperApriel-15b-Instruct.

Architecture Details

Mixer Types

Training Details

• Objective: Stochastic distillation from frozen Apriel-1.6 teacher
• Losses: Activation matching (𝓛_act), Forward KL (weight 0.1), Reverse KL (weight 0.9)
• Data: 266B tokens, curated mixture focused on reasoning and domain-specific data
• Sampling: Uniform local sampling (each layer independently samples a mixer type)
• Compute: Up to 192 H100 GPUs
• Training framework: Fast-LLM

How to Use

This checkpoint is intended as a foundation for fine-tuning and research, not for direct inference. For a ready-to-use model with optimized deployment presets and full serving instructions, see SuperApriel-15b-Instruct.

Loading for evaluation

If you need to load this checkpoint for evaluation or experimentation, copy a preset config from SuperApriel-15b-Instruct to select a specific mixer placement. The Base and Instruct checkpoints share the same architecture and config format — preset configs from Instruct work with this checkpoint.

For example, to load with the all-attention placement:

1. Download a preset config.json from SuperApriel-15b-Instruct/preset_configs/all-attention/
2. Place it as this model's config.json
3. Load with vLLM or Transformers following the Instruct README instructions

Note: This model requires trust_remote_code=True as it uses custom architecture code for the multi-mixer supernet.

Note: When serving with vLLM, custom placements must include at least one attention-type layer (FA or SWA). Configurations using only recurrent mixers (GDN/KDA) are not currently supported due to a vLLM KV cache coordinator limitation. All shipped Instruct presets satisfy this requirement.

Intended Use

SuperApriel-15b-Base is designed as a foundation checkpoint for:

• Fine-tuning with custom placement strategies on domain-specific data
• Research on hybrid architectures and mixer placement optimization
• Placement search and Pareto frontier exploration using the optimization toolkit

It is not intended for direct deployment without further fine-tuning or for safety-critical applications without human oversight.

Limitations

• Factual accuracy: May produce incorrect, misleading, or outdated content. Outputs should be verified before use in critical contexts.
• Bias: May reflect societal, cultural, or systemic biases present in training data.
• Ethics: Do not use the model to produce harmful, unlawful, or unethical content.
• Language: Strongest performance is in English. Output quality may degrade in underrepresented languages.
• Critical use: Not suitable for medical, legal, financial, or other high-risk applications without safeguards.
• Base model: This is a distillation checkpoint without instruction tuning. For instruction-following use cases, see SuperApriel-15b-Instruct.

Security and Responsible Use

Security Responsibilities: Deployers and users are strongly encouraged to align their security practices with established frameworks and regulatory guidelines such as the EU AI Act and the NIST AI Risk Management Framework (RMF).

Guidelines for Deployers:

• Regularly conduct robustness assessments to identify and mitigate adversarial inputs.
• Implement validation and filtering processes to prevent harmful or biased outputs.
• Continuously perform data privacy checks to guard against unintended data leaks.
• Document and communicate the model's limitations, intended usage, and known security risks to all end-users.
• Schedule periodic security reviews and updates to address emerging threats and vulnerabilities.

Guidelines for Users:

• Follow established security policies and usage guidelines provided by deployers.
• Protect and manage sensitive information when interacting with the model.
• Report anomalies, suspicious behavior, or unsafe outputs to deployers or developers.
• Maintain human oversight and apply judgment to mitigate potential security or ethical risks during interactions.

Disclaimer: Users accept responsibility for securely deploying, managing, and using this open-source LLM. The model is provided "as-is," without explicit or implied warranty regarding security or fitness for any specific application or environment.

Software

• Training stack: Fast-LLM
• Serving: Fast-LLM vLLM plugin

License

MIT

Citation

@misc{super_apriel_2026,
  title        = {Super Apriel: One Checkpoint, Many Speeds},
  author       = {ServiceNow Language Models Lab},
  year         = {2026},
  eprint       = {2604.19877},
  archivePrefix= {arXiv},
  primaryClass = {cs.CL}
}