3.cxd5 c6! is a half-correct gambit, which isn't so easy to refute.
But I guess that in 99% of the cases Black did not intend something like that.
White can take the pawn and play Nf3, defending d4. If Bg4, white can hold the extra pawn with e3 but black gets compensation. More interesting for white may be to return the pawn with Nc3, getting lots of development instead. If ...BxNf3 ef ...Qxd4, white's natural move is Qb3.
3.cxd5 c6! is a half-correct gambit, which isn't so easy to refute.
But I guess that in 99% of the cases Black did not intend something like that.
or maybe 3...c5
There are negatives and positives there. The saying goes "give him enough rope and he'll hang himself but white has encouraging choices, including accepting the gambit by 4. dc, playing for a Grunfeld with 4. Nc3 (probably not such a good idea) but also 4. e4.
It is necessary to see the continuation (7...Qxd4 8.Nxd4-Bb4 9.f3)
Far from being convincing, Black could even be happy because Black seems to play an equal opportunity position.
After I am not a gosu etc. but I can watch games of strong artificial intelligences playing against themselves and make a more objective opinion to know if the position is losing for Black if the position is played by strong players [who in this case are very strong in tactics and calculation].
To whoever said white needs to find 4. Nf3, I dunno if I really agree with that; maybe it’s the most accurate or something but 4. e4 Nf6 5. Nc3 e5 6. Nf3 exd4 7. Qxd4 is also very cozy for white. That would still be enough to put this opening mostly out of business at high level IMO
Yes, 4. e4 is a mistake. It isn't winning for white, so it isn't enough to put it out of business. It's equal or a very small edge for white. 4. Nf3 is stronger. It isn't winning because black can try to reach a Grunfeld; but it's better than after 4. e4.
How would you know?
It is necessary to see the continuation (7...Qxd4 8.Nxd4-Bb4 9.f3)
Far from being convincing, Black could even be happy because Black seems to play an equal opportunity position.
After I am not a gosu etc. but I can watch games of strong artificial intelligences playing against themselves and make a more objective opinion to know if the position is losing for Black if the position is played by strong players [who in this case are very strong in tactics and calculation].
f3 is not a challenging move to find whatsoever. White has a significant advantage.
To whoever said white needs to find 4. Nf3, I dunno if I really agree with that; maybe it’s the most accurate or something but 4. e4 Nf6 5. Nc3 e5 6. Nf3 exd4 7. Qxd4 is also very cozy for white. That would still be enough to put this opening mostly out of business at high level IMO
Yes, 4. e4 is a mistake. It isn't winning for white, so it isn't enough to put it out of business. It's equal or a very small edge for white. 4. Nf3 is stronger. It isn't winning because black can try to reach a Grunfeld; but it's better than after 4. e4.
How would you know?
Possibly by having a better understanding than yours. A mistake often made is to think that higher rating means better understanding.
After white allows black to play e5, it's black that gets the comfortable position. Maybe white likes the quiet position. Maybe white will play d5 but all the same, white's winning chances have diminished after allowing e5, which frees black's game.
Optimissed, I have been on these forums a very long time, long enough that of course in some of those years I was a low-rated teenager. But I have yet to see you make a good point. In that whole time.
I’m sure at some point it happened, by accident, but I haven’t seen it, and I’ve interacted with you plenty. If you could find an example, then maybe I’d believe your claims about “understanding.”
Hi dpnorman and Optimissed! What's the issue?
Claimed subjective “understanding” vs objectivity.
1. d4 d5 2. c4 Nf6 3. cxd5 Nxd5 4. e4 Nf6 5. Nc3 e5 6. Nf3 exd4 7. Qxd4 Qxd4 8. Nxd4 Bb4 9. f3. Would you describe black as having “the comfortable position?” If not, do you have no chess understanding? 
f3 is not a challenging move to find whatsoever. White has a significant advantage.
it can't be significant I did the test by making play Fritz 5.32 against Hiarcs in 15m in this position and Hiarcs wins.
Optimissed, I have been on these forums a very long time, long enough that of course in some of those years I was a low-rated teenager. But I have yet to see you make a good point. In that whole time.
I’m sure at some point it happened, by accident, but I haven’t seen it, and I’ve interacted with you plenty. If you could find an example, then maybe I’d believe your claims about “understanding.”
