Ki-Empowered Strikes

Starting at 6th level, your unarmed strikes count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.

Would damage from a monk with this ability standing in an Antimagic Field do full of half damage to a target with resistance to non-magical bludgeoning, slashing and piercing damage?

 I'd say no since Ki are magical

Lore on Magic of Ki aside, except for title Ki-Empowered Strike is in no way related to Ki feature, which is not specifically said to be magical but mystic energy. So it should work fine.

Quote from Bluesman3535 >>

Ki-Empowered Strikes

Starting at 6th level, your unarmed strikes count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.

Would damage from a monk with this ability standing in an Antimagic Field do full of half damage to a target with resistance to non-magical bludgeoning, slashing and piercing damage?

I would say that an Antimagic field would not affect the Ki-Empowered Strikes feature (nor any other Ki features). And that's because I see nothing in the Ki features that says it is magical nor does it fit with what the SAC says is needed for a thing to be affected by an Antimagic Field.

The Magic of Ki

Monks make careful study of a magical energy that most monastic traditions call ki. This energy is an element of the magic that suffuses the multiverse—specifically, the element that flows through living bodies.

I want to say ki would be unaffected since it seems an awful lot like the magic that suffuses dragons that allows them to breathe elemental blasts - the type of "natural magic" which is not affected by antimagic - but I could see it going either way. You could argue the feature grants the same benefits as a spell (which is one of the determinants of whether something is "magic magic" versus "natural magic") since there are spells that make weapons deal magical damage.

Looking at RAI, antimagic suppreses magical weapons and the reason monks get this feature is to put their fists on par with magical weapons, so it would make sense that the fists would be affected the same way. On the other hand, allowing it to work could be a nice way to give the monk a bit of spotlight and some cool implied lore. They could use it.

Okay, I think I've found the two relevant passages for consideration:

Within the sphere, spells can’t be cast, summoned creatures disappear, and even magic items become mundane

Spells and other magical effects, except those created by an artifact or a deity, are suppressed in the sphere and can’t protrude into it.

The first line could suggest that the effect is primarily intended to function against spells and magic items, but the "other magical effects" part of the second line muddies the water considerably, given that 5e lacks a clear definition/identifier of what constitutes a "magical effect" (as per above, a dragon's breath weapon? Their Frightful Presence? The elemental damage to a chromatic dragon's bite attacks?). Honestly, I'd be willing to say that anything that is described as a somewhat distinct phenomenon from "regular magic" and isn't a "you cast X spell" feature is exempt on a non-caster class; most notably the Fighter and Rogue psionic subclasses and Monks. But ultimately the exact scope seems to be left up to DM's determination.

Quote from pocketmouse >>

The Magic of Ki

Monks make careful study of a magical energy that most monastic traditions call ki. This energy is an element of the magic that suffuses the multiverse—specifically, the element that flows through living bodies.

 Yea but that is from the fluffiest of fluffy texts in the intro for Monks. If you read the text of the actual class feature they don't use "magic", they call it "mystic" instead.

Quote from The_Ace_of_Rogues >>

The first line could suggest that the effect is primarily intended to function against spells and magic items, but the "other magical effects" part of the second line muddies the water considerably, given that 5e lacks a clear definition/identifier of what constitutes a "magical effect" (as per above, a dragon's breath weapon? Their Frightful Presence? The elemental damage to a chromatic dragon's bite attacks?). Honestly, I'd be willing to say that anything that is described as a somewhat distinct phenomenon from "regular magic" and isn't a "you cast X spell" feature is exempt on a non-caster class; most notably the Fighter and Rogue psionic subclasses and Monks. But ultimately the exact scope seems to be left up to DM's determination.

Yes there is definitely a bit left for the DM to rule on because it is not that clearly defined. But they have tried to clear it up some in the SAC.

(here is the full text)

Determining whether a game feature is magical is straightforward. Ask yourself these questions about the feature:

• Is it a magic item?
• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?
• Is it a spell attack?
• Is it fueled by the use of spell slots?
• Does its description say it’s magical?

If your answer to any of those questions is yes, the feature is magical.

And for Ki the answer is no to all questions and thus I'm fine with ruling it to not be magical.

