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BAR

Allen Institute for AIOpen WeightsPending Human Review

BAR, or Branch-Adapt-Route, is Ai2’s released modular language-model family built from an Olmo 2 7B anchor and independently trained capability experts. Math, coding, tool-use, and safety experts are combined through a router into a final five-expert mixture, enabling capability updates without retraining the full model. The public checkpoints include the original anchor, intermediate two-expert combinations, and final combined model as variants. This is a concrete weight release supporting a post-training method, rather than a framework-only announcement. Expert merging and routing must be evaluated for interactions and task quality.

2026-04-20
Five experts derived from 7B backbone; total undisclosed
Modular mixture-of-experts Transformer
Apache-2.0

Specifications

Parameters
Five experts derived from 7B backbone; total undisclosed
Architecture
Modular mixture-of-experts Transformer
License
Apache-2.0
Type
text
Modalities
text

Benchmark Scores

Advanced Specifications

Model Family
BAR
API Access
Not Available
Chat Interface
Not Available
Variants
7B anchor2x7B expert pairs5x7B combined

Capabilities & Limitations

Capabilities
reasoningcodingtool usemodular adaptation
Known Limitations
Research checkpointsIndividual experts and the combined model have different behavior
Notable Use Cases
modular post-training researchspecialist composition

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