GWR now know (and have known for 6 months) they are stuck with the 150, 158, 166, 166 fleet for another 2.5 years to 25th June 2025 (or at Operators option to 25th June 2028, so 5.5 years). Just rechecked DfT contract and is is binary choice of dates, not an upto.
Does at least allow them to order enough spare parts to cover remaining 5.5 years, and seeing as already had 6 months to order long lead time (and special order) parts, would hope the depots soon have store room full of spares, so downtime awaiting parts goes away for few years.
It seems an appropriate time of year to also point out that there is a section in contract regarding Boxing Day services from December 2023