Does the NEC require antioxidant compound on aluminum wire?

Not directly. Section 110.3(B) requires you to follow the connector manufacturer instructions, so compound is mandatory only when those instructions call for it.

What is AA-8000 aluminum?

AA-8000 series is the electrical grade aluminum alloy that 310.3(B) requires for solid 12 through 8 AWG and stranded 8 AWG through 1000 kcmil aluminum conductors. It replaced the older AA-1350 alloy used in 1960s and 1970s branch circuit wiring.

Can I use dielectric grease instead of a listed antioxidant?

No. When the connector instructions require a joint compound, it must be a product listed or identified for that purpose. Ordinary dielectric grease is not an equivalent substitute.

What does the NEC say about antioxidant compound on aluminum conductors?

The NEC has no section that says apply antioxidant to aluminum conductors. What it has is Section 110.3(B), which requires listed or labeled equipment to be installed and used in accordance with any instructions included in the listing or labeling. If the lug, connector, or splice device you are using has instructions that say to apply a listed joint compound, then applying it is mandatory and skipping it is a 110.3(B) violation. If the connector is listed for use without compound, and many modern ones are, then you are not required to add it.

Read the connector instructions, not the internet

Compression connectors from the major manufacturers are frequently supplied prefilled with an inhibitor sealed under a cap or a tape. Those need nothing added. Many mechanical set screw lugs are listed for aluminum without compound, and their instruction sheets say so explicitly. A handful of older mechanical connectors and most field-applied compression sleeves for direct burial still call for it. There is no universal answer, which is exactly why 110.3(B) points you at the paperwork in the box.

When compound is called for, use a product listed for the purpose. The instruction sheet will typically name a compound or reference a listing category. A random tube of dielectric grease from the parts store is not an equivalent. Some antioxidant compounds are conductive and carry zinc or other particles intended to abrade the oxide film during tightening. Getting that on the insulation or into a device is messy but harmless. Getting a non-listed grease into a connection can be worse than nothing.

The rule that actually matters more: AA-8000

Section 310.3(B) requires solid aluminum conductors 8, 10, and 12 AWG, and stranded aluminum conductors 8 AWG through 1000 kcmil, marked as AA-8000 series electrical grade aluminum alloy conductor material as specified in the standards. The old AA-1350 series that gave aluminum branch circuit wiring its bad reputation in the 1960s and 1970s is no longer permitted for these applications. AA-8000 alloy has creep and thermal expansion characteristics much closer to copper, which is why properly torqued modern aluminum feeders perform well.

Torque is the other half of the job

Section 110.14(D) requires terminations to be tightened to the manufacturer specified torque value using a calibrated torque tool where a torque value is provided. This is not optional and it applies to copper and aluminum alike. A loose aluminum lug will fail no matter how much compound you applied. Wire brush the conductor if the connector instructions call for it, apply the specified compound if required, land the conductor, and torque it to the marked value.

Field takeaway

No blanket NEC requirement for antioxidant. Follow 110.3(B) and the connector instructions. Use AA-8000 series aluminum building wire per 310.3(B). Torque every termination to the marked value with a calibrated tool per 110.14(D).