"We were able to win the following concession: that the United States could offer Article 5-like protection, which is one of the real reasons why Ukraine wants to be in NATO," he told CNN.
Witkoff said it was the first time he had heard Putin agree to that.
European Commission President Ursula von der Leyen, speaking at a news conference in Brussels with Ukrainian President Volodymyr Zelenskiy, said that "we welcome President Trump's willingness to contribute to Article 5-like security guarantees for Ukraine. and the 'coalition of the willing' -including the European Union - is ready to do its share".
Witkoff, offering some of the first details of what was discussed at Friday's summit in Alaska, said the two sides agreeing to "robust security guarantees that I would describe as game-changing".
He added that Russia said that it would make a legislative commitment not to go after any additional territory in Ukraine.
Zelenskiy thanked the United States for recent signals that it was willing to support security guarantees for Ukraine but said the details remained unclear.
"It is important that America agrees to work with Europe to provide security guarantees for Ukraine," he said, "But there are no details how it will work, and what America's role will be, Europe's role will be and what the EU can do and this is our main task, we need security to work in practice like Article 5 of NATO, and we consider EU accession to be part of the security guarantees."
Witkoff defended Trump's decision to abandon his push for Russian to agree to an immediate ceasefire, saying the president had pivoted toward a peace deal to end the three-and-a-half-year war because so much progress was made.
"We covered almost all the other issues necessary for a peace deal," Witkoff said.
"We began to see some moderation in the way they're thinking about getting to a final peace deal," he said.
US Secretary of State Marco Rubio insisted there would be "additional consequences" as Trump warned before meeting with Putin, if they failed to reach a ceasefire.
But Rubio noted that there was not going to be any sort of deal on a truce reached when Ukraine was not at the talks.
"Now, ultimately, if there isn't a peace agreement, if there isn't an end of this war, the president's been clear: there are going to be consequences," Rubio said on US broadcaster ABC.
"But we're trying to avoid that. And the way we're trying to avoid those consequences is with an even better consequence, which is peace, the end of hostilities."
He also said "we're not at the precipice of a peace agreement" and that getting there would not be easy and would take a lot of work.
"We made progress in the sense that we identified potential areas of agreement but there remains some big areas of disagreement. So we're still a long ways off," Rubio said.
Zelenskiy and European leaders are scheduled to meet Monday with Trump at the White House.
They heard from the president after his meeting with Putin.
"I think everybody agreed that we had made progress. Maybe not enough for a peace deal but we are on the path for the first time," Witkoff said.
He added: "The fundamental issue, which is some sort of land swap, which is obviously ultimately in the control of the Ukrainians - that could not have been discussed at this meeting" with Putin.
"We intend to discuss it on Monday. Hopefully we have some clarity on it and hopefully that ends up in a peace deal very, very soon."
