In terms of size, the model range was slotted between the medium-duty Loadstar (and the S-Series that replaced it) and severe-service Paystar series.

At the end of the 1970s, the 4300 was offered with some of the largest-displacement diesel engines ever fitted in a road-going vehicle, including the 450 hp Cummins KT inline-6 (1150 cubic inches) and the Caterpillar 3408 V8 (1099 cubic inches).Following the corporate transition of International Harvester to Navistar, the Transtar 4370 series was rebranded as the International 9370; alongside the retirement of the Transtar name, the standard-length 4270 was discontinued.

The cab structure was carried over, with Navistar adding a more prominent hood and grille (distinguished by vertically-stacked headlamps).

[2] Though less radical in design than the Ford Aeromax or the Kenworth T600, the 9400 further improved aerodynamics through optional skirted fuel tanks.

In 1992, the luxuriously appointed 9400 Midnight Eagle Limited Edition was introduced; offered only with the Caterpillar 3406 diesel engine, it had a leather interior with wood trim and a fully color-coordinated exterior.

The same year, the 9000 series (with the exception of the 9300) received an exterior update, including a redesign of the grille, front bumper, and headlamp surrounds.

For 1999, the 9900 was introduced to replace the 9300; again fitted with a squared-off long hood, the twin headlights were surrounded by chrome trim faired into the fenders.

To enlarge the drivers' compartment, the firewall of the cab was moved forward; this change replaced two-pane flat windshield glass with a single-piece curved design (along with cowl-mounted wipers).

[4] In contrast to the rest of the sloped-hood model line, the 9900i and 9900ix were configured with straight hoods,[7] and the 9900ix was offered only with premium Eagle trim.