Where has Sepia filter gone?

I too enjoyed the Sepia filter—it takes the harshness out of BW when other image adjustments don't quite do the job. I have tried to emulate the old sepia filter on the new Photos, but it takes ages to adjust and is never quite right—not rich enough. However, I found a save on another Mac site—use Preview to make the adjustment. The Tools contains, within its Image Adjust, a slider for Sepia. The instructions given are to slide the Saturation all the way left (essentially makes photo BW), then slide the Sepia to the right. You can adjust the tone better, actually, than with the old iPhoto sepia filter.

Photos for Mac has exactly the same filters as Photos on iOS devices.

You may want to file a feature request for both Photos apps using the feedback form:

Apple - Photos - Feedback

As a work-around, try to use the either the Color adjustment to simulate it:

Reduce the Saturation and shift the Cast:

As Leonie mentioned, you could simulate it in the color section. Although, as my personal suggestion, if you are not simulating a certain time period in history, I wouldn't use it. The Sepia look is ancient in photographic terms and was due to the actual film look that was used at the time. Nowadays, more Instagram-type filters are used, and I guess that's why Apple chose to update its filters with more current trends.

At the end of the day, it's up to you what you like but I cringe every time I see a Sepia photo that doesn't actually reflect that time period. If you are looking for a more dramatic look, which Sepia really isn't, I suggest you try a good Black & White editor. Photos' B&W filters and settings however leave something to be desired though, but check out "Tonality" on the Mac Appstore. Tons of great presets for all types of looks and fine grained control if you need it. And yes, you can also do Sepia if you must... 😉