What it is
The Omega 9300 / 9900 family is the chronograph counterpart to the time-only 8800/8900 Master Co-Axial line. Same architectural family: co-axial escapement, silicon Si14 hairspring, METAS Master Chronometer certification (0/+5 sec/day in case, 15,000-gauss anti-magnetism, six-position rate testing). The chronograph adds column-wheel switching and a vertical clutch: the chrono seconds hand starts and stops without the small jitter of horizontally-coupled chronographs. The 9300 launched in 2011 in the new Speedmaster Co-Axial Chronograph; the 9900 (4 Hz, 60-hour reserve, refined finishing) launched in 2016 as the chronograph-line evolution. Together they power the modern Omega chronograph catalogue outside the manual-wind Moonwatch (which uses the 3861).
"9300 vs 9900"
Both calibers run on the same architectural family but serve slightly different watches. 9300: 60-hour reserve, 54 jewels, 32 mm diameter; goes in the Speedmaster Co-Axial Chronograph 9300 family and Planet Ocean Chronograph (some refs). 9900: 60-hour reserve, 54 jewels, 32 mm diameter; the refined 2016 successor with redesigned bridges, slightly higher finishing standard, used in the current Speedmaster Racing, Aqua Terra Worldtimer Chronograph, and Planet Ocean Chronograph (later refs). The differences are subtle; both are METAS-certified Master Chronometers.
What is new vs the 1861/3861 Moonwatch chrono
Three things. Self-winding: the 9300/9900 is automatic; the Moonwatch 3861 is hand-wound. Co-axial escapement: the 9300/9900 uses Omega's signature 3-level co-axial; the 3861 also has co-axial but in a manual-wind layout. Vertical clutch: the 9300/9900 chronograph engages through axial coupling, eliminating the small "amplitude drop" you see when a horizontally-clutched chronograph starts. The 3861 is cam-actuated with a horizontal clutch (preserving the 1968 Moonwatch feel). For everyday wear the 9300/9900 is mechanically more advanced; for heritage and Moonwatch traditions the 3861 holds the line.
Watches it powers
The 9300 powers the original Speedmaster Co-Axial Chronograph (44 mm, 2011+), Planet Ocean Chronograph 45.5 mm (some refs), Aqua Terra GMT Chronograph (some refs). The 9900 powers the modern Speedmaster Racing 44 mm (2016+), Planet Ocean Chronograph 45.5 mm (later refs), Aqua Terra Worldtimer Chronograph 43 mm (2017+). The chronograph-only Moonwatch line (Speedmaster Pro, Snoopy editions, etc.) uses the manual-wind 3861 and is a separate caliber family.
Service notes
Service for a 9300/9900 watch runs CHF 700-1,000 at Omega, with the standard 2-year warranty and METAS recertification. Recommended interval: 8-10 years, same as the broader Master Co-Axial family. Independent service is increasingly possible; the silicon hairspring and co-axial parts are now widely available through the Omega service network. Compared to the lateral-clutch Lemania 1873 Moonwatch chronos, the 9300/9900 is significantly more service-tolerant: longer intervals, less-sensitive lubrication.
