Madeleine McCann's parents have said they remain hopeful she will be found after the size of the detective team investigating her disappearance was scaled down.
Kate and Gerry McCann said they "fully understand" the decision by Scotland Yard to reduce the number of officers working on the case from 29 to four.
The Metropolitan Police said the vast majority of the work of Operation Grange, which was launched at the request of the government in 2011, has now been completed.
However, the force insisted the inquiry has not reached a conclusion, with the team now following a small number of "focused lines of investigation".
It was also revealed that more than 60 "persons of interest" have been investigated , 650 sex offenders "considered" and 8,685 reports of potential sightings of Madeleine probed.
Madeleine was three when she went missing from the family's holiday apartment in Portugal's Algarve on May 3 2007, triggering one of the most high-profile missing persons investigations of all time.
Her parents said: "We would like to thank all the staff from Operation Grange for the meticulous and painstaking work that they have carried out over the last four and a half years. The scale and difficulty of their task has never been in doubt.
"We are reassured that the investigation to find Madeleine has been significantly progressed and the (Met) has a much clearer picture of the events in Praia da Luz leading up to Madeleine's abduction in 2007.
"Given that the review phase of the investigation is essentially completed, we fully understand the reasons why the team is being reduced.
"Whilst we do not know what happened to Madeleine, we remain hopeful that she may still be found given the ongoing lines of inquiry. "
Announcing the "new structure", Scotland Yard disclosed that more than 40,000 documents have been collated as police brought all of the material relating to the case - from UK and foreign police, as well as private investigators - together for the first time.
Once this work was completed, the review became a full investigation in July 2012, and since then officers have taken 1,338 statements and collected 1,027 exhibits.
Some 560 lines of inquiry were identified and more than 30 requests sent to countries across the world asking for work to be undertaken. On average the team received 200 emails a week.
A Met spokesman said: "For an investigation of this size, the extraordinary circumstances of investigating a missing child four years later in another country, the vast wealth of information and theories, it was always going to be an immense task and required a full team of 29 staff working on it.
"A team of four officers will continue to work solely on the Grange investigation.The inquiry has not reached a conclusion, there are still focused lines of investigation to be pursued."
Assistant Commissioner Mark Rowley, who has overseen the inquiry since 2012, said it has been "painstaking and thorough", bringing together in one place what was "disparate information across the world".
He said: "This work has enabled us to better understand events in Praia da Luz the night Madeleine McCann went missing and ensure every possible measure is being taken to find out what happened to her.
"We still have very definite lines to pursue which is why we are keeping a dedicated team of officers working on the case."
He said Portuguese police are "fully committed" to probing Madeleine's disappearance.
The investigation has cost more than £10 million so far and the Home Office has budgeted for another £2 million until next April.
Mr Rowley added: "The Met was asked to take on this exceptional case as one of national interest.
"We were happy to bring our expertise to bear only on the basis that it would not detract from the policing of London; and the Home Office have additionally funded the investigation above normal grants to the Met. That will continue at the reduced level."
Detective Chief Inspector Nicola Wall will continue to head Operation Grange.