Striker Robson-Kanu, 27, who is expected to be part of Wales' squad for the European Championships, has spent seven seasons with the club.
Former West Ham and Sunderland defender Ferdinand, 31, has suffered with injuries in two seasons at Reading.
Academy graduate Cox, 29, who rejoined the club in summer 2014, has struggled for goals in the last two campaigns.
The Championship club have also confirmed that six loan players who represented them this season have all returned to their parent clubs.
Defender Andrew Taylor, midfielders Ola John and Alex Fernandez and striker Matej Vydra follow the departures of Chelsea pair Michael Hector and Lucas Piazon, who left the club last month.

At least 80 people were killed during the attack on the 1,500-seat venue during a sell-out gig by US rock group Eagles of Death Metal.
University of Nottingham student Hanna Corbett said there was blood all around and people lying on top of each other.
The student, originally from St Albans, said she thought she and her friend were about to die.
She said people inside did not realise straight away what was happening.
"It sounded like fireworks or firecrackers and it wasn't until people started screaming and the lead singer ran off stage [that people knew something was wrong].
"The lights went on and everyone just dropped to the floor," the 21-year-old history student said.
"There was blood all around and people were hugging each other."
Describing laying on the floor, with the gunmen on the balcony, Ms Corbett said: "It felt like ages but it could have been just five to 10 minutes - there was this banging which seemed like a real gun - I'd never heard one before.
"[People were] crawling over each other, just trying to climb out of fire exits. It was pretty inhumane - a nightmare.
"I thought it was like that heroic thing on the train," when a suspected radical Islamist was overcome by six passengers.
"I thought someone would just stop them - but the guns kept going and I thought 'this is the end'."
Ms Corbett said luckily she and her friend Jack Konda, 21, also a student in Nottingham, managed to get out.
He said: "We were dealt a pretty lucky hand to have been so close to it and get out pretty much unscathed."
A French journalist captured the horror of people fleeing from gunmen who stormed the venue.
Le Monde newspaper reporter Daniel Psenny was himself shot as he tried to help a man who collapsed on the pavement outside.

Shamima Begum and Amira Abase, both 15, and Kadiza Sultana, 16, left home in February to join the Islamic State (IS) group, and two of them are now married.
The families are not identifying which of the girls have married.
Tasnime Akunjee, who represents the families, says it "does not bode well" that those girls will now return.
The Bethnal Green Academy pupils flew from Gatwick to Turkey on 17 February after telling their parents they were going out for the day. They later entered Syria and are thought to be in Raqqa, the self-styled capital of the so-called Islamic State.
Mr Akunjee said the girls had contacted their families "some weeks ago" to tell them of the marriages, which took place "some time ago".
He added: "The families learned that the girls were not together in Raqqa three months ago, and it was because two of them were married.
"They are distraught, because it doesn't bode well for their return. The girls are starting to grow roots socially, and deep roots."
Mr Akunjee said the men the girls married are in their 20s, but said it is not known whether they are IS fighters.
However, the Guardian reports that the two schoolgirls married in ceremonies approved by IS authorities.
The three girls had been studying for their GCSEs at the school in Tower Hamlets, east London - where they have been described as "straight-A students".
A fourth girl from the school is believed to have travelled to Syria in December.
Mr Akunjee also said a video published by the Daily Telegraph claiming to show the girls in Raqqa, in the care of a woman handler, is unlikely to be them.
"The girls were not together at the time of the video," he said. "It's unlikely that they would have been under the aegis of the leader of a woman's centre."
Reading are to release Hal Robson-Kanu, Anton Ferdinand and Simon Cox after their current contracts expired.
[NEXT_CONCEPT]
A student has spoken of the "nightmare" of being caught up in the attack on the Bataclan concert hall in Paris.
[NEXT_CONCEPT]
The families of two east London schoolgirls who travelled to Syria are "distraught" after learning they have married, their solicitor has said.