Source: EU Portal
The latest Top of the Tree special takes you along the Soviet heavy line up to the well-rounded 
X 
IS-4 . Take advantage of great discounts, missions, and bonuses to climb the Tech Tree and strike your opponents hard on the battlefield!
The tanks in the Soviet Tech Tree line offer a great balance of armor, maneuverability, and firepower, but the best of them all is right at Tier X. Barge onto the scene with the IS-4! An excellent all-around tank, this steely Soviet doesn’t boast any extraordinary stats, but it has no noteworthy weaknesses, either. Played well, it can adapt to various roles on the battlefield, while its 122 mm gun, large 2,500 HP pool, and strong turret and side armor make it a tough opponent to face and take down. The well-angled and low profile will keep you out of mischief, and its top speed of 43 km/h, which is unusual for a heavy, lets you flee the scene at a surprising pace. Clamber aboard today!
Make your way up the Tech Tree from October 20 at 07:00 CEST (UTC+2) through November 20 at 06:00 CET (UTC+1), and take advantage of great discounts and missions all the way to the top. Don’t forget that you have 10 days to purchase an extra boost if you want to speed things up!
Available from October 20 at 07:00 CEST (UTC+2) through November 20 at 06:00 CET (UTC+1)
You’ll have something to fight for every day for a month! This includes 
XP per vehicle every day, Crew XP bonuses, and other significant rewards to help you reach Tier X. You can find more information about the missions below:
Crew XP
Reward:
x2 Crew XP
Objective:
- Play a battle
- Be among the top 7 on your team by base XP earned
Restrictions:
- Only in Random Battles
- Only available for the vehicles featured in this special
Damaging Push
Rewards:
6,500 XP
x1 Personal Reserve: +50% to Combat XP for 1 hour
Objective:
- Cause 20,000 HP of damage over any number of battles
Restrictions:
- Only in Random Battles
- Only in the following vehicles:
- Can be completed 10 times per account
- XP will be credited to the vehicle you complete the mission with
Push Through!
Rewards:
- 20,000 XP
Objective:
- Cause 200,000 HP of damage over any number of battles
Restrictions:
- Only in Random Battles
- Only in the following vehicles:
- Once per account
- XP will be credited to the vehicle you complete the mission with
IS-4
Rewards:
x1 Large Repair Kit
x1 Large First Aid Kit
x1 Automatic Fire Extinguisher- x1 Personal Reserve: +300% to Crew XP for 1 hour
Objective:
- Play 5 battles
- Be among the top 10 on your team by base XP earned
Restrictions:
- Only in Random Battles
- Repeatable
- Only available for the X IS-4
This is actually true. When I played it the IS-4 felt like what an IS would be if brought to its logical extreme. I’d argue this is one of the most balanced Tier 10 tanks period, a rarity in today’s game.