The Magic of Ki

Monks make careful study of a magical energy that most monastic traditions call ki. This energy is an element of the magic that suffuses the multiverse — specifically, the element that flows through living bodies. Monks harness this power within themselves to create magical effects and exceed their bodies’ physical capabilities, and some of their special attacks can hinder the flow of ki in their opponents. Using this energy, monks channel uncanny speed and strength into their unarmed strikes. As they gain experience, their martial training and their mastery of ki gives them more power over their bodies and the bodies of their foes.
https://www.dndbeyond.com/sources/phb/monk#TheMagicofKi

If this wasn't the first or second thing on monks I would be more incline to agree with the reasoning that its not magical. But the two bolded lines say its magical in nature and it creates magical effects.

“Starting at 6th level, your unarmed strikes count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.”

I would say anti magic field has no effect. Your attacks are not magical they just count as magical for the sole purpose of overcoming resistance. 

But that’s my opinion, and it’s changing in 1DD to force or bludgeoning damage at 6th level

If the text box I put above wasn't the second thing from both dndbeyond and its the same in the original players hand book I would agree. But that defines Ki as a type of magic. And with the line below that shows even more that it normally flows through them to work there abilities. 

 Using this energy, monks channel uncanny speed and strength into their unarmed strikes. 

I appreciate all the replies.   When this happened, I ruled that the monk’s blows weren’t considered magical inside the Antimagic field.   Afterwards, I second guessed my decision and discussed at the table.   We didn’t come to a solid conclusion either.  Arguments could be made for either side..

should this happen again, I think I’d rule differently.  The flavor text suggests otherwise, but I don’t make rulings on flavor text.  What pushes me over the edge is how incredibly nerfing antimagic field is.   Four 18th level PCs and 2 dropped in the fight (an orobas demon from Tome of Beasts).  The paladin had a girdle of frost giant Strength .  Without it Str was 13    I think letting the monk do full damage would have ended the fight 2 rounds earlier.  As someone above said, giving this to the monk kinda is cool and a way to overcome slightly this very powerful spell

It is very much a DM call but if ki empowered strikes are surpressed by an anti magic field because i is magical any monk feature that either uses ki points or in the description says is sourced by ki is also surpressed:

It could also be taken a step further

• "Using this energy [ki], monks channel uncanny speed and strength into their unarmed strikes." Uncanny speed and strength into unarmed attacks can only be a desciption of Martial Arts so martial arts is empowered by ki and is therefore surpressed in an anti magic field.  
• "Whatever their discipline, monks are united in their ability to magically harness the energy that flows in their bodies. Whether channeled as a striking display of combat prowess or a subtler focus of defensive ability and speed, this energy infuses all that a monk does." Defensive ability and speed can refer to things like unarmoured movement, evasion and deflect missiles. So pretty much any monk feature is reliant on magic and therefore is surpressed in an anti magic field

The game should be fun however so I would definately not do anything so extreme on the poor monk. Monks are so underpowered you could let this be his chance to shine or you could decide something that reduces their effectiveness without making then useless for example saying anything that uses ki points woint work but anything else is OK. What ever the DM decides should be straight forward enough to quickly explainj to the monk either on the roll of initiative or after their first round that they find something didn't work as expected.

The main problem is that resistance/immunity to normal weapons is not suppressed in an antimagic field (in 3e, both got suppressed).

I would say since the Druid Wildshape is suppressed that the KI Empowered strikes are as well.

Quote from Thezzaruz >>

Quote from Bluesman3535 >>

Ki-Empowered Strikes

Starting at 6th level, your unarmed strikes count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.

Would damage from a monk with this ability standing in an Antimagic Field do full of half damage to a target with resistance to non-magical bludgeoning, slashing and piercing damage?

I would say that an Antimagic field would not affect the Ki-Empowered Strikes feature (nor any other Ki features). And that's because I see nothing in the Ki features that says it is magical nor does it fit with what the SAC says is needed for a thing to be affected by an Antimagic Field.

ki-empowered strikes explicitly count as magical in the text you quoted. Whether ki in general is magical is beside this point.

