Sanofi and AstraZeneca are touting an innovative, open model of collaboration that will see the direct exchange of 210,000 compounds between the two companies’ proprietary libraries.

Announced in late November, the deal gives both companies free access to each other’s usually closely guarded compounds. Each company is free to develop any of the shared compounds without any financial obligation and without restrictions on targeted disease areas.

The collaboration will enhance the chemical diversity of the compound collections and allow them to screen a broader, more diverse chemical group as the starting point in developing new small-molecule drugs.

The exchanged compounds specifically were selected to play off differences from their own current libraries, the companies say. They will be exchanged in large enough quantities to enable the receiving company to carry out high throughput screening for several years to determine if they are active against a certain target. If a compound matches a target, it then can be modified to optimize its structure before being classified as a “lead compound” and entering development.

Even though the drugmakers work in similar disease areas like oncology, there is little chance that they would develop similar drugs even using the same compound, because the companies have different R&D methods.

This is a unique agreement, as large pharmaceutical companies typically seek to expand their pipelines by licensing drugs from smaller biotech firms, or just buying them outright. AstraZeneca also has struck compound sharing agreements with smaller companies, but nothing at this scale with a major player like Sanofi.