These options can be exercised at their initial maturity date /I but are extended to T2 if the option is out-of-the-money at ti. The payoff from a writer-extendible call option at time T1 (T1 < T2) is (via "The Complete Guide to Option Pricing Formulas")
c(S, X1, X2, t1, T2) = (S - X1) if S>= X1 else cBSM(S, X2, T2-T1)
and for a writer-extendible put is
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![WMT: Writer Extendible Option [Loxx]](https://s3.tradingview.com/4/4eCSgAnR_mid.png "Writer Extendible Option [Loxx]")
