# Microsoft Research — Improving synthesis prediction of small molecules at scale with RetroChimera

- Company: Microsoft Research (microsoft.com)
- Announced: 2026-09-21T15:30:19+00:00
- Category: open-weight-release
- Coverage: not counted
- Announcement: yes
- Group: models
- Source: https://www.microsoft.com/en-us/research/blog/improving-synthesis-prediction-of-small-molecules-at-scale-with-retrochimera/
- Record: https://forck.live/items/12722-improving-synthesis-prediction-of-small-molecules-at-scale-with-retrochimera
- Subject: Research / Phi
- Open weights: yes
- Models affected: RetroChimera, R-SMILES 2, NeuralLoc
- License: MIT license

Microsoft Research published RetroChimera, an open-weight retrosynthesis model that predicts synthesis routes for small molecules by combining two complementary neural models—R-SMILES 2 and NeuralLoc—using a learned ensembling strategy. In blind tests, expert chemists preferred RetroChimera's reaction predictions over preceding models and literature reactions. The implementation and weights are available on GitHub and via Microsoft Foundry.

## Evidence

Verbatim from https://www.microsoft.com/en-us/research/blog/improving-synthesis-prediction-of-small-molecules-at-scale-with-retrochimera/:

> In blind tests, expert chemists preferred disconnections of complex molecules suggested by RetroChimera over those obtained from its constituent sub-models, as well as those from more established approaches, and even from the test set itself.

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Record: https://forck.live/items/12722-improving-synthesis-prediction-of-small-molecules-at-scale-with-retrochimera
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