For more than a century, September in baseball looked different from every other month. Rosters expanded from 25 players to as many as 40, and the final stretch of the pennant race was played by teams that had grown by half.
That ended in 2020. Here is what the two systems actually looked like side by side.
| The old system | Today | |
|---|---|---|
| Roster before September | 25 | 26 |
| Roster from Sept. 1 | Up to 40 | 28 |
| Pitcher limit | None at all | 13, rising to 14 |
| Expansion compulsory? | No — clubs chose | Yes — all 28 filled |
| Teams expanded equally? | No — wide variation | Yes — identical |
| Prospect debuts | Concentrated in September | Mostly June and July |
What September Used to Feel Like
A club could dress nearly 40 players. Managers used relievers one batter at a time. Rosters filled with third catchers, pinch-runners who did nothing else, and a dozen arms who would never appear in a meaningful inning.
For fans of eliminated teams it was the best month of the year — a parade of unfamiliar names, some of whom would matter in three seasons. The phrase "cup of coffee" belongs to that era: a career minor leaguer getting a handful of September days that would be the whole of his major league record.
Why It Ended
Three complaints, all long-standing.
The games were different. A pennant race decided in September was decided under rules that hadn’t applied in the five months that created it.
The games were longer. Unlimited pitchers meant unlimited pitching changes, at precisely the point in the season when the sport most wanted to hold an audience.
The games weren’t fair. Because expansion was optional and depth varied, two clubs fighting for the same wild card could meet with materially different roster sizes. That was an advantage produced by payroll and farm depth rather than by baseball.
What Was Gained
Consistency, mainly. Every team now plays September with the same 28 players and the same 14-pitcher ceiling, so the month that decides the season is played under the rules that produced it.
The mandatory element matters too. Under the old system a club could decline to expand and save money; now nobody can gain an edge that way.
What Was Lost
The cups of coffee, mostly. Far fewer career minor leaguers now reach the majors at all, because two spots per club leaves no room for sentiment.
The showcase moved as well. Prospect debuts are now concentrated in June and July, when a club has months to evaluate rather than weeks — which arguably serves the player better, but removes what used to make September distinctive.
Our page on why MLB ended 40-man rosters goes deeper on the reasoning, and September roster rules covers the current system in full.
The Bottom Line
September rosters once expanded from 25 players to as many as 40, with no pitcher limit and no obligation to expand at all. Since 2020 the limit has been 28 with a 14-pitcher cap, and filling every spot is compulsory. The change made September consistent with the rest of the season, at the cost of the month’s oldest tradition.