As you may well know, it's been possible for a long time now to convert different types of Xbox Game Pass tiers into other ones - one of the most popular methods has been to convert Xbox Game Pass Core into an Ultimate membership.
For example, until recently, you'd have been able to convert Core into Ultimate at a 3:2 ratio - meaning that 90 days of Xbox Game Pass Core would equal 60 days of Xbox Game Pass Ultimate. The idea behind this was to ensure that if you decided to upgrade to a higher-priced tier, you'd still get some value out of the time left on your old Core membership.
"When you upgrade to Xbox Game Pass Ultimate, we’ll convert any prepaid time you have on Xbox Game Pass or EA Play subscriptions and apply it toward Xbox Game Pass Ultimate at the current conversion ratio, up to a maximum of 36 months."
This is still a method you can use if you want to upgrade to a higher tier of Xbox Game Pass (or if you've found cheap Core codes that can be used to get the best deal), but as of today, the conversion rate has changed. Now, Xbox Game Pass Core converts into Ultimate at a 2:1 ratio - meaning 90 days of Core equals 45 days of Ultimate.
Here's a breakdown of all the new Xbox Game Pass conversion rates for Xbox Game Pass Ultimate. Keep in mind that these ratios only apply for people who aren't currently subscribed to the Ultimate tier already.
Xbox Game Pass Core Conversion Ratio - 2:1
Any remaining time will convert to Xbox Game Pass Ultimate time at a ratio of 2:1 and be rounded up to the next full day. For example, 90 days remaining of Xbox Game Pass Core will convert to 45 days of Xbox Game Pass Ultimate time.
PC Game Pass Conversion Ratio - 3:2
Any remaining time will convert to Xbox Game Pass Ultimate time at a ratio of 3:2 and be rounded up to the next full day. For example, 90 days remaining of PC Game Pass will convert to 60 days of Xbox Game Pass Ultimate time.
Xbox Game Pass Standard and Game Pass for Console Conversion Ratio - 4:3
Any remaining time will convert to Xbox Game Pass Ultimate time at a ratio of 4:3 and be rounded up to the next full day. For example, 90 days remaining of Xbox Game Pass Standard or Game Pass for Console will convert to 68 days of Xbox Game Pass Ultimate time.
EA Play Conversion Ratio - 3:1
Any remaining time will convert to Xbox Game Pass Ultimate time at a ratio of 3:1 and be rounded up to the next full day. For example, 90 days remaining of EA Play will convert to 30 days of Xbox Game Pass Ultimate time.
In addition to this, if you wish to upgrade your Xbox Game Pass Core membership into the new Xbox Game Pass Standard tier, the ratio is 3:2. The difference here is that you can only convert up to 13 months' worth of prepaid Xbox Game Pass Core into a Standard membership, whereas conversions into Ultimate can be up to 36 months' worth.
If you're looking for the TL;DR of all this, it's basically that the conversion rates have gotten worse for Xbox Game Pass Ultimate specifically, meaning that you'll get less value out of converting from Core to Ultimate than you would have done in the past. It's not the first time we've seen this - something similar happened back in July of last year.