Apriel-1.5-15b-Thinker
Authors: name: Shruthan Radhakrishna; name: Aman Tiwari; name: Aanjaneya Shukla; name: Masoud Hashemi; name: Rishabh Maheshwary; name: Shiva Krishna Reddy Malay; name: Jash Mehta; name: Pulkit Pattnaik; name: Saloni Mittal; name: Khalil Slimi; name: Kelechi Ogueji; name: Akintunde Oladipo; name: Soham Parikh; name: Oluwanifemi Bamgbose; name: Toby Liang; name: Ahmed Masry; name: Khyati Mahajan; name: Sai Rajeswar Mudumba; name: Vikas Yadav; name: Sathwik Tejaswi Madhusudhan; name: Torsten Scholak; name: Sagar Davasam; name: Srinivas Sunkara; name: Nicholas Chapados
Published: 2025-10-01 17:29:35

Abstract: We present Apriel-1.5-15B-Thinker, a 15-billion parameter open-weights
multimodal reasoning model that achieves frontier-level performance through
training design rather than sheer scale. Starting from Pixtral-12B, we apply a
progressive three-stage methodology: (1) depth upscaling to expand reasoning
capacity without pretraining from scratch, (2) staged continual pre-training
that first develops foundational text and vision understanding, then enhances
visual reasoning through targeted synthetic data generation addressing spatial
structure, compositional understanding, and fine-grained perception, and (3)
high-quality text-only supervised fine-tuning on curated instruction-response
pairs with explicit reasoning traces spanning mathematics, coding, science, and
tool use. Notably, our model achieves competitive results without reinforcement
learning or preference optimization, isolating the contribution of our
data-centric continual pre-training approach. On the Artificial Analysis
Intelligence Index, Apriel-1.5-15B-Thinker attains a score of 52, matching
DeepSeek-R1-0528 despite requiring significantly fewer computational resources.
Across ten image benchmarks, its performance is on average within five points
of Gemini-2.5-Flash and Claude Sonnet-3.7, a key achievement for a model
operating within single-GPU deployment constraints. Our results demonstrate
that thoughtful mid-training 2 design can close substantial capability gaps
without massive scale, making frontier-level multimodal reasoning accessible to
organizations with limited infrastructure. We release the model checkpoint, all
training recipes, and evaluation protocols under the MIT license to to advance
open-source research.