We are considering challenging an Indian patent. Which route should we use?

There are four, and they are not mutually exclusive:

1. Pre-grant opposition — cheapest and available to anyone, but now subject to a maintainability filter and a fee, and it delays rather than concludes.

2. Post-grant opposition — a full evidentiary proceeding before the Patent Office, but the twelve-month window is short and easily missed if grants are not being monitored.

3. Revocation under Section 64 — before the High Court, without the twelve-month constraint.

4. Counterclaim for revocation in an infringement suit, which is the usual defensive route once proceedings have begun.

The choice turns on timing, on whether you want the patent narrowed or removed, on the strength of the prior art, and on whether you would rather be visible to the patentee at this stage. Watch services on published applications are what make options 1 and 2 realistically available.