Thanks to Will Keeler for getting this answer from Pella Windows:
Argon has been the gas most often used in IG for several decades now. In some applications, Krypton is used and performs better and allows thinner Insulating Glass (IG), but is cost prohibitive, and becoming more cost prohibitive recently because of its use in other industries along with reduced worldwide capacity to extract Krypton from air.
Generally, desiccants adsorb as opposed to absorb. See the following for the difference. Read about the difference
Several desiccants are still used to pull out moisture between panes of glass at the time of IG build as well as collect any moisture that gets through the IG seals. These include silica and molecular sieves. These desiccants pull out moisture and can collect volatile organic compounds that may be present in internal components like grilles, etc. but are designed to not adsorb the insulating gases like argon or krypton. Below is an old primer on desiccants. It’s old, but still relevant and fairly easy to digest.  Read about desiccants
As far as overall trends, desiccants continue to be made with higher and high adsorption capacities. Sealants continue to be made with better moisture barrier properties (Moisture vapor transmission rate or MVTR). From a product reliability standpoint, window and door certification bodies now include IG durability testing as part of their certification programs. From an overall energy perspective, codes and energy star and other bodies are encouraging, and in some cases requiring, lower u-values which is changing the low-e types that are being used and will likely start to move the industry into a more widespread use of triple IG and perhaps more advanced solutions (electrochromics, VIG, suspended films, etc.)

Failure Development

by Kenton Shepard

Double-pane insulated glass (IG) windows consist of two hermetically sealed panes of glass separated by an aluminum or stainless-steel spacer that contains silica beads that act as desiccants; they absorb moisture. The panes are sealed around this spacer with sealants like silicone or polyisobutylene. Some manufacturers use both to form primary and secondary seals that help extend the lifespan of the sealed unit.

Air in the space between the window panes expands when sun shines on the window, increasing air pressure between the panes. At night the window cools and air pressure between panes drops. If air pressure between the panes is higher or lower than the ambient air pressure (air pressure outside the panes) pressure will be created on the seals. During the day, high air pressure will try to push air out from between the panes and at night low pressure will try to pull air into this space. This is called "thermal cycling" or "thermal pumping".

Seals have to resist thermal cycling, UV radiation, moisture ingress, and must retain any inert gas (like argon) installed between the panes.

As windows age, the sealant that hermetically seals the space between panes ages, increasing amounts of air move into and out of the airspace between the panes. Water vapor entering this airspace is adsorbed by silica desiccant beads installed behind aluminum spacers installed around the perimeter of the glass assembly.

Eventually, this desiccant becomes saturated and can no longer absorb moisture. Moisture vapor in the airspace then condenses on the interior of the panes.

Especially during initial failure, condensation may be visible only when the window is exposed to direct sunlight. Over time, this condensation will first stain- and then etch- the glass in a manner that is permanently visible.

Stages of Damage

Stage 1. Condensation appears when the window is in sunlight but disappears when it is in shade.

Stage 2. Condensation appears when the window is in sunlight and leaves stains when it is in shade.

Stage 3. Window is permanently stained and the glass is etched.

Repair of Windows with Failed Seals

Companies exist that offer to repair failed seals by various means. I recommend that you not make a recommendation other than that the client contact a qualified contractor or window manufacturer to discuss options and costs for repair or replacement, although I typically mention that replacement is more common.

Multiple-pane Windows

Windows may also be triple-pane, typically built using the same methods as double-pane or may be double-pane with a film down the center. In film-type windows, the film lifespan may be much shorter than the lifespan of other components.