EDIT: Upon further consideration, I'll concede that this text may only consider them magical in the context of bypassing resistance/immunity. So if a monk punched a goblin within the field, it might not be suppressed because it may not be considered magical in that context. But if the monk tried to punch a werewolf inside the field, it wouldn't work because it would be a suppressed magical attack = a nonmagical attack. So maybe the strike is only magical when it needs to be, in which case, it gets suppressed and loses its function anyway :)

Tweets are not RAW, but ki-empowered strikes are intended to be considered magical within the context of an AMF. So there's no harm in taking that reading of the feature.

This is a really good question from the original post -- it doesn't seem completely clear which way it should be ruled.

The portions of the Antimagic Field description that are most likely to apply are:

Spells and other magical effects, except those created by an artifact or a deity, are suppressed in the sphere and can't protrude into it . . . While an effect is suppressed, it doesn't function, but the time it spends suppressed counts against its duration.

and

Spells: Any active spell or other magical effect on a creature or an object in the sphere is suppressed while the creature or object is in it.

So, the key question is whether or not a Ki-Empowered Strike is a magical effect.  The key text from the Monk class that relates to this are:

monks are united in their ability to magically harness the energy that flows in their bodies . . .this energy infuses all that a monk does.

and 

Monks make careful study of a magical energy that most monastic traditions call ki. This energy is an element of the magic that suffuses the multiverse—specifically, the element that flows through living bodies. Monks harness this power within themselves to create magical effects and exceed their bodies’ physical capabilities

and

Using this energy, monks channel uncanny speed and strength into their unarmed strikes. As they gain experience, their martial training and their mastery of ki gives them more power over their bodies and the bodies of their foes.

and

Ki

Starting at 2nd level, your training allows you to harness the mystic energy of ki. Your access to this energy is represented by a number of ki points.

and finally:

Ki-Empowered Strikes

Starting at 6th level, your unarmed strikes count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.

Given all of this information together, I agree with the general consensus that a Ki-Empowered Strike involves a magical effect on a creature (on the Monk) that enhances his unarmed strikes.  This magical effect is suppressed while the Monk is located within an Antimagic Field.

I do not think that it's accurate to say that everything a Monk can do is magical and is therefore suppressed.  After all, the ability to harness ki at all is listed as a 2nd level Monk ability.  So, any ability or class feature that a Monk already has at 1st Level cannot be initially associated with ki -- these abilities come from his spiritual contemplation and rigorous martial arts training within the monastic community.  This includes the Unarmored Defense and Martial Arts class features.  The Martial Arts class feature allows for larger than normal damage dealt by unarmed strikes.

So, when a Monk attempts a Ki-Empowered Strike in an Antimagic Field, the entire attack is not suppressed.  The attack proceeds and hits or misses as normal.  The Monk starts with the same base damage as he normally would with his unarmed strikes.  But the additional attribute of overcoming non-magical resistances is suppressed because that enhanced aspect of the unarmed strike comes from a magical effect on the Monk.  So, if he was attacking a target that had resistance to bludgeoning damage then his damage output vs that target would be halved.

Quote from Drakkon >>

If the text box I put above wasn't the second thing from both dndbeyond and its the same in the original players hand book I would agree. But that defines Ki as a type of magic. And with the line below that shows even more that it normally flows through them to work there abilities. 

 Using this energy, monks channel uncanny speed and strength into their unarmed strikes. 

I would take the opposite view tbh, the fact that it is the general descriptive text that say it means I put little weight to it.

The text of the Ki feature doesn't call it magical, it uses "mystic" instead and I would rate that as a lot more important for deciding how the feature works (as it is the actual rules text of the class feature). If you decide Ki is a magical thing then you loose all the things that use Ki so no flurry, no step of the wind or patient defense and no stunning strike and so on (unarmored defense, deflect missile and martial arts though do not use Ki so they should be fine).

Quote from Timeless_DnD >>

I would say since the Druid Wildshape is suppressed that the KI Empowered strikes are as well.

Well that feature does explicitly call it magical though so that's a clear difference.

you can use your action to magically assume the shape of a beast

Quote from Thezzaruz >>

I would take the opposite view tbh, the fact that it is the general descriptive text that say it means I put little weight to it.

Out of curiosity, is there a reason why you assign descriptive text a lower authenticity from a rules perspective?