Israel and the United States have reached an agreement that will provide Israel an unprecedented amount of military aid over a decade.

The State Department said the agreement, known as a memo of understanding, will be signed Wednesday afternoon. Jacob Nagel, Israel’s acting national security adviser, arrived in Washington on Tuesday morning to sign on behalf of his country.

[Israel and U.S. close to a deal on biggest military aid package ever]

The agreement is expected to give Israel as much as $3.8 billion a year over 10 years, more aid than the United States has ever provided to any country. That represents a significant increase over the $3.1 billion the United States gives annually now, a figure that increases to about $3.5 billion a year with aid supplements approved by Congress. That is also much lower than the $4 billion to $5 billion a year that Israeli Prime Minister Benjamin Netanyahu sought.

Netanyahu appears to have agreed to some other major concessions. The newspaper Haaretz reported that he agreed to limit Israel’s ability to lobby Congress for more aid, unless it is at war. The Israeli leader also agreed that Israel will not ask Congress for more aid to develop missile defense systems.

In another concession that was controversial in Israel’s ­defense industry, Netanyahu agreed to phase out a special arrangement that for decades has allowed Israel to spend 26 percent of U.S. aid on defense research, development and procurement. No other country receiving U.S. funding is allowed to do so. But Israel was granted that exception in the 1980s so it could build up its nascent defense infrastructure. With Israel’s defense industry now thriving, the Obama administration wanted U.S. aid directed to American companies providing goods and services.

[Chart: The two countries that eat up the most U.S. military aid]

U.S. officials declined to comment on the specifics of the agreement.

Negotiations for the aid package have been underway since November to replace a memo of understanding that will end in 2018. The new agreement will run from 2019 through 2028.

Salai Meridor, who was Israel’s ambassador when the last agreement was signed, welcomed the deal, despite some reservations.

“I don’t measure this relationship by the dollar number and whatever the exact number is. It is a reflection of the great relationship between the state of Israel and America,” he said.

But Meridor called it disappointing to have limitations on Israel requesting more aid from Congress in the future.

“Many of the important initiatives that have cemented the relationship have been the result of Congress’s initiative,” he said. “I think this is an element of the agreement we might all regret in the future.”

The talks have been complicated by substantive, political and personal differences. Netanyahu and President Obama have had a famously contentious relationship that reached a boiling point in 2015 when the Israeli leader appeared before Congress to lobby against the Iran nuclear deal.

The Obama administration wanted the increased military aid package completed before the end of his term to demonstrate the United States’ commitment to Israeli security after the agreement with Iran.

“It’s a good deal for Israel and a good deal for the United States,” said Ilan Goldenberg, a fellow at the Center for a New American Security. “It sends a signal to those in the region that the U.S.-Israel relationship is a bedrock in the Middle East. Whatever difficult relationship exists between the president and the prime minister, at a strategic level, the relationship is better than that. Even if Obama and Netanyahu don’t like each other very much, Israel and the United States are willing to make a commitment to Israel’s security.”

The agreement has political advantages for both leaders. Netanyahu has been criticized for his aggressive tactics on the Iran nuclear deal, with critics saying he has poisoned relations with Israel’s greatest ally. Obama has insisted that the United States remains Israel’s biggest protector, despite any personal and political differences with the prime minister.

“In financial terms, Israel maybe could have gotten more in the summer of 2015 than the summer of 2016,” said David Makovsky, a fellow with the Washington Institute for Near East Policy. “But it’s still an increase. What seems to have driven the idea of coming to closure on this now is that both sides would like to get this done before the election.”

Israel remains concerned about the threat posed by Iran, particularly now that its isolation has been eroded with the Iran nuclear deal.

“We do not want this to be interpreted as being compensated for a deal we did not consent to,” said Eran Lerman, a former deputy national security adviser to the prime minister.

“We know Israel was not alone in the region of feeling worried about the consequences,” he added.

It remains to be seen whether the $3.8 billion a year represents a ceiling or a floor. The agreement appears to rein in Israel’s ability to ask for more money. But members of Congress, particularly those involved in appropriations, have expressed a reluctance to give up their ability to allocate money based on their sense of priorities.

Eglash reported from Jerusalem. William Booth in Jerusalem contributed to this report.

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