Some info adapted from an earlier answer I wrote:

There isn't a single Russian archive, but there's a single federal Russian archival agency - Rosarkhiv, which it oversees a number of archives. Fifteen major archives, in fact.

The State Archives of the Russian Federation is the main archive, and includes state documents from pre-Revolutionary times. For Communist Party of the Soviet Union archives, these are mostly in two separate archives: the Russian State Archive of Socio-Political History (RGASPI) has party records mostly prior to 1952, while records since are in the Russian Archive of Contemporary History (RGANI). These latter have a lot of still-classified material (ostensibly to protect still-living persons).

Of course in addition to these, there are governmental archives not under Rosarkhiv. These include the archive of the President of the Russian Federation, as well as the archives of the Foreign Ministry, Intelligence Services, and the military. These are essentially "working archives", meaning that they are actively in use by governmental agencies, and are hard to get into. Items from the KGB and NKVD (and other iterations of the secret police) were supposed to be declassified and transferred to Rosarkhiv in the early 1990s, but this never happened. In 1991, one could in theory wander into the KGB archives and look at whatever you wanted, but as J. Arch Getty noted in 1996, this was an incredibly brief power vacuum for all the Russian archives, and thereafter, even in the early 1990s, when Rosarkhiv erred on the side of public transparency, it needed to restrict access to at least be in line with standard world archival practices.

Since 2000 archival access for researchers has been decidedly mixed. It can be (like dealing with any Russian governmental agency) an agonizingly slow and uncertain bureaucratic process to gain access to archives, often heavily relying on personal connections. Items that are available can suddenly be classified. Nevertheless, the general trend is towards declassification, notably with items from Stalin's personal archives being declassified and released in the past several years.

The hardest items to access - and increasingly so - tend to be NKVD archives. Again note that they aren't part of Rosarkhiv, and a researcher needs to get permission from the FSB to access them. In 2019 Russian courts sided with the FSB in barring access to troika panel documents from the Stalin-era purges, while even more worryingly it is destroying records of Gulag inmates once those individuals have reached the age of 80.

So the trend has been towards more difficulty in accessing files, but it is still nowhere near the complete classification and secrecy of the Soviet era. It really depends what you are trying to research and where (remember that Russia is a federation, so there are regional archives as well as central archives - similarly the other former Soviet Socialist Republics have their own archive systems, which range from wide open to slammed shut).

Historians also have to use ingenuity to bypass obstacles in dealing with the various archival systems and levels of classified access. A notable example I can think of is Russian historian Oleg Khlevniuk, a senior researcher at GARF. Although most NKVD archives and documents are classified, he managed to hunt down literal carbon copies of NKVD documents attached to memos and circulars in unclassified party and prosecutorial archives.

Short version: Yes.

After the Soviet Union collapsed, a lot of information was made available to scholars, including Western scholars, which allowed copies to be made and translated. Now these were not "declassified" in the sense that there was an organised effort to decide what should and shouldn't be available, and more that in the chaos of the Soviet Union's collapse, a lot of records were ignored or made readily available.

Now, context is important here. Military and truly sensitive documents would have been much more closely guarded and were not readily available. The opening up of documents also came in fits and starts, depending on the state of the Russian government. There was a period in the 90s when the Russian government sort to distance itself from its Communist past and so party documents regarding the Gulag and some practices, including historical KGB practices, were made publicly available. Some of these documents were already available to Russians as part of Glasnot, which was Gorbachev's attempt to relax the state control over the population and allow more criticism of the Communist party, in the hopes that the party would reform itself into a more genuinely liberal and democratic institution. Once the Soviet Union itself collapsed all these pre-existing documents were opened up to the west for translation, as well as all new records that were now up for grabs in the chaos of the Soviet state and Communist party collapse. Many of these historic records had not been available in the west before.

One final thought though, the KGB is often used as a lazy short-hand to refer to all Soviet control over its population. Now the KGB was a very effective spy organisation, but the documents would have come from various local and national archives and might not have been sourced from the KGB itself, although some KGB sources would have been made available in the tumultuous times after the collapse.