You're wrong about the issue we're discussing and you aren't willing to learn. Grow up.
f3 is not a challenging move to find whatsoever. White has a significant advantage.
it can't be significant I did the test by making play Fritz 5.32 against Hiarcs in 15m in this position and Hiarcs wins.
We’ll add that to the record, but only for comedic effect. Not sure but I think Fritz 5.32 is older than me.
Optimissed, I have been on these forums a very long time, long enough that of course in some of those years I was a low-rated teenager. But I have yet to see you make a good point. In that whole time.
I’m sure at some point it happened, by accident, but I haven’t seen it, and I’ve interacted with you plenty. If you could find an example, then maybe I’d believe your claims about “understanding.”
You're wrong about the issue we're discussing and you aren't willing to learn. Grow up.
Funny FWIW I was discussing this opening not long ago with an IM friend of mine; LogoCzar knows who he is. He even told me he never bothered with 4. Nf3, even as he was FM+, because 4. e4 seemed plenty strong enough, and more to his taste.
Now if he told me that black has a comfortable position there, I would listen, because I know he has a very deep understanding of chess. You’ve shown time and time again that you don’t, so if you tell me something, I’m indeed going to be less inclined to listen.
As Jerry once said to George, sometimes when I’m interacting with you I have the thought “the very fact that you oppose this makes me think I’m onto something.”
We’ll add that to the record, but only for comedic effect. Not sure but I think Fritz 5.32 is older than me.
It doesn't matter if Fritz 5.32 is an old program because it is very strong and if the program can't win against Hiarcs in a position with an advantage significant, it means the advantage is not as significant as that.
Then I stop the dialogue because I feel that the arguments will only be attacks on the person.
We’ll add that to the record, but only for comedic effect. Not sure but I think Fritz 5.32 is older than me.
It doesn't matter if Fritz 5.32 is an old program because it is very strong and if the program can't win against Hiarcs in a position with an advantage that would be significant it means that this advantage is not that significant.
Then I stop the dialogue because I feel that the arguments will only be attacks on the person.
Depends on the definition of significant. But based on this, it seems likely to me you could feed it all kinds of strong non-decisive positions vs modern engines and it wouldn’t survive. The fact that it even lost says much less about the position at hand, and more about the difference in strength between those computers.
We’ll add that to the record, but only for comedic effect. Not sure but I think Fritz 5.32 is older than me.
It doesn't matter if Fritz 5.32 is an old program because it is very strong and if the program can't win against Hiarcs in a position with an advantage that would be significant it means the advantage is not as significant as that.
Then I stop the dialogue because I feel that the arguments will only be attacks on the person.
Even if that version of HIARCS is 8 years old, it still has an ELO of over 3.000 (I know, because I owned HIARCS too). That makes it 500 ELO stronger than that version of Fritz. That matters a lot.
Hi dpnorman and Optimissed! What's the issue?
Hi, just an online forum bully, who has more manners than he has good sense. You can ignore them or you can tell them what you think of them.
It looks like both 4.Nf3 and 4.e4 are strong - from my point of view. I'd think twice about insulting dpnorman because he has quite a deep understanding of chess and a deserved reputation for being collaborative. I'd imagine that he will accept your apology if you don't make anything personal and go back to discussing your chess ideas without invalidating his.
Hi dpnorman and Optimissed! What's the issue?
Claimed subjective “understanding” vs objectivity.
1. d4 d5 2. c4 Nf6 3. cxd5 Nxd5 4. e4 Nf6 5. Nc3 e5 6. Nf3 exd4 7. Qxd4 Qxd4 8. Nxd4 Bb4 9. f3. Would you describe black as having “the comfortable position?” If not, do you have no chess understanding?
Looks like White is better. If I'm missing something, I'd like to hear reasons, not insults.
To whoever said white needs to find 4. Nf3, I dunno if I really agree with that; maybe it’s the most accurate or something but 4. e4 Nf6 5. Nc3 e5 6. Nf3 exd4 7. Qxd4 is also very cozy for white. That would still be enough to put this opening mostly out of business at high level IMO
Yes, 4. e4 is a mistake. It isn't winning for white, so it isn't enough to put it out of business. It's equal or a very small edge for white. 4. Nf3 is stronger. It isn't winning because black can try to reach a Grunfeld; but it's better than after 4. e4.