CIM 2026: A BQ Corridor That Bites Back After Mile 22

California International Marathon is one of the most reliably fast December road races in the country — a net-downhill, point-to-point course from Folsom to Sacramento that consistently delivers Boston-qualifier times — yet the data across its two most recent editions shows the field paying a real price for early optimism. Median finishes have hovered around 4:11, and more than half the field has run positive splits both years.

By the numbers

The race has grown. The 2024 edition drew 370 finishers; 2025 pushed that to 450, an increase of roughly 22 percent. Median finish time tightened slightly — from 4:12:42 in 2024 to 4:10:29 in 2025 — even as the field expanded, which suggests the growth brought faster runners into the mix, not slower ones. The 75th-percentile mark held nearly flat (4:44:46 to 4:45:41), so the back of the field barely moved; the improvement was concentrated near the front. The top 10% cutoff shifted from 3:15:22 to 3:12:49, a meaningful two-and-a-half-minute tightening at the sharp end.

Where the course bites

The 2025 fade curve tells a clear story. The field rolls through the opening 5K at 9:21/mi, then actually accelerates into the 10K segment (9:12/mi) — aided by the steepest downhill section, which drops 111 feet in the first 5K and another 46 feet through 10K. The course flattens and briefly climbs between 10K and 15K (+17 ft), and median pace reflects it, softening to 9:27/mi. Things tighten again through 20K (9:20/mi) before a brief apparent surge at the half (9:02/mi for that short segment). From 25K onward it's a steady, unambiguous grind: 9:20, 9:24, 9:35, 9:35 — and the final 1.3 miles offers no late kick, closing at 9:28/mi.

Pacing reality check

The positive-split problem is persistent but improving. In 2024, 65% of finishers ran the second half slower than the first, with an average second-half slowdown of 9.1%. In 2025 — a colder, more overcast day — those numbers improved: 57% positive-split, average slowdown of 6.1%, and 168 runners (roughly 37% of the field) managed a negative split. The cooler 2025 conditions almost certainly helped; temperatures sat between 36–46°F against 2024's warmer 49–59°F, and the humidity was notably higher in 2025 yet the results were better. Cold, calm air appears to be a genuine friend to this field.

The weather question

The 2026 forecast — 38–48°F, mist, ~43°F at the gun, wind at ~8 mph, and 93% humidity — is the coldest and most humid of the three editions in this dataset. It closely resembles 2025's conditions in temperature but adds meaningful wind and precipitation. The 2025 data suggests that cold air can suppress the fade curve; the added wind and mist in 2026 introduce variables the dataset hasn't yet captured. Runners should expect the downhill early miles to feel fast but potentially slick.

What it takes

What to watch

The field's growth trajectory is the headline trend. A third straight increase would confirm CIM as a rising fixture on the West Coast marathon calendar. Whether the 2026 field cracks 500 finishers is worth tracking. Second, the positive-split rate dropped 8 points from 2024 to 2025 — can that improvement continue toward parity, or does the 2026 mist and wind push the fade curve back toward 2024 territory? Finally, the top-10% cutoff has tightened two years running; if that trend holds, sub-3:10 may soon become the threshold for the field's elite tier.