RAM on the engine.

They have what appears to be a working head mounted display

The Kh-58UShE ARM (1,400-lb., Mach 4, range of 130 nm) fits in the weapons bay

The internal weapons bay is huge because of the widely spaced engines

Some are interesting as they relate to the aircraft, but there are also some details that might say a lot about potential Russian anti-stealth techniques. (Paid Subscription Required)

The ordinary:

• They are developing an improved performance engine for the aircraft.
• They will be applying radar absorbent material to the spinner and inlet guide vanes. (see pic)
• They are integrating a helmet mounted display early in the process. The dual visor approach, where there is an inner visor for the display, and an outer one for glare and environmental protection.
• They are looking at using thrust vectoring, counteracted by the aerodynamic controls, to reduce the rear aspect radar signature of the engine.

The more interesting:

• The internal weapons bay can accommodate very large weapons, including ultra long range air to air and anti-radar missiles.

This is a statement of where they think that future war is going:

Also likely to be carried internally by the T-50 is the RVV-BD (long-range air-to-air missile), a modernized version of the Vympel R-37 that was designed for the MiG-31M Foxhound-B but never put into production. Its total external dimensions are within centimeters of the Kh-58UShE with wings folded. It seems likely that the T-50 forward bay has been designed around the minimum-risk RVV-BD, with the Kh-58 being modified to fit the same envelope.

Both weapons are long-range types. The Kh-58UShE is a 1,400-lb., Mach 4 weapon with a range up to 130 nm from a 65,000-ft. launch altitude, and the RVV-BD has a claimed maximum range of 110 nm against a head-on target. This indicates a different operational philosophy from U.S. stealth aircraft, for which a key principle has been to use stealth to permit the use of short-range, low-cost weapons.

Later in the article, they discuss updates to the radar suite (radar suits, actually) for the S-400 Triumph (SA-21 Growler), which incorporates multi-frequency band radars:

The 55Zh6ME comprises three truck-mounted radar “modules,” operating in metric (VHF), decametric (L) and centimetric (S) bands, all with active, electronically scanned array (AESA) radars. The VHF unit has an antenna area of 235 sq. meters (2,530 sq. ft.), carrying 168 VHF transmit-receive modules, and is claimed to be able to detect a target with a radar cross-section of 1 sq. meter at 510 km range and 30,000 meters altitude in jamming conditions. The radars can be deployed in 15 min., NNIIRT says.

The new 55Zh6UME has a smaller VHF array (with a 430-km range under the same conditions) with an L-band AESA trailer-mounted on the same structure, facing the opposite direction.

I think that the Russians believe that increasing processing power allowing for the fusion of disparate sensors to reduce the effectiveness of stealth.

It’s likely that they are right.