CIM has built a reputation not just for its course but for how quickly it fills up. In recent years, entry into the race has become something you plan for well in advance rather than something you can decide on a few weeks out. This guide covers how the registration process generally works and what that means for anyone planning to run it, without pinning down specific prices or dates that change from year to year.

How CIM structures registration

CIM typically sells marathon entry through a tiered system, with each tier offering a different level of protection rather than a different race experience. An entry-level tier is usually the cheapest but offers no flexibility if your plans change — it can't be transferred or deferred. A mid-level tier generally allows a transfer to another runner or down to the relay if you can't run, and the top tier usually adds the ability to defer your entry to a future year on top of that. All tiers typically go on sale at the same time on a first-come, first-served basis rather than unlocking one after another — but each tier has its own limited allotment, and in practice the cheapest, unprotected tier tends to sell out first, with the pricier, more flexible options taking somewhat longer to run out.

Why it sells out early

CIM has a well-documented history of selling out all of its entry tiers, and in recent years that sellout has arrived earlier and earlier as demand has grown. The race's reputation as a fast, well-organized course plays a direct role here — as more runners target it specifically for a qualifying attempt, more of them register as soon as entries open rather than waiting. The practical upshot is that treating CIM as a race you can register for a few months out is increasingly risky.

What to do if you're planning to run

• Register as close to opening as you reasonably can, rather than waiting to see how your training or travel plans firm up first.
• Sign up for the race's official communications so you know exactly when registration opens rather than finding out after the fact.
• Weigh the cost of a more flexible, higher tier against how likely your plans are to change — a cheaper, unprotected entry is a real risk if your season is uncertain.
• If you already have a bib you can no longer use, look into the official transfer process rather than letting it go to waste; CIM has historically run a structured window each fall for transferring protected entries to another runner.

Official transfers vs. informal bib swaps

Because CIM sells out so reliably, a secondary market for bibs tends to spring up on social media and local running forums every year. CIM has built an official transfer system specifically to reduce the risk of fraudulent bib sales, including a dedicated message board for runners looking to arrange a legitimate transfer during the official window. Using that official process, rather than an informal cash handoff with a stranger online, protects both the buyer and the seller — the buyer gets a bib that's actually registered to them, and the seller gets confirmation the transfer went through rather than just a promise.

Backup options if it sells out

If the standard tiers close before you register, CIM has historically opened two separate backup routes rather than one combined path. One is a free-to-enter drawing for a limited number of remaining protected spots — if you're selected, you're simply charged the standard price for that entry tier. The other skips the drawing entirely: you can secure a protected entry immediately by paying a mandatory charity donation on top of the standard entry fee. A marathon relay format is also typically available for teams who want to experience the course without each runner covering the full distance, and it has its own registration timeline worth checking independently. None of these backup routes are guaranteed to be open in any given year, so the safest plan is still registering for the standard tiers as early as possible.

Registration and your training plan

Because CIM's registration timeline is largely disconnected from a typical marathon training cycle — you're often committing to the race a full year or more ahead of the fitness you'll actually bring to the start line — it's worth registering for the race you want to run in an ideal season, not waiting until you're confident your training will go perfectly. Injuries, life events, and simple changes of plan happen to every runner, which is exactly why the higher, more flexible entry tiers exist: they cost more precisely because they're insurance against the version of your training block that doesn't go as planned, and that insurance is only worth buying before you know whether you'll need it — by the time an injury or a schedule conflict shows up, the window to add that protection has already closed, and no amount of money at that point can buy back a flexible entry you didn't originally purchase.